Blindness in the UK -prevalence

8/9/2019 Blindness in the UK -prevalence

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The prevalence of visual impairment in the UK

A review of the literature

Rosemary Tate, Liam Smeeth, Jennifer Evans, Astrid Fletcherept of Epidemiolo!y " #opulation $ealth

London School of $y!iene " Tropical %edicine

&hris 'wen St (eor!e)s $ospital %edical School

Alic*a Rudnic+a olfson -nstitute of #reventive %edicine

Report commissioned .y the Royal /ational -nstitute for the 0lind

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Ac+nowled!ements

Fundin! for the review was provided .y the Royal /ational -nstitute for the 0lind

Advisory Committee

Li2 0ates 3irector &orporate #olicy, Ashton, Lei!h " i!an #rimary &are Trust4

#rof -an 0ruce 35'L#R'F, &ity University4

#rof Alistair Fielder 3#rofessor of 'phthalmolo!y, -mperial &olle!e London and estern Eye

$ospital4

r &arol Lupton 3#olicy Research #ro!ramme, epartment of $ealth

r An!ela %c&ulla!h 3Research irector, The #oc+lin!ton Trust4

R/-0

Lesley6Anne Ale7ander 3&hief E7ecutive4

/i!el &harles 3Research evelopment %ana!er4Fa2ilet $adi 3irector of #olicy4

r Adam 'c+elford 3Assistant irector, Education and Employment4

%any than+s also to Sue Keil at R/-0 who provided e7tra information for &hapter 89 Special

than+s to /i!el &harles for commissionin! this pro*ect and for invalua.le support and advice9

Authors details

Rosemary Tate #h, research fellow, London School of $y!iene " Tropical %edicine 3now at

-nstitute of &hild $ealth4

Liam Smeeth %R, Senior clinical lecturer in epidemiolo!y, London School of $y!iene "

Tropical %edicineJennifer Evans #h, lecturer in epidemiolo!y, London School of $y!iene " Tropical %edicine

Astrid Fletcher #h, #rofessor of epidemiolo!y, London School of $y!iene " Tropical

%edicine

&hris 'wen #h, Senior Research Fellow in Epidemiolo!y, St (eor!e:s $ospital %edical

School

Alic*a Rudnic+a #h, Lecturer in Epidemiolo!y " %edical Statistics, olfson -nstitute of

#reventive %edicine

Contribution of authors

Rosemary Tate undertoo+ the literature review and preparation of main ta.les9 Liam Smeeth

reviewed and updated &hapter 8 on &hildren9 Jenny Evans contri.uted the section on .lindnessre!istrations and provided critical comments on the review9 &hris 'wen and Alic*a Rudnic+a

carried out the analyses and wrote the material for &hapter ;9

Astrid Fletcher too+ overall responsi.ility for the pro*ect and wrote the Summary, &hapter < and

&hapter =9

Authors potential conflict of interest

ata on self reported visual difficulties and visual acuity measures reviewed in this report comes

from the %R& funded Trial of assessment and mana!ement of older people in the community

3#rincipal -nvesti!ator Astrid Fletcher4, the associated causes of vision impairment study funded

.y the The #oc+lin!ton Trust 3with Jenny Evans and Richard ormald4 and the nested %R&

funded trial of screenin! for vision impairment within the main %R& Trial 3with Liam Smeeth49


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Summary

e identified three approaches to descri.in! visual pro.lems in the population9

uestions to disa.ility scales9 %ost studies have used >uestions

on difficulty in ?readin! newsprint@ as minimum criteria for difficulties with seein!9

9 &linical measures, predominantly visual acuity9 istance visual acuity is the .asis for

cate!orisin! vision impairment in the $' -nternational &lassification of iseases

3-&49 %ost studies have measured distance acuity usin! an illuminated Snellen chart9

5isual acuity can .e measured with usual aids if worn i9e9 contact lenses or !lasses

3?presentin! vision@4 or after full refraction for refractive error 3?.est corrected visual

acuity@49 -n surveys full refraction may not .e availa.le and studies may use pinhole

correction to try to remove some of the refractive error 3pinhole corrected visual acuity49

Results may .e presented as .inocular vision or as vision in the .etter eye9 The $'

-& classifications use .est corrected visual acuity ie vision in the .etter eye after full

correction9 5ision impairment is defined as a Snellen acuity B;C


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population a!ed


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from //S provided .y r van der #ols and unpu.lished data on 5A B;C


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results for visual impairment from that report were .ased on si!ht tests alone without e7cludin!

possi.le remedia.le conditions 3such as refractive error and cataracts4 the re!istera.le

component is li+ely to have .een considera.ly overestimated 3around two fold49 e showed that,

.ased on other studies which have collected data on the causes of vision impairment, the

num.ers li+ely to .e re!istered .ecause of permanent vision loss and the actual num.ersre!istered from epartment of $ealth statistics were of a similar ma!nitude 3and differed .y

a.out uired in interpretation of any sin!le estimate of the prevalence of visualimpairment or .lindness amon! children in the UK9 $owever, usin! a .road and pra!matic

definition of visual loss sufficiently poor as to mean a child is identified as .ein! in need of

special educational or social services, the e7istin! data su!!est a prevalence of visual impairment

in the re!ion of


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Estimates .ased on self report from !overnment surveys are less relia.le than estimates .ased on

visual acuity .ecause of concerns a.out the validity of the >uestions and the poorer response

rates9 -n addition, these estimates are li+ely to .e a su.stantial overestimate of the num.ers since

they include people with minimal pro.lems9

Estimates .ased on visual acuity measurements from the representative studies of the older

population are sufficiently consistent for !eneral purposes of plannin! and estimation of the

proportion and num.ers of people in the UK with vision impairment9 $owever we caution that

these estimates are seen as appro7imations and not as ?ta.lets of stone@ as prevalence estimates

will vary from place to place and over time and .ecause all estimates carry a ran!e of uncertainty

as shown .y the 8H confidence intervals9

Estimatin! the prevalence of vision impairment for future older populations re>uires assumptions

a.out temporal trends in the underlyin! conditions, and future levels of service provision and

upta+e9 /o data are availa.le on temporal trends in the incidence of refractive error, cataracts ora!e related macular de!eneration and such data would .e prohi.itively e7pensive to o.tain9 The

estimated increase in the proportion of people with a!e related macular de!eneration eli!i.le for

re!istration has .een calculated to increase .y uestionnaires or

scales for measurin! self reported vision pro.lems or vision related >uality of life9 e emphasi2e

the need to thorou!hly test all >uestions .efore use in surveys9

e encountered difficulties in understandin! the methods and .asis for calculations in some of

the reports we reviewed due to a lac+ of clarity and transparency in the reportin! of data9 e

recommend that reports which present novel research findin!s 3.ut are not su.mitted for

pu.lication in academic *ournals4 should conform to the same standards of reportin! as the

;


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formal peer review process of academic *ournals 3for e7ample as pu.lished .y the -nternational

&ouncil of %edical Editors49 Further details are !iven in &hapter =9

Recommendations for further research

%ost studies have .een done in the older population and there is a scarcity of data in youn!er

adult a!e !roups in the UK9 A review of epidemiolo!ical studies performed in estern Europe,

/orth America and Australia coverin! the a!e !roup 1 to 8 years found the prevalence of

.lindness was 191D and of visual acuity ;CI to ;CID was 191=H9 These fi!ures a!ree well with

the prevalence of re!istrations in a similar a!e ran!e and we conclude that re!istration data

provide reasona.ly accurate estimates of the prevalence of serious vision impairment in the

youn!er adult a!e !roups9 -nformation is lac+in! on less severe levels of visual impairment9

ue to the lac+ of data on the prevalence of visual pro.lems, visual impairment or specific types

of eye disease in ethnic !roups in the UK population, studies in ethnic !roups are re>uired9

The reasons for hi!her levels of vision impairment in women and in more deprived social !roups

re>uires further understandin!, in particular the e7tent, if any, to which this reflects under

utilisation of services9

The reasons for hi!h levels of treata.le conditions in the older population re>uire further

investi!ation9 -n particular information is re>uired on pu.lic awareness of si!ns and symptoms of

treata.le conditions, and .arriers to service utilisation and access9

/ew strate!ies to identify the most cost effective way of screenin! the older population for

vision impairment are ur!ently needed9

=


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Chapter 1

-ntroduction

D


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5alid and relia.le estimates of the levels of vision impairment in a population are important to a

num.er of a!encies and professional !roups, which include national policy ma+ers, health and

social service providers, health professionals, pu.lic health departments and academic

institutions includin! epidemiolo!ists and voluntary sector or!ani2ations9 e emphasi2e validity

and relia.ility as +ey data re>uirements9 Users of data on visual pro.lems need to .e reassured

that the measures are valid i9e9 measurin! vision pro.lems relevant to the use to which the data

will .e put9 -n this conte7t we define relia.le to mean that the estimates are o.tained from well

conducted studies, measured without .ias and with a hi!h level of precision9 Althou!h user

perspectives may vary in emphasis and focus the critical information re>uired relates to the

classic epidemiolo!ical >uestionsG $ow much, ho, here, hen, and hy All these

>uestions re>uire a clear definition of hat is the pro.lem9 e will discuss the hat >uestion

at the end of this section althou!h of course it normally would .e the startin! point in any study9

How much of a disease/condition is there in a population?

-n >uantifyin! how much of a condition there is in a population, different measures are used9

#revalence is a measure of the num.er of people with a diseaseC condition at a particular time

point in relation to the total num.er of people in the population9 This is typically e7pressed in

terms of a proportion 3usually H4 and sometimes descri.ed as a prevalence rate9 A prevalence

measure re>uires a time reference which relates to the point at which the estimates are made, e9!9

over a few days or months or annually9 'ften however the period is not clearly descri.ed9 For

most surveys the prevalence is point prevalence9

-ncidence is a measure that descri.es the num.er of new cases of the diseaseCcondition that occur

over a specified time period in people who were diseaseCcondition free at the start of the period9/um.ers of people in a population with the diseaseCcondition at a particular time point are

estimated .y applyin! prevalence rates, which are usually o.tained from surveys, to national

population estimates9

These measures are all useful .ecause they each provide a different perspective9 #revalence

rates descri.e the relative importance of a diseaseCcondition in terms of how common it is9 This

aids in prioriti2in! the diseasesCconditions which ma+es the lar!est contri.utions to a

population)s ill health9 Epidemiolo!ists use prevalence data from a num.er of international

populations for comparative purposes as a first step in understandin! the aetiolo!y or ris+ factors

related to a diseaseCcondition9 &rucial to interpretation of these data are a!e standardisations to

ensure that the population data .ein! compared are ad*usted for any a!e differences as for most

diseases a!e is the ma*or pro!nostic factor of mor.idity9 -ncidence data provide information onthe natural history of a diseaseCconditionM identifyin! people and the associated ris+ factors

which .est predict the development of the diseaseCcondition9 The !ap .etween prevalence and

incidence is also a measure of whether a diseaseCcondition is chronic or curative9 The actual

num.ers in a population are vital for plannin! services and to voluntary sector or!ani2ations for

understandin! the si2e of the client !roup on whose .ehalf they are campai!nin!9

8H confidence intervals9 Althou!h prevalence or incidence rates are a sin!le num.er, the

estimates should .e presented with their 8H confidence intervals9 8H confidence intervals

!ive the ran!e i9e9 an upper and lower .oundary within which the true .ut un+nown estimate will

lie9 The 8H is a measure of our certainty a.out this ran!e i9e9 we are 8H certain9

Who has the disease/condition?


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#revalence measures are usually descri.ed .y the ma*or demo!raphic characteristics of a!e

!roup and se7, .ecause these data are easy to collect and .ecause most diseaseCconditions vary

considera.ly across a!e !roups9 Se7 differences may also .e important su!!estin! either

difference in aetiolo!y or in access to services9 'ther factors of relevance at the population level

may .e socio6economic status and ethnic !roup .oth to identify whether there are different su.populations for needs assessment, and access to services and to su!!est possi.le factors in

aetiolo!y9

There is an important distinction .etween the num.ers in a population with a diseaseC condition

and those su. !roups in a population who have the hi!hest proportion of a diseaseCcondition9 The

classic e7ample is where the hi!hest prevalence occurs in the older a!e !roups .ut the actual

num.ers in the population with the condition may .e mainly contri.uted from youn!er a!e

!roups with lower prevalence9 This simply reflects the much lower proportions of the older a!e

!roups in the population9

Where do people with the disease/condition live?

(eo!raphical information such as re!ional, ur.anCrural and, for some conditions, livin!circumstances 3in the community or in communal esta.lishments such as nursin! and residential

homes4 may help to estimate re>uirements for local service provision and, in the case of livin!

circumstances, where the main tar!et population may .e identified9 As descri.ed a.ove at an

international level these data are useful for su!!estin! possi.le true differences .etween

populations in the prevalence of ris+ factors

When?

Temporal data descri.e chan!es in the prevalence or incidence of a conditionCdisease usually

over a fairly e7tended time period for chronic conditions9 Temporal data may .e provided from

routinely collected national statistics 3e9!9 mortality, cancer incidence4 or .y comparin! cross

sectional information such as from surveys collected at different years9 There are a num.er of

methodolo!ical pitfalls in interpretin! temporal dataG definitions of diseaseCconditions may have

chan!ed, the reported num.er of cases may have apparently increased as a result of !reater

awareness or improved dia!nostic procedures, .etter treatment may lead to reduced prevalence

.ut not incidence9 Temporal chan!es in num.ers only and not in rates are especially misleadin!

as there is no indication of the underlyin! population9 -ncreases or decreases in num.ers may

simply reflect chan!es in the population structure9 -nterpretation of 0lindness and #artial Si!ht

re!istrations is such an e7ample9

Why?

Understandin! why some people in a population !et a diseaseCcondition compared to others whodo not is the main area for epidemiolo!ical research and outside the prime focus of this report9

What is the problem?

A num.er of terms are used to descri.e visual pro.lems and we will discuss these in !reater

detail9 As an introduction to this area we note that the choice of terminolo!y and of measurement

instruments is influenced .y the purpose for which the information is re>uired9 e need to

distin!uish .etween measures which relate to understandin! of the underlyin! clinical

conditionCdisease and those which descri.e the impact of the conditionCdisease on the person)s

function and everyday life9 The o.*ective of clinical measures of vision is to descri.e the level of

visual loss and the reasons for this9 Since at the population level in the UK most vision pro.lems


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are due to refractive error, untreated cataracts, a!e6related macular de!eneration, dia.etic

retinopathy and !laucoma, a service provider perspective would include the need for specific

data that assists in plannin! for services and treatments that includeG optometry, cataract sur!ery

and other clinical treatments, low vision aids, and for some conditions, fre>uent hospital visits

for monitorin!9%ost importantly, estimates of the prevalence of visual impairment in a population will vary over

time and .etween populations accordin! to the proportion of untreated .ut remedia.le vision

pro.lems9 Thus, measures of vision loss alone are a first step to descri.in! the population

.urden .ut are not informative unless we understand what the pro.lem is due to9 Althou!h we

would e7pect a hi!h correlation .etween functional difficulties descri.ed .y a person and a

clinical measure, a person)s functional pro.lems will .e also influenced .y a num.er of .oth

personal and situational factors9 &linicians will also use patients) perspectives as an ad*unct to

.oth understandin! at an individual level of the impact of the pro.lem on a person, and at a

!roup level to evaluate the effectives of clinical treatments and services9

Measurement of Vision and Visual Problems

A recent report to the -nternational &ouncil of 'phthalmolo!y Nuently in UK .ased population studies9

uestions to disa.ility scales

9 &linical measures, predominantly visual acuity9

9 5ision related ?>uality of life@ descri.in! the impact of vision pro.lems on everyday

functionin! and well6.ein! 3few studies at present49

1 Vision difficulties

1.1 OPCS disability uestions

-n most of the UK national surveys carried out .y the !overnment survey services 3'ffice of

/ational Statistics, previously 'ffice of #opulation &ensus and Surveys '#&S4 which are

descri.ed in this report a num.er of >uestions related to difficulties with seein! were used 3Ta.le

uestions on seein! were part of a set of scales from four lin+edsurveys that were carried out to esta.lish the prevalence and type of disa.ility in the UK9 The

concept of disa.ility was heavily influenced .y the $' classification of -nternational

&lassification of -mpairments, isa.ilities and $andicaps 3-&-$4 NOwhich drew distinctions

.etween impairments 3? loss or a.normality of psycholo!ical, physiolo!ical or anatomical

structure or function@4, disability3? restriction or lac+ of a.ility 3resultin! from an impairment4

to perform an activity in the manner or within the ran!e considered normal for a human .ein!@4

and handicap3? a disadvanta!e for a !iven individual, resultin! from an impairment or

disa.ility that limits or prevents the fulfilment of a role dependin! on a!e, se7 and social and

cultural factors for that individual49 The -&-$ classification of disa.ility was adopted for the

'#&S surveysM separate scales were developed for


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was ran+ed on a uestionnaire was used as a >uic+ and easy method of identifyin! people with

disa.ilities for a further more detailed assessment 3Ta.le uestionnaire 3SG ?difficulty readin! ordinary

newspaper print@ and Suestions have hi!h sensitivity 3i9e9 people with vision pro.lems

are not missed49 Specificity is also critical .ecause estimates may .e .iased .y false positives9

Sift >uestions can also .e used to measure prevalence .ased only on the two sift >uestions as+ed9

%any of the estimates presented in the report are .ased on the com.ined prevalence of S andCor

SD9 -n later surveys, different >uestions from the Seein! difficulty scale were used e9!9 in the

$ealth Survey for En!land N, IO prevalence was .ased on a positive answer to SD ?&annot see

well enou!h to reco!nise a friend across a road@ with SI ?&annot see well enou!h to reco!nise a

friend who is an arms len!th away@ .ein! as+ed for a positive response to SD9

1.! Other uestions used in surveys.

The En!lish Lon!itudinal Study on A!ein! 3ELSA4 N8O moves away from the ?difficulty@ or

?cannot@ style of >uestions in the '#&S surveys to as+in! people to rate their vision, overall and

for two specific e7amples9 #articipants were as+ed to rate their eyesi!ht, usin! !lasses or

corrective lenses, as e7cellent, very !ood, !ood, fair or poor9 They were also as+ed to rate how

!ood their eyesi!ht was for seein! thin!s at a distance and for seein! thin!s close up9

! Clinical measures

A num.er of clinical measures e7ist of which the most commonly used and internationally

accepted is visual acuity9 'ther clinical measures include visual fields, colour vision, contrast

sensitivity, li!htCdar+ adaptation and motion perception9 5isual acuity and, to a lesser e7tent,

visual fields are measures that are practical to use in population .ased studies9 'ther clinical

measures descri.ed a.ove are used mainly in the clinical settin! for dia!nosis and for clinical

research9 The current consensus is that these other clinical measures are not yet suita.le for use

in the populationN;O9 Further wor+ is re>uired to refine the use of such measures and

demonstrate their added value, over that of visual acuity, in characterisation of visual loss at the

population level9

Visual acuity


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5isual acuity is the .asis for cate!orisin! vision impairment in the $' -nternational

&lassification of iseases 3-&


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Trainin! and >uality control of fieldwor+ers in population .ased surveys is a.solutely essential

to ensure relia.le results9

Visual fields

5isual field loss is more comple7 to characterise than visual acuity9 $owever visual field loss canoccur independently of visual acuity9 A recent report on standards for characteri2ation of vision

less and visual functionin! concluded that more wor+ needed to .e done to develop !ood

methods for testin! visual fields in population surveysN;O9 Automated perimetery is the

recommended method for field surveys .ut re>uires more e7pertise and care than measurement

of visual acuity9 The -&' report NuestionG central fields are the most important for identification of the underlyin! cause of vision

loss, such as !laucoma while peripheral fields are a more relevant measure of the conse>uences

of the underlyin! condition9 A 5isual Field score has .een developed which provides a sin!le

summary score .ased on assi!nin! points for every point seen on a visual field !rid9 This score

has .een correlated with orientation and mo.ility performance scores9 There are to date no data

on the use of the 5isual Field scores in the UK population9 Such data that are availa.le on visualfields are in the conte7t of estimatin! the prevalence of !laucoma and include other criteria such

as cupG disc ratio, and intra6ocular pressure9

"lindness and partial Sight Registration in the #$The num.er of .lind people in 0ritain has .een recorded since


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S0 in Scotland and return these to relevant !overnment a!encies 3epartment of $ealth,

Scottish E7ecutive and elsh assem.ly4 whose *o. it is to analyse and pu.lish these data9

ata from Scotland is most easily availa.le .ein! online and up to date 3pu.lished to year end

%arch 11 3httpGCCwww9scotland9!ov9u+,accessed Septem.er


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&hapter 8G 5ision impairment in children

&hapter ;G 5ision related >uality of life

&hapter =G &onclusions and Recommendations

The literature was ascertained 3i4 from a #u.%ed search usin! the +ey words PPprevalenceQPPvisualQ and PP.lindnessQ 3ii4 .y as+in! the advisory !roup mem.ers for relevant pu.lications

and 3iii4 searchin! the .i.lio!raphy of those most recently pu.lished9


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Ta.le


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Ta.le


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These definitions of have .een proposed as alternatives to the terminolo!y of Low 5ision which may .e confused with people eli!i.le for Low 5ision services

/o Li!ht #erception


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Chapter !

Vision %ifficulties in Adults


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-ncluded in this section are all studies which have used self reported responses to >uestions on

pro.lems with vision related tas+s 3vision difficulties4 or to self assessment of vision 3as

descri.ed in the previous chapter4 3Ta.le 9uestions on health pro.lems and disa.ilities9 Those related

to seein! were ?difficulty reco!nisin! a friend across the road even if !lasses or contact lenses

are worn@ and ?difficulty readin! ordinary newspaper print even if !lasses or contact lenses areworn@9 #eople with disa.ilities were then followed up and interviewed9

The response rate to the screenin! >uestionnaire was D1H9 There were D,Iuestion relatin! to lon!6term health pro.lem or disa.ility9 81H

of those over ;8 and all those a!ed under ;8 were selected for interview 3n


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Communal 2stablishments

A list of institutions held .y the 5ital Statistics 0ranch of the #opulation Statistics division of the

'#&S 3appro7imately 1,111 entries4 and an e>uivalent list from the (eneral Re!istrar:s 'ffice

for Scotland was used as the samplin! frame9 $ospitals, homes and hostels were included9

Educational esta.lishments, places of detention and military esta.lishments were e7cluded9


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Figure !13Flow chart showin! the num.ers of participants at each sta!e of the '#&S


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Figure !!3Flow chart showin! the num.ers of participants at each sta!e of the '#&S uestionnaire to measure disa.ility .ased on successive ?siftin!@ was used which

allowed in6depth interviews to .e carried out on those screened into the survey as positives9 This

approach is cost effective .ecause lar!e num.ers of people with no disa.ility do not need to .einterviewed in depth9 The disa.ility scales and sift >uestions are descri.ed in detail in the report9

The selection process of the < in I or < in


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%isability in 4reat "ritain3 Results From the 5ffice for 6ational Statistics *56S- 1++78+9

%isability Follo&:#p to the Family Resources Survey *4rundy et al.1+++-.!70

Summary

This report is .ased on interviews o.tained from a su.set of those interviewed in the uestions on lon! standin!

illness or disa.ility9 'verall H of the 88D disa.led adults included in the survey were

classified as havin! a ?seein!@ disa.ility9 The estimated wei!hted prevalence of visual disa.ility

in adults a!ed


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Figure !;3Flow chart showin! the samplin! procedures and num.ers included at each sta!e of

the '#&S


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ealth Survey for 2ngland %isability among older people *%5 !


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males a!ed ;86= and =H for those over D1 and for females


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Results

-nterviews were achieved with only ;I1 39H4 of the uestions were

repeated for the R/-0, participants claimed they had never had a seein! pro.lem or their si!ht

had improved 3see ta.le 949 Appro7imately 1H from the FRS survey fell into this cate!ory

and 88H of those from the '%/-0US surveys9 'f the uestions on

vision and other disa.ilities as part of a !eneral purpose >uestionnaire9

Ta.le 9

#eople at least S on previous

survey

FRS '/S survey

/


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Figure !/3Flow chart showin! the num.ers of participants at each sta!e of the

samplin! of the random components of the R/-0


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MRC )rial of Assessment and management of older people in the community *Smeeth et al

!Methods

The %R& Trial of the Assessment and %ana!ement of 'lder #eople in the &ommunity is a

cluster randomised trial comparin! different methods of multidimensional screenin! in people

a!ed =8 years and over NO9 'ne hundred and si7 !eneral practices from the UK %edical

Research &ouncil (eneral #ractice Research Framewor+ were recruited to the trial9 The practices

were recruited from En!land, ales and Scotland and were stratified to provide a representative

sample of the mortality e7perience 3Standardised %ortality Ratio4 and deprivation 3Jarman

Score4 of !eneral practices within 0ritain9 -n each practice all patients a!ed =8 years and over

were invited to ta+e part e7cludin! those in lon! term care or with a terminal disease9 The trial

consisted of two arms9 -n the ?universal@ arm, all participants received a .rief health

>uestionnaire followed .y a more detailed assessment .y a practice nurse9 -n the ?tar!eted@ arm,all participants received a .rief >uestionnaire .ut only those who ?tri!!ered@ on predefined

responses received a detailed assessment9 #ractices were also randomised to one of three

methods of administerin! the .rief >uestionnaireG postal, lay interviewer, practice nurse9 The

.rief >uestionnaire included a sin!le >uestion on si!ht9 G#o you have difficulty in seein$

newsprint% even if you are wearin$ $lasses?#articipants were !iven a choice of three responsesG

&o difficulty% ' little difficulty anda lot of difficulty. The visual acuity tests in the detailed nurse

assessment are descri.ed in &hapter 9

Results

'f I,=D eli!i.le patients, ,1 people responded to the .rief >uestionnaire, an overall

response rate of =D91H9 %en were more li+ely to respond than women 3D198H versus =;9=H,#B1911


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2nglish ?ongitudinal Study of Ageing *2?SA- ./0

The ELSA sample was drawn from households previously respondin! to the $ealth Survey for

En!land 3$SE4 durin!


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Chapter summary

The estimates of the prevalence of visual difficulties in the different studies are summarised in

Ta.les 9 and 9I9 As SD?cannot reco!nise a friend across the road@ is a worst severity than the

>uestion S ?difficulty readin! newspaper@, the estimates from the surveys that have used at

least S are considered to!ether9 The fi!ures show some consistency for the older a!e !roups

with most studies showin! a prevalence in the over =8s of around 8H to 1H for readin!

difficulties or worse9 The e7ception is the second R/-0C'/S 111 survey which reports a lower

prevalence for the over =8s a!e !roup9 The overall prevalence in the adult population a!ed


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)able !1 Summary of studies considered in this Chapter

Survey A!e

/um.er

surveyed Response

'/S isa.ility survey


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Ta.le 9G #revalence of reported visual difficulties amon! adults in (reat 0ritain9

Survey #opulation 'ri!inalSampleSi2e

&riteria forprevalence estimates

Se7 A!e #revalenceH

'#&S


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%R& trial of

assessment of olderpeopleNDO3additional results

provided .y AF4

representative

of mortalityanddeprivation inthe UK

a!ed =8

e7cludin!those innursin!homes

Reportin! ? a lot of

difficulty@ in readin!newsprint

F

=86DI D91 3=9, D9=4

D8


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Chapter ;

Population:based surveys using visual acuity measurements

1


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The methods employed for each survey are shown in Ta.le 9< and the +ey results are presented

in Ta.le 99 Since most of the relevant material is presented in these ta.les, only a short

summary of each survey is provided in the followin! te7t9 The e7ception to this is the


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Methods

The study was a random sample from an inner London !eneral practice9 1= su.*ects a!ed ;8

3response rate of =H4 were e7amined in a day centre for the elderly9 Su.*ects underwent a fulleye e7am .y an ophthalmolo!ist9 0inocular distance visual acuity was measured usin! Snellen

charts and .est monocular m Son+sen Silver acuity in each eye, with spectacles if normally

worn9 /ear vision was recorded as .ein! a.le to a.le to read /; with normal readin! correction9

&onfidence intervals were calculated .y e7act methods for small proportions and normal

appro7imation to .inomial distri.ution for lar!er ones9

Results

The prevalence of .lindness was


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Comment

The study had hi!h response rates and a moderate sample si2e9 &onfidence intervals were

presented9 The eye e7amination was conducted .y ophthalmolo!ists9 The report was mainly

concerned with the prevalence of eye conditions and there is very little information .y levels of

visual acuity or .y a!e and !ender specific rates9 /o data are presented on visual acuity levels inthe .etter eye for comparative purposes with other data9

Visual acuity measurements in a national sample of "ritish elderly people *van der Pols et

al.!


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Prevalence of visual impairment in people aged 9/ years and older in "ritain3 results from

the MRC trial of assessment and management of older people in the community *2vans et

al.!Summary


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means that a proportion of people with refractive errors may have .een underestimated9 The

study sample e7cluded those in lon! stay hospital or nursin! homes9

'hat is the prevalence of visual impairment in the general and diabetic populations3 are

there ethnic and gender differences *ay&ard et al.!Summary

This was a population6.ased cross6sectional o.servational study investi!atin! the prevalence of

visual impairment and ethnic and !ender differences in the !eneral and dia.etic population in

Leicestershire of all a!es 3149 Usin! capture mar+ recapture methods, the prevalence of

.lindness and partial si!ht in the !eneral and dia.etic populations was estimated to .e 198H and

uestions S or SD 3as descri.ed in ta.le


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"lind and partially sighted adults in "ritain3 )he R6@" survey *"ruce et al 1++1- .;90

Summary

This report was an investi!ation of .lind and partially si!hted people and their needs .y the

R/-09 The survey was .ased on interviews with 88 people, two thirds of whom wererespondents to the


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2stimating prevalence and numbers

The population prevalence for private households .y a!e !roups were calculated .y usin!, as the

denominator, the actual num.ers in these a!e !roups in the full '#&S sample applyin! the

relevant wei!htin! to the ;1 !roup who were successively under sampled9 The numerator was

the DI people 3descri.ed a.ove4 a.ove who had a si!ht test in the '#&S sample and who

fulfilled the visual acuity distance or near vision criterion descri.ed a.ove9 These people were

distri.uted .y a!e !roupG 868 3


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Fi!ure 9< Samplin! procedures


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Comment

The R/-0 '#&S sample was derived from si!ht test results of people who were a sample of

those who reported a seein! disa.ility9 As Fi!ure 9 shows the identification of these people

assumes that the sift process and seein! disa.ility >uestions have hi!h sensitivity so that people

with visual impairment were not missed at the successive sta!es9 Additionally, one third of theinterviews were o.tained from a non6randomly sampled population and since these people were

a!!re!ated with the '#&S sample for almost all analyses, it is not possi.le to e7amine the results

separately for the national sample9 $owever the estimates of prevalence and num.ers were

carried out separately9 Althou!h at each sta!e of sample selection the response rates are

reasona.le 3varyin! from ;8H for the needs survey to D


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Chapter summary

This chapter includes data from si7 studies and two '#&SCR/-0 reports9 'nly two studies 3the

%R& Assessment trial N8Oand the //S study NIO4 and the two '#&SCR/-0 reports N=, =O

were .ased on samples coverin! the whole of 0ritain9 The others are from selected re!ions, twoin London N, Oand two in LeicestershireN1, ;O 9

The %R& Assessment Trial is much the lar!est with


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The /orth London Study estimates are also very hi!h which a!ain may a!ain .e peculiar to the

/orth London population9 The prevalence estimates for the two '/SCR/-0 studies are very

similar for the a!e !roups


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Ta.le 9< #opulation .ased surveys usin! visual acuity measurements 6 methods

/ame Location and

date ofsurvey

Aims -nclusionCE7clusion

&riteria

esi!n and methods 5isualmeasurement

Sample si2e Responserates

/um.ere7amined

emo!raphic

/orthLondon

Study

Reidy et al9


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%R&Assessment

Trial

Evans et al9

11N8O

(reat0ritain


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ormald et

al9


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Ta.le 9 #opulation .ased surveys usin! visual acuity measurements 6 results9

Study Key Results

#resentin! visual acuity B;C


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=86= ;< I9D 9; to 89 I9 9< to 89 19; 19 to

19

D9 =9< to


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F ;=


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;86=I 0oth


58/120

omen ;


59/120

All I=I 9I 9D

R/-0


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Ta.le 9 #revalence H of visual impairment and .lindness in different studies


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Chapter >

Causes of Visual @mpairment

I


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@ntroduction

This chapter reports the results from five UK population6.ased prevalence studies that have

investi!ated the causes of visual impairment9 The methods employed .y each survey are shown

in Ta.le I9< and the results are presented in Ta.le I99

A study of the prevalence of eye disease in the elderly in an 2nglish community *4ibson et

al 1+,/- .;10

Summary

IDI su.*ects livin! in %elton %ow.ray a!ed =; were e7amined .y an ophthalmolo!ist and an

ophthalmic optician9 The prevalence of eye diseases associated with a visual acuity of less than

;C was I;9


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Comment

The results were .ased on ri!orous clinical e7amination and clearly defined criteria9 The

definitions were .ased on very minimal levels of visual acuity 3B;C4 and, for macular

de!eneration, de!enerative chan!es which included very early maculopathy9

Visual problems in the elderly population and implications for services *'ormald et

al.1++!- .;!0

Summary

1= people a!e ;8 and over, from an inner London health centre, were e7amined in order to

determine the prevalence of common eye pro.lems9 The ma*ority of those with .est corrected

visual impairment had cataract9

Methods

Samplin! methods are descri.ed in &hapter 9 The central visual field was tested with the

$enson &FS1119-ntraocular pressure was tested with the #er+ins mar+ tonometer with the slit

lamp9 After dilation with tropicamide


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Methods

The samples were stratified .y a!e 3I168 and ;149 ; su.*ects were measured at a specialist

eye clinic for visual acuity, near and distance vision , full refraction and split lamp

.iomicroscopy9 #er+ins applanation tonometry and fundus e7amination with direct and .inocular

indirect ophthalmoscopy after pupillary dilation9 E7amination for cataract was carried out .y

direct ophthalmoscopy after mydriasis and direct and retroillumination with the slit lamp9 A!e

related cataract was said to .e present when the .est6corrected visual acuity was ;C or worse in

the affected eye and this was attri.uta.le to lens opacity9 A!e related macular de!eneration was

defined .y the presence of de!enerative chan!es to!ether with a .est6corrected visual acuity of

;C or worse9 #eople with a history of secondary of con!enital cause of macular disease were

e7cluded from the a!e6related macular de!eneration cate!ory9 The criteria for the dia!nosis of

dia.etic retinopathy were a history of dia.etes and the presence of microaneurysms, dot

haemorrha!es, hard e7udates, microvascular a.normalities or neovasculari2ation9 The dia!nosis

of open6an!le !laucoma was made if there was !laucomatous cuppin! of the optic disc and an

intra6ocular pressure a.ove < mm$! and an open anterior cham.er an!le and !laucomatousfield defects9

Results

'f the == that attended for e7amination


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Methods

The samplin! methods were descri.ed in &hapter 9 5isual acuity, autorefraction, and field

e7aminations were carried out .y a trained ophthalmic nurse9 The remainder of the e7amination

was .y ophthalmolo!ists9 Refractive status was ascertained .y usin! the $umphrey 8D1

autorefractor9 5isual fields were assessed in all su.*ects .y the =; point visual fields of the

$umphrey =1 screener, with readin! correction9 Anterior se!ment e7amination was carried out

usin! a slit lamp9 Lens, vitreous, and retinal e7aminations were done after pupil dilatation9

&omparison with L'&S -- standard photo!raphs was used to record cataract type and density9

#eople were classified as havin! cataract causin! visual impairment when the visual acuity in

one or .oth eyes was poorer than ;C


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main causes were refractive error 3


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hospital records and no direct eye e7am was availa.le9 -n around a >uarter the cause was

un+nown9 The nursin! home population was not included9

Chapter summary

This chapter summarises five surveys that provide population prevalence rates of 3mainly a!e6

related4 eye diseases9 'ne study NO is .ased on a sample coverin! the whole of (reat 0ritain,

the others are from selected re!ions, two in London N, Oand two in Leicestershire N


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.ased were not corrected for refractive error, or included people with opera.le cataract, for

e7ample, then these will .e over6estimates of the num.er of people re>uirin! re!istration9 Since

8H of the over =8s in the R/-0 study self reported the main cause of the vision pro.lem as due

to cataracts it is li+ely that the hi!h fi!ures reported .y R/-0 are .ecause cataracts and pro.a.ly

also refractive error have .een included9 As no ophthalmolo!ical e7am was conducted in theR/-0 sample this cannot .e confirmed9

I


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Ta.le I9< Studies on causes of visual impairment %ethods/ame Location Aims -nclusion

CE7clusion&riteria

Samplesi2e

Responserates

/um.er-ncluded

A!eCse7 etc

(i.son et al9


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Ta.le I9 Studies on causes of visual impairment Results

ormald et al


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as et al9


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(laucoma


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Ta.le I9 #revalence of visual acuity .efore and after e7clusion of cataracts and refractive error 3RE4 usin! data reported from individual studies on the

causes of visual impairment as reviewed in the chapter

Study 5isual impairment criterion A!e (roup

H#revalenc

e

H of visual

impairment


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Ta.le I9I Estimated prevalence of re!istered .lind and partially si!hted in En!land in 11< 3calculated .y the authors4I9

All a!es 16I 86


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Ta.le I98 Actual re!istration fi!ures for 111 for people a!ed =8 and over in En!land N


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Chapter 5

Prevalence of visual disability and visual impairmentin children in the United Kingdom

8=


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@ntroduction

This chapter summarises the literature relatin! to the prevalence of visual impairment in children

in the UK9 The first section concentrates on nationwide surveys, a num.er of which R/-0

played a leadin! role in9 ata from the lar!er local 3rather than national4 surveys are thensummarised9

The methods for each national survey are summarised in ta.le 898 and the results in ta.le 89;9

The surveys from !eo!raphically defined areas are summarised in ta.le 89=9

There are no a!reed definitions of visual impairment amon! children, an issue discussed in detail

elsewhere9 NI1O Terms such as visual impairment and visual disa.ility have .een used to mean

different thin!s in different studies and conte7ts9 As far as possi.le, we have therefore defined

what the outcomes were in the various studies9

)he prevalence of disability among children= 5PCS surveys of disability in 4reat "ritain*"one et al 1+,+- .>10

Summary

This is the report of the


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c4 who attends a special school or special or remedial unit of an ordinary school because of

health or behaviour problem % disabilities or learnin$ difficulties?

d4 who attends an ordinary school but is limited in tain$ part in school activities because

of health or behaviour problems or disabilities?

e4 whose health % behaviour of development causes worry that he or she may have a lon$

term health problem% physical or mental disability or handicap?0

All households with the answer ?yes@ to one or more of these 3sift4 >uestions were included in

the sample for interview9 The >uestions and severity scores are shown in ta.le 89uestions shown in ta.le 89


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Figure /13Flow chart showin! the num.ers of participants at each sta!e of the '#&S


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)able /13Seein! Severity scores for children a!ed ;6


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)able /!3Seein! Severity Scores for children a!ed 8 and under N0one and %elt2er


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Communal establishments

A list of institutions providin! residential care for children was o.tained from various

!overnment departments9 This list was then sent to the !eneral mana!ers of health authorities,

directors of social services, directors at the administrative head>uarters of voluntary andcharita.le or!anisations, and chief education officers as+in! the recipients to amend and update

it9 The desi!n is shown in fi!ure 899 ,I< esta.lishments were found in this way9 -n order to

identify those esta.lishments that contained children who were eli!i.le a ?census form@ was sent

to each of these esta.lishments as+in! for the name and a!e of each child and indicates whether

they were disa.led9 The form stated thatG

-' child should be re$arded as disabled if he/she has difficulties with everyday activities

because of a lon$term health problem. his includes physical% mental and behavioural problems

which are chronic in nature.2

The same interview >uestions were as+ed as in the private households) children:s survey9-nterviews were o.tained for a ma7imum of I children in each esta.lishment9 For the communal

esta.lishments a wei!ht was applied to compensate for inclusion of different proportions of

institutions accordin! to the num.er of residents9 -n .oth surveys wei!hts were applied to allow

for non6response and to .rin! the sample estimates up to the population estimates9

;


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Figure /!3Flow chart showin! the num.ers of participants at each sta!e of the '#&S


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Results

,I< esta.lishments were sent the census forms9 =H responded9 The hi!hest response rates

were from esta.lishments administered .y health authorities 3D8H4 and the lowest from

esta.lishments run .y voluntary and charita.le or!anisations 3=;H49 The analysis of data in thecensus forms indicated that ;D= 38H4 of institutions were eli!i.le to .e included in the survey9

The ma*ority of the remainin! =8H were short6term homes9 All esta.lishments with more than !0

Summary

This report is concerned with .lind and partially si!hted children and their needs9 The survey

was .ased on interviews carried out in April and %ay


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re!ion with a pro.a.ility accordin! to the total num.er of school children in the area9 out of

the = selected LEA:s co6operated in the survey9

The prevalence estimates were .ased on the num.er of school children 3a!ed .etween and


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Scotland and ales9 There were over


87/120

Results

-nformation was o.tained from LEAs representin! =;H of the population a!ed less than

Summary

A postal >uestionnaire of local education authorities 3LEAs4 carried out .y R/-0 in 119 A

prevalence estimate of 9ICuestionnaire as+ed a.out num.ers of children, a detailed a!e .rea+down and

presence of other disa.ilities9

Results

The response rate was ;8H9 A prevalence estimate of 9IC


88/120

Summary

The prevalence and causes of partial si!ht and .lindness were investi!ated in


89/120

Results

Five children had .est corrected visual acuity of less than ;C;19 All were re!istered .lind9 'ne

additional child who had never .een ophthalmolo!ically assessed was also included 3in the upper

estimate for prevalence4 who was thou!ht to .e .lind followin! measles encephalitis and ;

month of a!e and who attended a school for educationally severely a.normal9 Ei!ht children had.est corrected visual acuity of .etween ;CI and ;C;1 inclusive9 'nly three had .een re!istered

as partially si!hted and none as .lind9 A further three children had presentin! 5A B;CI that

improved to 5A;CI after correction9 Two children were reported as havin! refractive errors,

no dia!nosis was determined for the other child9 These three children were included in the upper

prevalence estimate of partial si!ht9

Comment

The study included a lar!e proportion 3over 1H4 of children .orn in one wee+ in


90/120

Results

'f I newly dia!nosed children, ; 3==H4 had additional non6ophthalmic disorders or

impairments 3S5-C0L plus49 Total yearly incidence was hi!hest in the first year of life, .ein! IW1

38H &- W;6IW84 per


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impairment as their primary special educational need9 This !ives a prevalence of 98C


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)able // Methods used in the national surveys of visual impairment in children

6ame ?ocation

and

date of

survey

@nclusion

82Dclusion

Criteria

%esign and

methods

Visual

measurement

Sample siEe Response

rates

6umber

@ncluded

5PCS

isa.ility

Survey

30one etal.


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6ame ?ocation

and

date of

survey

@nclusion

82Dclusion

Criteria

%esign and

methods

Visual

measurement

Sample siEe Response

rates

6umber

@ncluded

#ec+am


94/120

)able /7 Prevalence estimates obtained from the surveys of visual impairment in children

Survey 'hat the prevalence estimate refers to Age Prevalence

estimate

81


95/120

Locally based surveys

There have .een a num.er of estimates of visual impairment in !eo!raphically defined

populations in the United Kin!dom9 The main characteristics and findin!s of the lar!er and more

ri!orous studies are presented in ta.le 89=9 The Flana!an study is nota.le .ecause it comes from/orthern -relandG the national surveys presented a.ove were all restricted to (reat 0ritain9

These studies have used a ran!e of methods, sources, and definitions, outcome measures,

limitin! the scope to !enerate a summary estimate9 $owever, the findin!s are .roadly similar to

the national surveys of visual impairment, with prevalence estimates around


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Ta.le 89=9 &haracteristics and findin!s of surveys in !eo!raphically defined populations

Study and

year

Setting Method Main findings

&rofts


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5verall comments

%efinitions used

A +ey issue is the variation in definitions used for visual impairment and in the criteria used .y

local education authorities to identify children in need of services9 'ne survey as+ed visualimpairment services how they identified visually impaired children and multi6disa.led visually

impaired children9 The criteria are descri.ed in ta.les 89D and 89 .elow9

)able /,3 criteria used by visual impairment services to identify a visually impaired child

from a sample of 1/! providers *Clunies:Ross 1++9-.>;0

A child who is Veducationally si!nificantly visually impaired)9

(enerally this means children with a visual acuity of ;C


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The variation in definitions and policies was hi!hli!hted in the recent report from ales

3summarised in ta.le 89 = a.ove4 carried out .y the elsh Assem.ly (overnment in 119 This

report noted that ?Xthere are considera.le differences in policies for referrals across the elsh LEAs9@ and that ?-n some areas the service for visually impaired children and youn!

people has included children and youn! people with a sli!ht reduction in visual acuity who may

only .e seen .y them twice6yearly or annually9 -n other areas, these childrenCyoun! people would

not meet the descriptors for intervention9@ N8O9 The 5isual -mpairment Scotland pro*ect

N8Oused a modified version of a visual impairment classification system first developed in

Scandinavia, called the /'RSY/ system N8IO9 The tar!et population was ?children with

si!nificant visual impairment@ under the a!e of ual to or worse than ;C


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Chapter 7

Visual acuity and vision related uality of life

D


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@ntroduction

5isual acuity is a !ood indication of the de!ree of vision loss, .ut may not reflect an individual)s

own perception of how vision affects their everyday life, from the a.ility to perform every day

tas+s or the psycholo!ical and social conse>uences of reduced vision9 A num.er of>uestionnaires have .een developed, primarily in the US, to measure visual function C vision

related >uality of life N8;O9 'nly two scales6 the /ational Eye -nstitute 5isual Function

uestionnaire 3/E-65F4 N8=O and the -ndian 5ision Function uestionnaire 3-/65F4 N8DO

were developed from patient elicited pro.lem statements collected from focus !roups, in

contrast to other scales developed from clinical *ud!ement9 The need for a specific measure of

visual function led to the development of A 8uestionnaire was ori!inally devised in the

US from focus !roups of people with ma*or causes of eye disease The /E- 8uestionnaire was later shortened to 8 items, .ased predominantly on the responses from those

with eye disease and visual impairment, and also from a minority !roup without eye disease N8O9

The /E-65F 8 has .een used in used to show that those with a!e6related macular disease

N;1O, !laucoma N;uestionnaire has also .een used to show the lon!itudinal .enefit of vision reha.ilitation

amon!st a !roup without correcta.le visual impairment9N;;, ;=O espite some concerns a.out

the ran!e of measurement o.tained with the /E-65F N;DO, it has also .een used in adult

populations 3a!ed I1 years or more4 to show that those with visual impairment have lower scores

compared to those without reduced visual acuity N;, =1O9 Use of the /E- 5F in non US

populations is more limited especially amon! the older population who are li+ely to e7perience

hi!her levels of visual difficulties than youn!er a!e !roups9 To our +nowled!e there are no

pu.lished vision function data from a population .ased UK sample9 A nested trial within the

%R& Elderly Trial permitted the possi.ility of collectin! these data9 Full details of the nested

trial desi!n and results have .een pu.lished elsewhere N=


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impairment 3acuity less than ;C


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B;C


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Ta.le ;9< /E- 5F 8 uestions and su.6scale scores

/E-65F su.6scale /um.er of

>uestions used toderive su.6scale

score

/E-65F >uestion

num.ers used

uestions as+ed

(eneral health < < #erception of overall health 38 levels4

(eneral vision < #erception of eyesi!ht 3; levels4

'cular pain I,uirin!

near vision, and findin! somethin! on a crowded shelf

istance activities D,,


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Ta.le ;9 /E-65F 8 scores and association with visual acuity

62@ VFG subscales Responses by

category

6 *-

6umber *- &ith

VAH781! in each

category of 62@:

VFG subscale

5R VAH781! *+/

C@-

6umber *- &ith

VAH781, in each

category of 62@:

VFG subscale

5R VAH781, *+/

C@-

Mean logMAR Snellen euivalent

4eneral health

/o pro.lems


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Total


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#6value B1911< B1911< B1911uired9

As descri.ed in &hapter < the methods of measurin! visual pro.lems use two different

approachesG self reported visual difficulties 3reviewed in &hapter 4 and clinical measures of

visual acuity 3reviewed in &hapter 49

Prevalence of visual difficulties

The estimates of visual difficulties 3descri.ed as visual disa.ility in some studies4 derivepredominantly from lar!e !overnment surveys and show, when usin! similar survey methods

and criteria for visual disa.ility, 3as in the '#&S surveys of


110/120

are derived are not clearly presented they are of the order of 81H or less in most !overnment

surveys9 The representativeness of the surveyed population is therefore difficult to assess9

e advise a!ainst the use of data on self reported si!ht pro.lems to estimate the levels of visual

impairment in the population9

Prevalence of visual impairment

Studies usin! visual acuity measurements have used various criteria for definitions and cut points

of visual impairment9 The results from two studiesG /ational iet and /utrition Study 3//S4,

and %R& Assessment Trial that were nationally representative of the older population and use

uncorrected presentin! 5A and similar cut points are !iven in the ta.le .elow 3unpu.lished data

from //S provided .y r van der #ols and unpu.lished data on 5A B;C


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Two studies provided estimates of .lindness usin! international criteria of 5A B C;19 -n the

%R& assessment trial the estimates for the =8 a!e !roup were 9< 38H &-


112/120

-nternational data also provide some reassurance that the prevalence of re!istera.le vision in the

UK is similar to that e7pected from the population studies9 -n a recent poolin! of studies

predominantly from the USA N=O the prevalence of .lindness .ased on .est corrected 5A BC;1

was very similar to the percent prevalence for re!istration fi!ures for En!land in the compara.le

a!e !roups 3as shown in Ta.le I9I49

Estimates of re!istera.le visual impairment due to a!e related macular de!eneration in the UK

also su!!est !ood a!reement .etween predictions and o.servations N=I, =8O9 'wen at al N=IO

pooled the data from international studies to provide a!e specific prevalence rates for visually

impairin! a!e related macular de!eneration and applied these rates to the UK population to

o.tain e7pected num.ers of those eli!i.le for re!istration9 The estimated num.ers were uestions on seein! difficulty for a variety of ethnic !roups and found that

the hi!hest levels were in 0lac+ &ari..ean populations with low rates for Asians9 At present the

data are too sparse and unrelia.le to comment on the prevalence of visual impairment or specific

types of eye disease in different ethnic !roups9

The reasons for hi!her levels of vision impairment in women re>uires further understandin!, in

particular the e7tent to which this reflects under utilisation of services9

The reasons for hi!h levels of treata.le conditions in the older population re>uires further

investi!ation9 Some indications of possi.le .arriers was provided .y our randomised trial of


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screenin! visual acuity .y a practice nurse N=uent intervention, and screenin! did not reduce levels of visual

impairment9 Key e7planations for the lac+ of effect identified were under6detection of

uncorrected refractive error and that only around half the recommendations for referral to an

ophthalmolo!ist resulted in referral .y the !eneral practitioners9 -n addition participantsthemselves reported an unwillin!ness to self6refer to optometry services for further assessment,

citin! fear of costs and lac+ of perceived need9

Recommendations

Policy

The estimates provided from the studies of visual acuity for the older population are sufficiently

consistent for !eneral purposes of plannin! and estimatin! the num.ers of people in the UK with

vision impairment9 $owever we caution that these estimates are seen as appro7imations and notas ?ta.lets of stone@ as prevalence estimates will vary from place to place and over time and

.ecause all estimates carry a ran!e of uncertainty 3as e7pressed .y the 8H confidence interval49

Studies in the older population have also consistently shown that a.out 81H of visual

impairment is due to treata.le conditions i9e9 cataract and refractive error9 This proportion

diminishes with increasin! a!e due to the hi!her prevalence of a!e related macular de!eneration

as a cause of vision impairment9 -ncreased awareness of these facts is important for a!encies

dealin! with visually impaired people9 Appropriate action e9!9 media campai!ns and advocacy is

re>uired to ensure that .oth eye care providers and older people themselves are aware of these

conditions and of the current unaccepta.ly hi!h levels of untreated conditions9

Strate!ies to identify the most cost effective way of tar!etin! the older population, includin!

novel approaches to screenin! older people, are ur!ently needed

Standards for Reporting and Measurement

e have shown the considera.le variation in definitions and cut points used in the UK .ased

studies9 This applies even more at the international level especially when comparin! data with

the US where very different definitions on .lindness and low vision are used9 A recent $'

-nformal &onsultation or+in! (roup N;O has made recommendations for measurin! acuity andit is hoped that this will !o some way to improvin! the consistency of reportin! across studies9

The or+in! (roup recommended that vision assessment in population6.ased studies should

include a measurement of visual acuity usin! Lo!%AR charts at distance and near under

standardi2ed conditions9 -nformation collected should recordG 3i4 monocular and .inocular

distance presentin! visual acuity, whether a method of vision correction is used 3e9!9 spectacles4

and, if so, the type and power of vision correction deviceM 3ii4 monocular and .inocular near

presentin! visual acuity at I1 cm, whether a method of vision correction is used 3e9!9 spectacles4

and, if so, the type and power of vision correction deviceM 3iii4 monocular and .inocular .est6

corrected visual acuity at distance and near, followin! refraction usin! an a!e6appropriate

addition for near acuity9 Few UK studies have used .est corrected visual acuity lar!ely .ecause

of the e7tra resources re>uired to collect these data9 #resentin! .inocular vision impairment

I


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pro.a.ly represents the measurement of vision most closely related to vision e7perienced .y the

individual9 $owever, an additional measurement of .est corrected visual acuity would clearly

identify the level of refractive error and the remainin! vision loss due to eye diseases9 The

or+in! (roup also su!!ested that revisions should .e made to the cate!orisation of visual

acuity as in -&6uality of life9 e emphasi2e the need to thorou!hly test all >uestions

.efore use in surveys9

There was a su.stantial lac+ of clarity and detail in some of the reports that we reviewed9 e

recommend that reports which present novel research findin!s 3.ut are not su.mitted for

pu.lication in academic *ournals4 should conform to the same standards of reportin! as the

formal peer review process of academic *ournalsM for e7ample the !uidelines of the -nternational

&ommittee of %edical Journal Editors N==O(www9icm*e9or!).

8


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Ta.le =9< Recommendations for cate!orisation of visual acuity N;O

&ate!ory #resentin! distance visual acuity

orse thanG E>ual to or .etter thanG

%ild or no visual

impairment

1

;C


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References


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9 Ro.inson R,eutsch J, Jones $S, Youn!son6Reilly S, $amlin %, hur*on L et al,

Unreco!nised and unre!istered visual impairment9 0r J 'phthalmol9 uestionnaire to elderly peopleG findin!s from The %R& Trial of the Assessment and

%ana!ement of Elderly #eople in the &ommunity9 0%J 11


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mana!ement of older people in the community9 0r J 'phthalmolo!y 11IM DDG ;86

=19

I19 #raat A and K9 S, efinin! si!ht difficulties for education and employment research9

0ritish Journal of 5isual -mpairment 11M


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89 %an!ione &%, Lee #, (utierre2 #R, Sprit2er K, 0erry S, $ays R, evelopment of

the 86item /ational Eye -nstitute 5isual Function uestionnaire9 Arch 'phthalmol

11uestionnaire as

an interval measure of visual a.ility in low vision9 5ision Res 11


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=I9 'wen &(, Fletcher AE, ono!hue %, Rudnic+a AR9, $ow .i! is the .urden of visual

loss caused .y a!e6related macular de!eneration in the UK 0r J 'phthalmolo!y,

11M D=G

Blindness in the UK -prevalence

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