CLINICAL EXAMINATION OF VISUAL SYSTEM

JUST A REVISION……

Some formulas and concepts … Some tips to remember certain aspects in

clinics.. “Normal Values” Few questions for discussion…

ACCOMMODATION Amplitude of accommodation

Hofstetter formula Maximum = 25 – 0.4 X age Average = 18.5 – 0.3 X age Minimum = 15 – 0.25 X age

AC/A

AC/A=IPD (in cms) + NWD (in meters)(horizontal near phoria (Hn)-horizontal distance phoria (Hf))

Eso is taken as plus and exo is taken as minus while the values are entered in the formula

Low and high AC/A in relation to excess or insufficiency. Insufficiency always has a low AC/A e.g. CI, DI

(insufficient = low) Excess always has a high AC/A e.g. CE, DE (excess =

high)

Treatment of vergence dysfunction High AC/A = Excess (CE, DE) = lenses are Effective in

treatment Normal AC/A = (Basic Eso, Basic Exo) sometimes effective Low AC/A = Insufficiency (CI, DI) = lenses are Ineffective

in treatment.

Way to remember that plus lenses induces exo

The plus sign (+) looks like an rotated X

VERGENCE What prism stimulates what type of vergence

Mnemonic = “BIN BOP”

BI stimulates Negative Fusional Vergence Negative implies divergence

BO stimulates Positive Fusional Vergence Positive implies convergence .

Prism The prism makes the eye deviate in the direction of the apex When correcting eye deviations, point the APEX toward the

direction of deviation

EOM

Intort

Intort

Also remember SIn RAd

1 = 2PD 1MM = 7

7 or 15 prism

15 or 30 prism

30 or 60 prism

45or 90 prism 45°or > 90

prism

Between center of pupil and pupillary border.

Pupillary border.

Between pupillary border and limbus

Limbus

Beyond limbus

Recording Position of Reflex

HESS CHART

PURPOSE: To diagnose paretic/paralytic muscle. EQUIPMENT: Red-green filter Hess screen(a screen that has a red

dot in 8 inner positions and 16 outer positions)

Green light projector

PROCEDURE

The test is done at a distance of 50 cms from the Hess screen with the red-green goggles over the patient’s habitual correction.

The eye with the green filter is the testing eye and the eye with the red filter is the fixating eye.

The patient is asked to coincide the green light projector against the individual red dots.

Recording: - The two charts are compared - The smaller chart indicates

the eye with the paretic muscle - Larger chart eye with the

normal but over acting muscle

THE FOLLOWING ARE TRUE ABOUT HESS'S TEST: a. Ocular dissociation is necessary

b. It can be used to calculate the amount of ocular deviation

c. A visual acuity of better than 6/12 is essential

for the testing

d. The eye with restricted movement usually has a smaller field on the the Hess's chart

e. It can be used to test the field of binocular single vision.

True

True

True

True

False

DIPLOPIA CHARTING

Purpose: To diagnose paretic muscles.

Equipment: Red - Green filter Streak light

PROCEDURE

The patient is asked to wear the red-green goggles over his habitual correction with the red filter in front of the right eye.

The patient is asked to fixate the streak light with his paretic eye (in order to elicit the maximum deviation).

The light is moved from the primary position into all of the other eight directions of gaze.

For each direction the patient is asked to inform the examiner about the kind of diplopia he experiences (horizontal/vertical/crossed/uncrossed) and the amount of separation between the red and green light

The direction of greatest separation will identify the paretic muscles

NORMAL VALUES

Parameters Normal findings

Visual Acuity in Log MAR 0.0

Monocular Visual field (T,I,N,S) 90,70,60,50 degrees

Pupil diameter 3 – 5

Pinhole Diameter 1.2mm

Central AC depth 3.6mm

Peripheral AC depth VH grade IV

Axial Length 24mm

Corneal Diameter 11.7 mm

CCT 0.52mm

Peripheral corneal thickness 0.7mm

IOP 10-21 mm Hg

NPC Less than 10 cms ( 6cms according to scheimen)

Crystalline lens thickness 3.5 to 4 mm

Steropsis 40 arc seconds

Optic disc size 1.5mm in dia

Distance and direction of macula from optic disc

500 microns temporal to disc

Dimension of normal blind spot in degrees

9 V, 7 H

Anterior Curvature of lens 10mm

Posterior curvature of lens 6mm

Standard room illumination

Luminance of back lit snellen drum 120-150 cd/m2

Illuminance for externally illuminated chart

480 – 600 lux

Ideal letter contrast of visual acuity chart

90 %

Standard Visual acuity opto type Snellen optotype

Letter size of 6/60 82.7mm

1.32 mm pinhole can neutralize 4 D of power

Ideal visual acuity chart for preschoolers

Lea’s symbols

Ideal visual acuity chart for school children

Snellen Acuity

Moderate visual impairment range 6/18 to 6/60

Profound Visual impairment range Less than 6/60

Dioptric range measurable with the lensometer ( manual)

+24D to -24 D

Donder’s table for 10 yrs 14 D

20 yrs 10 D

30yrs 7 D

40yrs 4.50 D

50yrs 2.50 D

60 yrs 0.75 D

Expand PERRLA Pupils Equal Round Reacting to Light and Accommodation

Ideal field test for central scotoma Amsler’s grid

Ideal visual acuity methods/ charts for infants

CSM, Fixation tests.OKN, Preferential Looking tests

Corneal endothelial cell density 3000-4000cells/mm2

VVID 10.6mm

Types of test plates in Ishihara Transformation plate, vanishing plate,Hidden digit, diagnostic plates

Blink rate 14-17 blinks/ minute

Schimmer;’s test 1 More than 15 mm in 5 minutes

TBUT More than 10 seconds

Normal LPS action 15 - 18mm

MRD 1 4 – 4.5 mm

Fusional range in synaptophore +25 degrees to -5 degrees

PFH 9- 12 mm

HVID 11.7mm

Cup to disc ratio 0.3 to 0.5

TEST Normal values Std deviation

Distance Cover test 1 exophoria +/- 2

Near cover test 3 exophoria +/-3

AC/A ratio 4/1 +/-3

Distance NFV X/7/4 4/3/2

Near NFV 13/21/13 4/4/5

Distance PFV 9/19/10 4/8/4

Near PFV 17/21/11 5/6/7

NPC Break: 5cmsRecovery:7 cms

Break: +/- 2.5 cms recovery: +/- 3

Monocular Accommodative facility

5.5 – 7 cpm +-2.5 cpm

Binocular Accommodative facility

5-10 cpm +/- 5 cpm

MEM +0.50 +/- 0.25

NRA +2.00 +- 0.50

PRA -2.37 +/-1.00

QUESTIONS…

THE FOLLOWING ABOUT FRESNEL'S PRISM ARE TRUE: a. its power is determined the thickness of the base

b. the visual acuity is affected by the power of the prism

c. it is normal fitted to the front of the spectacle

d. the maximum prismatic power than an adult can tolerate is usually around 15 dioptres

e. dividing the strength of the prism between the two eyes improves the comfort of the patientTrue

false

false

false

True

REGARDING THE FUSIONAL RESERVES:

a. the horizontal fusional reserve is higher than the vertical fusional reserve

b. the positive fusional reserve is higher for distance than near

c. the positive fusional reserve is affected by the subject's accommodative reserve

d. the horizontal fusional reserve decreases with age

e. the vertical fusional reserve is decreased in patient with reduced accommodative reserve

True

False

True

True

False

WITH REGARD TO BAGOLINI'S GLASSES:

a. the test is only useful for adult b. contain two lenses one with striation set at 90

degrees and the other at 180 degrees

c. amblyopia in one eye always result in perception of only one line

d. a cross is only seen in subjects with binocular single vision

e. can be used to test the presence of abnormal retinal correspondence when combined with cover / uncover testing

True

False

False

False

True

THE RANGE OF STEREOSCOPIC VISION AS MEASURED BY THE FOLLOWING TESTS ARE TRUE:

a. 3000 to 60 seconds of arc with the Frisby's test

b. 3000 to 40 seconds of arc with the Titmus test

c. 480 to 15 seconds of arc with the TNO test

d. 1200 to 600 seconds of arc with the Lang stereostest

e. 3000 to 15 seconds with the synotophore

True

False

False

True

True

MYOPIC SHIFT OCCURS IN:

a. keratoconus b. spasm of the ciliary body

c. staphyloma

d. lens subluxation

e. brittle diabetes

True

True

True

True

True

INDUCED HYPEROPIA OCCURS IN:

a. cystoid macular oedema

b. wearing of RGP lens

c. presbyopia

d. nuclear sclerosis

e. posterior dislocation of the lens

True

True

True

True

False

THE FOLLOWING ARE TRUE ABOUT INDIRECT OPHTHALMOSCOPY:

a. the aerial image of the retina is formed between the subject's eye and the condensing lens

b. the aerial image of the retina is an inverted real image

c. in an emmetrope, a 30D condensing lens produces a larger retinal images than a 20D lens

d. in an emmetrope, a 30D condensing lens gives a larger visual field than a 20D lens

e. for a given condensing lens, the aerial image of a hypermetropic retina is larger than a myope.

True

True

True

False

False

THE FOLLOWING ARE TRUE ABOUT DIRECT OPHTHALMOSCOPY:

a. the field of view is about 25º

b. refractive error has a significant effect

c. the magnification is 15X

d. the field of view increases as the distance between the observer and the patient increases

e. the fundus of a patient with high astigmatism can be sharpened with correcting lenses

False

False

False

True

True

IN COLOUR VISION TESTING:

a. the illumination should be equivalent to the morning daylight in northern hemisphere

b. Farnsworth-Munsell hue 100 test uses 84 coloured discs

c. the discs of Farnsworth-Munsell hue 100 tests have the same brightness and saturation.

d. D-15 is a modified Farnsworth-Munsell (FM) hue 100

e. Ishihara is most useful for picking up congenital red-green defect

False

True

True

True

True

Amsler's grid: a. Should be read at 60cm

b. when used at the correct distance each square subtend one degree of arc on the retina

c. Of the most commonly used type contains 360 small squares

d. Of the most commonly used type contains small squares each measuring 5 X 5mm

e. Is useful for self-monitoring in patients at risk of retinal detachment

False

False

False

True

True

IN APPLANATION TONOMETRY

a. the area flattened is 13.06mm²

b. based on Imbert-Fick principle

c. the intraocular pressure (IOP) can be calculated by the

formula area=force/IOP

d. increased corneal curvature is associated with a falsely

high IOP

True

True

True

False

THE FOLLOWING ARE TRUE ABOUT THE JONES' TEST IN A PATIENT WITH EPIPHORA:

a. It is used to detect functional epiphora

b. It should be performed before syringing of the nasolacrimal system

c. A positive Jones I test suggests either hypersecretion or functional epiphora

d. A positive Jones II test suggests partial blockage below the lacrimal sac

e. Jones II test is not necessary if Jones I test is positive

True

True

True

True

False

IN THE MEASUREMENT OF THE PALPEBRAL FISSURE:

a. in patients with malposition of the lower lid, MRD gives a more accurate measurement of ptosis than the nterpalpebral fissure

b. MRD is the distance between the upper eyelid margin and the corneal light reflex in the primary gaze

c. ptosis is present if the MRD is less than 2 mm

d. the MRD is increased in facial nerve palsy

e. in normal persons, the upper lid is at the level of the limbus

True

True

True

True

False

THE FOLLOWING ARE TRUE ABOUT HERTEL'S EXOPHTHALMOMETER:

a. the measurement may be affected by the presence of strabismus

b. the foot plate should rest on the lateral canthus rather than the orbital for accurate reading

c. patients of African origin has a higher normal reading than European

d. a difference in readings between the two eyes of up to 5 mm is normal in up to 50% of the population

e. can be used to monitor the progress of Grave's eye disease

True

True

True

False

False

SLIT LAMP ILLUMINATION TECHNIQUES

1. DIFFUSE ILLUMINATION

Settings Microscope positioned at 0° Angle of slit illumination

system approx. 30° - 50° Desired Mx.

Main Applications General surveys of anterior eye

segments. Assessment of soft contact

lenses.

2. DIRECT FOCAL ILLUMINATION

Main Applications Illuminating and viewing

path intersect in the area to be examined (e.g. Individual corneal layers)

Cells in the aqueous humour.

The crystalline lens is viewed.

Settings The angle between

illuminating and viewing path should be as large as possible (up to 90°)

Slit length should be kept small (about 0.1 mm to 0.2 mm)

Mx variable

DIRECT FOCAL ILLUMINATION

3. INDIRECT ILLUMINATION

Settings Narrow to medium

slit width Desired Mx

The axes of illuminating and viewing path do not intersect at the point of image focus.

Reflected, indirect light illuminates the area of the anterior chamber or cornea to be examined.

This method provide glare free viewing, always seen along with direct illumination

4. RETRO ILLUMINATION There are two types of

retro-illumination. Direct retro-illumination

caused by direct reflection at surfaces such as the iris, crystalline lens or the fundus.

Indirect retroillumination caused by diffuse reflection in the medium, i.e. at all scattering media and surfaces in the anterior and posterior segments

Settings The slit width 1 - 2

mm wide and 4 - 5 mm high.

Direct alignment.

5. SPECULAR REFLECTION

Illumination and viewing system positioned such that the angle of incidence is equal to the angle of reflection .

Can see tear film, epithelium, posterior endothelium and keratic precipitates.

Settings This method is

monocular procedure.

High magnification

SCLEROTIC SCATTER

Settings A narrow vertical slit (1-

1.5mm in width) is directed in line with the temporal (or nasal) limbus.

Magnification as low as 6x - 10x is used

The room illumination is kept as dark as possible.

The principle behind sclerotic scatter is total internal reflection.

A halo of light will be observed around the limbus as light is internally reflected within the cornea, but scattered by the sclera.

Corneal opacity, edema or foreign body will be made visible by the scattering light, appearing as bright patches against the dark background of the iris and pupil.

7. OSCILLATORY ILLUMINATION A beam of light is rocked back and forth by moving the illuminating

arm or rotating the prism or mirror.

Occasional aqueous floaters are easier to observe.

8. TANGENTIAL ILLUMINATION The iris is examined under very oblique illumination while

the microscope is aligned directly in front of the eye.

Useful for examining tumours and naevi of the iris.

IN SLIT-LAMP EXAMINATION:

a. specular reflection is useful in examining the corneal endothelium

b. the angle of incidence and reflection are equal in specular reflection

c. total internal reflection is used in sclerotic scatter

d. in retroillumination, a secondary light source is used to illuminate a more anterior surface

e. corneal oedema is best highlighted with retroillumination