Desarrollo de Queratocono Con LC

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Development of Keratoconus After Contact Lens WearPatient Characteristics

Marian S. Macsai, MD; Gary A. Varley, MD; Jay H. Krachmer, MD

\s=b\A retrospective review of 398 eyes of199 patients with keratoconus revealed106 eyes of 53 patients with an associa-

tion between contact lens wear and thedevelopment of keratoconus. The ab-sence of keratoconus at the time of con-

tact lens fitting was confirmed by slit-lampexamination, keratometry readings, andmanifest refraction. Keratoconus was di-

agnosed after a mean of 12.2 years ofcontact lens wear. This group was com-

pared with patients with sporadic kerato-conus with either no history of contactlens wear or a history of contact lens wearafter the diagnosis. They were older at thetime of diagnosis, had central vs decen-tered cones, and had a tendency towardflatter corneal curvatures. We believe that

these patients suggest that long-term con-tact lens wear is a factor that can lead to

keratoconus.

(Arch Ophthalmol. 1990;108:534-538)

/" eratoconus (KCN) is a noninflam-matory disorder of the cornea

characterized by progressive conicalectasia with protrusion of the thinnedarea.1 It results in increasing myopiawith irregular astigmatism. Inferiorsteepening, corneal thinning, and irregular astigmatism may be the earliest signs of KCN. Other clinical signsinclude an epithelial iron ring, anterior stromal scarring, and striae anterior to Descemet's membrane (Vogt'sstriae). Early in its course, optical correction is achieved through spectacles.As the irregular astigmatism progresses, rigid contact lenses can bequite successful in restoring vision.When patients either have poor visionwith a contact lens or cannot wear one,surgery is performed.

The cause of KCN remains unclear.

Proposed causes include biochemical

alterations in collagenor

proteoglycanphysiologic activity.2'8 Many conditions in which KCN occurs have common causative factors. One group is

patients in whom an abnormality incollagen physiologic activity is an underlying theme. This includes Ehlers-Danlos syndrome, osteogenesis imperfecta, Marfan's syndrome, mitral valveprolapse, and other connective-tissuediseases.9 Familial cases, suggestingan inherited origin, have also beenreported.1015 Another group indicatesocular trauma as a common causativefactor. This includes Down's syndrome, atopy, Leber's congenitalamaurosis, and a history of mechanical eye rubbing.1626 Long-term contactlens wear may represent anothersource of ocular trauma. We definesporadic KCN as existing in a patientwho does not have Down's

syndrome,atopic disease, systemic collagen disease, a tapetoretinal degeneration, ahistory of eye rubbing, or a family history of KCN.

The relationship between contactlens wear and KCN has been controversial. In 1965 Hartstein27 reported 12cases of corneal warpage due to contact lenses. In 4 of these patients, theinduced astigmatism was permanent,and 1 patient developed KCN. In 1968Hartstein28 described an additional 4

patients in whom KCN developedwhile wearing hard contact lenses.

Three of these were patients with pre-fitting corneal astigmatism of lessthan 0.50 diopter (D). Two additionalcases of hard contact lens wearers whodeveloped KCN were reported byNauheim29 in 1969. Gasset et al30 proposed a circumstantial causal relationship between hard contact lens wearand the development of KCN. Despiteisolated reports of KCN developing inhard contact lens wearers, this association has been difficult to clarify. Manypatients with myopia and high astigmatism receive contact lenses for correction, and in these cases, it is not

surprising that KCN was diagnosedduring contact lens wear.

The numerous reports in the literature of patients with minimal myopiain whom KCN was diagnosed whilewearing contact lenses certainly suggest a relationship.282931 We have undertaken this study to answer twoquestions: Is there a group of patientsin whom long-term contact lens wearwas the probable cause of the development of KCN? If so, is KCN in contactlens wearers historically and clinicallydifferent from sporadic KCN?

MATERIALS AND METHODS

We retrospectively reviewed 386 charts of

patients seen in the Iowa Lions CorneaCenter, Iowa City, from 1984 through 1989with the diagnosis of KCN. Patients wereremoved from the study if they had any ofthe following exclusion criteria: previouspenetrating keratoplasty (35 patients); unobtainable pre-contact lens fit data (19 patients); Marian's syndrome (2 patients);Down's syndrome (37 patients); Leber'scongenital amaurosis (3 patients); previousocular surgery (2 patients); KCN with pellucid marginal degeneration (12 patients);eczema, asthma, or hay fever (55 patients);amblyopia (6 patients); family history ofKCN (10 patients); or a history of habitualeye rubbing (6 patients). Therefore, thisstudy group consists of 199 patients withsporadic KCN.

Historical data reviewed included age atthe time of examination, age at the time ofdiagnosis of KCN, sex, the history of contact lens wear before the diagnosis of KCN,and the history of contact lens wear afterthe diagnosis of KCN. Additional data collected on patients with a history of contactlens wear before the diagnosis of KCNincluded slit-lamp examination findings,manifest refraction, keratometry readingsprior to the fit of contact lenses, the reasonfor the contact lens fitting, the type of contact lenses worn, and the wear time including hours per day and number of years.

All patients received a complete eye ex

amination in the Iowa Lions Cornea Center.For this study, ocular data included Snellenvisual acuity with best manifest refraction,Snellen visual acuity with contact lenses,keratometry readings, the presence of inferior steepening, the amount of inferiorsteepening, cone location, and the presenceof an iron ring, anterior stromal scarring,or Vogt's striae. In addition, pachymetrywas performed on some of the patients centrally and equal distances above and belowthe center of the cornea using a Haag-Streit(Haag-Streit Ag, Berne, Switzerland) optical pachymeter or ultrasonic pachymetry(Pachysonic II, Teknar, Ine, St Louis, Mo)depending on the date of examination. All

patientswere

seen by one of us (J.H.K.). Theamount of inferior steepening was determined using the Soper Topogometer (To-pogometer Co, Houston, Tex) on a Bausch &Lomb Keratometer (Bausch & Lomb Ine,Rochester, NY). Cone location was determined by using both a Keeler-Kline Kera-toscope (Keeler Instruments Ine, Broomall,Pa) and slit-lamp examination. If the apexof the cone was in the central portion of thecornea, as defined by the vertical level of aconstricted pupil, it was determined to becentral (Figs 1 through 3).

The minimal criteria used to define KCNare a central or paracentral area of cornealthinning and protrusion that is detectable

Accepted for publication October 11, 1989.From the Iowa Lions Cornea Center, Depart-

ment of Ophthalmology, University of Iowa Hos-pital, Iowa City. Dr. Macsai is now with theDepartment of Ophthalmology, West VirginiaUniversity, Morganstown. Dr Varley is now withthe Department of Ophthalmology, the Cleveland(Ohio) Clinic Foundation.

Reprint requests to Iowa Lions Cornea Center,Department of Ophthalmology, University ofIowa Hospitals, Iowa City, IA 52242 (Dr Krach-mer).

on October 6, 2010www.archophthalmol.comDownloaded from
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Fig 1.Low-magnification lateral view of acentral cone in a patient with a long-term ( 11.5years) history of contact lens wear before the

diagnosis of keratoconus.

Fig 2.

Slit-lamp photograph of a central conein a patient with a long-term (13.0 years) history of contact lens wear before the diagnosis

of keratoconus. Note the presence of an ironring (arrows) and anterior stromal scarring.

Fig 3.

Slit-lamp photograph of an inferiorcone in sporadic keratoconus in a patient without a history of contact lens wear. Note the

presence of an iron ring (arrow) and anteriorstromal scarring.

Table 1.

Sex Distribution

Sex, No. (%)

M Total

Contact lens usebefore

keratoconus 24 (45.3) 29 (54.7) 53Keratoconus

before contact

lens use 34 (43.6) 44 (56.4) 78Keratoconus

with no

contact

lens use 29 (42.6) 39 (57.4) 68Total 87(43.7)112(56.3) 199

on slit-lamp examination in a patient withirregular keratometric mires and no signsof previous corneal inflammation. To measure inferior steepening, patients wereseated at a Bausch & Lomb Keratometer.The keratometry mires were aligned in thevertical axis while the patient fixated centrally on the Soper Topogometer. The fixation light on the topogometer was movedsuperiorly and the keratometer mires wereobserved as the patient looked up. If themires separated, then the presence of infe

rior steepeningwas

confirmed. The amountof inferior steepening was quantitated byrealigning the keratometry mires while thepatient looked up, and the change in diopters was recorded.

To establish whether inferior steepeningor a thin central cornea was present in normal patients with or without a history ofcontact lens wear, 100 eyes of 50 normalcontrols of similar age and sex distributionwere examined. Twenty-five controls fromthe University of Iowa contact lens clinicwho had a history of contact lens wear wereexamined. In addition, 25 University ofIowa employees who had no history of contact lens wear served as controls. Controls

were examined 20 minutes after lenseswereremoved. Keratometry readings and thepresence and amount of inferior steepeningwere recorded after slit-lamp examination.Corneal thickness was determined centrally and at two points peripherally in the3-, 6-, 9-, and 12-o'clock meridians using ultrasonic pachymetry. A thin central corneawas defined as either a central reading ofless than 0.490 mm or a paracentralpachymetry reading that was less than thecentral reading. The central cornea thickness criteria were selected based on the

Prospective Evaluation of Radial Kerato-tomy (PERK) Study, in which 90% of thepatients had a central corneal thicknessgreater than 0.490 mm," and all paracentral readings were greater than the centralreadings.33

Three groups of patients were established. The first group was defined as patients with a history of contact lens wearbefore the diagnosis of KCN. The absence ofKCN at the time of contact lens fitting wasconfirmed by slit-lamp examination, keratometry readings, and manifest refraction.The second group included patients withKCN and no history of contact lens wearprior to or after the diagnosis of KCN. The

third group included patients with diagnosis of KCN before wearing contact lenses.In the group of patients with a history of

contact lens wear before the diagnosis ofKCN, a paired t test was performed to compare the manifest refraction prior to contact lens fit with that at the time of examination. Similarly, keratometry readingswere analyzed with a paired t test.

In addition to these three patient groupsdefined by a history of contact lens wear,three KCN severity categories were definedbased on Snellen visual acuity. Visual acuity better than 20/40 with spectacles wasdefined as mild KCN. Moderate KCN included eyes in which the visual acuity with

spectacles was 20/40 or worse and visualacuity with best contact lens fit was betterthan 20/80. Severe KCN was defined as visual acuity with best contact lens fit equalto or worse than 20/80. The eyes within eachof the three patient groups were comparedsuch that eyes of equal severity were analyzed using an overall t test evaluating ageat the time of diagnosis, age at the time ofexamination, manifest refraction, keratometry, amount of inferior steepening, andpachymetry at the apex of the cone. 2analysis was used to compare the cone

location, iron ring, presence of anteriorstromal scarring, and Vogt's striae.

RESULTS

A retrospective review was done on386 patients. We excluded 187 patientsfor reasons previously stated. A totalof 199 patients were included, 87(43.7% ) of whom were women and 112(56.3% ) of whom were men. Sex distribution was similar within each groupof patients (Table 1). No patients hadunilateral KCN. The average age at thetime of diagnosis in patients with ahistory of contact lens wear before thediagnosis of KCN was 32.0 years(range, 26.5 to 53 years) in female patients and 31.3 years (range, 25 to 48years) in male patients. They were fitwith lenses at a mean age of 20 years(range, 13 to 36 years). Nine (17%)were fit at age 25 years or older. Patients with KCN who had not worncontact lenses and those in whom KCNwas diagnosed before contact lens fitting were significantly younger(P < .0001) at the time of diagnosis(Table 2). Ninety-seven percent werediagnosed at 25 years old or younger.



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Table 2.Patient Age at the Time of Diagnosis

Mean Age, y (Range) [SD] by Sex

M

Contact lens use before keratoconus_32.0 (26.5-53) [3.95]_31.3 (25-48) [4.35]Keratoconus before contact lens use_19.6 (13.5-25.5) [2.81]_18.0 (13-24) [2.57]Keratoconus with no contact lens use 18.0 (14-28) [2.65] 19.3 (13.5-29) [3.51]

Table 3.Patient Age at the Time of Examination

Mean age, y (Range) [SD] by Sex

M

Contact lens use before keratoconus 33.4 (27-56) [4.75] 32.5 (26-53.5) [4.21]Keratoconus before contact lens use 30.6 (15-43) [5.28] 29.0 (16-46) [5.10]Keratoconus with no contact lens use 31.8 (14.5-48) [3.85] 29.3 (15.5-51) [4.45]

There was no statistically significantdifference in patient age at the time ofexamination (Table 3).

Of the 199 patients, 53 (27% ) had ahistory of contact lens wear beforeKCN, 68 (34% ) had no history of con

tact lenswear before or after the

diagnosis of KCN, and 78 (39% ) had a history of KCN before wearing contactlenses. These three patient groupswere classified by KCN severity (defined in the "Materials and Methods"

section) according to Table 4.The 53 patients with a history of

contact lens wear before the diagnosisof KCN had been wearing contactlenses for an average of 12.2 years(range, 5.5 to 22 years) for 15.2 hoursper day. All 53 patients had an area ofcentral or paracentral corneal thinning and irregular keratometric astig

matism or inferior steepening. In addition, 98 (92.5%) of 106 eyes hadeither Vogt's striae, an iron ring, oranterior stromal scarring. The 8 eyesthat had only the minimal criteriaused to define KCN were in patientswhose other eye had more advancedKCN. Of these 53 patients, 47 (89.0% )wore hard polymethylmethacrylatelenses, 3 (5.5%) wore soft contactlenses, and 3 (5.5%) wore gas-permeable contact lenses. Five (9.5% ) of the53 patients in this group were examined in our department prior to fit. Theremaining 48 (90.5%) were examined

by referring ophthalmologists and optometrists. Cosmesis was the reasonfor the contact lens fitting in 48 patients (90.5% ), while 2 (3.8% ) were fitfor anisometropia and 3 (5.7%) werefit for high axial myopia.

Fifty eyes of 25 control patients (average age, 28.5 years; 48% women, 52%men), with a history of contact lenswear for an average of 9.3 years (range,4.5 to 15.0 years) for 12.4 hours per day,were examined for inferior steepeningand a thin central cornea. Fifteen control group patients wore hard poly-

methylmethacrylate lenses, 5 wore gas-permeable lenses, and 5 wore soft contact lenses. No controls with a historyof contact lens wear demonstrated inferior steepening. Two control eyes ofdifferent patients had central corneal

pachymetry readingsof less than 0.490

mm (0.479 mm and 0.483 mm), neitherof which demonstrated inferior steepening or irregular astigmatism. Noperipheral corneal pachymetry readings were less than the central reading.

Fifty eyes of 25 controls (averageage, 27 years; 52% men, 48% women)with no history of contact lens wearwere examined. One control demonstrated 0.75 D OD of inferior steepening and 1.0 D OS. The other 48 eyesdemonstrated no inferior steepening.Three eyes had central pachymetry

readings of less than 0.49 mm (0.475mm, 0.479 mm, and 0.481 mm). No inferior steepening or irregular astigmatism was found in these eyes. No peripheral corneal pachymetry readingswere less than the central reading.

Paired t test analysis of the patientswith a history of contact lens wear before the diagnosis of KCN, comparingmanifest refractions prior to fit withmanifest refractions at the time of di

agnosis of KCN, revealed a statistically significant increase in myopiaand astigmatism in the mild and moderate groups (P < .0001) and in the severe group (P < .02). However, thenumber of patients in the severe groupwas too small to rely on the results ofthe paired t test. The paired t test forthe same group, comparing the keratometry readings prior to contact lensfit with keratometry readings at thetime of diagnosis of KCN, revealed astatistically significant increase inastigmatism in the mild and moderategroups (P < .0001) and in the severegroup (P < .02). However, again, thenumber of patients in the severe groupwas too small to rely on this test of

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Table 4.Categorization ofKeratoconus by Severity at the Time

of Examination

No. (%) of Eyes by Severity

Mild Moderate Severe

Contact lens

use before

keratoconus 44 (42.0) 59 (56.0) 3 (3)Keratoconus

before contactlens use 97(63.0) 51(32.0) 8(5)

Keratoconuswith no

contact

lens use 79 (58.0) 52 (38.0) 5 (4)

analysis. All patients with a history ofcontact lens wear before the diagnosisof KCN had less than 1.25 D of cylinderby manifest refraction and keratometry readings before they were fit.

An overall t test was performedcomparing the keratometry readings,manifest refraction, amount of inferior steepening, and pachymetry read

ingsin the

mild, moderate,and severe

KCN groups with a history of contactlens wear before the diagnosis of KCNwith eyes of equal severity in patientgroups where either contact lenseswere never worn or were fitted afterthe diagnosis. The overall t test ofkeratometry readings showed thatthese patients had significantly flatterreadings when compared with both ofthe other mild groups (P < .001) andthe moderate group in which lenseswere fit after the diagnosis (P < .005).Differences in the other groups werenot statistically significant, but there

was a trend toward flatter curvatures(Table 5). No statistically significantdifference was found in manifest re

fraction, the amount of inferior steepening, pachymetry readings, or thepresence of an iron ring, anterior stromal scarring, or Vogt's striae in thesegroups. Iron lines were not seen in 12

eyes (11.5% ) of patients with a historyof contact lens wear before the diagnosis of KCN, 13 eyes (8.3% ) diagnosedwith KCN before contact lens wear,and 16 eyes (11.7% ) with no history ofcontact lens wear.

X2 Analysis compared the cone loca

tion in the mild, moderate, and severecategories of patients with a history ofcontact lens wear before the diagnosisof KCN with patients in the othergroups (Table 6). There was a statistically significant difference (P < .0001)in every category, demonstrating acentral cone in patients with a historyof contact lens wear prior to the diagnosis of KCN. No eyes in any categorieswere noted to have superior cones. Ineach category, cone location was notrecorded in less than 15% of the patient charts.



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Table 5.Average Keratometry Readings*

Mean SD Keratometry Readingsby Severity Group, Diopters


Contact lens use before keratoconus 44.34 2.00

45.11 2.8646.82 4.00

48.80 4.56

54.12

58.37

1.24

3.36

Keratoconus before contact lens use 46.45

47.554.93t5.81t

48.20 5.3249.47 5.50

57.50

61.50

6.73

4.20

Keratoconus with no contact lens use 50.4952.67

6.55t8.10t

50.32 5.5853.83 7.12

57.00

64.67

2.83

4.53

Flat and steep keratometry readings were compared separately.\P < .001 compared with the contact lens use before keratoconus group.%P < .005 compared with the contact lens use before keratoconus group.

Table 6.Cone Location*

No. (%) by Severity Group for Keratoconus


Contact lens use before keratoconus 35 (79.6) central 45 (76.2) central 3 (100) central5 (11.4) inferior 8 (13.5) inferior 0 inferior

_4 (9.0)NR_6 (10.2)NR_NR_Keratoconus before contact lens use 3 (3.2) central 3 (5.2) central 0 central

71 (81.6) inferior 49 (86.0) Inferior 6 (100) inferior

_13 (14.9)NR_5 (8.8) NR_0NR_Keratoconus with no contact lens use 5 (5.2) central 2 (5.1) central 0 central

82 (85.4) inferior 35 (89.7) inferior 7 (100) inferior9 (9.4) NR 2(5.1)NR 0 NR*

NR indicates not recorded.

COMMENT

We realize that we cannotprove thatcontact lens wear has caused the development of KCN in all of these patients. It is possible that KCN wouldhave developed regardless of contactlens wear or that extremely subtlesigns of KCN may have been missed oninitial examination. In each of these

patients, pre-contact lenses fit keratometry readings and manifest refractions demonstrated less than 1.25 D ofregular keratometric cylinder, andpaired t test evaluation demonstrateda significant change in manifest refraction and keratometry readings(P < .0001). In 48 patients (90.5%) thereason for contact lens fitting was cos-mesis, according to the patients'charts. It is possible that the need forcontact lens fitting could have arisendue to an early undetected centralcone; however, review of these patients' charts reveals that only 5 patients

(9.5%)were fit for anisometro-

pia. All eyes of these 53 patients hadclinically detectable corneal thinningand protrusion with irregular astigmatism. We define a cornea with contact lens warpage syndrome as thathaving irregular astigmatism withoutother features of KCN such as thin

ning, protrusion, or an iron ring. All106 eyes of patients who wore contactlenses before the diagnosis of KCN hadcorneal thinning and protrusion andtherefore fall under our definition ofKCN and not corneal warpage syn-

drome. No patients underwent contactlens withdrawal to see if these changesreversed. It is our practice to withdrawcontact lenses in patients with contactlens warpage syndrome to see if thereis a resolution of irregular astigmatism. However, we do not withdrawcontact lenses in patients who havecorneal thinning and protrusion andtherefore KCN by our definition.

The patients with a history of contact lens wear before the diagnosis ofKCN were significantly older at thetime of diagnosis than the other patients (P < .0001). The patients' agesat the time of diagnosis of KCN wereobtained from patient charts (either atthe University of Iowa or at the referring physician's office). However, it isimpossible to know when KCN developed. Despite the fact that the age atthe time of diagnosis is not the same asthe age of onset, the difference in agebetween these groups is significant.We believe that the most

likelyreason

for the age difference is that it takesyears for contact lenses to induce KCN.It is possible that the contact lensmasked the visual disturbance of earlyKCN, although it is difficult to imaginethe existence of KCN for so many yearswithout the diagnosis being made. Thethree patient groups had comparabledisease stages of KCN at the time ofexamination, thereby countering thepossibility that increased age at thetime of diagnosis was due to delayedrecognition (Table 4).

Table 7.Keratoconus after Contact

Lens Wear: Patient Characteristics

Normal examination findings before long-termcontact lens wear

Older at the time of diagnosis of keratoconus(P< .0001)

History of contact lens wear prior to diagnosis of keratoconus

Central cone location (P < .0001)Tendency toward flatter keratometry read

ings

Patientswere

divided into severitygroups to examine whether differenceswere dependent on severity, 2 Analysis demonstrated a statistically significant (P < .0001) difference in cone location in mild, moderate, and severecategories. Patients fit before thediagnosis of KCN typically demonstrated a central cone while an inferiorcone was observed in patients withKCN with no history of contact lenswear and in patients who had worncontact lenses after the diagnosis ofKCN. We assume that the presence ofthe contact lens influenced the location

of the cone. It is tempting to speculatethat contact lens rigidity may have aneffect on cone location" and keratometry readings in these patients, resulting in central cones and flatter keratometry readings. Corneal hypoxia dueto decreased oxygen permeability mayalso be a contributing factor, especially in those patients wearing hardpolymethylmethacrylate lenses. However, as yet we do not have an animalmodel for the development of KCN after contact lens wear, and the role ofcontact lens rigidity and oxygen permeability is unclear.

It is interesting that of these 53 patients fit with contact lenses before thediagnosis of KCN, 3 patients had wornonly soft contact lenses and 3 patientshad worn only gas-permeable contactlenses. After completing this study, weexamined an additional patient inwhom soft contact lenses were wornfor 10 years who developed features ofcontact-lens induced KCN.

In reviewing the charts, two patientswere found in whom KCN developed inthe only eye fit with a contact lens. Oneof these patients was a 45-year-oldman

diagnosedwith unilateral

aph-akia and who was postoperatively fitwith a hard contact lens. There was nohistory of previous trauma. Ten yearsafter wearing the lens for an averageof 16 hours per day, the patient developed KCN in his aphakic eye; his othereye was normal. The other patient wasa 31-year-old man who had undergonebilateral strabismus surgery for exotropia. His left eye remained ambly-opic and his right eye was fit with ahard contact lens for cosmesis. After13.6 years of wearing the lens for an



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average of 14 hours per day, he developed KCN in the right eye; his left cornea was normal. These patients further support our theory that KCN candevelop in contact lens wearers, but dueto the history of ocular surgery, bothpatients were excluded from this study.

We did not set out to determine the

frequency with which contact lenswearers might develop KCN. The prevalence of patients fit before the diagnosis of KCN in our population was13.7%

(53/386). However,ours is a re

ferral-based practice and we cannotinfer th; ,t this is the prevalence in thegeneral population of patients withKCN. As a result of the bias introducedby our referral-based practice, it is notpossible to determine the incidence ofKCN in the general population of contact lens wearers. In addition, 60 patients were excluded from this studydue to unavailable data, amblyopia, orprevious surgery. It is possible that theinclusion of these patients could havealtered our results considerably. Itwould be interesting to compare the

overall incidence of KCN before thedevelopment of contact lenses with theoverall incidence today. An increasemay further support that contact lenswear may play role in the development of KCN. Unfortunately, thesedata are not available.

To exclude the existence of inferiorsteepening or a thin central cornea inpeople without KCN, we examined 100control eyes. Fifty eyes with a comparable long-term history of contact lenswear were examined to test the possibility that inferior steepening or a thincentral cornea can be found as a typical finding in contact lens wearers.Five of our control eyes (2 with a history of contact lens wear) demonstrated a central corneal thickness ofless than 0.49 mm, and 1 control whodid not have a history of contact lenswear did have inferior steepening butdid not have a thin central cornea. Asof this writing, this patient has notdeveloped KCN, though we will continue to observe her.

We believe that the wearing of contact lenses involves trauma to the cornea that in most cases either is not severe enough or the

patientis not sus

ceptible to the development of KCNover a long wearing time. However, insome patients, wearing contact lensesalong with other probable traumaticcauses of KCN, such as Down's syndrome, Leber's congenital amaurosis,atopy, and significant history of eyerubbing, may cause KCN. Despite thepresence of an adequate tear film between the contact lens and cornea, it iseasy to recognize that long-term contact lens wear may be a source of ocular trauma. We cannot say with abso-

lute certainty that these 53 patientsdeveloped KCN because of the contactlenses and would not have done sowithout the contact lenses. It is clear,at the very least, that contact lenseshave influenced the corneal topography (central cone location, tendencytoward flatter curvature). Nine (17% )of the 53 patients were fit at the age of25 years or older, at which time theydid not have KCN. In the two othergroups, 97% of the patients were diagnosed with KCN

bythe

ageof 25

years.On the basis of age alone, it is unlikelythat these 9 patients would have developed KCN without the contactlenses. The mean age of diagnosis inthe group of 53 patients was also distinctly higher than that for the othertwo groups. The previously mentionedunilateral cases further substantiatethe association between contact lensesand KCN. The question is whethercontact lenses caused the disorder inall or just some of the group of 53 patients (Table 7).

As a result of our findings, we rec

ommend that contact lens wearers befollowed up closely. Follow-up examinations should include monitoring forthe earliest signs of KCN, includingirregular astigmatism, increasing myopia, and inferior steepening. Furtherconsiderations for early detectionwould include serial measurements ofcorneal thickness. If any of the above

signs were to develop, we would recommend discontinuation of contactlens use. However, we cannot be surethese signs will not progress regardless of discontinuing contact lens wear.

This project was supported in part by an unre-stricted grant from Research to Prevent Blind-ness Inc, New York, NY.

This project was awarded the P. J. LeinfelderAward for the Outstanding Fellow ResearchProject at the University of Iowa (Iowa City) in1989.

The authors gratefully acknowledge the contri-butions of Jill A. Fishbaugh, RN, BSN, for datacollation; James Hulbert, PhD, for statisticalanalysis; Cathi Miller, FCLSA; and Colleen A.Howe, OD, all of Iowa City, for providing controlpatients for this study; and Michael Lynn, PhD,Atlanta, Ga, for providing us with data from thePERK Study.

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