Britishlournal ofOphthalmology, 1990,74:67-72

ORIGINAL ARTICLES

Epikeratophakia for aphakia, keratoconus,and myopia

Brett L Halliday

AbstractA series of 67 cases of epikeratophakia ispresented with an average time from surgery of12.2 months. For aphakia there was a delay inthe recovery of vision, but by nine months 83%of 57 patients achieved an acuity equal to,or within 1 line of, the preoperative value.57% were corrected to within 3 dioptres ofemmetropia, but in the latter part of the series75% were within this range. Astigmatism andreduced contrast sensitivity, especially in thepresence of glare, were important complica-tions. For keratoconus, 86% of seven patientswith over two months of follow-up achieved aspectacle corrected acuity of6/9 or better. Onepatient had surgery for myopia and obtainedthe desired refractive correction.

Barraquer pioneered the use of the cryolathe inrefractive surgery about 30 years ago. His tech-nique ofkeratomileusis never gained widespreadpopularity. In contrast, epikeratophakia, intro-duced in 1980, has been taken up enthusiastic-ally, especially in the United States. By 1986 over1500 surgeons had been certified by AllerganMedical Optics (California, USA) to use theirepikeratophakia lenses.

Keratomileusis failed to become widelyaccepted owing to problems with the technique.The range of refractive correction is limited toabout 12 dioptres, and the surgical technique isinvasive, with a lamellar disc of the patient's owncornea turned on a cryolathe to provide therefractive correction. Complications associatedwith keratomileusis include corneal perforationand cryolathe damage to the lamellar disc.

In contrast, epikeratophakia has a wide rangeof possible correction (up to about 30 dioptres ofhyperopia or myopia), is largely non-invasive,and is usually reversible. Cryolathe lens manu-

Moorfields Eye Hospital,London ECIV 2PDB L HallidayCorrespondence to:B L Halliday, FRCS.

Accepted for publication23 August 1989

D Traumatic cataract

" Congenital cataractC* g Cataract other)

ok MKeratoeonve

0 O O f O O OMYfz2

Ag. (years)Figure 1: Distribution ofdiagnosis with age ofpatient.

facture may be centralised, allowing surgery tobe performed by any corneal surgeon withoutrequiring specialised equipment. Epikerato-phakia with a plano lens may also be used to treatcertain cases of keratoconus.Although there have been some case reports of

failed epikeratophakia,' large published series(mostly from the United States) have generallyconcluded that epikeratophakia is a worthwhileprocedure.'3 Despite this, the number ofBritish surgeons performing the techniqueremains very small.

This paper presents a series of all the cases ofepikeratophakia performed by the author to dateand defines the categories of patients who maybenefit from this procedure.

Patients and methods

SELECTION OF PATIENTSPatients were referred to the corneal clinicat Moorfields Eye Hospital where they wereassessed as potential candidates for surgery.Epikeratophakia was only considered whensimpler alternatives such as spectacle or contactlens correction were considered inappropriate.Most patients had tried and failed contact lenswear, though in a few monocularly aphakicchildren, where contact lens correction wasthought likely to fail, epikeratophakia was per-formed as the primary treatment.

Adult monocular aphakes suitable for surgeryincluded those who had had previous intra-capsular extraction on one eye followed byextracapsular extraction with intraocularimplant on the fellow eye. Other potentiallysuitable patients included those with a history ofuveitis who had had extracapsular surgery per-formed electively without lens implant and thosewho were aphakic following traumatic cataract.Bilateral aphakia was considered as an indicationfor epikeratophakia only in patients intolerantof a contact lens who preferred to remainuncorrected rather than wear spectacles.

Keratoconus patients whose corneal irregu-larity was such that spectacle correction wasimpossible, yet who had good acuity with adiagnostic contact lens, were considered idealcandidates for surgery. Patients with enoughcentral scar to reduce contact lens acuity weretreated by penetrating keratoplasty.

Patients who were equally myopic in each eyewere not considered suitable candidates for

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surgery, as without exception they were manag-ing with either contact lenses or spectacles.Monocular myopes who were uncorrected intheir myopic eye were considered for surgery onthe myopic eye, as were those with one eyemarkedly more myopic than the other.

In all cases the referring surgeon felt that themore invasive surgical alternatives, such assecondary intraocular lens implantation foraphakia, penetrating keratoplasty for kerato-conus, or radial keratotomy for myopia, werecontraindicated.

LENS MANUFACTUREFor the first six procedures commercially pro-duced lenses were imported from the UnitedStates. For the remainder lenses were manu-factured by the author using donor corneas thathad been stored either in K-Sol or McCarey-Kaufman storage medium.A typical epikeratophakia lens has a central

optical zone and a thin peripheral wing which issutured to hold the lens in place. Most of thelenses were made with a specially developedcryolathe (Citycrown Sales, 14 Kempston Close,Gatehouse Way, Aylesbury, Buckinghamshire),which has a facility for automatically making asmooth transition between the radius of cut usedfor the optical zone and the radius used for thewing. Thirteen lenses were made on a lathewithout this facility, and for these the transitionbetween optical zone and wing was mademanually. Alternatively, lenses were made with asingle radius of cut, so that the optical zone inthese extended to the edge of the lens. 14 Detaileddescriptions of the formulae used to lathe thelenses has been published.14-16

SURGICAL TECHNIQUEThe basic technique of epikeratophakia consistsof initially removing corneal epithelium, thendissecting a peripheral pocket for the wing of thelens, which is then sutured in place. The exacttechnique employed evolved over this series.Thorough removal of corneal epithelium is

necessary so that there is no subsequent cellularproliferation at the interface between the epiker-atophakia lens and host cornea. Epitheliumperipheral to the lens should be left intact, as it is

0 6 12 18Months from surgery

Figure 2: The probability ofan aphakic patient achieving a visual acuity of6/12 (dotted line)and 6/9 (solid line) is plotted against timefor surgery.

from this peripheral cornea that epithelialregeneration covers the epikeratophakia lens.Failure of prompt re-epithelialisation may beassociated with melting of the lens and infectivekeratitis. For the initial seven cases absolutealcohol was used to drench the patient's cornea toaid removal of the epithelium. Unfortunatelythis proved to be associated with delay in subse-quent re-epithelialisation. Subsequently ascalpel blade was used to remove epithelium, andthe use of alcohol was confined to a final wipewith a barely damp swab, care being taken toavoid peripheral cornea.The next step in the operation is to create a

pocket for the insertion ofthe wing ofthe lens. Inmost cases a 7 or 7 5 mm diameter Hessburg-Baron suction trephine was used to make apartial thickness trephination to a depth ofabout180 lim. A 21 gauge needle, bent to 900 2 mmfrom the end, was then used to dissect a pocket,parallel to the corneal surface, from the base ofthe partial thickness trephination extendingperipherally. In the initial four cases an annularwedge of cornea was removed from the insideedge of the trephination. In 10 cases no trephinewas used. For these cases after circular markhad been made on the cornea an annulus (ofBowman's layer and underlying corneal stroma)was excised with a razor blade and Paufique'sknife. This approach was used for some of the 13lenses made without a peripheral wing, whichwere simply sewn on to the surface of the cornea,allowing the 'bare area' of the annulus toapproximate the deep surface of the lens. 14The final part of the operation is to fix the lens

in place. In all but two cases this was done with10-0 monofilament sutures. Initially 16 sutureswere used, but it soon became apparent thateight sutures were usually sufficient. Exception-ally up to 24 sutures were used for those lensesmade without a peripheral wing that were sewnon to the surface of the cornea. In two cases afibrin glue (Tisseal; Immuno Ltd, Sevenoaks,Kent) was used to fix the lens in place of sutures.For aphakia and myopia the sutures were nottied tightly. For keratoconus very tight sutureswere tied while an assistant pressed firmly toreduce the ectatic cornea.For all the keratoconus cases the sutures were

6/6

5 6/12U45a.0.4 6/24

0a-

6/60 6/24 6/12 6/6

Pro-op acuityFigure 3: Scattergram showing postoperative acuity againstpreoperative acuityfor all aphakic patients with at least ninemonths offollow-up.

I

0a

0

0b.=L

0.5

0 _

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Epikeratophakiaforaphakia, keratoconus, and myopia

tied with the help of an operative placido disc,sutures being added or removed as dictated bythe symmetry of the reflex in an attempt toreduce induced astigmatism. This technique wasalso used for the most recent aphakic cases.

In all cases the operation was completed with asubconjunctival injection of antibiotic and theeye padded until the next morning. In 17 casesearly in the series a bandage contact lens (75%water content, back central optic radius 9 mm,overall diameter 15 mm) was used until theepithelium had regenerated to cover the cornea.Subsequently eyes have been left to epithelialisewithout the use of contact lenses, eye pads, or lidsutures. 17

Postoperatively topical antibiotic and weaksteroid drops were used, usually three times aday, for about eight weeks. During this timesutures were removed from the aphakic andmyopic cases, but for keratoconus the sutureswere left in place unless they became loose orwere inducing astigmatism. Patients wererefracted at regular intervals, starting as soon asthe epikeratophakia lens had cleared sufficiently.To provide more information on visual function,selected patients had contrast sensitivitymeasurements in both the operated eye and inthe fellow, normal eye. A computer controlledsystem was used with sinusoidal gratings dis-played on a television monitor with an averageluminance of 14 cd/m2. As some patients hadreported a reduction in vision in bright light, themeasurements of contrast sensitivity wererepeated in the presence of a glare source ofluminance 300 cd/m2 (Brightness Acuity Tester;Mentor Inc, USA).

ResultsFrom October 1986 to May 1989, 67 epikerato-phakia procedures were performed: 25 were fortraumatic aphakia, 16 for aphakia followingintracapsular cataract extraction, 12 for aphakiafollowing congenital cataract extraction, 4 foraphakia following extracapsular cataract extrac-tion, 9 for keratoconus, and 1 for myopia. Theaverage age of the patients was 34 years (range 1

1000

>b

c 1000

(0

to

00

to 82). Figure 1 shows in detail the distributionof age and diagnosis. The average time fromsurgery was 12 2 months (range 1 to 32).Most of the patients had an uneventful post-

operative course, with rapid re-epithelialisationof the epikeratophakia lens and with steadilyimproving lens clarity paralleled by improve-ment in corrected visual acuity. Loosening ofsutures was a very common complication, andthese were removed as required.The time taken for complete epithelialisation

of 10 consecutive patients managed with abandage contact lens was compared with thetime taken by the next 10 patients managedwithout a contact lens. The contact lens grouptook an average of 3 9 days to completeepithelialisation (range 3 to 5 days), whereas theuntreated group took 3-8 days (range 3 to 5days). Re-epithelialisation when successful wascomplete by seven days postoperatively.

APHAKIA - VISUAL RESULTRecovery ofvisual acuity after epikeratophakia isknown to be slow. In this series the visual acuityof individual patients steadily improved overperiods as long as a year after surgery. Twenty-five cases of epikeratophakia for aphakia with apreoperative acuity of at least 6/9 were studied indetail to analyse this recovery of acuity. Theaverage age in this group was 47 years (range9-82). Survival (Kaplan-Meir type) analysis wasused to plot the probability of achieving acuitiesof 6/12 and 6/9 at a given time after surgery (Fig2). This shows that it took 4-4 months for 50% ofcases to reach an acuity of 6/12 and 4-8 months toreach 6/9.

Figure 3 is a scattergram plotting postopera-tive against preoperative acuity for all aphakiccases with at least nine months of follow-up. Ofthe 18 cases plotted 11 (61%) achieved theirpreoperative acuity and 15 (83%) achieved anacuity within one line of the preoperative value.All ofthe three cases that failed to reach this levelof acuity had clinically clear epikeratophakialenses. One of these cases had developed disci-form senile macular degeneration, one had a highcylinder (7 dioptres), and the other had noapparent reason for poor acuity.

Contrast sensitivity was measured in fourpatients. In every case the Snellen acuity in theepikeratophakic eye was 6/9 or better, and thiswas not reduced by the presence of the glaresource. Figure 4 shows a typical result. In theabsence of glare the contrast sensitivity of theepikeratophakic eye was approximately 0-75 logunits worse than the phakic, fellow eye. In thepresence of glare the relative deficit in theepikeratophakic eye increased to over 1 log unit.Full details of the contrast sensitivity measure-ments in these patients have been publishedelsewhere. 18

1 10Spatial Frequency (cycles/degree)

Figure 4: Contrast sensitivity is plotted against spatialfrequency for a patientfollowingaphakia epikeratophakia. Squares represent the epikeratophakia eye; circles represent thenormal, fellow eye. Filled symbols indicate testing under normal conditions; open symbolsindicate testing in the presence ofglare.

APHAKIA - REFRACTIVE RESULTFigure 5 is a scattergram showing correctionachieved (spherical equivalent, dioptres) againstpreoperative refraction. 57% of patients were-corrected within 3 dioptres of the desired value.The remaining 43% were outside this range and

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2000

0 15

0 5 10 15 20Pro-op refraction (dioptres)

Figure 5: Scattergram showing achieved refractive chantagainst preoperative refraction for aphakic patients.

thus, in general, unable to be satisfact(corrected with spectacles. Results improvedsiderably as formulae for lathing were modiover the period of this study. For the firs-lenses made only 25% were within 3 dioptrcthe desired correction, whereas for the rrecent 12 cases 75% were within this range.

Postoperative astigmatism varied from 0dioptres. The average magnitude wasdioptres, with 43% of cases having a cylindcover 3 dioptres. This problem has showtendency to improve over the duration ofstudy: 50% of the first 12 cases had a cylind(over 3 dioptres, whereas for the most recencases., only 25% had cylinders over this value

PAEDIATRIC APHAKIASixteen cases of aphakic epikeratophakia iperformed on children aged 10 years or unRefractive and visual results, where availahave been included in Figures 2, 3, and S. T1 provides more details. Nine out of 13refracted (69%), were corrected to withindioptres of emmnetropia. Two children instudy were seriously undercorrected. Pal6 had a microphthalnnic eye and congercataract. Lensectomy was performed at almonth, but contact lens wear proved inciingly difficult so epikeratophakia was perfor

TABLE I Results in pediatric aphakia

Age Follow-up Postop.Patient no. (years) Diagnosis (months) Preop. acuity Postop. refraction

acuity1 1 C (U) 7 NK NK Approx piano2 3 T 7 NK 6/18 500/-100>3 3 T 1 NK NK NR4 3 T 3 NK NK 2-00 sph5 3 T 1 NK NK NR6 4 C (U, M) 8 CF 6/60 16-00/-2-00>7 5 T 5 NK 6/18 -2-00 sph8 5 T 1 NK NK 6-00 sph9 5 C (U) 3 CF CF Approx piano10(lefteye) 7 C(B) 14 6/24 6/36 2 50/-4 50>10(righteye) 7 C(B) 5 6/60 6/60 200/-4-00>11 7 T 2 6/12 6/24 2 50/-6-00>12 8 C (B) 22 6/60 6/60 -2-00 sph13 8 T 5 6/6 6/12 +10-00/-3-25>14 9 T 6 6/6 6/6 +1-00/-150>15 10 C (B) 1 6/18 NK NR

C=congenital cataract. U-unilateral. B=bilateral. T=unilateral traumatic cataract.M=microphthalmic eye. CF=counting fingers. NK=acuity not known. NR=not refracted.

7 at the age of 4 years. A correction of 32 dioptreswas needed, but only half of this was achieved.Nevertheless, with amblyopia therapy vision inthis eye has improved to 6/60, and the patient isnow 61/2years old. Patient 13 received only about60% of the desired correction, and epikerato-phakia may be repeated. Postoperative binocularfunction has been recorded in two cases; patient2 can fuse images on the synoptophore over alimited range, and patient 14 achieves rudi-mentary stereopsis. Patient 15 has had hisepikeratophakia lens removed as detailed below.

APHAKIA - COMPLICATIONS

25 Both epikeratophakia lenses that were glued inplace became dislodged by the second postopera-

,ge tive day. Both lenses were removed, and newlenses were sutured in place without furthercomplication.Two cases failed to epithelialise postopera-

rily tively despite intensive inpatient managementcon- including the use of bandage contact lenses, eyefield pads, and lid taping. In both cases it provedit 12 necessary to remove the epikeratophakia lenses of about four weeks after surgery. In one case theremost was no obvious reason, but the other patient

(number 15 in the paediatric aphakia group) hadto 8 severe icthyosis, which may have been con-

2rof tributory.Two cases had epithelial breakdowns aftertn a uncomplicated initial epithelialisation. The firstthe developed a linear defect two months after

ir of surgery. This was treated with topical antibioticsLt 12 only, and healed within one week. The second

patient had a larger area ofdefect that occurred attwo weeks. This was managed with a bandagecontact lens. This defect recurred at threemonths and was again successfully managed with

were a contact lens, leaving a clear epikeratophakiader. lens. One patient has had recurrent filamentaryIble, keratitis that has required topical acetyl cysteineable 5%; the lens has remained clear.eyes Late lens removal, between six and 13 monthsin 3 after surgery, has been required in eight cases.this Under topical anaesthesia the wing ofthe lens was

tLient dissected out of its pocket, and then the lensfital peeled away easily from the host cornea. In allge 1 these patients re-epithelialisation was with-reas- out problems. Five lenses were removed formed incorrect refractive result (an average of 5-8

dioptres of undercorrection). One lens wasremoved for high astigmatism (7 dioptres), onewhen the penetrating keratoplasty that it wassewn over failed, and one removed when visual

TABLE II Results in keratoconus

Epikeratophakiaforaphakia, keratoconus, and myopia

acuity failed to improve beyond 6/24 despite apreoperative acuity of 6/9. Four patients havesince received a secondary lens implant, twohave had repeat epikeratophakia, and two havenot had further surgery.

Interface opacities have not been an importantproblem. In five cases typical small, midperi-pheral, putty grey areas have appeared at theinterface. All these patients have now beenfollowed up for at least six months, and the areasof presumed epithelial cell proliferation do notappear to be progressing and none impinge onthe visual axis.

KERATOCONUSTable 2 shows the results for each keratoconuspatient. All patients were intolerant of contactlenses, and the preoperative acuity shown is thebest that was possible with spectacle correction.Six out of seven patients (86%) with more thantwo months' follow-up achieved a good resultwith spectacle corrected acuity of 6/9 or better.The remaining patient achieved 6/12 but withvery high cylinder and required penetratingkeratoplasty.

MYOPIAThe single myopic patient treated has a preopera-tive refraction of -15 dioptres in the right eye(acuity 6/9) and -30 dioptres in the left (acuity6/36). Epikeratophakia was performed on theleft eye, aiming to balance its refraction to that ofthe right eye. After one month of follow-up theacuity in the left eye was 6/60 with a correction of- 15 dioptres.

DiscussionThe improvement in the results over the series,in terms of spherical error and astigmatism,represents a learning curve for both lens manu-facture and surgical technique.Twelve (21%) of the aphakic lenses were

removed. This is a rather higher proportion thanfound in the other series where overall 6% ofover900 were removed.4I9 Seven of the 12 removalsin this series may be attributed to the learningcurve; five were removed for serious under-correction, and two were removed following theuse of fibrin glue. One lens failed because ofunderlying graft failure.

Results in paediatric aphakia are difficult tocompare from study to study. Paediatric patientsform a very diverse group with varying ages,often unknown duration of cataract, and varyingtimes from cataract surgery to correction ofaphakia. Maintaining full time contact lenscorrection is difficult, and the delay in restoringclarity after epikeratophakia may be important.Refraction and acuity are difficult to assess, andproblems in maintaining occlusion limit theresults of amblyopia therapy. Babies under theage of 1 year were not considered for epikerato-phakia in this study, as it has been found that inthis age group there is a marked shift to myopiaas the eye grows. 19 Children beyond the age whenamblyopia is a problem who suffer traumaticcataract often choose not to persevere with

contact lens correction, lose binocular function,and their vision becomes divergent. Thepresence or rudimentary stereopsis in paediatricpatient 14 is therefore encouraging.

Postoperative epithelialisation appeared tobe much faster in this series than in manyothers. Apart from the two cases where primaryre-epithelialisation failed, every eye wasfully epithelialised by seven days, with anaverage time of less than four days. In contrastother reports have variously found only 75%epithelialised by one week,20 average times to re-epithelialisation of 13 days,2' and 15% of casestaking more than two weeks.'2 The explanationfor this and for the fact that in this series routineuse of bandage contact lenses, eye pads, or lidsutures did not seem necessary, may relate to themanufacturing and surgical techniques used.Most lenses used in this series were not lyophil-ised. Lyophilisation is needed to ship lenses,but the process inflicts additional damage toBowman's layer of the lens22 and so may inhibitre-epithelialisation. The surgical technique usedprevented alcohol from damaging peripheralcornea which may otherwise have retarded re-epithelialisation.The time course for the recovery of visual

acuity has not previously been reported withsurvival (Kaplan-Meir type) analysis. Reportsagree, however, that many months may berequired for recovery of visual acuity aftersurgery.40112 The 83% of patients in this studywho achieved an acuity within 1 Snellen line ofthe preoperative value by nine months is veryclose to the 82% that achieved this level morethan three months after suture removal in a studyof 150 patients.4The reduction found in contrast sensitivity,

especially in the presence of glare, may explainthe subjective experience of- some patients thattheir epikeratophakic eye does not provide asgood vision as their fellow eye. The reduction incontrast sensitivity has been confirmed else-where,23 and comparison has been made withcontrast sensitivity of phakic and contact lenscorrected eyes. 18The single case of myopia resulted in the

desired refractive correction, and the patient isdelighted with the result. The largest reportedseries ofmyopic epikeratophakia found that 58%of patients were corrected to within 20% of therequired refraction.5 In comparison with thecorresponding series of adult aphakia, it wasnecessary to remove over twice as many lenses inthe myopic group. Serious overcorrection of therefractive error seems to be more of a problemwith myopic than with aphakic corrections.24Myopic lenses are no longer supplied by AllerganMedical Optics, who are now concentratingresearch on other means of correcting myopia.20The results from this study are broadly similar

to those reported elsewhere. The main differenceis that patients treated in the early part ofthis study had relatively inaccurate refractivecorrections. Improved lathing formulae latereliminated this difference.

Epikeratophakia for aphakia is a far fromperfect operation. The majority of patients mayexpect to need spectacle overcorrection, andabout one-quarter will be more than 3 dioptres

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from the desired refraction. Furthermore thequality of vision is suboptimal, with reducedcontrast sensitivity especially in the presence ofglare. For keratoconus the results so far seemhighly encouraging. Patients have had restora-tion ofgood spectacle acuity without the need forpenetrating keratoplasty. There are not enoughmyopic patients in this series to enable a firmconclusion to be reached, but the solitary casetreated has done well.

Selection of patients for epikeratophakia is, aswith any operation, dependent on balancing theprobable benefits with the potential complica-tions. This study has confirmed that epikerato-phakia is a very safe and mostly reversibleprocedure.

For aphakia epikeratophakia is indicatedwhere spectacle or contact lens correction isimpracticable and where a secondary implant iseither impossible, such as following severeanterior segment trauma, or highly inadvisable,such as in children. Where a secondary anteriorchamber implant is technically feasible, adecision must be made in each individual casewhere the increased safety of epikeratophakiaover intraocular surgery justifies the relativelypoor accuracy of refractive result, reduced con-trast sensitivity, and delay in visual recovery.

For keratoconus the results so far favourepikeratophakia as the preferred management ofpatients with poor spectacle acuity and contactlens intolerance who have good diagnostic con-tact lens acuity. The more invasive penetratingkeratoplasty may be performed if epikerato-phakia subsequently fails. Epikeratophakia is apotentially valuable addition to the armamen-tarium of the ophthalmic surgeon. For carefullyselected patients it can provide worthwhile visualimprovement without the risk of intraocularsurgery.My thanks to the British Medical Association for their generoussupport via the Middlemore Fund and to the surgeons ofMoorfields Eye Hospital for their advice and support.1 Binder PS, Zambia EY. Why do some epikeratoplasties fail?

Arch Ophthalmol 1987; 105: 63-9.

2 Tamaki K, Yamaguchi T, McDonald MB, Kaufman HE.Histological study of epikeratophakia tissue lenses formyopia removed from two patients. Ophthalmology 1986; 93:1502-8.

3 Goodman GL, Peiffer RL, Werblin TP. Failed epikerato-plasty for keratoconus. Cornea 1986; 5: 29-34.

4 McDonald MB, Kaufman HE, Aquavella JV, et al. Thenationwide study of epikeratophakia for aphakia in adults.AmJ Ophthalmol 1987; 103: 358-65.

5 McDonald MB, Kaufman HE, Aquavella JV, et al. Thenationwide study of epikeratophakia for myopia. Am JOphthalmol 1987; 103: 375-83.

6 McDonald MB, Kaufman HE, Durrie DS. Epikeratophakiafor keratoconus, the nationwide study. Arch Ophthalmol1986; 104: 1294-300.

7 Morgan KS, McDonald MB, Hiles DA, et al. The nationwidestudy of epikeratophakia for aphakia in children. Am JOphthalmol 1987; 103: 366-74.

8 Morgan KS, McDonald MB, Hiles DA, et al. The nationwidestudy of epikeratophakia for aphakia in older children.Ophthalmology 1988; 95: 526-31.

9 Uusitalo RJ, Lehtosalo J. Visual, refractive and keratometricresults ofepikeratophakia in children. A two year follow-up.Arch Ophthalmol 1989; 107: 358-63.

10 Durrie DS, Habrich DL, Dietze TR. Secondary intraocularimplantation vs epikeratophakia for the treatment ofaphakia. AmJ Ophthalmol 1987; 103: 384-91.

11 Steinert RF, Wagoner MD. Long term comparison ofepikeratoplasty and penetrating keratoplasty forkeratoconus. Arch Ophthalmol 1988; 106: 493-6.

12 Lass JH, Stocker EG, Fritz ME, Collie DM. Epikeratoplasty:the surgical correction of aphakia, myopia and keratoconus.Ophthalmology 1987; 94: 912-25.

13 Dietze TR, Durrie DS. Indications and treatment ofkeratoconus using epikeratophakia. Ophthalmology 1988;95: 236-44.

14 Halliday BL. Manufacture of epikeratophakia lens. Eye 1988;2: 395-9.

15 Halliday BL. A computer program for the calculation of theback radius of cut for aphakia epikeratophakia lenses. In:Oliveira LNF de, ed. Ophthalmology today. Amsterdam:Elsevier, 1988: 145-51.

16 Halliday BL. Simplified formulas for lathing epikeratophakialenses. Ophthalmic Surg 1989; 20: 337-41.

17 Steinert RF, Grene RB. Postoperative management ofepikeratoplasty. J Cataract Refract Surg 1988; 14: 255-64.

18 Harper RA, Halliday BL. Glare and contrast sensitivity incontact lens corrected aphakia, epikeratophakia and pseudo-phakia. Eye 1989; 3: 562-70.

19 Arffa RC, Marvelli TL, Morgan KS. Long-term follow-up ofrefractive and keratometric results of pediatric epikerato-phakia. Arch Ophthalmol 1986; 104: 668-70.

20 AMO Kerato-Lens Update 1989; 6: no. 1.21 Wagoner MD, Steinert RF. Temporary tarsorrhaphy

enhances reepithelialization after epikeratoplasty. ArchOphthalmol 1988; 106: 13-4.

22 Binder PS, Zavala EY, Baumgartner SD, Nayak SK.Combined morphologic effects of cryolathing and lyophili-zation on epikeratoplasty lenticules. Arch Ophthalmol 1986;104:671-9.

23 Mannis MJ, Zadnik K, Johnson C, Adams C. Contrastsensitivity function after epikeratophakia. Cornea 1988; 7:280-4.

24 Nichols BD, Lindstrom RL, Spigelman AV. The surgicalmanagement of overcorrection in myopic epikeratophakia.AmJ Ophthalmol 1988; 105: 354-6.

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