British Journal of Ophthalmology 1996;80:545-548 545 Role of epithelial hyperplasia in regression following photorefractive keratectomy Br J Ophthalmol: first published as 10.1136/bjo.80.6.545 on 1 June 1996. Downloaded from

Charline A Gauthier, Brien A Holden, Daniel Epstein, Bj6rn Tengroth, Per Fagerholm, Helene Hamberg-Nystr6m

Abstract Materials and methods Aim-To determine the relation between SUBJECTS epithelial hyperplasia and regression of We examined subjects who had previously had effect after photorefractive keratectomy PRK performed on one eye for correction of (PRK). myopia (Table 1). Out of approximately 800 Methods-Seventy unilaterally treated pa- patients treated at our clinic with the Excimed tients with PRK were examined. All eyes UV200LA excimer laser (Summit Technology, had been treated with the Summit exci- Waltham, MA, USA), 216 were unilateral at mer laser 27 (SD 7) months previously the time the study was conducted. Study with zone diameters of 4.1 to 5.0 mm. The subjects were asked to participate by letter or in untreated fellow eyes served as controls. person in advance or when they presented to Epithelial thickness was measured cen- the clinic for their regularly scheduled follow trally with a thin slit optical pachometer up, and 70 were able to participate. The and manifest subjective refraction was reasons why the participating subjects re- performed. mained unilaterally treated are given in Table Results-The epithelium was 21% thicker 2. All eyes were free of any obvious ocular in the treated eye (p<0.0001). The relation disease. Informed consent was obtained from between refractive regression and epithe- all subjects. lial hyperplasia was significant (r=0.41; The unoperated eye was used as the control p<0.OOl). in all cases. Subjects were asked to remove Conclusions-Epithelial hyperplasia after their contact lens from the untreated eye at PRK correlated with the myopic shift least 1 night before the study visit. Five (including hyperopia reduction) after subjects presented to the clinic wearing soft treatment with the Summit laser. A model lenses in their control eye and the lenses were http://bjo.bmj.com/ is proposed suggesting that both subepi- removed immediately. Although contact lens thelial and epithelial layers contribute to induced hypoxia may cause stromal swelling, Cooperative Research regression in the Summit treated eyes O'Leary et alF have shown that the corneal epi- Centre for Eye with 18 gm of epithelial hyperplasia con- thelium does not swell even after 6 hours of Research and tributing each dioptre ofregression. anoxia. Therefore contact lens induced Technology, (BrJ7 Ophthalmol 1996;80:545-548) oedema would not be expected to have affected and Cornea and on September 28, 2021 by guest. Protected copyright. Contact Lens Research the epithelial thickness and these subjects were Unit, School of included in the study. Optometry, Despite the growing popularity ofphotorefrac- University ofNew tive keratectomy (PRK) and the relatively high SURGICAL PROCEDURES South Wales, Sydney, patient satisfaction with the results,' the prob- All patients had PRK performed for myopia by Australia C A Gauthier lems of individual predictability and long term one of four surgeons (BT, DE, PF, HHN). All B A Holden stability of refraction remain. The aetiology surgeries were performed in Stockholm, Sweden. of myopic regression is still unclear.2' It Surgical factors are summarised in Table 1. Department of has been widely suggested that there is a The surgical procedure was preceded by Ophthalmology, relation between regression and epithelial topical anaesthesia with amethocaine (tetra- University Hospital, hyperplasia and/or stromal remodelling.2 4-8 caine) 0.5%, and marking of the treatment Uppsala, Sweden D Epstein Epithelial hyperplasia has been reported zone. With the patient fixating an internal fixa- histologically9"4 and clinically.25 However, the tion target within the laser, a 5.0 mm radial St Erik's Eye Hospital, relation between epithelial hyperplasia and keratotomy marker with cross hairs was Karolinska Institutet, refractive changes has not been investigated. centred on the entrance pupil and pressed on Stockholm, Sweden Epstein et al'6 have questioned the stromal the cornea to delineate the treatment zone. B Tengroth remodelling hypothesis with their report of the Removal of the central corneal epithelium was P Fagerholm H presence of the original pattern of laser performed manually with a Beaver blade Hamberg-Nystrom ablation rings below the epithelium as long as 2 (Becton Dickinson, AcuteCare, Franklin Correspondence to: years after surgery. We have yet to understand Lakes, NJ, USA). With the patient again fixat- Charline Gauthier, PhD, the ways in which different components of the ing the same target, PRK was performed with Cooperative Research Centre for Eye Research and corneal wound healing process contribute to the Summit argon fluoride laser with spectral Technology, University of the postoperative refractive outcome. emission at 193 nm and pulse frequency fixed New SouthWales, Sydney, The aim of this study was to determine if at 10 Hz. The pulse energy resulted in a radiant NSW 2052, Australia. there is a relation between epithelial hyper- exposure of 180 mJ/cm'. The number of pulses Accepted for publication plasia and refractive regression (myopic shift) was computed by a proprietary algorithm. All 11 March 1996 after PRK. subjects had less than 1 D of astigmatism and 546 Gauthier, Holden, Epstein, Tengroth, Fagerholm, Hamberg-Nystrom

Table 1 Subject details and laser variables (600 000 lux), higher magnification (32x), thinner slit width (12 jm), and wider angle Sample size 70 between observation and illumination systems Br J Ophthalmol: first published as 10.1136/bjo.80.6.545 on 1 June 1996. Downloaded from Males:females (%) 56:44 Right eyes treated 51 (730) than those used in conventional optical Age at time of study (years): pachometry. It has an accuracy of 4-7 Mean (SD) 34 (9) gm Minimum 21 depending on the experience of the user. The Maximum 55 pachometer was fitted with a precision potenti- Follow up time (months): ometer to monitor electronically the position of Mean (SD) 27 (7) Minimum 13 the rotatable pachometer plate to an accuracy Maximum 37 of 3 minutes of arc. The voltage output gener- Attempted correction (D): ated by the potentiometer is input directly into Mean (SD) -4.1 (1.5) Minimum -1.8 a personal computer which is programmed to Maximum -8.0 convert voltage readings to thickness values Pulse frequency (Hz) 10 and store readings for each subject. This data Pulse energy (mJ/cm2) 180 Ablation zone diameter (mm): storage system guards against examiner bias by Mean (SD) 4.6 (0.2) automatically storing the thickness values in Minimum 4.1 Maximum 5.0 the computer without the examiner being Ablation depth (pm): aware of the results during measurement. The Mean (SD) 36 (13) corneal measurement location is maintained Minimum 15 Maximum 74 vertically and horizontally by two small align- ment light emitting diodes (LEDs). These lights also ensure normality of the incident were treated with spherical ablations. Em- light with the corneal surface. The pachometer metropia was the desired outcome in all eyes. system was calibrated using a series of hard Patients received an ablation with a diameter of contact lenses of known thickness. 4.1 (n=2), 4.3 (n=6), 4.5 (n=47), or 5.0 mm Epithelial thickness was measured at a (n=15). central corneal position located by having the Postoperative treatment consisted of subject fixate the light used for vertical cinchocaine-bibrocathol ointment (a combina- alignment. Ten measurements of epithelial tion of a topical anaesthetic and an antiseptic thickness were made for each of the averaged component in a paraffin/Vaseline base) for 1 recorded values. The average standard devia- day and patching overnight. Topical steroid tion of the 10 measurements was 3 gm. The (dexamethasone 1 mg/ml) therapy was started difference between the two eyes was taken as on the first postoperative day. Patients were the PRK treated eye value minus the control either treated for 3 months (five times daily for eye value. 1 month, three times daily for 1 month, and

once daily for 1 month) or for 5 weeks (five http://bjo.bmj.com/ times daily for the first week, with a subsequent Manifest subjective refraction reduction of dose by one drop per week). Two Manifest refractive error was determined using subjects were not prescribed corticosteroid standard subjective techniques without treatment immediately after surgery. Topical cycloplegia. Refraction was performed by a dexamethasone was reinstituted in 26% of trained ophthalmic technician at the 1 month Summit subjects for regression to a myopia of visit and by the operating surgeons at the 3, 6, at least 0.50 D. One subject was using topical 9, 12, 18, 24, 30, and 36 month visits. One on September 28, 2021 by guest. Protected copyright. dexamethasone once daily at the time of the independent observer (CAG) performed the study. refraction during the study visit at which epithelial thickness was measured. STUDY PROCEDURES For the purposes of this paper, the total Epithelial thickness amount of refractive regression was calculated Epithelial thickness measurements were per- as the change in refraction from the first post- formed by one unmasked observer (CAG). operative visit (1 month) until the study visit. The Payor-Holden micropachometer, a Haag- Therefore, total regression includes hyperopia Streit optical pachometer adapted to a Roden- reduction as well as any additional regression stock Model 2000 slit-lamp, was used to mea- from emmetropia to a myopic state. Refractive sure epithelial thickness.28 29 The instrument error is expressed as the spherical equivalent in allows epithelial thickness measurements to be all analyses. made by utilising a higher illumination level

STATISTICAL ANALYSIS Table 2 Reasons why subjects remained unilaterally Pearson's product moment regression analysis treated was used to determine relations between two sets of data. A paired Student's t test was used Number (%) Reason ofsubjects to test for differences between eyes in the same subject. A proportions test was used to detect Residual refraction error 29 (41) differences between two percentages. A one Monovision by choice 22 (31) Haloes around lights at night 8 (11) way analysis ofvariance (ANOVA) was used to Surgery of fellow eye booked 2 (3) test for significant differences in epithelial Waiting for sufficient time between eyes 0 hyperplasia among regression groups. The Not needed in other eye 5 (7) Financial strain 4 (6) Student Newman Keuls test was used to deter- mine which of these groups were different. Role ofepithelial hyperplasia in regressionfoUowing photorefractive keratectom5547

A 95% confidence level was chosen to denote MANIFEST SUBJECTIVE REFRACTION statistical significance and all statistical tests Figure 1 shows the mean refractive results over were two tailed. 36 months. Br J Ophthalmol: first published as 10.1136/bjo.80.6.545 on 1 June 1996. Downloaded from

EPITHELIAL HYPERPLASIA VERSUS REGRESSION Results The relation between epithelial hyperplasia and EPITHELIAL THICKNESS total regression was highly statistically significant The mean epithelial thickness in the PRK eye (r=0.41; p<0.001, Fig 2). Calculation ofthe rela- was 69 (SD 8) pm (range 52-95 pm) and in the tion between epithelial hyperplasia and regres- control eye was 57 (7) pm (range 38-75 pm). sion based on the equation derived in Figure 2 The epithelium in the PRK eye was signifi- predicts that without hyperplasia there is a cantly thicker by 12 (10) pm (21%) compared regression of 1.56 D, and for each additional with the control eye (p< 0.0001; 95% confi- 10 pm of hyperplasia there is 0.55 D of dence interval 9.35 to 14.3 pm). regression (18 pn for each dioptre ofregression). Figure 3 shows the mean epithelial hyperpla- sia grouped by the amount of total regression (ANOVA, p <0.001). There was a statistically significant difference in epithelial hyperplasia aL- (a) between groups with total regression from Coa) 0.00 D to 3.00 D and the group with greater than 4.00 D of total regression, and a) (b) between groups with total regression from cccoC. 0.00 D to 2.00 D and the group with regression of 3.12 D to 4.00 D. Discussion 12 15 18 21 24 27 30 The aim of this study was to determine the Postoperative time (months) contribution of epithelial hyperplasia to refrac- Figure 1 Postoperative refractive error (D) over time (months). Figures in brackets tive regression after PRK. Owing to the cross represent the sample size at each time point. Error bars represent standard deviations. sectional nature of the study design, subjects who where unilaterally treated were chosen so 8 as a con- y = 1.56 + 0.055x r = 1.41; p<0.001 that the untreated eye could be used A trol. The authors acknowledge that this group 6 A of patients may not be representative of PRK a patients in general as the study group had cho- * A 0 4 U * sen not to have their fellow eye treated.

.r5 It has been postulated that regression is http://bjo.bmj.com/ A A AA A 01) 2A ~A"AN& A A caused by epithelial hyperplasia and/or devel- A opment of new stromal collagen.2 3 6 Some 0) 2- * AA jA A 0- authors have suggested that reduction of the F- AA AAA A *I initial overcorrection is due to epithelial hyper- A I*4.1 *4.3 A4.5 plasia and that stromal regeneration is the *51 major source of the remaining regression.530 It -10 0 10 20 30 40 50 has also been proposed that regression is on September 28, 2021 by guest. Protected copyright. Epithelial hyperplasia (pm) related to the formation in the laser created 'bowl' of a subepithelial layer containing hyalu- ronic acid and other glycosaminoglycans which can alter corneal hydration and consequently Figure 2 Total regression (D) versus epithelial hyperplasia (,um). The thick line represents affect corneal curvature.'2 31 Wilson et al' the regression line. hypothesised that the healing of the corneal epithelium during the early postoperative 25 period results in an artificial and temporary ANOVA p<0.001 hyperflattening of the corneal contour which 23 (8) would occur if the epithelium was thicker in E 20 n=6 the periphery than in the centre ofthe ablation, co giving apparent initial overcorrection. They .r4 (14) ~~~~~~~~~~~~18 also suggested that a more pronounced stromal 15-n swelling at the wound edge could account for CD the apparent but temporary overcorrection. The 10 11(10) results of this study show that refractive .5 n =22 regression is related to the central epithelial ~~~~~9() hyperplasia occurring postoperatively in eyes o. n1 Wi 5 7 (6) treated with small (5 mm or less) ablation n=15 zones. This regression consists largely of a reduction in hyperopia occurring in the early 0 postoperative months (Fig 1). Since all of 0-1.0 1.12-2.0 2.12-3.0 3.12-4.0 >4.0 the subjects in this group were examined 12 Total regression (D) months after the operation, it is not possible to Figure 3 Mean amount ofepithelial hyperplasia (ym) versus total regression divided into confirm the time course ofepithelial hyperplasia. groups of 1 D stepsfor the Summit eyes. The means (SD) are shown in the bars. However, based on the refractive data collected 548 Gauthier, Holden, Epstein, Tengroth, Fagerholm, Hamberg-Nystrom

and the correlation of the refractive regression Kaufman HE. Changes in corneal topography after excimer laser photorefractive keratectomy for myopia. Oph- with the measured epithelial hyperplasia, it thalmology. 1991;98:1338-47. seems reasonable to hypothesise that most of 3 Colliac JP, Shammas HJ, Bart DJ. Photorefractive keratec- Br J Ophthalmol: first published as 10.1136/bjo.80.6.545 on 1 June 1996. Downloaded from tomy for the correction of myopia and astigmatism. Am J the hyperplasia develops in the early postop- Ophthalmol 1994;117:369-80. erative months since this is when the greatest 4 Fantes FE, Hanna KD,Waring GO, PouliquenY, Thompson KP, Savoldelli M. Wound healing after excimer laser rate of reduction in hyperopia occurs. In quan- keratomileusis (photorefractive keratectomy) in monkeys. titative histological studies of epithelial thick- Arch Ophthalmol 1990;108:665-75. 5 Seiler T, Kahle G, Kriegerowski M. Excimer laser (193 nm) ness after PRK in monkeys, Beuerman et al" myopic keratomileusis in sighted and blind human eyes. found that the epithelium increased in thick- Refract Corneal Surg 1990;6:165-73. 6 Binder PS. Excimer laser photoablation-clinical results ness over the first year reaching maximum and treatment of complications in 1992.[Editorial] Arch thickness at 12 months after operation with Ophthalmol 1992;110:1221-2. 7 Gartry DS, Kerr Muir MG, Marshall J. Excimer laser pho- inconsistent changes thereafter. Others have torefractive keratectomy. Ophthalmology 1992;99: 1209-19. found histological evidence of hyperplasia 8 Dausch D, Klein R, Schroder E, Dausch B. Excimer laser photorefractive keratectomy with tapered transition zone within the first month after ablation."6 for high myopia. J Cataract Refract Surg 1993;19:590-4. Reduction of the initial overcorrection because 9 Tuft S, Marshall J, Rothery S. Stromal remodelling following photorefractive keratectomy. Lasers in Ophthal- of epithelial hyperplasia has also been pro- mology 1987;1:177-83. posed by different authors.5 30 10 Marshall J, Trokel SL, Rothery S, Krueger RR. Long-term healing of the central cornea after photorefractive keratec- It has been proposed in this study that in the tomy using an excimer laser. Ophthalmology 1988;95: absence of epithelial hyperplasia there was 1411-21 11 Steinert RF, Puliafito CA. Laser corneal surgery. Int 1.56 D of regression, and for each 18 im Ophthalmol Clin 1988;28:150-4. increase in epithelial thickness there was a 1 D 12 Fagerholm P, Hamberg-Nystr6m H, Tengroth B. Wound healing and myopic regression following photorefractive increase in regression. This model of regres- keratectomy-a histological and histochemical study. Acta sion suggests that there is a non-epithelial Ophthalmol 1994;72:229-34. 13 Beuerman RW, McDonald MB, Shofaer RS, Munnerlyn component accounting for approximately 1.50 CR, Clapham TN, Salmeron B, et al. Quantitative D of regression and the remainder of the histological studies of primate corneas after excimer laser photorefractive keratectomy. Arch Ophthalmol 1994;112: regression is due to epithelial hyperplasia. 1103-10. Although stromal thickness was measured it 14 Taylor DM, L'Esperance, Del Pero RA, Roberts AD, Gigstad JE, Klintworth G, et al. Human excimer laser was not possible to evaluate its relation to lamellar keratectomy. Ophthalmology 1989;96:654-64. refractive error since the thickness of the 15 Hanna KD, Pouliquen Y, Waring Im GO, Savoldelli M, Cotter J, Morton K, et al. Corneal stromal wound healing stroma postoperatively is dependent on the in rabbits after 193-nm excimer laser surface ablation. amount of myopia that was corrected. Arch Ophthamol 1989;107:895-901. 16 Goodman GL, Trokel SL, StarkWj, Munnerlyn CR, Green The results of this study show that central WR. Corneal healing following laser refractive keratectomy. epithelial hyperplasia occurs postoperatively in Arch Ophthalmol 1989;107:1799-803. 17 Gaster RN, Binder PS, Coalwell K, Berns M, McCord RC, eyes treated with small (5 mm or less) ablation Burstein NL. Corneal surface ablation by 193nm excimer zones. The retrospective refractive data on the laser and wound healing in rabbits. Invest OphthalmolVis Sci 1989;30:90-8. study patients show that most of regression 18 Courant D, Fritsch P, Azema A, Bernard F, Botineau J, occurs in the early postoperative months as the Legate M, et al. Corneal wound healing after photo-kerato- http://bjo.bmj.com/ mileusis on the primate eye. Lasers and Light in Ophthalmol- hyperopic overcorrection subsides. Since it is ogy 1990;3:187-99. clear that regression after PRK must be due to 19 Malley DS, Steinert RE, Puliafito CA, Dobi ET. Immuno- fluorescence study of corneal wound healing after excimer the treatment zone 'filling in' with tissue, it is laser anterior keratectomy in the monkey eye. Arch not unreasonable to suggest that this tissue is at Ophthalmol 1990;108:1316-22. 20 McDonald MB, Frantz JM, Klyce SD, Beuerman RW, least in part the epithelium as others have Vamell R, Munnerlyn CR, et al. Central photorefractive shown histologically. The significant correla- keratectomy for myopia. Arch Ophthalmol 1990;108:

799-808. on September 28, 2021 by guest. Protected copyright. tion found in this study between refractive 21 Hanna KD, Pouliquen YM, Waring III GO, Savoldelli M, regression and measured epithelial hyperplasia Fantes F, Thompson KP. Corneal wound healing in mon- keys after repeated excimer laser photorefractive keratec- suggests that the two findings are related. A tomy. Arch Ophthamol 1992;110: 1286-91. model of the relation between epithelial hyper- 22 Maloney RK, Friedman M, Harmon R, Hayward M, Hagen K, Gailitis RP, et al. A prototype erodible mask delivery sys- plasia and regression was proposed stating that tem for the excimer laser. Ophthalmology 1993;100:542-9. approximately 1.50 D of regression was due to 23 Ramirez-Florez S, Maurice D. Inflammatory cells, refractive regression and haze after PRK. Invest Ophthalmol Vis Sci non-epithelial elements (a subepithelial lenti- 1993;34(suppl):704. cule and/or stromal remodelling) and that for 24 Beuerman RW, McDonald MB, Shofner RS, Munnerlyn CR, Clapham TN, Salmeron B, et al. Quantitative each 18 jm of epithelial hyperplasia an addi- histological studies of primate corneas after excimer laser tional 1 D of regression occurs. Prospective photorefractive keratectomy. Arch Ophthalmol 1994;112: 1103-10. studies of topographical epithelial, subepithe- 25 Gauthier CA, Epstein D, Holden BA, Tengroth B, lial, and stromal thickness are needed to better Fagerholm P, Hamberg-Nystrom H, et al. Epithelial delineate the contribution of the different cor- alterations following photorefractive keratectomy for myo- pia. I Refract Corneal Surg 1995;11: 1 13-8. neal layers to regression. 26 Epstein D, Tengroth B, Fagerholm P, Hamberg-Nystrom H. Excimer PRK for myopia. [Letter] Ophthalmology 1993;11: The authors are grateful for financial support from the Austra- 1605-6. lian Federal Government through the Cooperative Research 27 O'Leary DJ,Wilson G, Henson DB. The effect of anoxia on Centres (CRC) Program, the Cooperative Research Centre for the human corneal epithelium. Am J Optom Physiol Optics Eye Research and Technology, the Optometric Vision Research 1981;58:472-6. Foundation of Australia (Grant No SP94/35), the Swedish 28 Chan-Ling T, Pye DC. Pachometry: clinical and scientific Medical Research Council (Project No 8655), the Karolinska applications. In: Ruben M, Guillon M, eds. Contact lens Institutet, Kronprinsessan Margartas Arbetsnamnd, and Sti- practice. 1st ed. London: Chapman and Hall Medical, flelsen Tornspiran. 1994:414-20. The authors acknowledge Sister Ann-Margrethe Eriksson, 29 Holden BA, Polse KA, Fonn D, Mertz GW. Effects of cata- Miss Alexandra Viding, Miss Helen Fischer, and Miss Inger ract surgery on corneal function. Invest Ophthalmol Vis Sci NygArds for their assistance in conducting the study in Sweden, 1982;22:343-50. and Dr Helen Swarbrick for helpful comments on the 30 Tuft SJ, Gartry S, Rawe IM, Merk KM. Photorefractive manuscript. keratectomy: implications of corneal wound healing. Br J 1 Kahle G, Seiler T,Wollensak J. Report on psychosocial find- Ophthalmol 1993;77:243-7. ings and satisfaction among patients 1 year after excimer 31 Fitszimmons TD, Fagerhoim P, Harfstrand A, Schenholm laser photorefractive keratectomy. Refract Corneal Surg M. Hyaluronic acid in the rabbit cornea after excimer laser 1992;8:286-9. superficial keratectomy. Invest Ophthalmol Vis Sci 1992;33: 2 Wilson SE, Klyce SD, McDonald MB, Liu JC, 3011-6.