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.