Keratocyte loss and repopulation of anterior corneal stroma after de-epithelialization.

OBJECTIVE: To quantitate corneal keratocyte loss and repopulation of anterior stroma after de-epithelialization. METHODS: Fourteen white New Zealand rabbits, each weighing 2.3 to 3.2 kg, were divided into seven groups. Each rabbit underwent a bilateral 6-mm mechanical deepithelialization procedure. The rabbits were killed two at a time after 1, 3, 6, 8, 10, 14, and 28 days. The corneas were labeled for mitosis using 5-bromo-2-deoxyuridine and stained for keratocyte quantification. Three untreated rabbits were added as controls. RESULTS: Corneas that were not operated on showed a higher density of keratocyte nuclei within the anterior corneal stroma than in the posterior stroma. Following de-epithelialization, there was a decrease in the ratio of anterior-posterior keratocytes, with maximal decrease on the third postoperative day. Keratocyte repopulation was completed by day 14. Mitotic activity was seen on days 1, 3, and 6 in the anterior half of the de-epithelialized stroma. CONCLUSIONS: Anterior stromal keratocytes are lost after epithelial removal, but repopulation is complete within 2 weeks. These findings demonstrate a loss of keratocytes and their recovery after corneal epithelial removal, as well as an interaction between corneal epithelium and stroma in rabbits.

Autorefraction/autokeratometry and subjective refraction in untreated and photorefractive keratectomy-treated eyes.

OBJECTIVE: To examine the relative accuracy of autorefraction and autokeratometry (autorefraction/autokeratometry) and subjective refraction in untreated and photorefractive keratectomy (PRK)-treated eyes. DESIGN: Results of autorefraction/autokeratometry obtained by means of 2 contemporary devices (Nidek ARK 2000 and Canon Rk-3) were compared with those of subjective refraction in 48 untreated eyes and in 78 eyes treated with (PRK). RESULTS: A trend toward greater differences between subjective and objective methods in PRK-treated eyes was observed. Both autorefraction devices showed similarly higher differences from subjective readings in PRK-treated eyes with regard to sphere (P < .001) and cylinder (P = .02), but not axis (P =.4). For autokeratometry, the mean difference from manual readings was highly significant when all K readings were considered together, but not so for the individual differences in keratometric astigmatism (Canon RK-3 and Nidek ARK 2000 vs manual results: P =.03 and P =.93, respectively) and keratometric axis (Canon RK-3 and Nidek ARK 2000 vs manual results: P =.88 and P =.19, respectively). CONCLUSIONS: Refractive and keratometric readings obtained with the automated devices tested in this study varied more from those obtained with subjective methods when the eyes examined had been treated with PRK. Corneal topographical changes inherent in the wound-healing process may influence objective measurement with automated devices.

Photoastigmatic refractive keratectomy for primary treatment and revision of myopic astigmatism.

PURPOSE: To evaluate the results in 43 eyes treated with a rotating mask for myopic astigmatism and followed for up to 1 year. SETTING: Lucerne Eye Clinic, Cantonal Hospital, Lucerne, Switzerland. METHODS: Thirty-two patients (42 eyes) were selected to have photoastigmatic refractive keratectomy (PARK). In 33% (14 eyes), this treatment was the second or third ablation. The Aesculap Meditec MEL 60 excimer laser was operated in toe scanning slit mode, and a rotating mask was used. To evaluate cylindrical shaping, vector analysis was performed. RESULTS: One year after PARK, mean uncorrected visual acuity in all patients (26 eyes) improved from 20/160 preoperatively to 20/40. Surgically induced astigmatism in 20 of 26 eyes (77%) was within +/- 1.00 diopter (D) of the targeted induced astigmatism. At 1 year, 81% of patients who had primary excimer laser treatment for myopic astigmatism equivalent to -10.00 D or less were within +/- 1.00 D of target refraction compared with 44% of re-treated eyes. CONCLUSION: The result of PARK in eyes with low to moderate degrees of myopic astigmatism was satisfactory. However, in eyes with extensive scarring and wound healing activity after the first ablation, re-treatment was less predictable.

Prostaglandin E2 production after lamellar keratectomy and photorefractive keratectomy.

PURPOSE: To compare the levels of prostaglandin E2 (PGE2) in corneal tissue after 193-nanometer excimer laser keratectomy and mechanical keratectomy with a microkeratome. METHODS: Four rabbits underwent 193-nanometer excimer laser phototherapeutic keratectomy on one eye, and lamellar keratectomy with the microkeratome on the fellow eye. The corneas were harvested at 10 hours after the treatment and quantitated for PGE2 levels using an enzyme-linked immune assay. Control levels of PGE2 in untreated corneas were obtained from a previous study. RESULTS: Unoperated control corneas had low levels of PGE2 (1.79 +/- 1.0 pg/mL). Both surgical techniques resulted in a significant (p < .01) increase in PGE2. Corneas ablated mechanically with the microkeratome had an average PGE2 level of 15.48 +/-5.36 pg/mL, which represented an 8.6-fold increase compared to control; there was an additional 330% mean increase in PGE2 concentration in the laser-ablated corneas (51.29 +/- 36.08 pg/mL) compared to the corneas treated with mechanical lamellar keratectomy (p = .014). CONCLUSIONS: Mechanical and photochemical superficial keratectomies induce production of an inflammatory mediator, PGE2. The 193-nanometer excimer laser irradiation causes a greater increase of PGE2 production in the corneal tissue than does keratectomy with the microkeratome; this observation may support a role for cyclo-oxygenase inhibitors in postoperative therapy.