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Objective To examine the histologic and ultrastructural features of human corneas after successful laser in situ keratomileusis (LASIK) in 2 patients post mortem. Methods Portions of 4 corneas were processed for histology, transmission electron microscopy, and scanning electron microscopy. Results Case 1 had undergone LASIK 3 months prior to death and case 2 had undergone LASIK 20 months prior to death. A Hansatome (Bausch & Lomb Surgical Inc, Clarement, Calif) microkeratome with a 180-µm plate had been used for case 1 and an Automated Corneal Shaper (Chiron Corporation, Munich, Germany) with a 160-µm plate had been used for case 2. Histologically, the LASIK flap measured 160 µm and 150 µm in thickness in case 1 and case 2, respectively. Corneas from both cases exhibited minor epithelial ingrowth into the wound, reactive keratocytes at the wound margin, irregular collagen fibrils in the wound bed, and severed collagen bundles at the flap hinge. These findings were more pronounced in case 1 than in case 2, and the wound interface was virtually imperceptible in case 2. Additionally, the corneas from case 1 contained periodic acid-Schiff–positive electron dense material and wide-spaced collagen at the wound interface, and there was an absence of corneal nerves. Conclusions These findings show that changes caused by wound repair that are present at 3 months are minor 20 months after LASIK.

Objectives To study the effects of radial keratotomy (RK) and photorefractive keratectomy (PRK) on contrast sensitivity and glare disability using 4 different devices, and to correlate subjective complaints with objective scores of visual performance. Methods Preoperative contrast sensitivity for 30 eyes undergoing RK and 30 eyes undergoing PRK was compared with contrast sensitivity at 1, 3, and 6 months postoperatively using the CSV 1000, MCT (Multivision Contrast Tester) 8000, and Pelli-Robson chart. The BAT (Brightness Acuity Tester) and MCT 8000 were used to test for daytime and nighttime glare disability, respectively. At 3 and 6 months postoperatively, a questionnaire was administered to assess visual performance subjectively. Results Contrast sensitivity decreased after RK and PRK up to the sixth postoperative month, while glare disability was significantly increased at 1 month after PRK as determined by the MCT 8000 and the BAT, and at the third and sixth months after RK using the MCT 8000. Compared with RK, PRK significantly decreased contrast sensitivity as measured with the MCT 8000 at all spatial frequencies 1 month postoperatively. No significant difference in visual performance between patients undergoing RK and PRK was observed with the CSV 1000, the Pelli-Robson chart, or the BAT up to 6 months postoperatively. No consistent difference was found between glare disability scores of patients undergoing RK and PRK when measured with the MCT 8000. Subjective reports of problems with night driving and blurring correlated only with glare disability scores of the MCT 80003 months after RK. Conclusions Both RK and PRK reduce contrast sensitivity and cause glare disability; however, the relative effect is highly dependent on the time postoperative testing is performed and the instrument used for testing. Contrast sensitivity and glare disability, as measured by the instruments used in this study, do not accurately reflect patients' subjective assessment of visual performance in daily life.

• Five rhesus monkey eyes underwent repeated argon fluoride (193 nm) excimer laser myopic photorefractive keratectomy 3 months following an initial ablation that had produced mild subepithelial haze. At 3 months all eyes had development of a dense subepithelial opacity and a thickened epithelium (12 cells, 80 μm) with vacuolization of basal cells, fragmented basement membrane, and a layer of subepithelial fibrosis containing activated fibroblasts. By 6 months the opacity was clearing; epithelium was thinner (50 μm); subepithelial fibrosis was more lamellar. By 15 months only mild haze persisted clinically; epithelium was 30 μm thick, with persistent basal vacuolization and focal basement membrane disruption; subepithelial fibrous tissue was more organized. Early repeated excimer laser ablation of the monkey cornea apparently induces vigorous stromal wound healing. Use of shallower ablations, corticosteroids, or a longer delay between ablations may be necessary for repeated laser surgery to be practical clinically.

To the Editor. —The 193-nm wavelength generated by the argon fluoride excimer laser precisely ablates corneal tissue without evidence of adjacent thermal damage.1Lower-energy excimer wavelengths, including 248, 308, and 351 nm, have been investigated and found to produce a zone of adjacent thermal damage that increases with the wavelength. The mechanism by which far ultraviolet (UV) energy interacts with corneal tissue is controversial and poorly understood. Srinivasan and colleagues2have suggested that highly energetic far UV photons (6.4 eV at 193 nm) directly break the intramolecular bonds that link the collagen polymer together. This process is dependent on high corneal absorption of the wavelength and sufficient photon energy to induce bond disruption.2Other possible mechanisms include ultrafast thermal events in which heating is confined to a small volume of corneal tissue that is vaporized before significant thermal diffusion into surrounding cornea occurs. We irradiated human cadaver corneas