Ocular integrity after refractive procedures.

PURPOSE: The purpose of the study was to determine the integrity of human eyes after refractive procedures. METHODS: Whole human globes underwent either radial keratotomy (RK) with eight incisions, automated lamellar keratoplasty (ALK), photorefractive keratectomy (PRK), or excimer laser assisted in situ keratomileusis (LASIK). Eyes then were subjected to quantitatively increasing levels of trauma until rupture occurred. RESULTS: All eyes operated on required less energy to rupture as compared with that of control eyes. The mean number of trials required for rupture is as follows (energy doubled with each successive trial): normal, 4.29; LASIK, 3.80; ALK, 3.67; PRK, 3.60; and RK, 2.83. The level of energy required to rupture normal, ALK, PRK, and LASIK eyes was not significantly different. All RK eyes ruptured at incisions. Most ALK, PRK, and LASIK eyes ruptured near the flap edge or limbus. Most normal eyes ruptured with both corneal and scleral involvement. Age of tissue donors at the time of death and time elapsed between death and procedure were not significantly different between groups (P = 0.88 and 0.79, respectively). CONCLUSIONS: The energy required to rupture ALK, PRK, and LASIK eyes is not significantly different from that for normal eyes. The RK eyes ruptured with significantly less energy than did normal eyes. All RK eyes ruptured at incision sites.

The effect of optical defocus on the pattern electroretinogram in normal subjects and patients with Alzheimer's disease.

The pattern electroretinogram, thought to originate from the spatially sensitive inner retinal layers, was recorded in 16 patients with Alzheimer's disease and 16 age- and gender-matched control subjects under the following two test conditions: (1) optical defocus or inattention, without laser pointer, and (2) optical focus or attention, with laser pointer. By correcting for optical defocus with the laser pointer, control subjects increased their pattern electroretinogram amplitudes by 8% from a mean value of 2.65 microV (standard deviation, 1.12) to 2.87 microV (standard deviation, 0.93), whereas patients with Alzheimer's disease had a 19% increase in pattern electroretinogram amplitude from 2.20 microV (standard deviation, 0.86) to 2.62 microV (standard deviation, 0.64). By controlling for optical defocus, the coefficient of variation (standard deviation/mean) was reduced by 10% (from 42% to 32%) in normal subjects and by 14% (from 39% to 25%) in patients with Alzheimer's disease. A two-way analysis of variance (ANOVA) did not show a significant difference in amplitudes between populations, which indicates that the pattern electroretinogram may not be valuable in establishing an early diagnosis of Alzheimer's disease. In a second study conducted in 20 young, healthy normal subjects, plus lenses were used to defocus the checkerboard stimuli, before recording the pattern electroretinogram. We found that the pattern electroretinogram was extremely sensitive to optical defocusing such that the response amplitude decreased by 13% at 20/25 visual acuity and 19% at 20/30. Reduction of pattern electroretinogram amplitude caused by change in visual acuity is an independent source of artifact.(ABSTRACT TRUNCATED AT 250 WORDS)