Faculty Bibliography

The appearance of haze in the central cornea following photoablation with a 193 nm excimer laser is an important factor in the postoperative course of this procedure. Data from 37 human eyes treated with photorefractive keratectomy, 4 eyes treated with phototherapeutic keratectomy, and 5 untreated eyes were used to evaluate the ability of a commercially available opacity lensometer to provide an objective measure of corneal clarity. We found that the opacity lensometer was able to detect light scattered from the cornea but was not sufficiently sensitive to distinguish reliably among excimer-treated eyes with degrees of corneal haze evaluated as clear, trace, or 1+ by slit-lamp microscope examination. In untreated, clear corneas, the values obtained with the opacity lensometer in eyes measured with and without a clear contact lens were within one unit of each other for any given eye, but values from eye to eye varied over a range of six units. In a test simulating different amounts of corneal haze using contact lenses evenly coated with nail polish enamel, the log-transformed opacity lensometer values varied directly with percent light scattering as determined by spectrophotometry. These results suggest that the opacity lensometer measurements are reliable and reproducible, but that in the human cornea something is being measured by the opacity lensometer that is not taken into account in clinical slit-lamp microscope evaluation. Overall, it appears that, in its present form, this instrument is not useful to measure corneal clarity after excimer laser photoablation

In this study, we examined the correlations among various factors that may affect the results of central photorefractive keratectomy for myopia. Data analyzed from our studies of blind, partially sighted, and normally sighted eyes included patient age, attempted correction, time to re-epithelialization, postoperative corneal clarity, refraction (relative spherical equivalent), and uncorrected visual acuity. We found that larger attempted corrections resulted in less accurate refractions and poorer uncorrected visual acuity. Older patients tended to have better results than younger patients, regardless of the amount of attempted correction. The relationship between the amount of attempted correction and corneal clarity was weak. There was a statistical correlation between corneal clarity scores and uncorrected visual acuity, but the range of corneal clarity scores was small and even the highest scores were probably not in the range that interfered with vision, so the relationship was probably not causal. The rate of epithelial healing did not appear to affect either refractive or visual results, and was not affected by patient age. These findings may be useful in guiding future efforts to improve the results of this new surgical procedure for the correction of refractive error

The authors compared postkeratoplasty astigmatism over a 4-month period after surgery in a randomized, prospective study of two groups of patients (total N = 18) who received two different suture techniques. The test group N = 8) had a single running suture with postoperative suture adjustment; on the basis of computer-assisted topographic analysis, the suture was tightened in the flatter meridian and loosened in the steeper meridian in the first month after surgery. The control group (N = 10) had a standard double running suture procedure with no postoperative adjustment; the single running 10-0 nylon suture was removed 3 months after surgery. Four months after penetrating keratoplasty, mean (+/- standard deviation) astigmatism in the test group was 1.7 +/- 0.7 diopters (D), and all patients had less than 2.6 D of astigmatism. In the control group, mean astigmatism was significantly higher (5.4 +/- 2.4 D; range, 0.7-9.0 D; P less than 0.01). The results suggest that postkeratoplasty astigmatism can be reduced with the single running suture technique accompanied by postoperative suture adjustment

To determine whether exposure to the excimer laser beam results in the oncogenic transformation of cornea cells, tissue-cultured corneal keratocytes and intact corneas from an inbred strain of rat were exposed to ablative and subablative energies of the excimer laser beam. No evidence for cellular transformation was found. Neither the corneas nor the stromal keratocytes exposed to the laser beam were transformed into cells with unregulated growth potential. Both treated keratocytes and corneas were implanted subcutaneously in the same strain of rats; neither developed into tumors. In tissue culture, cells from cultures exposed to the excimer laser beam exhibited normal growth patterns, growing at the same rate as control, unexposed cells and exhibiting the same capacity to respond to the contact inhibition of growth as the control cells. These results suggest that the 193-nm excimer laser beam does not transform corneal keratocytes and that the energies emitted by this beam will not cause cell transformation when the excimer laser is used as a surgical tool in human eyes

Prior to undertaking a study in sighted human eyes, we performed photorefractive keratectomy with the 193-nm excimer laser for the correction of myopia in nine legally blind eyes to evaluate safety, efficacy, predictability, and stability. In most cases, reepithelialization was complete by 5 days after surgery; no recurrent erosions were seen. By the end of the 6-month study, all of the corneas had a 0 or 1+ clarity score, on a scale of 0 (clear) to 5+ (opaque). Keratometry and pachometry demonstrated stable flattening of the corneas. One month after surgery, changes in refraction evaluated by retinoscopy showed fair predictability, with no significant increase in refractive or keratometric astigmatism, followed by some regression of effect by the end of the study, possibly caused by anatomical remodeling. The amount of regression appeared to be directly related to the amount of correction intended, suggesting that this effect would not be clinically important in the treatment of mild to moderate myopia

Five patients with Down's syndrome underwent penetrating keratoplasty for keratoconus. In three patients, the indication for surgery was acute corneal hydrops, which had not resolved in the three months before surgery. The other two patients had corneal scars. Two patients had combined penetrating keratoplasty, cataract extraction, and intraocular lens insertion. Four of the five patients maintained clear grafts at their most recent follow-up examination. Two of the five patients had one or more graft reaction episodes; one graft was lost. Good results can be obtained in penetrating keratoplasty for keratoconus in patients with Down's syndrome who do not demonstrate a tendency toward excessive eye rubbing and for whom a single observant caretaker can be relied on to provide consistent postoperative care

The Prospective Evaluation of Radial Keratotomy Study is a nine-center clinical trial of a surgical technique to reduce simple myopia by making incisions in the cornea. There were 435 patients (one eye per patient is reported) enrolled in the study with a 91% follow-up rate at 4 years after surgery. After surgery, uncorrected visual acuity was 20/40 or better in 76% of eyes. Fifty-five percent of the eyes had a refractive error within +/- 1.00 diopter; 28% were undercorrected, and 17% were overcorrected by more than 1.00 D. The width of the prediction 90% interval for the refractive change was 4.42 D, indicating a lack of predictability. The refractive error was not stable in some eyes; between 6 months and 4 years after surgery, 23% of eyes had a continued effect of the surgery of more than 1.00 D. For 323 patients with both eyes operated on, 64% stated they wore no optical correction. There were few serious complications. Eleven eyes (3%) lost two or three lines of best corrected visual acuity. Two eyes developed delayed bacterial keratitis without significant loss in best corrected visual acuity

Photorefractive keratectomy for the correction of myopia was performed in 32 eyes of 16 green monkeys. The corneas healed satisfactorily, with normal formation of basal lamina and hemidesmosomal attachments visible in 14-week histologic specimens. No recurrent erosions were observed clinically. After a transient period of faint haze, all corneas were clear at 17 weeks and remained clear through the 1-year follow-up. In terms of accuracy, all corneas demonstrated a significant flattening compared with preoperative values, but no significant difference was seen between the groups with different intended corrections (1.5 and 3 diopters). The changes in corneal shape stabilized by 17 weeks, as measured by keratometry. The clinical results suggest that mechanical removal of the epithelium is preferable to laser ablation of the epithelium. Overall, the results demonstrate that excimer laser ablation of the corneal stroma can produce a stable diptric change in the primate cornea with good healing and long-term corneal clarity