Patricia A Williams

Analysis of astigmatic keratotomy

ABSTRACT Eighty‐two keratotomy procedures were performed for both idiopathic and postsurgical astigmatism or myopic astigmatism and analyzed for efficacy using vector and linear regression analysis. Delta keratometry values (delta K), were computed for each case as delta K in the desired axis of effect using vector analysis. Six different procedures were compared including both intersecting and nonintersecting trapezoidal keratotomy, relaxing incisions with compression sutures, T cuts with radial keratotomy, T cuts alone, and RK with elliptical optical zones. Our results showed that the greatest shifts occurred in the trapezoidal groups, whereas the most predictable effects occurred in the relaxing incision/compression suture group. Astigmatic keratotomy is capable of producing large shifts in corneal astigmatism; however, the accuracy of these procedures remains highly variable.

Trapezoidal Keratotomy: A Vector Analysis

Twenty-three eyes in 23 patients ranging from 61 to 83 years of age underwent trapezoidal astigmatic (Ruiz) keratotomy. Preoperative regular astigmatism ranged from 3.13 to 13.00 diopters by keratometry. Fourteen of the eyes had high regular astigmatism following penetrating keratoplasty, eight following cataract extraction, and one eye had no history of surgery. Patient follow-up ranged from 1 to 15 months with a mean of five months. Trigonometric vector analysis of the keratometric readings demonstrated that the magnitude of surgically induced change in corneal curvature was inversely proportional to the size of the optical zone and ranged from 1.28 to 14.21 diopters. Frequently, due to the axis of surgically induced change, the magnitude of change in corneal curvature failed to be reflected by an equal magnitude of reduction in the residual corneal astigmatic error, and in many cases a residual error was created in a meridian differing significantly from that of the preoperative astigmatic error. There is no statistically significant difference in the slopes of the linear regression lines relating change in corneal curvature to optical zone size between this series and our previously reported cadaver study.

Map-Fingerprint-Dot Changes in the Corneal Epithelial Basement Membrane Following Radial Keratotomy

Corneal epithelial opacities similar to those seen in corneal epithelial basement membrane dystrophy were seen in 33 of 71 eyes following radial keratotomy. These changes were clinically indistinguishable from those seen in map-fingerprint-dot dystrophy with map type changes seen most often. Basement membrane changes tended to be transient (persisting less than 3 months in 75.3% of eyes) and not usually visually significant. However, three eyes had changes which persisted for 12 months. Most eyes with basement membrane changes had involvement of less than one-half quadrant of the corneal (68%). Involvement of two or more quadrants occurred in 9.4% of eyes with these changes. One eye had visually significant changes which persisted for 3 months. There were no episodes of recurrent erosion.

Safety and efficacy of 2% methylcellulose in cat and monkey cataract-implant surgery

We evaluated the safety and efficacy of 2% methycellulose as an adjunct for cataract extraction with implantation in cat and monkey models. When used intraoperatively, methylcellulose reduced the iridovitreal bulge during surgery. No significant increase in clinical inflammation occurred nor was there statistically significant intraocular pressure elevation at 24 hours, 7 days, or 90 days. In the cat model, the central corneal thickness increased at day seven in both control and methylcellulose eyes; this thickness persisted to 90 days. The endothelial cell loss decreased significantly at day 90 in methylcellulose eyes. In the monkey model, no statistically significant increase in corneal thickness occurred in control or methylcellulose eyes at day seven. The endothelial cell loss was greater than in the cat model in both control and methylcellulose eyes; there was no statistically significant difference between the two. Two percent methylcellulose was safe in both the cat and monkey models. It facilitated surgery in both models and reduced the endothelial cell loss in the cat eye.

Ruptured Globe After Radial Keratotomy

acid treatment was immediately stopped and two months later the corneal calcification disappeared. Favorable results of topical retinoic acid therapy for disorders of the outer eye have been reported, with local irritation noted as the only side effect. Topical vitamin A treatment was also found to increase the healing of cataract incisions. Patients with dry eye syndrome who are treated with retinoic acid should be followed up carefully to watch for this possible side effect.

Contrast Sensitivity Under Photopic Conditions in the Prospective Evaluation of Radial Keratotomy (PERK) Study

We studied the effect of radial keratotomy on contrast sensitivity in 69 individuals with one eye operated and one eye unoperated in the Prospective Evaluation of Radial Keratotomy (PERK) Study, with a mean follow-up time of 13.8 months (range 6 months to 31 months). We tested contrast sensitivity under normal daylight conditions using both photographic plates and a computer-video apparatus. On average, we found no clinically meaningful loss of contrast sensitivity in eyes after radial keratotomy. However, eyes with radial keratotomy showed a statistically significant decrease in contrast sensitivity at the higher spatial frequencies of 12 and 18 cycles per degree, although all values were within the previously established normal range. Specifically, 44% of the patients had approximately the same contrast sensitivity in both eyes; 40% of the patients had 50% less contrast sensitivity in the operated eye than in the unoperated eye; 16% of the patients had 50% more contrast sensitivity in the operated eye than in the unoperated eye. Contrast sensitivity improved gradually in operated eyes between 6 months and 2 years after surgery. Eyes with radial keratotomy, in which the diameter of the pupil was the same size as or larger than the central clear zone, had slightly decreased contrast sensitivity compared to eyes in which the pupil was smaller than the clear zone.

Further Studies of Four Incision Radial Keratotomy

This investigation evaluated the results of radial keratotomy on 52 eyes in 30 patients; 32 eyes had follow-up of greater than one year. The spherical equivalent refraction for 91% of these patients was within 1 diopter of emmetropia. We have followed five eyes between one and two to three years after surgery, observing a continued effect of the surgery with a mean gain in the hyperopic direction of +0.72 diopters. Initial overcorrections must be avoided in radial keratotomy.

Surgical Treatment of Overcorrection Following Radial Keratotomy: Evaluation of Clinical Effectiveness

Secondary hyperopia following radial keratotomy (RK) may result from an initial overcorrection or from a continued effect of the procedure with time. We retrospectively evaluated the effect of surgical intervention for the management of overcorrection following RK in six patients who had undergone reopening of all RK incisions, followed by irrigation and closure of the incisions with 10-0 mersilene sutures. Three patients with prior 4-incision RK, with follow-up of 4 to 26 months, were steepened a mean of 1.63 diopters keratometrically; three patients with prior 8-incision RK, with follow-up of 3 to 12 months, were steepened a mean of 1.46 D keratometrically. Comparison of intraoperative with postoperative keratometry demonstrated a substantial loss of effect with time, which stabilized by 2 months in 4-incision RK patients and by 3 months in 8-incision RK patients. Nevertheless, placement of interrupted sutures across reopened radial incisions consistently induced central corneal steepening in these six patients.

Four incision radial keratotomy

ABSTRACT Radial keratotomy is a constantly evolving procedure. This paper investigates the value of four incision radial keratotomy. The possible advantages of fewer incisions include increased corneal stability, lower risk of perforation, less potential of endothelial cell loss, decreased chance of overcorrection, and simplification of the procedure. We evaluated the results of four incision radial keratotomy in 55 eyes of 31 patients. Follow‐up ranged from one to 18 months. Results in low myopia (‐2.00 to ‐3.12 diopters) show 93% of the patients were 20/40 or better, 90% were within ± 1 diopter of emmetropia, and no patients were overcorrected greater than I diopter. In moderate myopia (‐ 3.25 to ‐ 4.37 diopters), 84% of the patients were 20/40 or better, 92% were within &agr; 1 diopter of emmetropia, and no patients were overcorrected greater than 1 diopter. Regression analysis was performed and it was determined that the postoperative result was equal to .262 + [1.293 x preop spherical equivalent] ‐ [1.166 x optical zone] + [0.56 x depth] + [.038 x age], R = .87.

Epikeratophakia: Technique modifications and visual results compared to the national study+++

ABSTRACT Twenty‐eight epikeratophakia procedures have been performed at the University of Minnesota since December 1985. This report describes several technique modifications and compares the refractive and visual outcome of these cases with the national results. There have been 17 aphakic cases (13 adult and four pediatric), seven myopic procedures, and four keratoconus cases. Of the adult aphakic cases, 80% were within 3 diopters of emmetropia at six months, with four cases showing an undercorrection. In the myopic group, five cases showed an overcorrection at six months and all patients were within two Snellen lines or better than their preoperative best corrected vision. The, major complications included one graft removal for failure to epithelialize, an interface hematoma, and a severe overcorrection to +9.37 diopters in a myopic patient. A no‐keratectomy technique was used in the aphakic and myopic groups. A variation on centering the Hessburg‐Barron trephine and removing the epithelium was performed and allowed for more accurate trephine placement.