Helene Hamberg-Nyström

EXCIMER LASER PHOTOREFRACTIVE KERATECTOMY FOR MYOPIA; CLINICAL RESULTS IN SIGHTED EYES

PURPOSE To evaluate the refractive results of excimer laser photorefractive keratectomy (PRK) performed on normal, sighted myopic eyes; to assess the role of postoperative topical steroid treatment in patients with PRK; and to study the regression of effect. METHODS An argon fluoride 193-nm excimer laser was used. Photorefractive keratectomy was performed on 420 eyes with preoperative refraction ranging from -1.25 to -7.50 diopters (D). Minimum follow-up time was 12 months, and 194 of the eyes were followed for 15 months. Postoperative treatment generally consisted of topical dexamethasone for 3 months, but in a sub-study, some eyes were treated for only 5 weeks. RESULTS Mean refraction (spherical equivalent +/- standard deviation) at 12 months was -0.04 +/- 0.84 D and at 15 months -0.22 +/- 0.78 D. At 12 months postoperatively, 86% of the eyes were within 1.00 D of emmetropia, at 15 months 87%. At 12 months, 91% of the eyes had an uncorrected visual acuity of at least 20/40, at 15 months 87%. Eyes treated with dexamethasone for 3 months regressed significantly less than those treated for only 5 weeks (P < 0.01). Dexamethasone also was effective in reversing regression later in the postoperative course. Eyes with preoperative myopia up to 4.90 D had significantly better refractive results at 12 months than eyes with myopia ranging from 5.00 to 7.50 D (P < 0.01). CONCLUSION These data show that excimer laser PRK can correct myopia with good predictability. Results at 12 and 15 months tend to suggest stability of postoperative refraction. Regression of effect was more common in higher myopes. Topical steroids postoperatively seem to play a crucial role for the refractive result.

Twenty-four-month Follow-up of Excimer Laser Photorefractive Keratectomy for Myopia: Refractive and Visual Acuity Results

PURPOSE To evaluate the 24-month refractive outcome of excimer laser photorefractive keratectomy (PRK) performed on normal, sighted myopic eyes; and to assess the evolution of postoperative refraction, the accuracy of predicted correction, and the results in terms of uncorrected visual acuity. METHODS Photorefractive keratectomy was performed on 495 eyes, with a preoperative refraction ranging from -1.25 to -7.50 diopters (D). Ablation zone diameters of 4.3 and 4.5 mm were used. All patients were treated with a standard topical steroid regimen postoperatively. Minimum follow-up time was 24 months. RESULTS Mean refraction (spherical equivalent +/- standard deviation) at 24 months was -0.27 +/- 0.74 D, which was significantly (P < 0.01) different from the mean at 12 months (0.01 +/- 0.78 D). There was also a significant (P = 0.01) difference between the 12- and 18-month (-0.15 +/- 0.82 D) mean refractions. But there was no significant difference between the means at 18 and 24 months postoperatively. Subgroup analysis at 24 months showed that patients with low to moderate myopia (up to -3.90 D) had significantly better refractive outcomes than those with higher myopia. Also at 24 months, 91% of the eyes had an uncorrected visual acuity of at least 20/40, and 81.5% had an uncorrected visual acuity of at least 20/30. Correspondingly, 87.5% of the eyes were within 1.00 D of emmetropia, and 71.7% were within 0.50 D. Only 0.4% lost one line of best-corrected visual acuity, no eye lost two lines or more. CONCLUSIONS Refraction after PRK is slow to stabilize, but appears to reach stability by 18 to 24 months after surgery. The refractive results are reasonably predictable and compare well with those achieved with radial keratotomy.

Factors affecting epithelial hyperplasia after photorefractive keratectomy

Purpose: To determine the effect of patient age, postoperative time, ablation zone diameter and depth, attempted correction, and corneal topography on postoperative corneal epithelial thickness after photorefractive keratectomy (PRK). Setting: Private clinic and university hospital, Stockholm, Sweden. Methods: This retrospective, unmasked study comprised 136 myopic patients treated unilaterally with PRK. Seventy eyes had been treated with the Summit excimer laser 27 months ±7 (SD) earlier using ablation zone diameters of 4.1 to 5.0 mm. Sixty‐six eyes had been treated with the VISX excimer laser 6 ± 3 months earlier using a 6.0 mm zone diameter. The untreated fellow eyes served as controls. Epithelial thickness was measured at a standardized central corneal area with a modified optical pachymeter, and corneal topography was determined using computerized videokeratoscopy. Results: In the Summit group, the epithelial layer in the PRK eyes was 12.0 &mgr;m (21 %) thicker than in the control eyes (P < .001; 95% confidence interval [CI] 9.35 to 14.3 &mgr;m). This thickness differential correlated significantly with increased ablation depth and attempted correction. In the VISX group, the epithelium in the treated eyes was 7.0 &mgr;m (7%) thinner (P = .0009; 95% Cl −1.9 to −6.7 &mgr;m) and thickness did not correlate with ablation depth or attempted correction. There was no correlation between epithelial hyperplasia and patient age or postoperative followup. With the laser groups combined, epithelial hyperplasia was greater with smaller zone sizes and a greater rate of change in power at the edge of the ablation zone. Conclusion: The factors associated with an increase in epithelial thickness were small ablation zones, greater attempted corrections, and deeper ablations. Larger, smoother ablation profiles may result in less epithelial hyperplasia.

Wound healing and myopic regression following photorefractive keratectomy

Abstract Scrapings from the treated area of 17 patients who had undergone photorefractive keratectomy were analyzed. All patients had regressed to myopia and were scraped at the time of retreatment. Three scrapings from the epithelium of patients undergoing primary photorefractive keratectomy served as control. Formalin fixed and paraffin embedded, the specimens were sectioned and stained specifically for hyaluronic acid. Hematoxylin was used for counterstaining in all specimens. Scrapings revealed either epithelial hyperplasia (11 cases) or an increased amount of extracellular material (15 cases) or both (9 cases). Five of the specimens stained positive for hyaluronic acid. Four of these cases showed the highest degree of corneal haze. The latter suggests a role for hyaluronic acid formation in excessive wound healing, causing myopic regression. All patients had received prolonged topical steroid treatment, a measure that may suppress a normal occurrence of hyaluronic acid.

Epithelial Alterations Following Photorefractive Keratectomy for Myopia

BACKGROUND A retrospective observational study was conducted to test the hypothesis that there is clinically measurable epithelial hyperplasia after photorefractive keratectomy (PRK), and to determine its effect on the epithelial oxygen uptake rate. METHODS One hundred myopic eyes who had been previously treated unilaterally with PRK were examined. Fifty eyes were treated with the Summit excimer laser (Summit Technology, Waltham, Mass) 27 +/- 7 months previously with ablation zone diameters of 4.1, 4.3, 4.5, or 5.0 mm. Fifty eyes were treated with the VISX excimer laser (VISX Inc, Sunnyvale, Calif) 5 +/- 4 months previously with one ablation zone diameter of 6.0 mm. The untreated eyes served as controls. Epithelial thickness was measured at a standardized central area within the ablation zone with a modified optical pachometer. Oxygen uptake rate was measured in a subgroup of 30 eyes (20 Summit and 10 VISX). RESULTS The epithelium after PRK was 24% thicker than in the control eye in the Summit group (mean difference 13 +/- 10 microns; p < .01) and 7% thinner in the VISX group (mean difference -4 +/- 10 microns; p < .01). A higher oxygen uptake rate correlated with a thicker epithelium (r = 0.42; p < .05). CONCLUSIONS The epithelium was significantly thicker after PRK between 13 and 37 months after treatment with the Summit excimer laser using ablation zone diameters of 4.1 to 5.0 mm. The epithelium was thinner between 1 and 15 months after treatment with the VISX laser using an ablation zone diameter of 6.0 mm. An increase in oxygen uptake rate reflected the metabolic rate of a greater number of cells in the hyperplastic layer.

Excimer Retreatment of Regression After Photorefractive Keratectomy

Regression of effect is a well-established complication of excimer laser photorefractive keratectomy for the correction of myopia. In 17 eyes retreated with excimer photorefractive keratectomy, minimum follow-up time was six months. Mean (+/- SD) refraction at six months postoperatively was -0.97 +/- 2.10 diopters, significantly different (P < .01) from the pre-retreatment mean of -2.91 +/- 0.86 diopters. The 11 best eyes (six-month refraction < -1.00 diopter) had a mean refraction of +0.32 +/- 0.67 diopter. At six months after retreatment, 64.7% had an uncorrected visual acuity greater than or equal to 20/40, and 58.8% were within 1.00 diopter of emmetropia. Two eyes showed a loss of one to two Snellen lines at six months. There was no significant increase in mean haze after retreatment. While the percentage of eyes with uncorrected visual acuity greater than or equal to 20/40 and the percentage of eyes within 1.00 diopter of emmetropia were lower than in eyes which did not require retreatment, the results of this study indicate that the majority of photorefractive keratectomy regressions can be successfully retreated.

Effect of postoperative steroids on the refractive outcome of photorefractive keratectomy for myopia with the Summit excimer laser

ABSTRACT To assess the role of topical steroids following excimer laser photorefractive keratectomy (PRK) for myopia, we compared the refractive outcome in 100 eyes that did not receive steroids in the immediate postoperative period (untreated eyes) with 100 eyes that were treated with topical dexamethasone for three months postoperatively. Photorefractive keratectomy was performed with the Summit laser, using 4.3 mm and 4.5 mm ablation zones. At three months after surgery, the untreated eyes had a mean refraction of ‐0.97 ± 1.15 diopters (D), significantly different (P < .01) from the mean refraction (+0.46 ± 0.74 D) of the steroid‐treated eyes. By six months postoperatively, 86% of the untreated eyes had regressed to a myopia of at least 0.50 D, whereas only 23% of the steroid‐treated eyes had regressed. In a second study, we compared the results in 25 patients whose first PRK eye was treated with steroids after surgery but whose second eye was not. At three months postoperatively, mean refraction in the steroid‐treated eyes was +1.23 ± 0.71 D, significantly different (P < .01) from the mean of ‐0.45 ± 1.29 D in the untreated eyes. The refractive results in PRK eyes treated with the Summit unit and with relatively small ablation zone diameters showed that eyes that received dexamethasone postoperatively were less likely to regress to myopia.

Changes in corneal thickness and curvature after different excimer laser photorefractive procedures and their impact on intraocular pressure measurements

BackgroundExcimer laser refractive surgery alters the shape and thickness of the cornea by removing central corneal tissue with submicrometer precision. The aim of the study was to analyze the changes in central corneal thickness (CCT) and curvature before and after different excimer laser photorefractive procedures and their possible impact on intraocular pressure (IOP) estimations with Goldmann applanation tonometry.MethodsData on CCT, corneal curvature and IOP readings with Goldmann applanation tonometry before and after excimer laser photorefractive surgery were analyzed retrospectively. The data was further analyzed separately in two subgroups; the photorefractive keratectomy /laser-assisted subepithelial keratomileusis (PRK/LASEK) group and the laser in situ keratomileusis (LASIK) group.ResultsThe overall post-operative IOP readings were significantly lower than pre-operative values. There was a significant difference in the lowering of the IOP readings between the two subgroups: LASIK caused a lower IOP reading than PRK/LASEK.ConclusionThe change in corneal thickness and curvature affects the estimation of IOP with Goldmann applanation tonometry after excimer laser photorefractive surgery. The amount of reduction in IOP reading might be influenced by the specific laser surgical procedure. This is of clinical importance in the evaluation of any future glaucoma in the increasing number of patients who undergo photorefractive laser surgery.

Effect of Corticosteroids in Postoperative Care Following Photorefractive Keratectomies

Since the start of photorefractive keratectomy (PRK) Seiler has recommended the use of topical corticosteroids during the first 3 months after surgery. The rationale for this treatment was to diminish the inflammatory reaction as well as to control the keratocytes from producing collagen and creating scars. Our knowledge of corneal wound healing in general, and after PRK in particular, is very limited and the action of corticosteroids is still unclear. Corticosteroids, when given in comparatively large topical doses, create problems. Between 15 and 30% of patients are corticosteroid responders with increased intraocular pressure. This is a threat to the eye, and also a burden for the doctor as intraocular pressure has to be checked during the treatment. The risk for cataract formation after longer periods of topically administered corticosteroids also has been discussed. In order to decrease the rise in intraocular pressure, FML has been used in place of dexamethasone. During the 4 years follow up after PRK it has been reported that a number of patients do not regress or get a scar formation if they have not used corticosteroids in the postoperative period. The reasons to avoid topical corticosteroids in some patients are a misunderstanding of their instructions, or those who have had a history of herpes infection or glaucoma. A double-masked study of the effects of corticosteroids after PRK was performed by Gartry, et al in a small group of patients. After 6 months, the results revealed that there were no differences between the corticosteroid and the non-corticosteroid group. However, the standard deviation was high.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraocular pressure after extracapsular cataract extraction with implantation of posterior chamber lenses

ABSTRACT To determine factors which influence postoperative intraocular pressure (IOP) we retrospectively reviewed changes in pressure during the first postoperative week in 633 consecutive eyes undergoing extracapsular cataract extraction (ECCE) with implantation of a posterior chamber lens The material was restricted to four surgeons and two types of lenses IOP was measured preoperatively, one day and one week after surgery Glaucomatous eyes (n=113) as well as exfoliative non‐glaucomatous eyes (n=79) had a higher mean IOP (278 and 261 mmHg) the first postoperative day compared to ‘simple’ cataract eyes (201 mmHg) After one week mean IOP in glaucomatous eyes still remained elevated while exfoliative non‐glaucomatous eyes had regained preoperative values Mean IOP on the first postoperative day (188, 245, 231 and 132 mmHg respectively) was also dependent on surgeon To some extent the IOP could be correlated to tightness of suturing as estimated by keratometry Only one surgeon had significant difference between irrigated and non‐irrigated visco‐elastic substance Postoperative pressure was not only dependent on the status of the patient̂s eye, but factors for the individual surgeons seemed to be as important