Björn Tengroth

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.

Phototherapeutic keratectomy: long-term results in 166 eyes.

One hundred sixty-six eyes with corneal disease were treated with the excimer laser in order to ablate opacities, irregularities, or to improve wound healing. Postoperative follow up time was 15 months (range 6 to 28 months). An individual goal was set for each patient and 84% achieved the goal. The visual acuity change is given for each subgroup. Phototherapeutic keratectomy (PTK) was shown to be an advantageous surgical method, where the success is in the careful preoperative evaluation. One problem with the technique is the induced hyperopia.

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.

CHANGES IN THE CONTENT AND COMPOSITION OF COLLAGEN IN THE GLAUCOMATOUS EYE - BASIS FOR A NEW HYPOTHESIS FOR THE GENESIS OF CHRONIC OPEN ANGLE GLAUCOMA - A Preliminary Report

The pressure theory is still predominant in explaining the pathophysiology of the chronic open angle glaucoma. An insufficient drainage system resulting in an increased intraocular pressure is the hasis for this theory. The pressure will exert an effect upon the optic disc which either directly on the nerve fibres or indirectly via the vascular system will result in a characteristic optic atrophy. The collagen fibres, both in the trabeular meshwork of the anterior chamber and in the lamina cribrosa of the optic disc, form a mesh through which the aqueous humour and the nerve fibres, respectively, pass through the wall of the eye. A hypothesis explaining the pathophysiology of this disease, and based on the assumption that there is a primary change in the collagen molecules, resulting in a weaker structure than normal both in the trabeculae and in the laminae, is forwarded. The structures analysed for the content of hydroxypro‐line, hydroxylysine and proline were the trabecular meshwork, the sclera and the lamina cribrosa. Three categories of autopsy eyes were studied, i.e. normal eyes, glaucomatous eyes, and eyes under a suspicion of glaucoma. In the normal eyes, the collagen composition in the trabecular meshwork was different from that in the sclera and the lamina cribrosa. There is also a difference in the composition between the sclera and the lamina cribrosa. In glaucoma, the content and/Or the composition of the collagen molecules in the lamina were significantly changed. In the eyes under suspicion of glaucomathe same changes as in the glaucomatous eyes could be demonstrated. However, 5 of the 7 eyes in this category had no demonstrable nerve atrophy. The findings suggest that the change in collagen pattern is primary. This study has not demonstrated which types of collagen are present or the physical properties of this collagen. Further tests to demonstrate the different types of collagen and their rigidity are planned.

Treatment of corneal dystrophies with excimer laser

Abstract Thirty‐three eyes with different corneal dystrophies underwent phototherapeutic keratectomy to ablate corneal opacities, surface irregularities and corneal wounds. For most patients the treatment goal was to improve vision but also corneal woundhealing, glare problems and unstable refraction were indications for treatment. In 27 eyes with the treatment goal to improve vision, 23 improved 2 lines or more on the visual chart used. In none of the patients has the treatment led to a worsening of the condition. The mean follow‐up time was 9 months. Excimer laser ablation of corneal dystrophies seems to be a good treatment, which can improve visual functions considerably, heal corneal wounds and in this way postpone corneal grafting in many cases.

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.

LOW‐LUMINANCE MYOPIA AS MEASURED WITH A LASER OPTOMETER

Using a new version of the laser optometer, enabling testing at photopic, mesopic and scotopic luminance levels, studies were performed which confirmed earlier reports of large inter‐subject variability in the magnitude of twilight and night myopia. Indications that a sizeable section of the population manifests such low‐luminance myopia were also substantiated. Tests in a twilight model landscape showed no simple formula for calculating spectacle correction from laser optometer values. The optometer was able to filter out those not likely to need mesopic correction and to help select those who may need special optical correction at that luminance.