Refractive versus corneal changes after photorefracive keratectomy for astigmatism.

PURPOSE: To define measures of assessing success and subsequent ways to improve excimer laser treatment of astigmatism. METHODS: We studied 97 eyes of 79 patients, followed for 12 months, that underwent photorefractive keratectomy (PRK) for myopia and astigmatism with a VISX 20/20 excimer laser. Preoperative spherical equivalent refraction at the corneal plane was between -1.00 and -15.00 D. Mean preoperative refractive astigmatism at the spectacle plan was -2.17 +/- 1.05 D (range, -1.25 to -6.00 D), which is -1.81 +/- 0.86 D (range -1.04 to -4.97 D) when calculated at the corneal plane. All patients were examined before and after surgery; examination included refraction, keratometry, and topography measurement. RESULTS: The success in treatment of astigmatism appeared measurably less than the treatment of sphere when analogous indices were used for assessment. Success in astigmatism surgery improved, as measured by all parameters, after an additional 20% was applied to astigmatism treatment magnitude indicated by the VISX computer algorithm. The sequential modes of treatment undercorrected astigmatism magnitude to a greater extent than elliptical, but equivalent success rates were present in view of the greater astigmatic changes attempted using the sequential mode. The elliptical mode tended to produce a greater undercorrection of associated sphere (p = 0.313). Results measured by refraction showed a larger change than those measured by topography and keratometry. CONCLUSION: During PRK with the VISX 20/20 laser, adjustment for undercorrection of astigmatism treatment achieves a fuller correction of astigmatism. When measuring astigmatic changes, results are different when comparing refractive astigmatism changes with corneal astigmatism changes measured by keratometry and topography.

Effect of variations in surgical technique and patient management on outcomes of photorefractive keratectomy. Melbourne Excimer Laser Group.

PURPOSE: To describe variation in surgical and patient management and to assess their effect on 12-month outcomes of photorefractive keratectomy (PRK). METHODS: The following variations in surgical/patient management related to PRK were observed and assessed: treatment based on cycloplegic refraction, administration of anesthesia, marking of visual axis, diameter of zone marker, method of epithelial removal, use of intraoperative artificial tears, type of fixation during surgery, replacement of epithelium after surgery, use of a bandage contact lens or two pressure patches, and use of topical nonsteroidal antiinflammatory drugs after surgery. The outcomes assessed were spherical equivalent manifest refraction, spectacle-corrected visual acuity and uncorrected visual acuity. RESULTS: One year clinical outcomes were assessed prospectively for a group of 645 eyes that underwent PRK or photoastigmatic keratectomy. Spherical equivalent refraction and uncorrected visual acuity were better with decreasing amounts of preoperative myopia (both F > 30.0, both p = 0.0001). Although some surgical variations produced statistically significantly better uncorrected visual acuity on univariate analyses, none of the variations in the techniques assessed were found to be statistically significantly related to clinical outcomes after controlling for preoperative spherical equivalent refraction (all F < 2.5, all p > 0.10). None of the surgical variations were associated with loss of spectacle-corrected visual acuity (all p > 0.10). CONCLUSION: Clinical outcomes of PRK were not significantly affected by minor variations in clinical and surgical practice.

Undercorrection after excimer laser refractive surgery. Excimer Laser Group.

PURPOSE: The incidence and correlations of undercorrection were studied for 1 year after excimer laser surgery for myopia or myuopic astigmatism. METHODS: A consecutive series of 645 eyes of 440 patients were studied. Eyes were examined preoperatively and at 1, 3, 6, and 12 months after surgery. The parameters evaluated were visual acuity, refraction, and corneal clarity. RESULTS: Following excimer laser surgery, undercorrection of > or = -1.00 diopters gradually increased from 10% at 1 month to 40% at 12 months. Increasing degree of preoperative myopia was significantly associated with increasing occurrence of undercorrection at 3 months (chi 2 = 17.3, P < .001), 6 months (chi 2 = 53.6, P < .001), and 12 months (chi 2 = 64.8, P < .001). Undercorrection was more common in eyes that had had photorefractive keratectomy than in those that had had photoastigmatic refractive keratectomy (odds ratio, 0.40; 95% confidence interval, 0.25 to 0.60). At 1 year, a loss of 2 or more lines of best-corrected visual acuity was recorded in 38% of undercorrected patients. Loss of 2 or more lines of best-corrected visual acuity was more common in patients undercorrected by -1.00 diopter or more (odds ratio, 8.8; 95% confidence interval, 5.4 to 14.6). No relationship was seen between corneal haze and loss of best-corrected visual acuity. Undercorrection was not associated with age, gender, use of nonsteroidal anti-inflammatory drugs, bandage contact lens wear, or corneal haze. Patients with lower degrees of myopia reached a stable refraction more quickly. At 6 months, 71% were within +/- 0.5 diopter of 1-year refraction. Of 17 patients with undercorrection who were treated with topical corticosteroids, only one patient showed a permanent beneficial change. CONCLUSION: Occurrence of undercorrection is more common in patients with severe myopia and when simultaneous astigmatic corrections are undertaken.

Astigmatic change 1 year after excimer laser treatment of myopia and myopic astigmatism. Melbourne Excimer Laser Group.

PURPOSE: To evaluate the surgically induced astigmatism (SIA) 1 year after excimer laser photorefractive astigmatic keratectomy (PARK) and photorefractive keratectomy (PRK). SETTING: Royal Victorian Ear and Eye Hospital, Melbourne, Australia. METHODS: This study comprised 333 PARK patients and 155 PRK patients treated with a VISX 20/20 excimer laser and followed prospectively for 12 months. Vector analysis of the change in astigmatism was used to calculate the SIA in the PRK group and the percentage of astigmatism corrected in the PARK group. RESULTS: Among patients with low cylinders astigmatic correction varied greatly, particularly in those treated for large amounts of myopia. The spherical PRK treatments yielded a mean induced postoperative astigmatism of 0.47 diopter. There was a linear relationship between this inadvertent SIA and increasing myopia. CONCLUSION: Excimer laser surgery for myopia creates a low degree of random, unpredictable SIA that may be the result of irregular epithelial thickening during postoperative healing. This creates a background noise of astigmatic change upon which the targeted astigmatic correction is superimposed.

Relation of hormone and menopausal status to outcomes following excimer laser photorefractive keratectomy in women. Melbourne Excimer Laser Group.

PURPOSE: To examine the effect of hormone use, pregnancy and menopausal status on clinical outcomes following excimer laser surgery for myopia and myopic astigmatism. METHODS: Participants comprised all female patients of the Melbourne Excimer Laser Group (MELG). A standardised surgical protocol was followed by the 27 MELG members, using the VisX 20/20 excimer laser and included the prospective collection of the following information preoperatively and one, three, six and 12 months after the procedure: uncorrected and best corrected visual acuity with a LogMAR chart; best manifest refraction; and subjective assessment of corneal clarity. A survey that elicited information about oral contraceptive (OC) use, pregnancy history, surgical and natural menopause, and use of hormone replacement therapy (HRT) was mailed to all the women. RESULTS: A 77% response to the mailed survey was achieved. Two women were pregnant at the time of surgery, one became pregnant during the first month after surgery, and all three women were excluded from further analyses, although a review of two of the case histories revealed suboptimal clinical outcomes. Women taking OC were included in the control group after OC use was shown not to be associated with outcome. Women were grouped accordingly: control, n = 225, pre-menopausal on HRT, n = 7, post-menopausal not on HRT, n = 34; and post-menopausal on HRT, n = 21. The groups differed significantly with regard to age and preoperative spherical equivalent. After controlling for age and preoperative spherical equivalent, the mean number of uncorrected LogMAR letters read one year after surgery was significantly lower for the post-menopausal women on the HRT in comparison with the control group. Best corrected acuity and corneal clarity were not significantly different among the groups. DISCUSSION: These preliminary results suggest that the interaction of menopausal and HRT status could decrease the effectiveness of PRK and PARK, but require confirmation with a further study in a prospective manner using objective measures of corneal epithelial healing and serum hormone levels.

Comparison of results of excimer laser correction of all degrees of myopia at 12 months postoperatively. The Melbourne Excimer Laser Group.

UNLABELLED: To examine prospectively the efficacy and safety of photorefractive keratectomy and photoastigmatic refractive keratectomy. METHODS: We treated 645 eyes (440 patients) with a VisX Twenty/Twenty excimer laser and followed them up for 12 months. RESULTS: The percentage of eyes with myopia between -5.01 and -10.00 diopters spherical equivalent within 1 and 2 diopters of emmetropia at 12 months was 65% (123 of 189) and 90% (170 of 189), respectively, whereas the corresponding percentages for eyes with myopia greater than -10.00 diopters spherical equivalent were 39% (16 of 41) and 56% (23 of 41), and for eyes with myopia of -5.00 diopters spherical equivalent or less, 87% (238 of 273) and 99% (270 of 273), respectively. Uncorrected visual acuity of 20/20 and 20/40 or better at 12 months was attained in 47% (129 of 273) and 87% (237 of 273) of the eyes with myopia -5.00 diopters spherical equivalent or less, respectively. At 12 months, 48 (25%) of the 189 eyes with myopia between -5.01 and -10.00 diopters spherical equivalent had uncorrected visual acuity of 6/6 or better and 135 (71%), 6/12. At 12 months, one eye (2%) with myopia greater than -10.00 diopters spherical equivalent had uncorrected visual acuity of 6/6 and 11 (27%) of 41 eyes, 6/12. Ten (4%) of the 273 eyes with myopia of -5.00 diopters spherical equivalent or less, 15 (8%) of the 189 eyes with myopia between -5.01 and -10.00 diopters spherical equivalent, and nine (22%) of the 41 eyes with myopia greater than -10.00 diopters spherical equivalent had lost two or more LogMAR lines of best-corrected visual acuity at 12 months. CONCLUSION: Excimer laser surgery is highly reliable for myopia of -5.00 diopters spherical equivalent or less and is less reliable for greater myopia.

Predictability of excimer laser treatment of myopia. Melbourne Excimer Laser Group.

OBJECTIVE: To prospectively examine the predictability of excimer laser photorefractive keratectomy and photoastigmatic refractive keratectomy for myopia that ranged from -1 to -18 diopters (D). METHODS: Patients were treated with an excimer laser and followed up prospectively for 12 months. Low myopia was treated in one ablation zone (6.0 mm), high myopia in two ablation zones (5.0 and 6.0 mm), and extreme myopia in three ablation zones (4.5, 5.0, and 6.0 mm) with a maximum treatment of 15 D. Data were analyzed to determine the distribution of the various postoperative outcomes by preoperative myopia. RESULTS: Two hundred seventy-four low myopes, 189 high myopes, and 41 extreme myopes were available for 12-month follow-up. The re-treatment rate increased with preoperative myopia. The predictability of refraction and uncorrected and best corrected visual acuity progressively decreased with increasing myopia. The likelihood of losing lines of best corrected visual acuity and corneal haze increased with increasing myopia. CONCLUSION: These data should help in the counseling of patients about the likely outcome if they have excimer laser surgery to correct myopia.

Retreatment after excimer laser photorefractive keratectomy. The Melbourne Excimer Laser Group.

PURPOSE: To determine the risk factors for undercorrection of myopia after photorefractive keratectomy and to evaluate the efficacy and safety of retreatment. METHODS: A VISX Twenty/Twenty excimer laser was used to treat myopia and myopic astigmatism of up to -15.00 diopters (spherical equivalent) at the corneal plane. Retreatments were performed primarily for undercorrection with or without coexistent corneal haze or abnormalities on videokeratoscopy. Not every patient who was undercorrected requested retreatment. RESULTS: Of 645 eyes (440 patients) followed up for more than 12 months, 58 eyes (9%) required retreatment. The retreatment rate increased with increasing myopia: 17 (5%) eyes with myopia of less than -5.00 diopters, 30 (13%) eyes with myopia of -5.01 to -10.00 diopters, and 11 (19%) eyes with myopia of greater than -10.00 diopters required a second procedure. A higher retreatment rate was observed after astigmatic corrections than after spherical corrections. Corneal haze after retreatment was no greater than that observed after initial procedures. Twelve months after primary procedures, 378 (75%) of 504 eyes were within 1.00 diopter of emmetropia, whereas 27 (69%) of 39 eyes attained this result after retreatment. A total of 383 (76%) of 504 eyes attained uncorrected visual acuity of 20/40 or better after primary procedures, compared with 25 (64%) of 39 eyes after retreatment. CONCLUSIONS: The risk of undercorrection requiring retreatment after photorefractive keratectomy increases with the magnitude of the primary treatment. Although less successful than initial procedures, retreatment appears to enhance the results of photorefractive keratectomy.

Assessment of subjective pain following photorefractive keratectomy. Melbourne Excimer Laser Group.

BACKGROUND: Although researchers have reported that postoperative pain in patients undergoing excimer laser photorefractive keratectomy (PRK) surgery is common in the first 24 hours after excimer surgery, factors associated with increased postoperative pain have not been reported. The purpose of this study was to prospectively document self-reported pain following excimer laser surgery and explore associated factors. METHODS: Consecutive patients undergoing excimer laser photorefractive keratectomy (PRK) surgery to correct myopia and/or myopic astigmatism were asked to prospectively grade, on a four-point scale, the amount of pain they were experiencing immediately after treatment and again 2, 4, 8, 24, and 48 hours after surgery. They were also asked to record the type and dose of all medication taken during that time period. RESULTS: Pain questionnaires were returned by 62 patients (72%), ranging in age from 20 to 54 years. The mean self-reported pain overall peaked 24 hours after treatment. Amount of myopia and prior excimer experience were not related to use of analgesia or self-reported pain (both p > 0.10). Patients who had three additional topical drops of indomethacin postoperatively reported significantly less pain 24 hours after treatment (t = 5.95, p = 0.0001). CONCLUSION: These results have implications for the education of patients about the likely course of healing after PRK. A course of five drops of topical indomethacin should be evaluated with a randomized clinical trial to assess efficacy in inhibiting ocular pain after PRK.

One-year evaluation of excimer laser photorefractive keratectomy for myopia and myopic astigmatism. Melbourne Excimer Laser Group.

OBJECTIVE: To evaluate prospectively the efficacy and safety of excimer laser photorefractive keratectomy in the treatment of myopia and myopic astigmatism. METHODS: Up to 15 diopters (D) of myopia with or without astigmatism of less than 6 D was treated with an excimer laser (VISX Twenty/Twenty). One hundred fifty procedures have been followed up for more than 12 months. RESULTS: Postoperative refractions were generally stable after 3 months without significant early overcorrection. Of those eyes treated with spherical equivalents of 5 D or less, 96% were within 1 D of the targeted refraction after photorefractive keratectomy and 88% had uncorrected visual acuities of 20/40 or better. At 12 months, 77% of all 150 eyes treated achieved an uncorrected visual acuity of 20/40 or better and 81% were within 1 D of the intended correction. Nine eyes (6%) lost 2 or more lines of best corrected visual acuity and 14 (9%) gained 2 or more lines. Adverse reactions were reported in 12 patients (8%) during the postoperative period. CONCLUSIONS: Photorefractive keratectomy is capable of correcting low and moderate myopic errors with a relatively high degree of accuracy and safety. The predictability and stability of the postoperative refraction during the first 12 months seem to be good.