Refractive outcome of radial keratotomy: does the result of the first eye predict outcome in the second eye?

Effect of Anisometropia on the Predictability and Accuracy of Refractive Surgery

PURPOSE

To evaluate the predictability and accuracy of refractive surgery among adults with myopic anisometropia.

METHODS

Consecutive cases of myopic eyes that underwent bilateral laser-assisted in situ keratomileusis (LASIK) or bilateral photorefractive keratectomy (PRK) during a 12-year period in a single center were included. Myopic anisometropia was defined as a difference greater than 1.5 D in spherical equivalent between eyes preoperative.

RESULTS

A total of 10,046 paired, operated nonamblyopic eyes of 5023 patients were analyzed. Of these, 472 eyes of 236 (4.7%) patients had myopic anisometropia without amblyopia, and 9574 eyes of 4787 patients served as isometropic controls. After refractive surgery, in the anisometropic group the more myopic eye was corrected by +0.47 ± 0.78 (D) more than the contralateral eye (P < 0.0001). Relative to the target refraction, the more myopic eye was overcorrected by 0.21 ± 0.79 D compared with an undercorrection of 0.16 ± 0.60 D in the less myopic contralateral eye (P < 0.0001) and compared with an undercorrection of 0.15 ± 0.62 D in the isometropic controls (P < 0.0001). Additionally, the variability in the correction of the more myopic eyes was significantly higher compared with the less myopic contralateral eyes and isometropic controls (P < 0.0001). These trends were evident both in PRK and LASIK treatments. The effect of anisometropia was found to be independent of the magnitude of preoperative myopia or surgeon identity.

CONCLUSIONS

The more myopic eye of anisometropes undergoing refractive surgery has lower predictability and accuracy and tends to be overcorrected, whereas the less myopic eye has outcome similar to isometropic controls. These results suggest that refractive surgery nomograms should take into account anisometropia.

Comparing predictability between eyes after bilateral laser in situ keratomileusis: a theoretical analysis of simultaneous versus sequential procedures

OBJECTIVE

To compare the predictability of laser in situ keratomileusis (LASIK) between eyes of individuals to determine whether the refractive result of the first eye is useful in improving fellow eye outcomes.

DESIGN

Single-center case series.

PARTICIPANTS

One surgeon and 196 eyes of 98 patients.

INTERVENTION

All patients received sequential bilateral LASIK. The mean time between procedures was 11.6 days. Attempted corrections ranged from 2.30 to 12.00 diopters (D).

MAIN OUTCOME MEASURES

Predictability (achieved minus attempted correction), postoperative manifest refraction, and theoretical postoperative manifest refraction, using a proposed attempted correction on the second eye based on first eye results, were analyzed.

RESULTS

At 1 week, 1 month, and 3 months, predictability of the first operated eye was correlated with predictability of the fellow eye (1 week: mean 1st = 0.33 D, mean 2nd = 0.33 D, Pearson coefficient = 0.46, P < 0.0005; 1 month: mean 1st = 0.028 D, mean 2nd = -0.020 D, Pearson coefficient = 0.43, P < 0.0005; 3 months: mean 1st = -0.22 D, mean 2nd = -0.12 D, Pearson coefficient = 0.52, P < 0.0005). At the 3-month follow-up of the second eye, comparing the actual distance from emmetropia with that calculated using a theoretical proposed attempted correction based on the first eye refraction, distance from emmetropia was closer in the theoretical correction group. This finding was stronger in patients with preoperative myopia less than 5.5 D (P = 0.03). For this group, 93% of patients in the proposed attempted correction group would fall within 1.0 D of emmetropia compared to 80% found in the actual outcomes.

CONCLUSIONS

The refractive predictability between the two eyes of an individual after LASIK is correlated. Theoretically, therefore, one may be able to achieve correction closer to emmetropia in the second eye by applying the refractive predictability results from the first operated eye. In this study, using a theoretical proposed attempted correction in the second eye based on the first eye outcome, we have shown that better outcomes in the second eye are possible, particularly in low myopes. Thus, it may be advantageous to perform bilateral LASIK sequentially rather than simultaneously, using predictability outcomes from the first operated eye in planning fellow eye treatment. Moreover, waiting approximately 1 week was found to be potentially as effective as waiting longer periods of time between treatments. Further studies are necessary to better assess the actual clinical significance of these findings.

Photorefractive keratectomy versus laser in situ keratomileusis for moderate to high myopia. A randomized prospective study

OBJECTIVE

This report presents the results of a randomized clinical trial of photorefractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK).

DESIGN

A randomized, prospective multicenter clinical trial.

PARTICIPANTS

A total of 220 eyes of 220 patients entered the study cohort: 105 randomized to PRK and 115 to LASIK. The mean preoperative manifest refraction spherical equivalent was -9.23 diopters (D) in the PRK group and -9.30 D in the LASIK group.

INTERVENTION

All patients received a one-pass, multizone excimer laser ablation as part of either a PRK or LASIK procedure using the Summit Apex excimer laser. Attempted corrections ranged from 6.00 to 15.00 D.

MAIN OUTCOME MEASURES

Data on uncorrected and spectacle-corrected visual acuity, predictability,and stability of refraction, corneal haze, and flap complications were analyzed. Patients were observed for up to 6 months.

RESULTS

One day after surgery, 0 (0.0%) and 3 (4.5%) eyes in the PRK group saw 20/20 and 20/40 or better uncorrected, respectively, while 7 (10%) and 48 (68.6%) eyes in the LASIK group saw 20/20 and 20/40 or better, respectively. At 6 months after PRK, 13 (19.1%) and 45 (66.2%) eyes saw 20/20 and 20/40 or better, respectively, while after LASIK, 16 (26.2%) and 34 (55.7%) eyes saw 20/20 and 20/40 or better, respectively (odds ratio = 0.56 for likelihood of uncorrected visual acuity < 20/40 for PRK vs. LASIK, 95% confidence interval [CI] = 0.31-1.19). After PRK, 39 eyes (57.4%) were within 1.0 D of attempted correction compared with 24 eyes (40.7%) in the LASIK group (odds ratio = 0.50 for likelihood fo undercorrection 1.0 D for PRK vs. LASIK, 95% CI = 0.24-1.04); however, the standard deviation of the predictability was similar between groups: 1.01 D for PRK and 1.22 D for LASIK. From months 1 to 6, there was an average regression of 0.89 D in the PRK group and 0.55 D in the LASIK group. After PRK, eight eyes (11.8%) had a decrease in spectacle-corrected visual acuity of two Snellen lines or more; after LASIK, two eyes (3.2%) had a decrease of two lines or more (odds ratio = 3.89 for risk of loss of spectacle-corrected visual acuity for PRK vs. LASIK, 95% CI = 0.71-21.30). Only two eyes had postoperative spectacle-corrected visual acuity less than 20/32, however.

CONCLUSIONS

Although improvement in uncorrected visual acuity is more rapid in LASIK than in PRK, efficacy outcomes in the longer term generally are similar between the two procedures. There is a greater tendency toward undercorrection in LASIK eyes using the specific laser and nomogram in this study, but the scatter in achieved versus attempted correction is similar, suggesting little difference in the accuracy of the two procedures. A suggestion of decreased propensity for loss of spectacle-corrected visual acuity in LASIK eyes requires further investigation.