Risk factors for postoperative cylindrical prediction error after laser in situ keratomileusis for myopia and myopic astigmatism

Topographic and surgical risk factors for high postoperative residual astigmatism after small incision lenticule extraction in patients with different degrees of myopia: a retrospective cohort study

BACKGROUND

To evaluate the possible topographic and surgical risk factors for high postoperative residual astigmatism in patients who undergo small-incision lenticule extraction (SMILE) surgery and have different myopia degrees.

METHODS

A retrospective cohort study was conducted, and patients who underwent SMILE surgery were enrolled. A total of 80 and 150 eyes from 40 to 75 individuals, respectively, were selected as the low myopia and high myopia groups. The demographic data, visual acuity, refraction, topographic parameters and surgical settings were recorded. Multiple linear regression with interaction tests were performed to survey the risk factors for high postoperative residual astigmatism in each group.

RESULTS

Five (6.25%) and 9 (6.00%) eyes presented with high postoperative residual astigmatism in the low myopia and high myopia groups, respectively, but these differences were not significant (P = 0.569). A steep corneal curvature was correlated with a greater risk of high postoperative residual astigmatism in the low myopia group (P = 0.015), while a higher degree of cycloplegic cylinder power, steeper corneal curvature, greater topographic cylinder power, smaller optic zone and longer incision length were associated with a high rate of postoperative residual astigmatism in the high myopia group (all P < 0.05). In addition, the interaction effects of cycloplegic and topographic cylinder power and longer incision length on the incidence of high postoperative residual astigmatism development were more evident in the high myopia group than in the low myopia group (all P < 0.05).

CONCLUSIONS

A steep corneal curvature correlates with a high risk of high postoperative residual astigmatism after SMILE surgery, and a higher degree of cycloplegic and topographic cylinder and longer incision are associated with high postoperative residual astigmatism in individuals with high myopia.

Induced De Novo Astigmatism After Hyperopic LASIK Versus Myopic LASIK Surgery in Nonastigmatic Eyes

PURPOSE

To compare the astigmatism induced surgically (SIA) by spherical hyperopic laser in situ keratomileusis (H-LASIK) versus myopic laser in situ keratomileusis (M-LASIK) in nonastigmatic eyes.

METHODS

A retrospective study of patients who underwent LASIK surgery between 2005 and 2014 at the Care-Vision Laser Center, Israel. We calculated the mean absolute SIA and performed risk factor analysis for induced astigmatism. Differences between H-LASIK and M-LASIK were analyzed.

RESULTS

Eyes of 3877 patients who underwent M-LASIK and of 549 patients who underwent H-LASIK were nonastigmatic preoperatively and received a nonastigmatic treatment. Three months after surgery, hyperopic treatment induced more SIA (0.49 ± 0.48 D) than did myopic treatment (0.36 ± 0.4 D) (P < 0.001). In the H-LASIK group, the risk factors for induced astigmatism of >0.5 D were a higher preoperative refractive error (P = 0.003) and larger optical zone (7 vs. 6 mm). In the M-LASIK group, eyes with SIA >0.5 D tended to have steeper corneas preoperatively (43.8 ± 1.5 vs. 43.6 ± 1.4 D; P = 0.001), a higher spherical equivalent (-3.43 ± 1.53 Vs. -3.07 ± 1.45 P < 0.001), and smaller treatment zones (6 vs. 7 mm). In H-LASIK, the mean induced astigmatic axis was at 74.6 degrees.

CONCLUSIONS

There was a consistent trend toward more SIA in H-LASIK and in higher refractive error correction. In H-LASIK larger optical zones induce more SIA and in M-LASIK smaller ones caused it.

Laser-assisted subepithelial keratomileusis with mitomycin C for myopic astigmatism ≥2.00 diopters using a Zeiss MEL 80 Excimer

To examine the refractive and visual outcome of laser-assisted subepithelial keratomileusis (LASEK) with mitomycin C(MMC) in eyes with myopic astigmatism ≥2.00 diopters (D). This study comprised 82 eyes of 82 consecutive patients (37 male, 45 female; mean age at surgery 34.7 ± 9.0 years) with preoperative topographic astigmatism ≥2.00 D and mean preoperative spherical equivalent (SE) -4.50 ± 1.13 D. To assess whether the refractive results differed with the amount of corrected sphere, the data were separated by preoperative SE thereby defining two groups with SE < -5.00 D (-2.00 to -4.75 D) and ≥-5.00 D (-5.00 to -7.75 D). Mean manifest refraction spherical equivalent (MRSE) of -0.39 ± 0.52 D was obtained at the 6-months (5.4 ± 1.6 months) follow-up. The results were within ±1.00 D of the attempted correction in 89 % of patients. The mean postoperative corrected distant visual acuity was -0.02 ± 0.065 logMAR (range -0.10 to 0.15 logMAR). Sixty-seven (81.7 %) of all eyes did not change lines in safety. There was no statistically significant difference (P = 0.262) in safety between the SE groups. Mean efficacy was 0.89 ± 0.27. There was a statistically significant difference in efficacy (P = 0.024) between the preoperative SE groups. Larger ablation zones were associated with better visual outcome, confirmed by safety, efficacy and predictability. The data reported here demonstrated that LASEK using a Zeiss MEL 80 excimer laser with an additional application of MMC is a safe and efficient technique with predictable results for the correction of eyes with myopic astigmatism ≥2.00 D.

The effect of preoperative keratometry on visual outcomes after moderate myopic LASIK

Purpose

To evaluate visual outcomes in moderately myopic eyes with flat and steep corneas (preoperatively) that have been treated with laser-assisted in situ keratomileusis (LASIK).

Patients and methods

Records of ninety-six eyes with average preoperative keratometry (K) values between 39.9 and 42.0 diopters (D) (flat) were matched with 103 eyes with preoperative K values between 46.0 and 47.2 D (steep) that underwent LASIK between March 2007 and March 2010 for moderate myopia, and were retrospectively reviewed. The primary outcome measures used to determine the effect of preoperative keratometry on visual prognosis were refraction, visual acuity, change in keratometry (ΔK), and change in spherical equivalent (ΔSE), measured at 1, 3, 6, and 12 months postoperatively.

Results

Significant differences were found at 6 months postoperatively between the flat group and steep group in SE (P = 0.029), sphere (P = 0.018), ΔK (P = 0.002), percentage of eyes achieving SE of −0.25 to + 0.25 D (P = 0.0125), −0.26 to −0.50 D (P = 0.003), −0.51 to −1.00 D (P = 0.044), and the percentage of eyes achieving uncorrected distance visual acuity of 20/15 or better (P = 0.0006).

Conclusion

Moderately myopic eyes with flatter corneas preoperatively have better visual prognosis following LASIK compared with moderately myopic eyes with steeper corneas.