To determine if the residual corneal stromal bed of 250 µm is enough to prevent iatrogenic keratectasia in laser in situ keratomileusis (LASIK), we studied 958 patients who underwent LASIK from April 2000 to October 2003 retrospectively. The estimated probabilities of the residual stromal bed, that was less than 250 µm, were calculated using the publi- shed flap thickness data of Moria C&B microkeratome. Then we calculated the ratio of the real incidence of keratectasia to the expected the percentage of the patients with less than 250 µm residual stromal bed in our study. Using the LASIK flap thickness data of Miranda, Kezirian and Nagy, the expected probabilities that the residual stroma would be less than 250 µm were 8.8%, 4.3% and 1.5% of the 1,916 eyes respectively, while keratectasia developed in both eyes (0.1%) of 1 patient in our study. The estimated ratio of the keratectatic eyes to eyes with less than 250 µm stromal bed were 1.2-6.9%. Compared to the number of eyes with residual stromal thickness less than 250 m, the incidence of keratectasia was relatively low. The residual stromal bed thickness of more than 250 µm may possibly be safe, but further observations for long period are necessary.

Purpose:To evaluate rotational stability of Toric Implantable Collamer Lens (ICL) implantation to correct myopic astigmatism. Methods: We estimated the degree of Toric ICL rotation together with change in visual acuity and astigmatism in 118 eyes of 66 patients who underwent Toric ICL implantation and had a long-term mean follow-up period of 37 months. Results: After Toric ICL implantation, 107 (91%) out of 118 eyes showed uncorrected visual acuity of 0.8 or better. The mean postoperative astigmatism decreased to -0.64 ± 0.61 D from a mean preoperative astigmatism of -2.96 ± 1.13 D. The mean axis change of Toric ICL was 2.4 ± 3.8 degrees during follow-up period. Two (1.7%) out of 118 eyes showed the axis change of more than 10 degrees. These two eyes had a decrease in visual acuity, rotational axis change of 18 degrees and 30 degrees, respectively, and increases in astigmatism of 1.50 D and 1.00 D, respectively. The remaining 116 eyes (98.3%) showed excellent rotational stability without visual acuity decreasing Toric ICL rotation during the follow-up period. Conclusions: Toric ICL implantation to correct high myopia with astigmatism rarely has axis rotation and maintains excellent rotational stability for long-term follow-up.

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Purpose:We compared laser assisted in situ keratomileusis (LASIK) mode and photorefractive keratectomy (PRK) mode ablation methods in laser subepithelial keratomileusis (LASEK) surgery using the MEL-80 excimer laser. Methods: All patients were followed up for a minimum of 1 year. The PRK mode group consisted of 46 eyes of 23 patients and the LASIK mode group consisted of 97 eyes of 56 patients. The central corneal thickness (CCT), ablation thickness, manifest refractive error and uncorrected visual acuity were compared preoperatively, 1 month and 1 year postoperatively. Spherical equivalent (SE) of cycloplegic refraction at postoperative 1 month and the uncorrected visual acuity (UCVA) ratios of 1.0 or better at postoperative 1 year were compared between the two groups to evaluate clinical efficacy. Results: The SE of refractive error, CCT and target corneal ablation thickness of the two groups were not significantly different preoperatively. The PRK mode group obtained an actual ablation mean thickness of 82.8% of the target and the LASIK mode group obtained an actual ablation mean thickness of 94.1% of the target at postoperative 1 month. In each group, a statistically significant difference was observed between the actual corneal ablation thickness and target corneal ablation thickness. In the PRK mode group, the mean SE of postoperative 1 month cycloplegic refraction was +0.24 ± 0.47 D and in the LASIK mode group, +0.87 ± 0.54 D, indicating a statistically significant difference between the two groups. One year postoperatively, the UCVA ratios of 1.0 or better were 83% in the PRK mode group and 96% in the LASIK mode group, showing a statistically significant difference between the two groups. However, SE of manifest refractive error and CCT in the two groups were not statistically different at postoperative 1 year. Conclusions: The LASIK mode ablation method showed better results than the PRK mode ablation method in postoperative UCVA prognosis after LASEK surgery using the MEL-80 excimer laser.

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Purpose:To determine the risk factors and incidence of cataract formation over a long-term mean follow-up of 7.5 years after type V4 implantable collamer lens (ICL) implantation. Methods: We analyzed the preoperative, 3-month postoperative, 3-year postoperative, and last follow-up data of 228 eyes (118 patients) with mean preoperative spherical equivalent of -12.7 D and minimum postoperative follow-up of 3 years. Additionally, we determined the risk factors for cataract formation and calculated the 10.3 year cumulative cataract formation rate and 10.3 year cumulative cataract surgery rate using a survival curve. Results: After type V4 ICL implantation with minimum follow-up of 3 years, the calculated 10.3 year cumulative cataract formation rate was 20% and actual cataracts developed in 34 eyes (14.9%). The 10.3 year cumulative cataract surgery rate was 12% based on a survival curve and actual cataract surgery was performed in 12 eyes (5.3%). The risk factors for cataract formation were age (odds ratio [OR] = 1.10, p = 0.00), preoperative spherical equivalent (OR = 0.90, p = 0.00), crystalline lens thickness (OR = 9.54, p = 0.00), axial length (OR = 1.33, p = 0.00), 3 months postoperative vault (OR = 0.50, p = 0.03), and existence of peripheral touch between ICL optic margin and crystalline lens at last follow-up (OR = 7.84, p = 0.00). Conclusions:We suggest one of the main risk factors for cataract formation after ICL implantation is decreased central vault and peripheral touch between ICL optic margin and crystalline lens. J Korean Ophthalmol Soc 2015;56(6):835-846