Comparison of corneal flap thickness using a FS200 femtosecond laser and a moria SBK microkeratome.

AIM: To evaluate differences in flap thickness resulting from use of an Alcon Wavelight FS200 femtosecond laser and a MORIA SBK microkeratome when making a 110-µm-thick corneal flap and to identify the potential factors that affect corneal flap thickness. METHODS: A prospective case study was performed on 120 eyes of 60 patients who were divided into two groups for LASIK, each group consisting of 60 eyes (30 patients). The corneal flaps were created using an Alcon Wavelight FS200 femtosecond laser or a MORIA SBK microkeratome. The central corneal flap thickness was calculated by subtraction pachymetry. Age, central corneal thickness (CCT), spherical equivalent refraction, mean keratometry, and corneal diameter were recorded preoperatively for analysis. RESULTS: Cutting of all flaps was easily performed without intraoperative complications. In the Alcon Wavelight FS200 femtosecond laser group, the mean right and left corneal flap thicknesses were 114.0±6.6 µm (range: 98-126) and 111.4±7.6 µm (range: 98-122), respectively. The difference (2.6±9.1 µm) in the corneal flap thickness between the right and left eyes was not significant (t=1.59, P=0.12). Stepwise regression analysis indicated that the resulting corneal flap thickness was unrelated to the patient's age, preoperative CCT, spherical equivalent refraction, mean keratometry, or corneal diameter. In the MORIA SBK microkeratome group, the mean right and left corneal flap thicknesses were 110.6±7.4 µm (range: 97-125 µm) and 108.2±6.1 µm (range: 78-123 µm), respectively. The difference in the corneal flap thickness between the right and left eyes (2.4±6.5µm) was not significant (t=2.039, P=0.0506). The corneal flap thickness was positively correlated with the preoperative CCT through stepwise regression analysis (r=0.297, P=0.021). The corneal flap thickness was not related to age, spherical equivalent refraction, mean keratometry, or corneal diameter. The corneal flap thickness was estimated using the following equation: Tflap=67.77+0.076 CCT (F=5.63, P=0.021). CONCLUSION: Both the Alcon Wavelight FS200 femtosecond laser and the MORIA SBK microkeratome produced 110-µm-thick corneal flaps. The central corneal flap thickness was positively correlated with the preoperative CCT in MORIA SBK microkeratome surgery.

Aberration changes of the corneal anterior surface following discontinued use of rigid gas permeable contact lenses.

AIM: To record aberrations with a corneal topographic device on the anterior surface of the cornea at different time-points prior to wearing and following discontinued use of rigid gas permeable (RGP) contact lenses. The effect of wearing RGP on the anterior surface of the cornea was discussed to provide guidance for clinical refractive error correction. METHODS: The study objects were 24 eyes from 24 patients. All patients underwent identical examination procedures prior to lens use, as well as afterwards, including slit-lamp examination, non-contact tonometer measurement, computer optometry and corneal curvature measurement, subjective refraction test, and corneal topography analysis. The patients wore contact lenses everyday for 1 month and then discontinued. Corneal topographies were recorded at certain time points of 30 minutes, 1 day, 3, 7 and 14 days following use. RESULTS: Total corneal aberration at each time point following discontinued use of RGP contact lenses was less than the time point prior to use. Detailed results were as follows: root mean square (RMS) (pre)=(1.438±0.328)µm, RMS (30 minutes)=(1.076±0.355)µm, RMS (1 day)=(1.362±0.402)µm, RMS (3 days)=(1.373±0.398)µm, RMS (7 days)=(1.387±0.415)µm, and RMS (14 days)=(1.430±0.423)µm. Results showed that at 30 minutes after discontinued use of RGP contact lenses, almost all 2(nd)- and 3(rd)-order aberrations change. Quadrafoil Z10 and spherical Z12 of the 4(th)-order were also changed. Alterations to Z5, Z6, and Z12 at 1 day after discontinued use were significant differences compared with the time period prior to RGP use: Z5 and Z6 decreased, and Z12 increased slightly. Z5 and Z6 remained decreased at 3 days after discontinued use, but Z9 and Z10 continued to increase and Z12 returned to levels prior to RGP use. At 14 days after discontinued use, all aberrations were not significantly different from the values prior to use. CONCLUSION: The use RGP contact lenses greatly reduced total aberration of the anterior surface of the cornea. Changes to 2(nd)- and 3(rd)-order aberrations (including Z3, Z4, Z5, Z6, Z7, and Z8) were more significant. Following discontinued use of RGP contact lenses, the majority of lower order aberrations returned to original levels in a short period of time. During this process, a transient higher order aberration appeared, but all changes disappeared within 14 days after discontinued use of RGP contact lenses.

[Analysis of aberration changes of the corneal anterior surface following discontinued use of rigid gas permeable contact lenses].

OBJECTIVE: The present study used a corneal topographic device to record aberrations on the anterior surface of the cornea at different time-points prior to wearing and following discontinued use of rigid gas permeable (RGP) contact lenses. The effect of wearing RGPCL on the anterior surface of the cornea was discussed to provide guidance for clinical refractive error correction. METHODS: The study objects were 60 eyes from 30 patients. All patients underwent identical examination procedures prior to lens use, as well as afterwards, including slit-lamp examination, non-contact tonometer measurement, computer optometry & corneal curvature measurement, subjective refraction test, and corneal topography analysis. The patients wore contact lenses every day for 1 month and then discontinued. Corneal topographies were recorded at certain time points of 30 min, 1 day, 3 days, 1 week, and 2 weeks following use. RESULTS: Total corneal aberration at each time point following discontinued use of RGP contact lenses was less than the time point prior to use. Detailed results are as follows; root mean square (RMS) (pre) = (1.438 ± 0.328), RMS (30 min) = (1.076 ± 0.355), RMS (1 day) = (1.362 ± 0.402), RMS (3 day) = (1.373 ± 0.398), RMS (7 day) = (1.387 ± 0.415), and RMS (14 day) = (1.448 ± 0.423). Results showed that at 30 minutes after discontinued use of RGP contact lenses, almost all 2(nd)- and 3(rd)-order aberrations were altered. Quadrafoil Z10 and spherical Z12 of the 4(th)-order were also changed. Alterations to Z5, Z6, and Z12 at 1 day after discontinued use were significant compared with the time period prior to RGP use: Z5 and Z6 decreased, and Z12 increased slightly (F = 2.869 ∼ 5.549, P = 0.001 ∼ 0.042). Z5 and Z6 remained decreased at 3 days after discontinued use, but Z9 and Z10 continued to increase and Z12 returned to levels prior to RGP use (P > 0.05). At 2 weeks after discontinued use, all aberrations were not significantly different from the values prior to use (P > 0.05). CONCLUSIONS: The use RGP contact lenses greatly reduced total aberration of the anterior surface of the cornea. Changes to 2(nd)- and 3(rd)-order aberrations (including Z3, Z4, Z5, Z6, Z7, and Z8) were more significant. Following discontinued use of RGP contact lenses, the majority of lower order aberrations returned to original levels in a short period of time. During this process, a transient higher order aberration appeared, but all changes disappeared within 2 weeks after discontinued use of RGP contact lenses.

[The relationship between corneal astigmatism with a vector-based method and whole eye second order wavefront aberrations].

OBJECTIVE: To investigate the relationship between corneal astigmatism and second order wavefront aberration in myopic eyes. METHODS: The corneal astigmatism and the whole eye wavefront aberrations of both eyes of 246 subjects were measured using the Humphrey corneal topography and the WASCA wavefront analyzer. According to axial of the corneal astigmatism, the subjects were divided into five groups (WR(0), WR(180), AR, OA(45) and OA(135)). The corneal astigmatism was decomposed into J(45) and J(0) with a Vector-based method, and correlated with the 2nd order Zernike aberrations (C(3) and C(5)). RESULTS: The mean corneal astigmatisms for the five groups were -1.34 D x 6.87 degrees, -1.03 D x 23.15 degrees, -0.48 D x 89.55 degrees, -0.91 D x 156.87 degrees and -1.02 D x 176.74 degrees respectively. Most of the corneal J(45) and J(0) components were correlated significantly with the C(3) and the C(5) aberrations in the whole eye. While the correlation coefficients (R(2)) between the J(45) and the C(3) were 0.138, 0.119, 0.090, 0.526 and 0.501, the R(2) between the J(0) and the C(5) were 0.711, 0.736, 0.864, 0.866 and 0.785 for the five groups respectively. CONCLUSIONS: The corneal astigmatism plays an important role in determining the 2nd order wavefront aberration in the whole eye, and the combination processes between the corneal and internal astigmatism (compensation and/or addition) change with the axial of the corneal astigmatism.