Corneal Thickness Measurements Using 2 Kinds of Spectral Domain Optical Coherence Tomography, Pentacam, Ultrasound Pachymetry

PURPOSE: To compare the measurements of central corneal thickness (CCT) obtained using two kinds of spectral domain optical coherence tomography (OCT), Pentacam®, and ultrasound pachymetry (USP). METHODS: CCT was measured by Cirrus OCT®, Spectralis OCT®, Pentacam®, and USP in 32 eyes from 32 subjects without ocular disease of the anterior segment. RESULTS: The average CCT measurements using Cirrus OCT®, Spectralis OCT®, Pentacam®, and USP were 549.2 ± 28.7 µm, 545.2 ± 25.4 µm, 554.0 ± 27.8 µm, and 548.4 ± 27.9 µm respectively. The measurements were significantly highly correlated with each other (Pearson's correlation coefficient r > 0.9, all p-values < 0.001), but were significantly different (p < 0.001). The CCT 95% limits of agreement between Cirrus OCT® and Spectralis OCT®, Cirrus OCT® and Pentacam®, Cirrus OCT® and USP, Spectralis OCT® and Pentacam®, and Spectralis OCT® and USP were 27.70 µm, 26.1 µm, 26.97 µm, 22.91 µm, 35.59 µm, and 32.15 µm, respectively. CONCLUSIONS: The CCT values measured using the four devices were highly correlated with each other, but the measurement using Pentacam® was significantly thicker than that using USP. The measurements of the two kinds of spectral domain OCT were similar to those using USP. Therefore, these differences should be considered in clinical use, and measurements cannot be considered interchangeable.

Factors Affecting Long-term Myopic Regression after Laser In Situ Keratomileusis and Laser-assisted Subepithelial Keratectomy for Moderate Myopia

PURPOSE: High myopia is known to be a risk factor for long-term regression after laser refractive surgery. There have been few studies about the correction of moderate myopias that did not need retreatment after long-term follow-up. We evaluated 10 years of change in visual acuity and refractive power in eyes with moderate myopia after laser refractive surgery. METHODS: We included patients that had undergone laser in situ keratomileusis (LASIK) or laser-assisted subepithelial keratectomy (LASEK) to correct their myopia and that had at least 10 years of follow-up. We evaluated the stability of visual acuity in terms of safety, efficacy, and refractive changes at examinations 6 months and 1, 2, 5, 7, and 10 years after surgery. RESULTS: The study evaluated 62 eyes (36 eyes in LASIK patients and 26 eyes in LASEK patients). In both groups, the efficacy index tended to decrease, and it was consistently higher in the LASEK group compared to the LASIK group over the 10 years of follow-up. The safety index improved over 10 years and was always higher than 0.9 in both groups. The difference between the spherical equivalent at 6 months postoperatively and later periods was statistically significant after 5, 7, and 10 years in both groups (LASIK, p = 0.036, p = 0.003, and p < 0.001, respectively; LASEK, p = 0.006, p = 0.002, and p = 0.001, respectively). Ten years after surgery,26 eyes (66.7%) in the LASIK group and 19 eyes (73.1%) in the LASEK group had myopia greater than 1 diopter. In comparison with the thickness at 6 months postoperatively, central corneal thickness was significantly increased after 5, 7, and 10 years in both LASIK and LASEK groups (LASIK, p < 0.001, p < 0.001, and p < 0.001, respectively; LASEK, p = 0.01, p < 0.001, and p < 0.001, respectively). CONCLUSIONS: Moderately myopic eyes showed progressive myopic shifting and corneal thickening after LASIK and LASEK during 10 years of follow-up. We also found that early refractive regression may indicate the long-term refractive outcome.

Correlation between Trans-lamina Cribrosa Pressure Difference and Morphologic Parameters of Optic Disc in Normal Tension Glaucoma Patients

PURPOSE: To investigate the relationship between trans-lamina cribrosa pressure difference (TLCPD) and morphologic parameters of optic disc (OD) in normal tension glaucoma (NTG) patients. METHODS: Data from 31 NTG patients (31 eyes) and 29 controls (29 eyes) were analyzed retrospectively. Their cerebrospinal fluid pressure was estimated using diastolic pressure (DBP), body mass index (BMI) and age. TLCPD was defined as the difference of intraocular pressure (IOP) and the estimated cerebrospinal fluid pressure (ECSFP). Measurements of the rim area (RA), disc area (DA), average and vertical cup/disc (C/D) ratio, retinal nerve fiber layer thickness (RNFLT) and cup volume (CV) were taken for all patients using optical coherence tomography. The correlation between TLCPD and morphologic parameters of OD were assessed. RESULTS: There were no significant differences between the two groups in terms of age, DBP, IOP and spherical equivalent (SE) and BMI. The mean ECSFP was significantly higher in the controls (10.7 ± 2.8 vs. 12.2 ± 2.2 mm Hg, p = 0.031) and TLCPD was significantly higher in patients (2.4 ± 2.1 vs. 4.9 ± 3.7 mm Hg, p = 0.002). In the NTG group, there was a negative correlation between TLCPD and RA (r = -0.595) and positive correlations between TLCPD and the average C/D ratio (r = 0.504), vertical C/D ratio (r = 0.434) and CV (r = 0.420). Average RNLFT was also significantly correlated with TLCPD (r = -0.500) and RNFLT for four quadrants, except the nasal quadrant, in NTG patients. CONCLUSIONS: NTG patients had higher TLCPD. A higher TLCPD was associated with a narrower RA, larger C/D ratio, and thinner RNFLT.