Evaluation of peripapillary retinal nerve fiber layer thickness in myopic eyes by spectral-domain optical coherence tomography.

PURPOSE: To investigate the influence of myopia on peripapillary retinal nerve fiber layer (RNFL) thickness using Cirrus optical coherence tomography (OCT) in normal eyes. METHOD: Ninety-eight eyes of normal participants with various degrees of myopia were recruited in this study. The RNFL thickness was measured with high-definition (HD), spectral-domain Cirrus OCT (Cirrus HD-OCT; Carl Zeiss, Dublin, CA). The association between RNFL thickness and its spherical equivalent was evaluated with linear regression analysis. RESULTS: The RNFL thickness was 119.2±16.8 µm, 117.1±16.8 µm, 75.9±16.1 µm, and 64.9±9.8 µm in the superior, inferior, temporal, and nasal quadrants, respectively, with an average thickness of 94.3±8.6 µm. The mean RNFL thickness was thinner in highly and moderately myopic eyes (93±7.9 µm and 92.6±7.7 µm, respectively, P=0.0001) compared with low myopic eyes (102.2±9 µm). A significant linear correlation was found between the spherical equivalent and the RNFL thickness in the superior (r=0.386, P=0.0001) and inferior quadrants (r=0.448, P=0.0001), and the average RNFL thickness (r=0.373, P=0.0001). CONCLUSIONS: Myopia can be a confounding factor in the assessment of RNFL thickness attributed to its influence on the RNFL thickness. Therefore, we recommend a careful interpretation of RNFL data, especially those obtained from eyes with moderate-to-high myopia.

Analysis of pterygium size and induced corneal astigmatism.

PURPOSE: To study the relationship between pterygium size (extension, width, total area) and corneal astigmatism in eyes with unilateral primary pterygium. Also to determine the critical size for surgery before the occurrence of a significant corneal astigmatism. METHODS: This study was conducted on 77 eyes of 77 patients with unilateral primary pterygium. The extension and width were measured and the total area was calculated. Automated keratometry was used to determine corneal astigmatism. RESULTS: Pterygium extension ranged from 0.25 to 6.50 mm (mean, 2.0 +/- 1.2 mm), width ranged from 1.50 to 10.0 mm (mean, 4.19 +/- 1.5 mm), and total area ranged from 0.3 to 24.3 mm(2) (mean, 5.0 +/- 4.8 mm(2)). The mean value of corneal astigmatism was significantly (P < 0.0001) higher in pterygium-affected eyes (1.2 +/- 0.9 D) than control eyes (0.6 +/- 0.5 D). With-the-rule was the main type of pterygium-induced astigmatism (49.4%), followed by against-the-rule (36.4%) and oblique (14.3%). Pterygium extension had the best correlation (Pearson correlation coefficient r = 0.462, P < 0.001), followed by total area (r = 0.447, P < 0.002) and width (r = 0.348, P < 0.002). A stronger correlation was noted between pterygium size and the difference in corneal astigmatism between pterygium-affected eyes and control eyes. Pterygium induced 2 D of corneal astigmatism when its extension exceeded 2.2 mm, width exceeded 5 mm, or total area exceeded 6.25 mm(2). CONCLUSIONS: Pterygium extension and total area have a stronger correlation with corneal astigmatism than does width. Surgical intervention is indicated when pterygium extension exceeded 2.2 mm, width exceeded 5 mm, or total area exceeded 6.25 mm(2).