Symmetry analysis for detecting early glaucomatous changes in ocular hypertension using optical coherence tomography

To compare symmetry analysis of the retinal nerve fiber layer (RNFL) in ocular-hypertensive, normal, and glaucomatous eyes using optical coherence tomography (OCT). Thirty-three consecutive ocular-hypertensive patients (33 eyes), 25 normal volunteers (25 eyes), and 35 open-angle glaucoma patients (35 eyes) were enrolled in this study. Circular OCT scans were obtained using a diameter of 3.4 mm around the optic disc. RNFL thickness was measured, and a symmetry analysis was performed using symmetry ratios. To calculate the symmetry ratios, the circle was divided into the superior and inferior hemiretina. The superior hemiretina was further subdivided into three (area I, temporal 45 degrees; area II, superior 90 degrees; and area III, nasal 45 degrees ) or five (with areas 1-5, each spanning 36 degrees ) zones. The symmetry ratios were defined as the ratios comparing the RNFL thickness within each of the zones with that in the analogous zone in the inferior hemiretina. RNFL thickness measurements could distinguish glaucomatous eyes from other groups, but could not distinguish ocular-hypertensive from normal eyes. However, the symmetry analysis revealed differences between ocular-hypertensive and normal eyes in area II (mean +/- SD, 0.77 +/- 0.16 vs. 0.85 +/- 0.12, P = 0.0379). Early glaucomatous RNFL changes might exist in some areas of ocular-hypertensive eyes, and a symmetry analysis may be a useful method for detecting these changes.