Quantification of Retinal Nerve Fiber Layer Thickness in the Normal Subjects Using Optical Coherence Tomography

ABSTRACT

Optical coherence tomography is a new imaging technique analogous to ultrasound B scan that can provide cross sectional images of retina with approximately 10micrometer resolution. This study was designed to evaluate the quantification of nerve fiber layer [NFL] thickness in normal eyes using OCT. We studied 66 eyes of 66 subjects by conventional ophthalmoscopic physical examination, Humphrey central 30-2 visual fields, stereoscopic optic nerve head photography, retinal nerve fiber layer photography, HRT and OCT. Imaging with OCT was performed circumferentially around the optic nerve head with a circle diameter of 2.3mm & 3.4mm using an internal fixation technique. At a scan diameter of 2.3mm and 3.4mm, average, superior, inferior, nasal and temporal NFL thicknesses were 125.45 +/-19.05 micrometer, 150.33 +/-25.53micrometer, 154.55 +/-25.72 micrometer, 102.89 +/-29.13micrometer, and 92.65 +/-27.04micrometer and 109.02 +/-15.68 micrometer,135.53 +/-22.65 micrometer, 132.98 +/-20.19micrometer, 73.11 +/-26.85 micrometer and 89.70 +/-14.65 micrometer each. The NFL was thickest in the superior and inferior quadrants,thinnest in the nasal quadrant at a scan diameter of 2.3mm, and thinnest in the temporal quadrant at a scan diameter of 3.4 mm. In general the thickness for the 2.3 mm scans was greater than that for the 3.4mm scans.NFL thickness decreased significantly with age in the temporal quadrants [P<0.05]. At a scan diameter of 3.4 mm, NRA decreased significantly with decreased average NFL thickness and average NFL thickness decreased significantly with decreased disc area [P<0.05]. By direct investigation of the NFL with OCT, earlier diagnosis of glaucoma and earlier detection of glaucomatous progression can be made, before conventional signs such as visual field loss, cupping of the optic nerve head, and NFL defects are evident, thus allowing earlier treatment and reducing the damage.