REPRODUCIBILITY OF NERVE-FIBER LAYER THICKNESS MEASUREMENTS USING OPTICAL COHERENCE TOMOGRAPHY

Purpose: Optical coherence tomography (OCT) is a new technology that u ses near-infrared light in an interferometer to produce approximately 10-mu m resolution cross-sectional images of the tissue of interest. T he authors performed repeated quantitative assessment of nerve fiber l ayer thickness in individuals with normal and glaucomatous eyes, and t hey evaluated the reproducibility of these measurements. Methods: The authors studied 21 eyes of 21 subjects by OCT. Each subject underwent five repetitions of a series of scans on five separate occasions withi n a 1-month period. Each series consisted of three circular scans arou nd the optic nerve head (diameters, 2.9, 3.4, and 4.5 mm). Each series was performed separately using internal (fixation with same eye being studied) and external (fixation with contralateral eye) fixation tech niques, The eye studied and the sequence of testing were assigned rand omly. Results: Internal fixation (IF), in general, provides a slightly higher degree of reproducibility than external fixation (EF). Reprodu cibility was better in a given eye on a given visit than from visit to visit. Reproducibility as measured by intraclass correlation coeffici ents were as follows: circle diameter (CD), 2.9 mm, 0.51/0.57 (normal/ glaucoma) (IF), 0.43/0.54 (EF); CD, 3.4 mm, 0.56/0.52 (IF), 0.43/0.61 (EF); CD, 4.5 mm, 0.53/0.43 (IF), 0.42/0.49 (EF). Conclusions: Nerve f iber layer thickness can be reproducibly measured using OCT. Internal is superior to external fixation; each circle diameter tested provides adequate reproducibility.