Retinal nerve fiber layer analysis: relationship between optical coherence tomography and red-free photography

Comparison of retinal nerve fiber layer (RNFL) thickness measurements using optical coherence tomography (OCT) to the clinical standard red-free photography (evaluated semiquantitatively), in relation to functional visual field damage in primary open-angle glaucoma (POAG) patients, ocular hypertensives, and POAG suspects.

Concurrent, cross-sectional study. In four age-matched groups (42 patients with early to moderate POAG, 34 ocular hypertensives, 22 POAG suspects, and 25 normal controls), RNFL was assessed with OCT, standardized red-free photographic scoring method and standard achromatic perimetry.

OCT RNFL thickness decreases with increased RNFL damage (detected with red-free photography). The global average OCT RNFL thickness correlated significantly with the photographic total RNFL score (r = .650, P = .0001). Both OCT and photographic scoring system were able to find significantly thinner RNFL in the glaucoma group as compared with normals (P = .0001 for both), ocular hypertensives (P = .0001 for both), and suspects (P = .0001 for both). However, neither OCT nor photography could significantly differentiate between ocular hypertensives, suspects, and normals. Both OCT and photography were significantly correlated with VF loss. For the percentage of VF points depressed <5%, the correlation was highest for OCT (r = -0.615 for OCT and r = -0.476 for photography). OCT had a higher diagnostic accuracy than photography (86% and 77%, respectively).

For RNFL thickness measurements, the presence of high correlations between OCT, photographic scores, and functional visual field loss suggest the validity of OCT measurements. The higher diagnostic accuracy of OCT RNFL measurements suggests its potential advantage for detection of early cases of glaucoma.