Recent advances in the assessment of early glaucoma using Retinal Nerve Fiber Layer Analysis

Abstract

Glaucoma is a multi-factorial optic neuropathy characterized by progressive loss of retinal ganglion cells and their nerve fibers, which leads to characteristic loss of visual function.. Humans have a large reserve of retinal nerve fibers, and redundancy in the system may prevent detection of early functional damage. It has been estimated that up to 50% of fibers may be lost before a visual field defect is detectable with white-on-white perimetry. Furthermore, intraocular pressure and cup-to• disc ratio may not be sensitive or specific enough as indicators for the presence of glaucomatous optic neuropathy. Visual field testing may miss defects, especially early in the disease "pre-perimetric glaucoma'. It makes sense, therefore, to evaluate the RNFL for the diagnosis and follow-up of early glaucoma, prior to the development of characteristic visual field loss. (Choplin et al, 1998) A number of techniques are available for evaluation of the RNFL. These include red-free ophthalmoscopy and photography, optical coherence tomography, retinal topography by confocal scanning laser ophthalmoscopy, and scanning laser polarimetry. Red-free Ophthalmoscopy and Photography Use of a red-free (green) light to evaluate the RNFL may allow the visualization of defects. The healthy RNFL is usually highly reflective. and defects may be seen as dark areas surrounded by the more reflective healthy tissue. These defects will conncct to the optic disc, and widen peripherally, corresponding to the normal anatomy. This technique usually proves not to be practical in most practice situations. (Choplin et al, 1998)