The retinal nerve fiber layer (RNFL) is composed of retinal ganglion cell axons that are covered by astrocytes and bundled by Muller cell processes.¹

Glaucoma is a progressive optic neuropathy with characteristic and relative accelerated RNFL loss with associated morphologic changes to the optic nerve.^2,3 Localized RNFL defects are some of the earliest signs of glaucoma (average of 39% to 59% fewer retinal ganglion cells than age-matched normal subject)^3,4,5 and are less likely to be observed in advanced glaucoma due to diffuse RNFL loss and progression.^1,3 Such localized RNFL defects represent substantial amounts of retinal ganglion cell loss in the affected sector (even in the presence of normal visual fields) and are most common in the inferotemporal region followed by the superotemporal region.^3,4,5

Careful evaluation of the optic nerve complex in the inferotemporal and superotemporal regions for RNFL defects may be more sensitive than visual field testing in those already diagnosed with early glaucoma.⁶ The rate of RNFL loss appears to be faster (more than twice as fast) in glaucoma suspect patients who developed visual field defects than those who did not develop visual field defects.⁷