The Relationship between Retinal Ganglion Cell Function and Retinal Nerve Fiber Thickness in Early Glaucoma

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Abstract
Purpose. To compare relative reduction of retinal ganglion cell (RGC) function and retinal nerve fiber layer (RNFL) thickness in early glaucoma by means of steady-state pattern electroretinogram (PERG) and optical coherence tomography (OCT), respectively. methods. Eighty-four persons with suspected glaucoma due to disc abnormalities (GS: mean age 56.6 ± 13.8 years, standard automated perimetry [SAP] mean deviation [MD] −0.58 ± 1.34 dB) and 34 patients with early manifest glaucoma (EMG, mean age 65.9 ± 10.7 years, SAP MD −2.7 ± 4.5 dB) were tested with PERG and OCT. Both GS and EMG patients had small refractive errors, corrected visual acuity ≥20/25, and no systemic or retinal disease other than glaucoma. results. MDs from age-predicted normal values were larger for PERG amplitude (GS: −1.113 dB; EMG: −2.352 dB) compared with the PERG-matched RNFL thickness (GS: −0.217 dB; EMG: −0.725 dB). Deviations exceeding the lower 95% tolerance intervals of the normal population were more frequent for PERG amplitude (GS: 26%; EMG: 56%) than PERG-matched RNFL thickness (GS: 6%; EMG: 29%). conclusions. In early glaucoma, reduction in RGC electrical activity exceeds the proportion expected from lost RGC axons, suggesting that a population of viable RGCs in the central retina is dysfunctional. By combining PERG and OCT it is, in principle, possible to obtain unique information on reduced responsiveness of viable RGCs.