Increased Equivalent Input Noise in Glaucomatous Central Vision: Is it Due to Undersampling of Retinal Ganglion Cells?

Abstract

PURPOSE. Recent evidence shows that macular damage is common even in early stages of glaucoma. Here we investigated whether contrast sensitivity loss in the central vision of glaucoma patients is due to an increase in equivalent input noise (N eq), a decrease in calculation efficiency, or both. We also examined how retinal undersampling resulting from loss of retinal ganglion cells (RGCs) may affect N eq and calculation efficiency. METHODS. This study included 21 glaucoma patients and 23 age-matched normally sighted individuals. Threshold contrast for orientation discrimination was measured with a sinewave grating embedded in varying levels of external noise. Data were fitted to the linear amplifier model (LAM) to factor contrast sensitivity into N eq and calculation efficiency. We also correlated macular RGC counts estimated from structural (spectraldomain optical coherence tomography) and functional (standard automated perimetry Swedish interactive thresholding algorithm 10-2) data with either N eq or efficiency. Furthermore, using analytical and computer simulation approach, the relative effect of retinal undersampling on N eq and efficiency was evaluated by adding the RGC sampling module into the LAM. RESULTS. Compared with normal controls, glaucoma patients exhibited a significantly larger N eq without significant difference in efficiency. N eq was significantly correlated with Pelli-Robson contrast sensitivity and macular RGC counts. The results from analytical derivation and model simulation further demonstrated that N eq can be expressed as a function of internal noise and retinal sampling. CONCLUSIONS. Our results showed that equivalent input noise is significantly elevated in glaucomatous vision, thereby impairing foveal contrast sensitivity. Our findings further elucidated how undersampling at the retinal level may increase equivalent input noise.

A Unified Rule for Binocular Contrast Summation Applies to Normal Vision and Common Eye Diseases

“…The mechanism of binocular contrast summation is likely intact in our subjects with eye diseases, suggesting intact binocular processing in the visual cortex. Consistent with this possibility, previous contrast sensitivity studies have reported significantly higher equivalent input noise but relatively intact sampling efficiency in patients with glaucoma 34 and RP. 35 Sampling efficiency refers to how efficiently the visual system extracts and utilizes the available stimulus information.…”

High-Pass Visual Acuity Loss and Macular Structure-Function Relationship in Patients With Primary Open-Angle Glaucoma

“…Anderson et al 24 pointed out that the resolution performance for high-pass optotypes was limited by the RGC sampling density in much of the same way as gratings. Recently, Liu et al 33 confirmed that undersampling at the retinal level (loss of RGCs) resulted in elevated input noise in glaucomatous vision, which impaired foveal CS in glaucoma patients. In the current study, we found that glaucomatous eyes showed statistically significant but weak-to-moderate correlations between high-pass VA and the thinning of GCL+IPL thickness.…”

Identifying the Retinal Layers Linked to Human Contrast Sensitivity Via Deep Learning

“… 75 Our recent work using a computational model has also demonstrated that RGC undersampling may in part explain the loss of foveal contrast sensitivity in glaucoma patients. 76 RGC counts have also been related to visual perimetry representing light sensitivity across the visual field. 24 – 30 Particularly, a study done by Harwerth et al 31 showed that light sensitivity measured with visual perimetry is linearly related with either the thickness of ganglion cell layer or RGC counts.…”