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Lillian Chien, Rong Liu, MiYoung Kwon; A higher contrast requirement for letter recognition in glaucoma. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4697.
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© ARVO (1962-2015); The Authors (2016-present)
Glaucoma is a leading cause of world blindness, characterized by progressive loss of retinal ganglion cells. Unlike the conventional view that early glaucoma primarily affects peripheral vision, recent anatomical studies (e.g. Hood et al., 2013) have shown that glaucomatous injury involves the macula even in the early stages. However, little is known about whether and how this macular damage affects central visual function such as letter recognition. Here we examine whether glaucomatous damage requires a higher contrast for letter recognition in central vision.
Nine subjects were recruited: patients with Primary Open-Angle Glaucoma (mean age=59.5±5.1 yrs; mean MD better eye=-13.6±12.0 dB; mean MD worse eye=-8.5±10.2 dB) and age-similar normally-sighted subjects (mean age=54.0±5.3 yrs). Contrast requirement for letter recognition was measured using a letter-recognition task in the central visual field; subjects identified English alphabet letters presented at eight locations in the central 15° visual field. The threshold contrast for letter recognition was defined as a contrast level that yields 80% recognition accuracy. The retinal ganglion cell plus inner plexiform (RGC+) layer thickness was measured using Spectral-Optical Coherence Tomography (OCT) in the macula (corresponding to the central 20° visual field). The RGC+ layer thickness at each letter location was calculated from the RGC+ layer thickness of corresponding retinal areas after correcting for the displacement of retinal ganglion cells.
Compared to normal cohorts, glaucoma subjects showed a significant decrease in RGC+ layer thickness (by 19.2%, p<0.01). Similarly, glaucoma subjects showed a significant increase in the contrast threshold for letter recognition (by 107.4%, p=0.02). Furthermore, for both subject groups, RGC+ layer thickness significantly correlated with contrast threshold for letter recognition (r=-0.41, p<0.01).
Our results demonstrate that the RGC+ layer thickness is significantly thinner in the macula of glaucomatous eyes. This macular damage appears associated with a higher contrast requirement for letter recognition. Our findings further support the view that glaucomatous injury involves the macula even in mild to moderate glaucoma.Reference:Hood et al. Glaucomatous damage of the macula. Progress in retinal and eye research 32, 1-21, (2013).
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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