Objective Assessment of Retinal Ganglion Cell Function in Glaucoma
Subjectpupillary response to light; aging; pupillometry; glaucoma; electroretinogram; photopic negative response; vision; retinal ganglion cells
Glaucoma refers to a group of diseases causing progressive degeneration of the retinal ganglion cells. It is a clinical diagnosis based on the evidence of structural damage of the optic nerve head with corresponding visual field loss. Structural damage is assessed by visualization of the optic nerve head (ONH) through various imaging and observational techniques, while the behavioral loss of sensitivity is assessed with an automated perimeter. However, given the subjective nature of visual field assessment in patients, visual function examination suffers from high variability as well as patient and operator- related biases. To overcome these drawbacks, past research has focused on the use of objective methods of quantifying retinal function in patients with glaucoma such as electroretinograms, visually evoked potentials, pupillometry etc. Electroretinograms are objective, non-invasive method of assessing retinal function, and careful manipulation of the visual input or stimulus can result in extraction of signals particular to select classes of the retinal cells, and photopic negative response (PhNR) is a component of ERG that reflects primarily the retinal ganglion cell function. On the other hand, pupillary response to light, measured objectively with a pupillometer, also indicates the functional state of the retina and the pupillary pathway. Hence, the study of both ERGs and pupillary response to light provide an objective avenue of research towards understanding the mechanisms of neurodegeneration in glaucoma, possibly affecting the clinical care of the patients in the long run.