Arden Index is related to which of the following investigation?

Arden index is the ratio of the minimum amplitude during dark adaptation (dark trough) to the maximum during light exposure (light peak). A value greater than 1.8 is considered as normal. EOG reflects the presynaptic function of the retina, so any disease which interfere with the functional interplay between the retinal pigment epithelium and the photoreceptor will produce an abnormal or absent light rise in EOG. EOG is affected in retinitis pigmentosa, vitamin A deficiency, retinal detachment and toxic retinopathies. Ref: Ophthalmology by A.K Khurana, 4th edition, page 488-90.