Numerous psychophysical studies have reported that rod function is affected in the early stages of AMD.
1–5 However, these early studies
1–5 have been limited by two important considerations. First, when these studies were performed, AMD status was graded using only color fundus photographs. Multimodal imaging (MMI) was not available at the time to further phenotype the participants with newly described changes that contribute to risk of vision loss, such as the presence of subretinal drusenoid deposits (SDD), also referred to as reticular pseudodrusen.
6 Second, the ability to test rod function in earlier studies (primarily by determining the rod intercept time) was in large part limited to one location within the macula. Thus, rod functional topography and the structure–function relationship within the macula could not be obtained in previous studies.
1–5 These two limitations have started to be addressed with the widespread availability of MMI techniques and the development and manufacture of scotopic perimeters. The advances in MMI with fundus autofluorescence (FAF), near infrared (NIR), and spectral-domain optical coherence tomography (SD-OCT) imaging allowed features, such as SDD,
7–10 hyperreflective foci,
11–13 and nascent geographic atrophy (nGA),
14,15 all of which are considered to be associated with an increased risk of vision loss in AMD, to be identified. Instruments, such as the scotopic Nidek microperimeter (MP-1S; Nidek Technologies, Padova, Italy)
16 and the scotopic Macular Integrity Assessment (S-MAIA; CenterVue, Padova, Italy) microperimeter,
16,17 were designed to allow static rod-mediated function to be assessed at multiple locations within the macula in the one testing session.