This Rod-based Visual Function May Signal AMD

Rod-mediated dark adaptation is a time-consuming vision test, but since both study and fellow eyes show general agreement for future AMD risk, the researchers say that evaluating only one eye should be sufficient for understanding fellow-eye prognosis.  Photo: Jeffry Gerson, OD. Click image to enlarge. Studying visual function impairment in early and intermediate AMD can provide clues to disease progression. Previously, the Alabama Study on Early Age-Related Macular Degeneration (ALSTAR) demonstrated that older eyes with normal macular health and delayed rod-mediated dark adaptation (RMDA) were twice as likely to develop incident AMD at three years compared to eyes with normal dark adaptation.In the recently published ALSTAR2 study, the researchers sought to replicate the ALSTAR findings, determine whether delayed dark adaptation raises the risk for progression to intermediate AMD and to compare the risk of delayed RMDA to other visual functions for AMD incidence or progression. They found that RMDA is associated with progression and should be considered a functional outcome measure.The longitudinal study published in Ophthalmology analyzed 404 adults aged 60 and older with normal macular health or early AMD at baseline examination. All eyes underwent fundus photography, and AMD presence and severity were established using the AREDS nine-step classification system. The study eye underwent several tests, including RMDA, scotopic sensitivity, low luminance acuity, mesopic contrast sensitivity, mesopic light sensitivity, visual acuity and contrast sensitivity. Fundus photography and AREDS classification system were repeated at three years’ follow-up (n=329).    The researchers reported that normal older eyes with delayed RMDA were 3.54 (study eye) or 3.4 (fellow eye) times more likely to have incident AMD at three years, compared to those without delays. They didn’t find any associations between visual functions and AMD incidence, apart from low luminance visual acuity in the study eye.Eyes with early AMD at baseline with delayed dark adaptation were 3.89 (study eye) or 2.65 (fellow eye) times more likely to have progressed at follow-up. Visual functions weren’t associated with AMD progression.“RMDA is the only visual function of those tested associated with AMD incidence and progression over three years in eyes that are normal or have early AMD at baseline,” the researchers wrote in their study. Based on their results, they concluded that “other visual functions are not useful in this regard. Interventions that are eventually designed to arrest early AMD progression or preventative measures in those at risk should consider RMDA as a functional outcome measure.”Click here for the journal source. Owsley C, McGwin G, Clark ME, et al. Delayed rod-mediated dark adaptation is associated with incidence and early progression of age-related macular degeneration: ALSTAR2. Ophthalmology 2025. [Epub ahead of print].