The researchers at the Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, Melbourne, have reported that the five visual function parameters commonly used in the clinic showed that the rod intercept time (RIT) assay is the most discriminatory functional parameter in the early stages of AMD. Commenting on translational data, the researchers commented that, “the RIT could be considered for assessing visual function and evaluating efficacy of novel interventions aimed at improving retinal function in eyes with early stages of AMD”.
The research was aimed at measuring different types of visual function in intermediate age-related macular degeneration (iAMD) patients to determine which commonly used visual function test may be the most discriminatory test comparing individuals with iAMD to normal participants. The key visual function tests included BCVA, low luminance visual acuity (LLVA), mesopic microperimetry, dark adaptation and scotopic perimetry following photo-bleach, clinical eye examination, and multimodal retinal imaging in a single study visit. Each functional parameter were converted into a z-score so that all the parameters had a common scale to allow a direct comparison between different functional parameters. Following the results, forty-eight subjects (23 normal control, 25 iAMD) were recruited. While five parameters showed a significant reduction in function in iAMD eyes, compared to controls (P ≤ 0.003), the rod intercept time (RIT) detected the greatest reduction in function, followed by the scotopic sensitivity, mesopic sensitivity, BCVA, and LLVA, with the absolute mean z-score of 4.5, 2.2, 1.0, 1.0, and 1.2, respectively.
As defined in their research study, rod intercept time (RIT) was “the time, in minutes, for the stimuli to recover to a criterion level at –3.0 log units of stimulus intensity after an exposure to the photo-bleach derived from a modelling exponential decay function”. As commented in their report, most of the functional assessments in the study are not routinely performed in clinical practice under time-constraints, usually used in research settings to monitor AMD progression, or assess the efficacy of potential interventions for early stages of AMD. In conclusion, the researchers stated that, “a direct comparison of commonly used tests for detecting a functional deficit in eyes with the early stages of AMD was performed and the RIT appears to be the most sensitive parameter in detecting the presence and magnitude of functional abnormality in eyes with AMD. Testing RIT at multiple locations in the retina is likely to deliver the best data to help show a difference in progression between arms in an intervention study in iAMD”.