Measuring rod-mediated visual performance in ageing and age-related macular degeneration.

Purpose: To demonstrate the usefulness of the Maculogix AdaptDx for assessing rod-mediated visual function in ageing and age-related macular degeneration (AMD).Methods: 22 young healthy individuals (mean age 23 yrs), 34 older healthy individuals (mean age 71 yrs) and 17 individuals with intermediate AMD (mean age 76 yrs) were recruited as part of a study looking at the influence of macular pigment on rod-mediated performance. All individuals were assessed on the Maculogix AdaptDx which is a commercially available clinically friendly, short-duration dark adaptometer instrument. This instrument allows measurement of a significant amount of the rod portion of the dark adaptation curve to be measured within a reasonable testing time. The instrument uses the “rod intercept” as an estimate of dark adaptation speed rather than the slope of the curve as this provides a uniform method across individuals. The rod intercept is the time after photobleaching when the patient’s sensitivity recovers to a criterion light level where sensitivity recovery is completely rod-mediated. Results: There was a significant increase in the rod intercept time with age from a mean of 4.61 (±0.69) mins in the younger group to 9.8 (±4.6) mins in the older age group (p 12.3 min), indicating a significant rod-mediated visual function defect in some individuals with a normal fundus and ocular coherence tomography appearance. Individuals with intermediate AMD had a significantly higher rod intercept time (mean 32.4 ±12.8 min) than the age-matched older normal group (p 0.5 log units) had faster rod-mediated recovery (n=10, mean 29.1 minutes) than those with below average levels (n=7, mean =37.1 minutes), but this did not reach statistical significance (p=0.22).Conclusions: The AdaptDx can differentiate between younger and older individuals and those with age-related macular degeneration. The instrument has great potential for early identification of those at risk of AMD, stratifying AMD patients in the clinic by function and as a primary outcome measure in medical retinal clinical trials.