Dark adaptation as an indicator of AMD
A useful test for the detection of early AMD is dark adaptation (DA). Simply defined as the recovery of vision when going from daylight to darkness, DA has been shown to be a sensitive biomarker for AMD, even in its earliest stages.1
Studies also indicate that DA is severely impaired in patients who have normal visual acuity.2-4 However, despite its link to early AMD, DA testing is largely underused in clinical practice, perhaps due to the fact that traditional methods of measuring DA impairment can take up to an hour to complete.
To overcome the problems associated with traditional DA testing, a dark adaptometer known as the AdaptDx (MacuLogix Inc) was developed as a screening tool for AMD, retinitis pigmentosa and other macular degenerations. The device can aid in the diagnosis of early-stage, or subclinical, AMD before visual loss occurs and even before structural changes are observed, and adds to the information obtained from retina cameras and OCT imaging.
The adaptometer measures the rod intercept (RI) as an indicator of impaired DA; RI is the recovery time of scotopic sensitivity to a benchmark level, providing an objective and sensitive measurement of retinal function. An RI below 6.5 minutes is normal. An RI greater than 6.5 minutes is an early indicator of retinal disease, requiring additional testing.
The test can be easily performed and takes as little as 5 minutes per eye with no need for pre-adaptation or pupil dilation. Findings from a clinical study that included two cohorts of elderly adults, 127 with early-to-advanced AMD and 21 with normal retinas (as determined by fundus photography grading), showed that the adaptometer had a diagnostic sensitivity and specificity of 90.6% and 90.5%, respectively.
Additionally, the device demonstrated excellent reliability with a test-retest agreement of 94.7% between the first and second visits.4