First Author: J.Jolly UK
Co Author(s): A. Dubis R. MacLaren
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Dark adaptation is currently the gold standard method for assessing rod function. This is becoming more important as there are an increasing number of clinical trials for the treatment of rod-cone dystrophies. Dark adaptometry is a long process and can be a burden on patients. The Maculogix® has been developed as a screening tool, testing a localised area of retina for dark adaptation. It is a shorter, less onerous test and may present a viable alternative for the measurement of rod function.
Oxford University Hospitals NHS Trust, UK. Outpatients department.
A group of patients with choroideremia underwent scotopic testing with both full field dark adaptometry using the Espion 2 (Diagnosys LLC, Cambridge, UK) and localised measurements 5 degrees superior to the fovea using the AdaptDx (Maculogix®, PA, USA). The slope of adaptation over the initial 18 minutes was compared using the 2 techniques. This was performed as part of an ongoing gene therapy trial (NCT02407678).
Measurements were obtained for 20 eyes from 10 patients. On full field dark adaptometry, the mean ± SEM starting sensitivity was -1.95 ± 0.16 log cd.s/m2. Around the 18 minute mark, mean sensitivity was -3.68 ± 0.22 log cd.s/m2. The average change was an increase in sensitivity of 0.000163 ± 0.00013 log cd.s/m2 per second. The mean time to complete dark adaptation was 1780 seconds (30 minutes) and mean final sensitivity was -4.52 ± 0.30 log cd.s/m2. Sensitivity at 18 minutes and final sensitivity were well correlated (r = 0.85, p < 0.05). However, there was a systematic bias with the difference between the sensitivity at 18 minutes and peak sensitivity increasing as the final sensitivity increased (0.37 log cd.s/m2 per log unit). The adaptation measured by the Maculogix by 18 minutes was 0.05dB per second mean across the eyes. However, in 3 out of 20 eyes the Maculogix measurement was situated outside the area of surviving retina.
Dark adaptation measurements at 18 minutes appear to be a reasonable marker for final rod sensitivity. The Maculogix may be a viable option for this in patients with inherited retinal degeneration, as it is quicker and easier to perform than full field dark adaptation. More work is needed to address the interchangeability of results from different test locations to ensure testing is always done on intact retina as care must be taken to ensure thresholds are tested within surviving retina for accurate analysis.