Abstract
Purpose :
A major challenge in clinical trials for retinitis pigmentosa (RP) is the lack of standardized outcome measures that can measure treatment efficacy with respect to rod function. Although two-color dark-adapted perimetry (2cDAP) has the potential to topographically map rod- and cone-mediated loci, the necessary instrumentation is not widely available. Therefore, we developed a full-field 2cDAP protocol that utilizes an unmodified commercially-available perimeter.
Methods :
A total of 13 normally-sighted subjects and one RP patient underwent static perimetry using an Octopus 900 with standard color filters that enabled presentation of 450 nm (red) and 610 nm (blue) stimuli at 78 points spanning 48° nasally to 72° temporally and 48° inferiorly and 36° superiorly. Sensitivity at each point was measured in decibels of attenuation for red and blue stimuli at each point and used to calculate threshold luminance differences. Normal curves were generated by taking the mean at each point.
Results :
We saw no significant effect of occluding the fixation light with red filter paper (n=3; p=1.00). We also found no effect of dark adapting subjects for 30 minutes (n=7) compared to 45 minutes (n=6; p=1.00). Importantly, the sensitivity of normal subjects for the red stimulus exceeded the capabilities of the perimeter when using a size V target with 56% of tested loci detectable at the lowest luminance. Decreasing the size of the target to size IV and III resulted in 5.5% and 0.2% saturated loci, respectively. Saturated loci were rare when using the blue stimulus (<0.2%). Full-field 2cDAP demonstrated rod-mediated function across the visual field with a mean log threshold difference between red and blue of ~2, except at the fovea. Importantly, the cone-mediated function of the fovea was clearly delineated when using the size III (n=7) and size IV (n=10) targets, but not with the size V target (n=10). One RP patient, using a size V target, demonstrated a visual field with a clearly identifiable fovea as well as islands of preserved rod-mediated function bordered by cone-dependent regions that progressed to atrophic regions.
Conclusions :
We developed a full-field 2cDAP protocol using a commercially-available, “out-of-the-box”, perimeter that has the potential to provide a standardized method for topographically measuring rod-mediated disease progress or therapeutic response in patients with RP.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.