Abstract
Purpose :
Without the aid of sophisticated functional studies and molecular genetic testing, differentiating BCM and ACHM is challenging, especially in isolated male cases. Consistent with the fact that that S-cones are spared in BCM, it has been shown that specialized light-adapted chromatic (600nm, orange, and 440nm, blue-purple) automated perimetry is differentially affected in BCM (Luo et al. PLoS One 2015) and not in ACHM, but these techniques are available only in highly specialized Centers. Thus, we sought to develop and pilot a simple, clinician-friendly, relatively rapid perimetric approach to BCM/ACHM differential diagnosis.
Methods :
Out of a pool of 20 molecularly confirmed cases, 3 ACHM (all CNGB3 gene deletions or mutations) and 4 BCM patients (3 OPN1LW/OPN1MW gene cluster deletions and a C203R point mutation) were tested. Automated perimetry was performed with a Humphrey 30-2 SITA-Fast test, using fovea on, fluctuation and fixation/gaze control off options. Size-V stimuli were presented with dilated pupils, after at least 3 min of background adaptation. To probe mainly S-cones, standard SWAP was used (blue stimuli on a bright yellow background). To probe mainly L-cones, an identical test was performed on a standard white background with red stimuli, custom-selected from the “change parameters” menu.
Results :
Each BCM subject consistently exhibited markedly elevated to non-detectable thresholds to red-on-white stimuli and a range of normal to mildly elevated thresholds to blue-on-yellow stimuli, whereas each ACHM subject showed markedly elevated to non-detectable thresholds to both tests. Each pair of perimetries was completed within 45 to 50 minutes, adaptation time included (about 10-12 min of active testing time per eye).
Conclusions :
Our simple, clinician-friendly automated perimetry method allows for accurate differentiation between BCM and ACHM, and can be easily implemented in a routine eye care setting with minimal customization of the standard testing routines by following simple steps at the time of testing. We plan to further validate our method on a larger case series, estimate test-retest variability, and investigate possible trends for changes in these chromatic thresholds over time, to determine if this simple testing method may also be a useful outcome measure in gene therapy trials.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.