Dark adaptation in Duchenne muscular dystrophy with a short protocol

Abstract

Purpose : To investigate if Duchenne Muscular Dystrophy affects dark adaptation for the rods and cones of the eye with a new short psychophysical protocol.

Methods : In this pilot study two Duchenne Muscular Dystrophy (DMD) patients and eleven healthy volunteers were tested monocularly. The tests were conducted using the Roland Consult Darkadaptometer system. Instead of the standard 45-minute protocol we have developed a 8+6 minute test to be able to test DMD patients avoiding muscular fatigue. The protocol begins with one minute of bleaching with white light at 3000 cd/m². The first part of the test lasts 8 minutes to verify the separation of rod and cone adaptation levels (rod-cone break). For this interleaved red and green stimulation flashes of dynamically changing luminance (depending on patient response with a button control) are shown inside a Ganzfeld stimulator at 20 degrees temporal eccentricity. After a 5-minute interval with eyes closed, a 6-minute test session is performed with green stimuli only to test for rod adaptation.

Results : The test was evaluated with the control group having an average rod-cone break luminance of -1.82±0.087 log cd/m² at 148±71 seconds and an average stable rod adaptation luminance of -4.04±0.188 log cd/m². Relative to controls, the time and luminance for the rod-cone break of the first DMD patient (with genetic mutation upstream exon 30) falls within the normal range (Fig 1), just as the luminance of the stabilized rod adaptation level (Fig 2). The second DMD patient (with genetic mutation downstream exon 30) did not reach the rod/cone break within the 8 minutes of the first test phase while his stable red adaptation luminance level stayed within the control group’s range (-1,93 log cd/m²). Between the two DMD patients there was a large difference in the rod adaptation luminance (-4 log cd/m² vs -2.7 log cd/m²).

Conclusions : The newly developed short dark adaptation protocol used in this study performed well as verified with the control group since it demonstrated low variability among subjects. The DMD patient lacking only Dp427 genetic mutation had results that indicate a conservation of rod and cone adaptation in DMD while the lack of smaller DMD gene products, such as Dp260 (mainly expressed by the rods) of the second patient indicate impairment of rod vision affecting dark adaptation as well.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.