MacDx Foveal Dark Adaptation
MacDx, a new adaptometer, has a unique dark adaptation endpoint within the program that does not requires the patient to relocate to a second instrument following bleaching for dark adaptation endpoint determination. MacDx is a digital program designed for a graphic display device (GDD). The protocol calls for foveal bleaching by viewing a round light on the GDD screen (iPad, iPhone, Android, etc.) for a specified time, followed by viewing a Bull's Eye target where the white center is separated from a white peripheral ring by dark ring. The endpoint is relative, the moment the Bull's Eye center appears the same color and brightness as the peripheral ring. The screening method is 30 second bleaching duration.
The following experiment measures the relationship between red stimulus duration and dark adaptation recovery of an 81-year-old healthy subject with 20/20 acuity in each eye. In Figures 1 and 2 below are dark adaptation curves for subject AJH, right and left eyes. Five dark adaptation endpoints were taken at each bleaching interval: 5, 30, 90, 150 and 300 seconds. As the bleaching duration increases the foveal dark adaptation endpoints rise and the time to reach a final steady threshold value increase.
In comparison to the report of Mote and Riopelle5, their dark adaptation curve using the Hecht-Shlaer adaptometer appears very similar to the dark adaptation curve of MacDx adaptometer, compare Figure 1 and Figures to Figure 4. The data for the Figure 4 was extracted from the tables from their report5. The minutes of light adaptation (bleaching) from 15 to 300 minutes were plotted against minutes until final steady level for bleaching values for 565, 1130, 5650, and 11300 mL. As with MacDx, the slopes followed a logarithmic trendline. As the intensity, duration, or both, increase the initial foveal dark adaptation threshold rise and the time to reach a final steady thresholds value increase.
Reference 5. Mote, F.A., Riopelle, A.J. The effect of varying the intensity and the duration of pre-exposure upon subsequent dark adaptation in the human eye.
Journal of Comparative and Physiological Psychology, 46(1), 49–55.
OD: Dark adaptation following bleaching of 15, 30, 90, 150 and 300 seconds
OS: Dark adaptation following bleaching of 15, 30, 90, 150 and 300 seconds
Linear R2 close to 1.0 when DA of OD and OS are normal.
Figure 4. Mote, Riopelle (ref 5), Comparison of seconds of light adaptation at difference bleaching intensities and minutes for dark adaptation threshold stimulus steady state.