Implementation of CRT Technology for Assessment of Dark Adaptation Kinetics in AMD Patients.

Abstract

Abstract: : Purpose: To describe a method characterising a clinical test of the kinetics of cone and rod visual adaptation using cathode–ray–tube (CRT) technology. Methods: Cone and rod dark adaptation was measured with a foveated 2°, 500 ms spot target generated on a calibrated CRT monitor following a bleach produced by a photographic flash (∼27% pigment bleach). Neutral density filters (2.6ND) were used to expose key features of cone and rod recovery. A running estimate of threshold was returned by a YES/NO paradigm with a 1 sec response window using a modified Békésy tracking procedure. The tracking method used a 3dB–down/1dB–up logic with blanks randomly interleaved on 50% of trials. The kinetics of dark adaptation were established in controls (n=6) and persons with Age–related Macular Degeneration (AMD, n=27). Data were modelled using two exponential decays to describe the cone and rod components. Results: The average normal rod–cone break was 9.25±1.61 min with a cone time constant (Ctc) of 0.29±0.03 min and rod time constant (Rtc) of 1.15±0.56 min. In comparison the AMD group showed gross variability in recovery dynamics. Eight subjects (29.5%) had no rod–cone break by 30 minutes and delayed cone kinetics (Ctc 0.74±0.44, p<0.01). Five (18.5%) had a normal rod–cone break and recovery dynamics. For the remaining 14 subjects (52%), the average rod–cone break was delayed 22.3±5.36 mins (p<0.025) with slower cone (Ctc 0.47±0.24; p<0.05) and rod (Rtc 5.77±2.06; p<0.025) time constants. Conclusions: A CRT monitor coupled with an 8–bit video card and photographic flash can be used to isolate the important components of dark adaptation in humans. This method can be adopted as a simple clinical tool to characterise dark adaptation in patients with ocular pathology.

Keywords: age–related macular degeneration • clinical research methodology • photoreceptors: visual performance