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. 2017 Jun 5;6(3):15.
doi: 10.1167/tvst.6.3.15. eCollection 2017 Jun.

Natural History of Rod-Mediated Dark Adaptation over 2 Years in Intermediate Age-Related Macular Degeneration

Cynthia Owsley  1 , Mark E Clark  1 , Gerald McGwin Jr  1   2
Affiliations

Natural History of Rod-Mediated Dark Adaptation over 2 Years in Intermediate Age-Related Macular Degeneration

Cynthia Owsley et al. Transl Vis Sci Technol. .

Abstract

Purpose: To characterize the natural history of rod-mediated dark adaptation (RMDA) over 2 years in eyes with intermediate age-related macular degeneration (AMD). This information will be useful in understanding the potential of RMDA to serve as a functional endpoint in proof-of-concept studies and clinical trials on intermediate AMD.

Methods: RMDA was measured in eyes with intermediate AMD at baseline and follow-up visits over 2 years at 6, 12, 18, and 24 months. A computerized dark adaptometer measured sensitivity for targets centered at 11° on the superior vertical meridian of the retina. Rod intercept time (RIT) characterized the speed of dark adaptation and was defined as the duration (in minutes) required for sensitivity to reach a criterion level of 3.0 log units of attenuation of the stimulus.

Results: Mean change in RIT over 24 months for 30 eyes was 10.5 minutes (standard deviation 19.4), p < 0.0001; 73.3% of eyes had a RIT increase >1 minute, 56.7% had an increase >3 minutes, and 36.7% had an increase >6 minutes; for 26.7% RIT was unchanged (0- to 1-minute increase) or decreased. Greater increase in RIT over 24 months was associated with smoking.

Conclusions: RMDA slows in intermediate AMD over 2 years in most eyes. There was wide variability in RIT at both baseline and in the extent to which it increased over 24 months. A major risk factor for AMD, smoking, exacerbated RMDA slowing.

Translational relevance: RMDA as assessed by RIT may be useful as a functional endpoint in proof-of-concept studies and clinical trials on intermediate AMD with 2-year designs.

Keywords: age-related macular degeneration; dark adaptation; endpoint.

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Figures

Figure 1
Figure 1
Examples of dark adaptation plots for participants at baseline illustrating very fast recovery to very slow recovery of sensitivity. Color-coded vertical arrows above the abscissa indicate RIT computed by the AdaptDx for that participant.
Figure 2
Figure 2
Scatterplots showing the relationship between RIT at baseline and RIT at 24 months. Panel A shows data for eyes for which the AdaptDx software computed RIT automatically. Panel B shows data for eyes where recovery of sensitivity was so slow that the AdaptDx did not compute RIT. For these eyes we used nonlinear regression to estimate RIT, as described previously. Both panels show that for the vast majority of eyes, RIT at 24 months was greater than at baseline, signifying that the speed of RMDA had slowed over 24 months.
Figure 3
Figure 3
Representative examples of dark adaptation plots for four participants at baseline and 24 months. Panel A shows a participant with fast dark adaptation at baseline, which was unchanged 24 months later. Panels B, C, and D show examples of worsening dark adaptation delays (increased RIT) by the 24-month visit.
See this image and copyright information in PMC

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