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Lea D Bennett, Georgie Metz, Martin Klein, David G Birch; Test-retest variability on the Medmont dark-adapted chromatic (DAC) perimeter in controls and patients with inherited retinal disease (IRD). Invest. Ophthalmol. Vis. Sci. 2018;59(9):4046.
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© ARVO (1962-2015); The Authors (2016-present)
The retina contains approximately 120 million rods compared to 6 million cones, yet the clinical assessment of vision typically measures cone function. Using a novel perimeter (DAC, Medmont International Pty Ltd; Victoria, Australia), we have shown that rod function can be identified and quantified in normal controls and in patients with IRD. Here we report on the reliability of the DAC perimeter among controls and patients with IRD to determine whether DAC perimetry can be used for evaluating disease progression and as an outcome measure in clinical trials.
Two DAC exams were performed on the same day on 25 perimetry-familiar patients (ages 10-73 years) with IRD and 21 controls (ages 12-72 years). One eye was dilated and dark-adapted for 30-45 minutes. Sensitivity to a 505nm stimulus (spot size V) was tested at 103 points extending 72° temporal, 60° nasal, 36° superior, and 42° inferior with a DAC perimeter. Breaks were provided between tests as needed. Test-retest variability was analyzed for mean sensitivity (MS), central MS (CMS; 0-11°), mid-periphery MS (MPMS; 12-35°), and far periphery MS (FPMS; 36-72°) by calculating the coefficient of repeatability (CoR) and the upper and lower limits of agreement (LoA) using Bland Altman analysis.
Control MS and MPMS were 0.6dB higher for the 2nd test (p<0.01). No other between-test differences were significant for either group (Table 1). Age and eccentricity of test location were associated with the control’s sensitivity to the stimulus (p<0.005). Regression analysis showed that MS decreased by 0.3±0.1dB per decade (r=-0.6, p=0.007). CoR and LoA are shown in the table.
An increase in sensitivity for the 2nd DAC exam (control MS and MPMS) indicates a bias that should be considered when assessing baseline rod function. Overall, the CoRs were similar to other perimetry studies using different instruments for testing. The DAC is a reliable instrument to quantify scotopic vision in patients with IRD, which will be important for evaluating change over time in the course of disease or in clinical trials.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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