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Humza J Tahir, Elena Cerio, Neil RA Parry, Jeremiah MF Kelly, David Carden, Tariq M Aslam, Ian J Murray; Novel dual arc stimulus aids sensitive detection of early AMD. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2617. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The rate of recovery of rod vision following a bleach is emerging as highly clinically significant. It is systematically slowed in the older eye and in many clinical conditions, notably Age-Related Macular Degeneration (AMD). It is not known for certain whether this is a pan-retinal effect or if there are localised regions of impaired rod function. To address this issue a dual arc stimulus was developed that simultaneously samples sensitivity recovery in two retinal locations and we present data for three groups of observers, younger normals (n=13), older normals (n=13) and early AMD patients (AREDS grade 2 or 3, n=47).
Arc-shaped white stimuli were presented on an otherwise black CRT screen at two locations in the inferior visual field. Recovery of sensitivity to the two stimuli was measured concurrently using method of adjustment by alternately presenting them following a localised bleach of at least 80%. Neutral density filters were used to extend the luminance range of the CRT. Data were fitted by non-linear regression to either a seven- or five- parameter model to characterise the dark adaptation curves.
The two stimuli produced similar cone recovery curves within each normal age group. Rod recovery slope, S2, was significantly different between the tested locations for the normal age groups (young 6°=-0.21±0.03, 11°=-0.24±0.03, p=0.02; old, 6°=-0.18±0.05, 11°=-0.20±0.04, p=0.01) but not for the AMD group (6°=-0.10±0.06, 11°=-0.11±0.05, p=0.11). S2 slopes were significantly shallower at both testing locations in the AMD group compared to the age-matched normals (6° p <0.001 and 11° p<0.001). Alpha and beta points were significantly delayed in the AMD group compared to the age-matched normals at both testing locations (α, 6° p=0.035, 11°=0.038 and β, 6° p<0.001, 11° p<0.001). ROC analysis showed testing the extra location enhanced the diagnostic capability of the test in detecting early AMD.
The new technique increases the information yield without placing any additional demands on subjects. Previous findings regarding normal dark adaptation across the life span are confirmed. Additional novel data are revealed by the technique showing that the method has the potential to be of clinical benefit in detecting and monitoring early signs of disease of the outer retina, particularly AMD.
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