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Lindsay Rountree, Padraig Joseph Mulholland, Roger S Anderson, James E Morgan, David Garway-Heath, Tony Redmond; Quantifying the signal/noise ratio with perimetric stimuli optimised to probe changing spatial summation in glaucoma. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2852.
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© ARVO (1962-2015); The Authors (2016-present)
Guided by changes in spatial summation in glaucoma, we undertook a cross-sectional prospective study to compare disease signal, response variability, and signal/noise ratio (SNR) between perimetric stimuli varying in area, contrast, and both simultaneously, in patients with glaucoma and age-similar healthy controls.
Participants were 30 glaucoma patients (median [interquartile range] age: 70.4 years [66.2, 73.5], MD: -4.04dB [-9.65, -2.85]) and 20 controls (age: 69.3 years [66.1, 77.8], MD +0.38dB [-0.36, +0.91]). Using a 3-stage approach (1: staircase procedure; 2: short Method of Constant Stimuli (MOCS, 180 presentations); 3: extended MOCS (640 presentations)), threshold (50% seen) and response variability (slope) were measured for 200ms achromatic spot stimuli, presented at 4 diagonal locations (9.9° from fixation). Stimuli were: A - fixed contrast (ΔI: 0.5, starting within Ricco’s area), varying in area; C1 - fixed area (0.02deg2, within Ricco’s area), varying in contrast; AC - varying in both area and contrast simultaneously (starting within Ricco’s area); C2 - fixed area (0.15deg2), equivalent to Goldmann III, varying in contrast. Stimuli were defined by a common scale (energy: luminance x area x duration). Step size and visibility were equated across all stimulus forms. Total deviation (TD, calculated from healthy subjects for each stimulus form), slope, and SNR (TD/slope) were compared between stimuli per hemifield in three TD strata (upper, middle, lower, according to TD for the C2 stimulus).
Overall, the greatest disease signal was found with A and AC stimuli (Fig.1A). Response variability was least dependent on depth of defect with the A stimulus, and most for the C2 stimulus (Fig.1B). The SNR was greatest for the A stimulus, and the difference from that for the C2 stimulus was statistically significant in the superior hemifield in the middle (p=0.04) and lower (p=0.049) strata (Fig.2).
Area-modulated stimuli likely offer benefits for measuring glaucomatous changes in spatial summation, in the form of greater disease signal and least dependence on depth of defect than conventional fixed-area, contrast-modulated stimuli.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
(A) TD for each stimulus form as a function of C2 TD; (B) Response variability as a function of stimulus-specific TD; superior hemifield.
SNR across three TD (C2) strata in superior and inferior hemifields
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