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H.J. Wyatt, Y. Chen, W.H. Swanson; A New Pupil–based Approach To Glaucoma Testing: Design and Initial Testing . Invest. Ophthalmol. Vis. Sci. 2004;45(13):237.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Assessing visual field damage is essential to treating patients with glaucoma. Standard perimetry tests many locations with small stimuli, and is slow, demanding, and variable. In contrast, the pupillary light reflex (PLR) summates over large areas of the visual field. We have devised a pupil–based approach to rapid assessment of functional status, using just a few large stimuli. Methods:We developed stimuli based on patterns of glaucomatous loss, to maximize the correlation between stimulus area and probable damage. The test compares areas symmetric about the horizontal meridian, to exploit superior/inferior asymmetry typically found in glaucomatous damage. Three stimuli in the upper hemifield, together with their reflections about the horizontal meridian, cover much of the most vulnerable part of central visual field (20 deg nasal to 10 deg temporal; ± 10 deg vert); each stimulus captures an area of likely glaucomatous loss. To minimize variability, we developed a "subtractive" test, using an internal comparison. During a test, one stimulus and its reflection (presented on a computer monitor) are alternately turned on, for 1 sec each, in the visual field of the same eye. For the lower stimulus, the "on" luminance is fixed; for the upper stimulus, it cycles through 3 values. Luminance of a stimulus when "off" ≈ 0.001 cd/m^2; outside the stimuli, background = 5 cd/m^2. A complete cycle of 6 presentations lasts 6 sec; 3 cycles are averaged. Each stimulus onset elicits a pupil contraction, for which response amplitude R is determined. Treating the 6 presentations as 3 pairs, a response balance (RBal) is calculated for each pair; RBal = [R(upper) – R(lower)]/[R(upper) + R(lower)]; –1 < RBal < +1. The 3 RBal values from one test are fitted with a sigmoid function, which gives an estimate of "contrast balance"—the lower/upper contrast ratio for equal pupil responses. We tested 11 young normal subjects, using an infrared pupillometer to measure the PLR. Results: For all subjects and stimulus types, we were able to determine RBal, fit sigmoid functions, and estimate contrast balances. For all data pooled, contrast balance did not differ significantly from unity; however, individual subjects showed balances favoring lower or upper retina by up to 1.5 dB. Within–session variability was 0.5–1.0 dB; between–session variability was 0.2–0.6 dB. Conclusions: Our pupil–based technique provides rapid functional assessment of central visual field. Measurement of response balance yielded low variability in a normal population. The technique is suitable for further studies of patients with glaucoma and age–matched normal subjects.
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