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C. F. Carle, T. L. Maddess, M. Kolic, R. W. Essex, A. C. James; Hemifield Asymmetry in Direct and Consensual Pupil Responses to Multifocal Pupil Stimuli. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3051.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate topographic variation in contraction amplitudes of direct and consensual pupil responses to multifocal stimuli.
Pupillary contraction amplitudes were analysed from five studies undertaken over 15 months in which 120 normal subjects (mean age 54.0±13.7 years) were tested with differing subsets of 26 stimulus protocols. All stimuli were dichoptically presented and responses of both pupils were recorded concurrently. The multifocal stimulus arrays subtended ±30° of visual field and varied in: the number of stimulus regions (24, 40, 44 or 60), mean regional presentation interval (0.25, 0.5, 1, 4 or 16 s), and pulse time-course (33 to 150 ms flickered or steady). Luminance of the test-regions was 290 cd/m2 on a 10 cd/m2 background. For each protocol, the ratios between direct and consensual responses were calculated for each region and linear regression performed.
Independent of regional differences in sensitivity, direct responses within temporal hemifields were significantly larger than consensual in all stimulus protocols. Across the 26 protocols these differences ranged in magnitude between 9.2% (b = 0.38 dB, t (1496) = 2.46, p <.02) and 34.0% (b = 1.27 dB, t (1528) = 4.44, p <.00001). Whilst direct/consensual ratios differed between temporal and nasal regions they were reasonably uniform within each hemifield. This distribution did not directly relate to the pattern of regional sensitivity observed in response amplitudes which is believed to be due to variation in photoreceptor and ganglion cell density. The magnitude of temporal differences for each protocol was somewhat correlated with the mean size of pupil contractions for the particular protocols but more strongly with the mean baseline pupil diameter (r2 = 0.4268).
Stimulating the nasal retina produces larger direct than consensual responses in a pattern that does not correlate with that of afferent retinal sensitivity. The combination of uneven distribution of signals in efferent pupillary pathways accompanied by efferent response saturation is a possible cause.
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