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Shirin E Hassan; A Binocular Scotoma Causes a Person to Adopt a Safe Street-Crossing Strategy. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1049.
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Age-related macular degeneration (AMD) is the leading cause of blindness in western countries. As the disease progresses, sight debilitating central scotomata typically form. The aims of this study were to determine the effects of AMD on street-crossing decision-making and assess whether the presence of a binocular central scotoma resulted in the least safe crossing decisions.
Street-crossing decisions from 51 AMD subjects (17 subjects with a binocular scotoma and 34 subjects without a binocular scotoma) were compared to those made by 47 age-matched subjects with normal vision (controls). Street-crossing decisions were collected along a non-signalized one-way street for vehicular arrival times that ranged from 0.5 to 20 seconds in duration. Subjects used a 5-point rating scale to indicate whether they could cross the street before the approaching vehicle reached them. Street-crossing accuracy was calculated as the number of seconds that subjects over- or under-estimated the vehicular arrival time relative to their crossing time. Crossing decisions were considered safe, characterized as a positive accuracy score, when subjects under-estimated the vehicular arrival time relative to their crossing time. The converse was true for negative accuracy scores. Two linear mixed models with repeated measures for subject were ran to determine if crossing accuracy changed as a function of subject group; initially comparing AMD versus controls and then repeated to compare the effect of a binocular scotoma (AMD with binocular scotoma versus AMD with no binocular scotoma versus controls).
The AMD subjects on average significantly over-estimated vehicular arrival time (accuracy score = -0.13 seconds) compared to the controls (0.57 seconds, p=0.03). The AMD subjects without a binocular scotoma also on average over-estimated vehicular arrival time (-0.37 seconds) compared to either the controls (0.57 seconds, p=0.03) or the AMD subjects with a binocular scotoma (0.35 seconds, p=0.33). No significant difference in accuracy was found between the AMD subjects with a binocular scotoma and the controls (p=0.95).
Our data suggests that people with AMD with a binocular scotoma compensate for their reduced vision and make safe street-crossing decisions. For those with AMD with only a reduction in central vision but with no binocular scotoma, they have a tendency to make unsafe crossing decisions.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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