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A.P. Ginsburg, S. Subraminan; Functionally Significant Loss in Night Driving Visibility Distance Associated With FACT Contrast Sensitivity . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3466.
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Vision loss can result in decreased contrast sensitivity for a wide variety of reasons, such as cataract in the aging population. The question remains as to the functional significance of contrast senstivity loss for safety for a functionally important everyday task as visibility distance when driving at night. The FDA Device Group, ANSI and ISO have recommended sine–wave gratings and test parameters that standardizes contrast sensitivity testing. This study determines a safety relationship with those standards using the FACT contrast sensitivity chart and a loss of night driving visibility distance.
Visibility distance was determined for 29 normal subjects whose age ranged from 23 to 65 years (mean age = 44.9+12.9 years) using a FDA validated night driving simulator (NDS; VSRC, San Ramon, CA). The NDS visibility distances were determined from detection and identification of road signs and a pedestrian hazard during rural (55 mph) and city (35mph) nighttime driving scenes. FACT (Stereo Optical Co, Chicago, IL) linear sine–wave grating contrast sensitivity was also obtained from the same subjects using the CST–1800 view–in contrast sensitivity tester (VSRC, San Ramon, CA) at mesopic (0.3 cd/m2) luminance. Statistically significant correlations to visibility distance were obtained for 3, 6, 12 and 18 cpd, the highest correlation at 6 cpd, in agreement with many other visibility tasks (1). Linear statistical regression was used to estimate equations that significantly predict night visibility distances from the mesopic contrast sensitivity data at 6 cpd. The FDA criteria, classifying functionally significant loss in night driving visibility distance as 25% or greater, was used to determine functionally significant sine–wave grating contrast sensitivity loss using the regression equations.
The regression equations show night driving visibility distances decrease with decreased sine–wave contrast sensitivity, in agreement with other studies (1).
Contrast sensitivity of 1.60 log units (contrast sensitivity of 40) or less for the FACT linear sine–wave grating contrast sensitivity chart at 6 cpd (patch 5 or less at row C) is associated with a 25% or greater loss in night driving visibility distance. These data may be used to establish safety criteria for night driving visibility distance using the FACT contrast sensitivity chart for any contrast related vision loss. 1. Ginsburg AP. Contrast Sensitivity and Functional Vision. (2003) Inter. Ophthal. Clinics, Eds: Packer M, Fine IH, Hoffman RS. Lippincott, Williams and Wilkins, Philadelphia, PA., p 5–15.
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