Veterans with cataracts: visual disability in nighttime driving
Gary L. Mancil, OD1, Johnny R. Graham, PhD, PE,2 Rickilyn M. Mancil, MA, COMS, CLTV1, Ellis L. King, D.Eng, PE 2, Justin Carroll 2
 
1Salisbury VA Medical Center; 2University of North Carolina at Charlotte
Objectives: The purpose of this one-year pilot project was to gain a better understanding of the degree of functional impairment experienced veterans with varying degrees of cataract in reading highway signs under nighttime driving conditions involving glare. Additionally, this project considered the role of highway sign design modification in reducing visual disability.
Methods: Twenty-five drivers age 52 to 75 were enrolled and assigned to four groups: 1) Non-Visually Significant Cataracts (20/20-20/30); 2. Visually Significant Cataracts (20/40-20/100); 3. Pseudophakia (i.e., post cataract surgery with implants); and 4. Controls. There were five subjects in each group except for those without cataracts, in which there were ten. Clinical test protocols were completed to collect visual psychophysical data on high contrast visual acuity (EDTRS), peak contrast (Peli-Robson), low luminance visual acuity (SKILL), glare disability with high and low contrast acuity charts (Berkley), glare recovery, and visual fields (arc perimetry). Survey data was obtained using Driving Habits Questionnaire as well as selected items from the Activities of Daily Vision scale and the VFQ-25. A Field Experiment provided subjective evaluation of roadway signs under nighttime driving conditions. While seated in a stationary vehicle, subjects evaluated seven roadway signs with different retroreflectivity values and numerical legends placed on a length of simulated rural highway at nighttime under controlled luminance conditions.
 
Results: In this pilot project, the limited number of subjects per cell did not allow for meaningful descriptive analysis or statistical associations. However, trends from the survey results indicated that drivers without cataracts were more likely to drive themselves whereas those with cataracts shared driving "about equally" when someone else was in the car. Subjects with visually significant cataracts reported driving slower, having more difficulty making left turns, limiting their driving area, having difficulty on high traffic roads, and having more difficulty driving at night. The Field Experiment results showed that as the visual acuity of both eyes decreased, the ability to correctly identify roadway signs also decreased and that subjects with cataracts tend to correctly identify fewer signs. Subjects with visually significant cataracts and with early cataracts identified fewer signs correctly at all luminance levels with and without glare present. Reducing the viewing distance (i.e., decreasing resolution demand) improved performance somewhat. Performance also improved when luminance level of the highway sign increased. Paradoxically, glare improved performance of some subjects. Control subjects with no cataracts and pseudophakic subjects showed little difference in performance in reading highway signs.
 
Conclusions: Insufficient statistical power is provided in this pilot study. Based on the trends observed, the presence of cataracts in older veterans impairs ability to read highway signs at nighttime. This disability is increased under low luminance levels. Larger sized lettering used on highway signs may mediate this disability. Preliminary data suggests that surgical removal of cataracts with intra ocular lens implants (i.e., pseudophakia), improves performance to levels similar to older subjects without cataracts.
 
Funding acknowledgment: This study was funded by the VA Rehabilitation Research and Development Service, project #C2138PC.