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.