Evaluation of two nighttime mobility devices
for people with night blindness
Rickilyn M. Mancil, MA, COMS, CLVT1;
Gary L. Mancil, OD1, Ellis L. King DEng, PE2, Bruce B. Blasch, PhD3,
Claudine Legault, PhD4
1Salisbury
VA Medical Center; 2University of North Carolina at Charlotte; 3Atlanta
VA Rehab Research & Development Center; 4Wake Forest School of Medicine’s Department of
Biostatistics
Objectives: In this two-year project investigators
are comparing the effectiveness of the ITT Night Vision Viewer (ITT) to
the Wide Angle Mobility Lamp (WAML) as a low vision mobility device used
by veterans with night blindness [e.g., retinitis pigmentosa (RP)]. The
goals of this proposal are to: (1) evaluate the ITT Generation 3 and WAML
devices in regard to mechanical and human factors properties, (2) assess
effectiveness as a low vision mobility device to improve mobility of visually
impaired veterans with night blindness, and (3) compare effectiveness
as a low vision night mobility device with each other. The estimated 100,000
Americans affected with RP have a primary complaint of night blindness
which effects their independence. Over 100 veterans are treated annually
at VA Blind Rehab Centers and that number is further increased by local
eye clinics and VICTORS programs. As veterans continue to be prescribed
nighttime mobility devices to increase independence, objective information
regarding these devices is imperative.
Methods: Engineering
evaluation: (1) characteristics of the ITT and the WAML were recorded
in the laboratory and compared to the published specifications including
weight, light amplification, light output, battery life, etc; (2) the
devices were evaluated on how well each was suited for human use; and
(3) suggested improvements were developed that did not involve changing
the devices themselves. Rehabilitation evaluation: (1) subject selection, (2) evaluation in
a clinical setting completed under four conditions (standard day lighting
with habitual visual condition, dim lighting with habitual visual condition,
dim lighting with the WAML and with the ITT, all randomized), (3) evaluation
of function in a standardized, indoor light lab under the same four conditions,
(4) evaluation of function in a real, dynamic outdoor setting under nighttime
conditions, measuring habitual travel abilities and travel abilities with
the WAML and ITT, as well as real, nighttime abilities to read signage
with each of the three nighttime conditions, and (5) completion of surveys
for qualitative data collection.
Preliminary results: Approximately 60% of
the participants have completed testing. Trends in the clinical data collected
to date indicate that both visual fields and contrast sensitivity are
improved during nighttime conditions when using either device, though
performance with the WAML more closely approximates habitual daytime vision.
There is a loss of visual acuity with the ITT. Dark adaptation level has
been immeasurable for almost half the subjects. Subjects report improved
travel with both devices at night and greater improvement with the WAML
than the ITT. Subjects report that the head gear of the ITT is uncomfortable
and heavy and many prefer a binocular system due to problems judging distances.
Many report a decrease in contrast with the ITT. While the WAML tends
to be preferred, subjects are concerned about the effect of its bright
light on oncoming drivers.
Conclusions: Preliminary data suggests subjects
prefer and perform best with the WAML as compared to the ITT Night Vision
Viewer. Cost differences in these devices ($165 for the WAML and $3000
for the ITT) are significant. This objective evaluation of these devices
will show potential for increased independence, document pros and cons
of each device and provide important cost considerations for the VA.
Funding acknowledgment: Funded by the VA’s
Rehabilitation Research & Development Service Merit Review Program;
Mindy Aisen, MD, Director; Project Number C2244R. Project Dates 8/15/00
– 8/14/02.