Simulation of
Tunnel Acuity in Infantile Nystagmus Syndrome
L.F.
DellÕOsso, Ph.D.
From the Daroff-DellÕOsso Ocular Motility Laboratory, Louis Stokes Cleveland DVA Medical Center and CASE Medical Center; and the Depts. of Neurology and Biomedical Engineering, Case Western Reserve University, Cleveland OH, USA
OMLAB Report #072020
Written: 07/20/20; Placed on Web Page: 07/20/20; Last Modified: 07/20/20
Downloaded from: OMLAB.ORG
Send questions, comments,
and suggestions to: lfd@case.edu
This
work was supported in part by the Office of Research and Development, Medical
Research Service, Department of Veterans Affairs.
The
main detriment to good visual function in infantile nystagmus syndrome (INS) is
what I refer to as Òtunnel acuity.Ó That is, the limitation of high visual
acuity to a small range of gaze angles (the INS ÒnullÓ) and the sharp
deterioration of acuity as gaze is directed laterally to either side of that
region of peak acuity. The reduction of peak acuity due solely to the INS
waveform and its poor foveation-period quality is usually not severe, so those
patients with a very low peak acuity usually have a significant afferent visual
deficit in addition to their INS.
Figure 1. Photographic simulation of the pre-therapy
effects of a narrow field of high acuity that rapidly falls off as gaze is
directed laterally from it. Post-therapy, targets in lateral gaze are also seen
clearly. T&R, tenotomy and reattachment.
Figure
1 shows the result of foveal tunnel acuity on targets in the visual field. As
it illustrates, lateral targets cannot be seen pre-therapy with the same
clarity as those in the region of peak acuity (here shown in primary position).
Post-therapy the broadened high-acuity range of gaze angles makes face
recognition far easier and faster.
Tunnel Acuity Simulation
The following
exercise is recommended for all
ophthalmologists, optometrists, residents, fellows, and to visual and ocular
motor scientists, students, and post-docs. That is, anyone who sees INS
patients or studies INS; it is also recommended for the parents of a child with
INS who often want to understand Òhow their child sees.Ó Experiencing this
simulation will provide insights into the actual visual function deficits
experienced by those with INS. Perform as many of the exercises as you can.
NOTE: This is a
simulation of the loss of foveal
acuity in lateral gaze; it does not simulate the perceived visual world of an
INS patient. The latter is the same as for non-INS individuals, i.e., a stable
image that appears equally clear across the visual field. In both non-INS and
INS individuals, the brain compensates for the loss of acuity as an image
appears farther lateral to the fovea
1. Place two
vertical strips of translucent tape over each lens of your eye glasses leaving
a ¼Ó gap through which you can view the world with your normal acuity
(this simulates an approximately 10¡ high-acuity tunnel similar to the ÒnullÓ
region in INS. If you wear contacts or do not require refractive correction,
use a pair of full-lens, low-diopter reading glasses.
2. While seated,
read something or use your computer.
3. Walk about in
familiar or unfamiliar surroundings.
4. Try to identify
familiar faces in a crowded room.
5. Play catch using
a soft rubber ball.
6. Track a bird or
car traveling across your visual field.
7. While seated in
the driverÕs seat, simulate the following actions required during driving:
a)
Quickly look at the instrument panel
b)
Quickly look through the windshield at the left and right side of the road
c)
Quickly look through the upper right windshield at am imaginary street sign
d)
Quickly look through your rear, left-side, and right-side mirrors
WARNING: Do not turn
on the engine or attempt to drive.
The difficulties you
experience doing these simple, required real-life tasks should provide you with
a better understanding of the visual function deficits caused by INS, even
if BCVA is normal. More realistic simulations can be accomplished by
placing the gap between the two tapes at 15¡ to the left or right of center
(this will give you a right or left head turn for primary position fixation)
and by using small plus lenses to reduce your peak BCVA.
Although the
information contained in this paper and its downloading are free, please
acknowledge its source by citing the paper as follows:
DellÕOsso,
L.F.: Simulation of Tunnel
Acuity in Infantile Nystagmus Syndrome in Infantile Nystagmus Syndrome. OMLAB Report #072020, 1-3,
2020. http://www.omlab.org/Teaching/teaching.html