Testing device uses closed loop film cassettes to project programmed visual stimuli on screen which the observer views through a lens making the stimuli appear to be at optical infinity. Tester is useful for determining changes in glautomatous visual field sensitivity

Fitzgerald, J. W.

Haines, R. F.

Rositano, S. A.

English

NASA Technical Reports Server

May 1972	 B72-10203 
•	 NASA TECH BRIEF 	 IL 11 
Ames Research Center	 -4r 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Visual Sensitivity Tester 
The problem: 
The equipment ordinarily used for determining the 
available--visual field of the human eye and for locat-
ing retinal blind spots can not provide high quality 
data because they yield results which are not suffi-
ciently accurate and reproducible. Moreover, the 
objective qualities of tests performed with available 
equipment tend to be diluted by human involvement, 
for when the experimenter is required to move the 
visual stimulus over the patient's visual field and 
record the observer's comments, human reaction time 
and judgment play too large a role in the interpreta-
tion and recording of results. 
The solution: 
A visual sensitivity testing device which uses spe-
cially-prepared closed-loop film cassettes toproject 
programmed visual stimuli on a screen which the ob- 
server views through a lens that makes the stimuli 
appear to be at optical infinity. As a stimulus spot 
moves over the visual field, one pen of an X-Y-Y' re-
corder moves correspondingly to provide a permanent 
graphic record of the position of the stimulus. The 
second pen makes a record of when and where the 
observer sees the stimulus disappear and reappear. 
The correspondence or lack of correspondence be-
tween the two pen plots can be used as an indication 
of a particular change in visual function. 
How it's done: 
A commercially available 8-mm screen movie pro- 
jector was modified to include: (1) a photocell array 
to sense stimulus position, (2) an infinity viewing lens, 
(3) a bite-board and forehead support, (4) an eye
centering device, (5) a means for inserting both chro-
matic and neutral density optical filters in front of the 
viewing lens, (6) three visual fixation cross projectors, 
and (7) storage areas for all needed film cassettes 
and spare parts. 
A standard X-Y-Y' two-pen recorder is connected 
to the projector. One of the two pens is activated by 
the photocell array and corresponds to the direction 
of motion and position of a small white spot of light 
(stimulus) as seen on the viewing screen by the ob-
server. The second pen is actuated by a finger button, 
and the kind of vision test being conducted deter-
mines the use of this button. In any event, the second 
pen records when the observer senses or does not 
sense the stimulus. The correspondence or lack of 
correspondence between the two pen plots is used to 
inàicate visual function. 
The position of the observer is standardized prior 
to each test by adjusting the forehead rest and a bite 
plate bearing his dental impression so that he is able 
to see the position of the image of the particular fixa-
tion cross that has been selected for the test as he 
looks through the viewing lens with the eye centering 
plate in its rack. The plate is then removed. 
During the test, the observer keeps the direction of 
his gaze On the fixation cross, and holds the response 
button in readiness to react to the stimulus. The film 
cassettes provide programmed sequences of stimuli 
which consists of a small, white spot of light moving 
slowly across the field of view in various straight 
paths, appearing and disappearing unexpectedly. As 
long as the observer cannot see the stimulus, the but-
ton is to be depressed; it is to be released while he 
sees the stimulus. The electronic control unit inter-
prets stimulus position information furnished by the 
8 photocells, and directs the pens accordingly. The 
(continued overleaf) 
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design of this unit makes it possible to operate the 
response plotter in each of three modes: (1) auto- 
matically from screen images that operate the photo-
cells; (2) manually from the front face ofthe control 
unit; and (3) from an external device such as a digital 
computer. 
A standard two-pen X-Y-Y' recorder, associated 
with an electronic control unit, is connected to the 
projector to plot the stimulus in green ink and the 
response in red ink. Both pens move in parallel as 
they track the movement of the stimulus. However, 
the observer's response switch and the stimulus off/ 
on information cause the pens to drop onto the paper 
independently. The degree to which the observer's 
reactions correspond with the positions and actions 
of the stimulus is a direct measure of the retinal sen-
sitivity in the central visual field, and the X-Y-Y' polar 
plot displays this information unequivocally. 
As the vision tester is currently used, two types of 
tests are given. One determines the observer's visual 
sensitivity within a 300 arc from the fovea, and the 
other maps the size, shape, and location of the blind 
spot. In each case, a polar plot is developed, with 
motion of the pens being directed radially toward or 
away from the origin. To the eye, in the visual sensi-
tivity test, paths of the stimulus are toward or away 
from the fovea. In mapping the blind spot, the stim-
ulus moves into and out of the blind spot. A special 
calibration observation is made in this test to locate 
the fovea on the diagram. The fixation cross provides 
correlation. 
The tests described yield a direct indication of ex-
isting abnormalities in vision; when compiled for one 
subject over a period of time, they are a sensitive 
indicator of changes.
Notes: 
1. Initial impetus for development of the test appara-
tus was the need for daily measurement of the 
visual conditions of men confined for an extended 
time in a space vehicle simulation chamber. 
2. The tester is especially useful for determining 
changes in glautomatous visual field sensitivity be-
cause of the high degree of reproducibility of tests 
performed over long intervals of time. 
3. A wide variety of films can be prepared to provide 
special types of visual stimuli. 
4. The following documentation may be obtained 
from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: 
NASA TN D-6190 (N71-18971), Develop-
ment of an Automated Visual Sensitivity 
Tester. 
5. No additional documentation is available, Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B72-10203 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Mail Code 200-1A 
Ames Research Center 
Moffett Field, California 94035 
Source: Richard F. Haines, James W. FitzGerald, and

Salvador A. Rositano of

Ames Research Center

(ARC-10329) 
B72-10203	 Category 05


Visual sensitivity tester

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