Refractive strength of human eye is monitored by optometer that automatically and continuously images infrared test pattern onto the retina. Condition of focus of the eye at any instant is determined from optometer settings needed to maintain focus of the pattern on the retina

Cornsweet, T. N.

Crane, H. D.

English

NASA Technical Reports Server

November 1970	 CORRECTED COPY	 Brief 70-10401 
NASA TECH BRIEF 
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. 
Automatic Optometer Operates with Infrared Test Pattern 
The problem: 
To monitor the refractive strength of the human 
eye in order to study accommodation characteristics 
such as speed of response to changing views and 
maximum focusing power.
strength of the eye lens may be changing continually. 
Light reflected from the retina passes through the 
half-field stopS 2 and the corneal-reflection stop to 
the photodetector; the photodetector signal contains 
160 Hz component if the input image pattern is not in 
Visual 
Path
Dichroic 
Mirror
-Is. 
112
Bea  
Splitter
Eye
Isi 
'L3 1S2
Loudspeaker	 j Fiber Optic Bundle
Light 
Source
160 cps 
Photo-
Sensitive 
Detector
Corneal Stop' I
Integrator 
Photodetector 
jLJ 
J--- .Ipp_ -------------
VL4
The solution: 
An optometer that automatically and continuously 
images an infrared test pattern onto the retina; the 
condition of focus of the eye at any instant is deter-
mined from the optometer settings needed to maintain 
focus of the pattern on the retina. 
How it's done: 
Infrared light passing through a fiber optic bundle 
vibrating at about 160 Hz transverse to the image slit 
S 1 forms a bar pattern which is maintained at focus on 
the retina by servocontrol, even though the refractive
focus on the retina. The photodetector signal is 
directed to a phase-sensitive detector which furnishes 
to the servodriver a dc signal of the polarity and 
magnitude required to cause the servomotor to move 
the bar image at S 1 until there is a zero signal from the 
detector. The servomotor also controls the axial 
position of stopS2 through a mechanical linkage, 
maintaining it in the retinal image plane despite 
changes in the refractive strength of the eye. The 
integrator makes possible a zero position-error system. 
The time between the onset of a visual target dis- 
placement and the beginning of the resultant change 
(continued overleaf, 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights. 
https://ntrs.nasa.gov/search.jsp?R=19700000387 2020-03-17T00:47:57+00:00Z
D 
in accommodative strength can be measured by noting 
the time lapse between target displacement and 
initial motion of the servomotor. The rate of change 
of refractive strength of the eye can be measured 
from time plots of servomotor motions. 
Notes: 
1. Accommodation responses of five commercial air-
line pilots under 35 years of age were measured for 
2-diopter displacements of a target. For a target 
moving toward infinity, pilot response times were 
less than 1.5 seconds, but for a target moving to-
ward the subjects, response times varied from less 
than one to more than six seconds. 
2. A related instrument is described in NASA Tech 
Brief 70-10568.
3. Requests for further information may be directed 
to:
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP7040401 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to.NASA, Code 
GP, Washington, D.C. 20546. 
Source: T. N. Cornsweet and H. D. Crane of

Stanford Research Institute

under contract to

Ames Research Center

(ARC-10095)
. 
. 
S. 
Brief 70-10401	 Category 05


Automatic optometer operates with infrared test pattern

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