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Basic Physiological aspects — objective and measurable properties. 
Blue is a cool colour - here it represents the measurable properties, 
the more or less objective characteristics of the eyes, in short, the 
physiological aspects. 
    
  
Physiological 
UON Aspects 
narrow bases. 
The ANATOMY of the Eye signifies itself most clearly 
for photo-interpretation in the Interpupillary 
Distance (ToD.); the eye-base. This straight forward 
anatomical property is well known, but do designers of 
stereoscopes know the average value and the spread 
among a population? It is 64 * 9 mm, which requires an 
adjustment range of 55 —- 75 mm on the instrument, as 
large values are more likely to be found than the very 
And what is the significance for instruments that white military truck- 
drivers on the average have a 3mm smaller eyebase than their black 
colleagues? (Damon 1966). 
Other ergonomic points are the natural line of sight, and the normal 
viewing distance, 
[some relevant properties in this group: 
Position of the eye's entrance pupil (12 to 15 mm inwards) 
Natural line of Sight (horizontally to 45° downwards) 
Field of view for easy viewing (0.7 rad, somewhat smaller for colour) 
Distribution of Rods and Cones on retina (Rods along the outer edges, 
cones at the central fovea) 
Normal viewing distance (250 to 350 mm, depending on age) 
7. 
- uv. 
Physiological 
Aspects 
The card "INVOLUNTARY EYE MOVEMENTS" emphasizes the perpetual state 
of unrest, which is basic to any feedback system: small 
oscillations around the wanted position, for example 
directional vibrations as Tremor, Drift, Flicks and 
Saccadic eyemovements which occur in connection with 
convergence and fixation. In a similar manner, 
accomodation is maintained continuously, with a 
continual fine adjustment of the eyelens' curvature. 
With the introduction of stereo colour photographs, the old solution 
of flickering lights and a rotating disk in front of the eyes is applied 
again on projection plotters. Now, is it sure that in this case stereos- 
copie measurements are not impaired by ihe involuntary eye movements? 
Signals from both eyes do not arrive simultaneously at the brain, there 
can be à disturbed fusion,