![pupil size pupil size](https://blogs.bcm.edu/wp-content/uploads/2014/11/mouse-eye.png)
The subject wore the various sizes in counterbalanced order during the session.
![pupil size pupil size](https://m2.healio.com/~/media/journals/jrs/2006/11_november/10_3928_1081_597x_20061102_04/10_3928_1081597x_20061102_04_fig3.jpg)
Although the pupil diameter varied by a factor of nearly four, the extent of the visual field was only about 4° larger through the largest pupil than through the smallest in a total field of 30°. In an attempt to check on this point, I measured the visual angle of the field visible through the various pupils. If they are adequately close to the eyes, then the change in diameter will have little effect on the visual angle of the field seen by the subject. If the artificial pupils are too far from the eyes, they will act more as a field stop than a pupil.
Pupil size trial#
6, 3.2, 4.0, and 6.0 mm diam.) cut in black aluminum disks and worn in precision trial frames, as close to the cornea as possible. The subject sat with his head in a chin rest and viewed the apparatus through artificial pupils (1. Quency-of-seeing curve (percentage of "farther" judgments versus the absolute difference in distances of the test and reference rods) on cumulative probability paper and read the standard deviation of the equidistance setting from the plot. Thus a threshold determination was based on from 25 to 50 judgments, depending on the subject's consistency. I presented each setting an equal number of times (at least five and as many as ten times). Typically, the settings were 4.5 sec arc apart, but I also used separations of 2.25 and 9 sec arc for subjects who were more or less sensitive. There were five to seven settings, equally separated, during each determination, depending on the subject's initial performance. I set the middle rod at various positions r a n domly and asked the subject to report whether each s e t ting was closer or farther than the two outer r o d s. I then measured the localization e r r o r of the equidistant setting by the method of constant stimuli. F i r s t I determined the settings of the middle rod which the subject reported as either farther from him or n e a r e r to him than the outer rods about 90% of the time.
![pupil size pupil size](https://sm.mashable.com/mashable_sea/photo/default/photo-1566842833650-d8c386c25d22_ja8j.jpg)
The specific measure of stereoacuity was the variability of the setting which the subject made when he judged the middle rod to be the same distance from him as the two outer rods. The two outer rods were fixed in position 6 m from the subject in a line parallel to the aperture, which was 5.75 m from the subject. The subject saw the middle portion of three vertical, black rods (1.57 cm thick and 7.6 cm apart) through an aperture 1.2° high by 3. I measured stereoacuity with a three-rod HowardDolman apparatus. 1 3 Since stereoacuity is often related to visual acuity Copyright © 1976 by the Optical Society of AmericaĪnd depends on those factors which affect visual acuity, 1 4 the question a r i s e s as to how changes in pupil size affect stereoacuity. 11, 12 Consequently, it has been suggested that the main result of the changes in pupil size is not the control of the amount of light entering the eye but the p r o duction of the optimal depth of focus and the maximization of visual acuity. The poor acuity with small pupil diameters is due to diffraction, and the decline in acuity with a pupil diameter of more than 5 mm is thought to be caused by spherical a b e r r a tions. 2, February 1976īowitz 11 have shown that as pupil size increases, visual acuity typically improves up to a point and then d e clines as pupil diameter further i n c r e a s e s. 9 One comparison that does not appear to have been made is the effect of pupil size. The introduction of apertures or lenses between the observer and the test object, for example, has a different effect on the two p r o c e s s e s. 8 But not all variables affect them similarly. Stereoacuity and visual acuity a r e affected similarly by a wide variety of variables, such as luminance, 1 wavelength, 2 contrast, 3 retinal locus, 4 target movement, 5 ocular pursuit of a moving test object, 6 and observation distance 7 -the latter has been shown in both cases to be artif actual.
![pupil size pupil size](https://i.pinimg.com/originals/37/ba/9a/37ba9a1fc9ed4193b78ec5703754cf73.png)
Luria Naval Submarine Medical Research Laboratory, Groton, Connecticut 06340 (Received 7 June 1975)