Variations of the normal blind spot with special reference to the formation of a diagnostic scale. I. The form blind spot. II. The color blind spot
Wentworth, H.A.
American Journal of Ophthalmol 14(9-11): 889-904, 1118-1131
1931
Document Number: 689548
Blind spots of 200 normal eyes were mapped under conditions standardized as to illumination, size and color of test object, light adaptation, background and method of mapping. With test objects of white and of blue, red and green of the Heidelberg series of pigment papers, subtending a visual angle of 1° (degree) at a distance of 33 cm. from the eye, the areas obtained on a black background under 7 ft.-c. illumination varied from 6.8 sq. cm. to 17.5 sq. cm. for form (white); from 7.6 sq. cm. to 25.8 sq. cm. for blue; from 9.1 sq. cm. to 29.6 sq. cm. for red; and from 11.4 sq. cm. to 43.6 sq. cm. for green stimuli. The average values were 11.4 sq. cm., 15.11 sq. cm. 17.99 sq. cm. and 22.58 sq. cm. respectively. The average area of the blind spot for colored stimuli in the order named showed an increase of 33%, 58% and 98% over the average size for form stimuli. The average size increased somewhat with age. Also a skewing of the distribution curve, toward the larger values was found with age. The distribution curve rather than the average size is of most significance as a standard for diagnostic comparison. The longest axis of the blind spot was strictly vertical in only 10 percent of cases. The amount of deviation from the vertical averaged 6°. It seldom exceeded 15°. The distance of the center of the blind spot from the point of fixation varied from 12.56° to 18.74°, with an average value of 16.17°. The linear measurements of the blind spot were as follows: (1) Length: (form) range 6.15-9.59°, average 7.75°; (blue) range 6.6-13.0°, average 8.75°; (red) range 7.3-12.9°, average 9.63°; (green) range 7.8-14.9°, average 10.88°. (2) Breadth, maximum: (form) range 4.16-7.32°, average 5.49°; (blue) range 4.5-9.3°, average 6.26°; (red) range 5.0-9.8° average 6.98°; (green) range 5.3-12.2°, average 7.75°. The average blind spot extended 2.39° above the horizontal meridian of the field-5.56° below.