§ 4.76a
Computation of average concentric contraction of visual fields.
The extent of contraction of visual field in each eye is determined by recording the extent of the remaining visual fields in each of the eight 45 degree principal meridians. The number of degrees lost is determined at each meridian by subtracting the remaining degrees from the normal visual fields given in table III. The degrees lost are then added together to determine total degrees lost. This is subtracted from 500. The difference represents the total remaining degrees of visual field. The difference divided by eight represents the average contraction for rating purposes.
Table III—Normal Visual Field Extent at 8 Principal Meridians
Meridian
Normal degrees
Temporally
85
Down temporally
85
Down
65
Down nasally
50
Nasally
60
Up nasally
55
Up
45
Up temporally
55
Total
500
EC04NO91.005
Example of computation of concentric contraction under the schedule with abnormal findings taken from Figure 1.
Loss
Degrees
Temporally
55
Down temporally
55
Down
45
Down nasally
30
Nasally
40
Up nasally
35
Up
25
Up temporally
35
Total loss
320
Remaining field 500° minus 320° = 180°. 180° ÷ 8 = 221/2° average concentric contraction.
[43 FR 45352, Oct. 2, 1978]