Calculating Impairment of Visual Field (Average Concentric Contraction)
Above is an example of a completed visual field test:
NOTE:
The results have been simplified, as ultimately the curvature of the ring is NOT IMPORTANT. What is IMPORTANT are the points at which the ring crosses the eight lines.
Now lets try and calculate things. Looking at the chart, note each of the eight lines and the points at which the vision 'ring' touches each of the directional lines.
Left Eye
| Direction | Point of Intersection (°) |
|---|---|
| Temporally | 30 |
| Down temporally | 30 |
| Down | 20 |
| Down nasally | 20 |
| Nasally | 20 |
| Up nasally | 20 |
| Up | 20 |
| Up temporally | 20 |
Now we add everything up 30 + 30 + 20 + 20 + 20 + 20 + 20 + 20 = 180.
Great! Now we need to get the average impairment so, divide 180 by 8.
180/8 = 22.5
Our Veteran here has an average concentric contraction of 22.5° for their left eye.
Right Eye
| Direction | Point of Intersection (°) |
|---|---|
| Temporally | 85 |
| Down temporally | 80 |
| Down | 60 |
| Down nasally | 5 |
| Nasally | 60 |
| Up nasally | 55 |
| Up | 45 |
| Up temporally | 60 |
You should have gotten an average concentric contraction of 62.5°.
Technically, their right eye has no impairment as it has the a total field of vision of 500°. But I hope it reinforced the concept for you in any event.
Now onto the ratings!
Plugging the average impairments into the Visual Field Rating Schedule would have given you an evaluation of 10% for the left eye and no rating for the right eye.