The ratio of the optic disc diameter to the distance between the optic disc and macula correlates with visual acuity in a patient with optic nerve hypoplasia.
Visual acuity groups (Borchert et al):
(1) light perception only
(2) 20/200
(3) better than 20/200
Calculation of the disc-macula distance and disc diameter (Figure 4, page 175, Marsh-Tootle and Alexander; Figure 4, page 1042, Dutton):
(1) Measurement is performed on photographs of the optic fundus.
(2) The vertical and horizontal diameter of the optic disc are measured.
(3) The average disc diameter is the average of the vertical and horizontal disc diameter. This takes into account that the disc may be asymmetrical.
(4) The disc-macula distance is the horizontal distance from the center of the disc to the center of the macula.
ratio of the horizontal disc diameter to disc-macula distance (Borchert et al) =
= (horizontal disc diameter in mm) / (disc to macula distance in mm)
ratio of disc-macula distance to average disc diameter (Marsh-Tootle, Zeki) =
= (disc to macula distance in mm) / (average disc diameter)
|
Ratio DD to DM
|
Visual Acuity
|
|
<= 0.15
|
light perception only
|
|
0.16 to 0.30
|
20/200
|
|
> 0.30
|
better than 20/200
|
For Marsh-Toole and Alexander (1994), Zeki (1991) and Dutton (2004) optic nerve hypoplasia was suspected with a DM-to-DD ratio > 3.0 and very likely if > 4.0.
