Surgery for exotropia
(monocular recess/resect)
Amount of exotropia 
(prism dioptres D)
Lateral rectus recession
(mm)
Medial rectus resection
(mm)
15
4
3
20
5
4
25
6
5
30
7
6
40
8
6
50
9
7
60
10
8
70
10
9
80
10
10
X
Note: One common mistake during strabismus surgery is recessing instead of resecting a muscle 
and vice versa. It is recommended that recession should be performed before resection so that if
the mistake were discovered during the course of the opertion, the recessed muscle can still be 
resected.
Main page Success in MRCOphth