A 5 year-old boy is esotropic as shown below.
Orthoptic assessment reveals an esotropia of 60 D with a visual acuity of 6/6 in the right eye and 6/24 in the left. The AC/ A ratio is 7.

Cylcoplegic refraction gives the following results:

Right eye + 2.00 DS
Left eye + 8.00 DS

Interpupillary distance with distant fixation.

Interpupillary distance with cover test and distant fixation.

a. What will happen to the esotropia when he wears the 
     glasses?

b. What is the interpupillary distance (in mm) for the 
     glasses?

 

Answer to a
A significant reduction of esotropia.
As the AC/A ratio is 7 and the refractive error
is 8 prism dioptre for the left esotropic eye. 
Wearing the glasses will reduce the esotropia by 7 x 8 = 56 prism dioptre. 
The residual esotropia will be 60 - 56 = 4 prism dioptre esotropia.

 

Answer to b
About 50 mm. 
The interpupillary distance for a patient with
accommodative esotropia should be taken with
both eyes in fixation. In this case, the cover test 
shows the interpupillary distance to be about 50mm.
Without the cover test, the interpupillary distance is about 45 mm.
 

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