In a 4 BO prism test with the prism placed over the right eye, if the left eye moves outward and then re-fixates, this is considered which of the following?

In a 4 BO prism test with the prism placed over the right eye, if the left eye moves outward and then re-fixates, this is considered which of the following?

• A. Normal finding
• B. OD suppression
• C. OS suppression
• D. Diplopia

Answer: (A)

This test measures fusional vergence and how the eyes maintain single vision when one eye’s image is shifted by a prism. Placing a base-out prism over the right eye temporarily displaces that eye’s image outward, so the brain must adjust to keep the two eyes aligned. A brief outward drift of the other eye followed by quick re-fixation shows that the vergence system can re-establish alignment and fuse the images, which is a normal, healthy response. There isn’t lingering diplopia or a persistent suppression pattern, so this transient disconjugate movement is consistent with normal binocular function. If there were true suppression or persistent diplopia, the eye movements or perception wouldn’t normalize with re-fixation in this way.

This test measures fusional vergence and how the eyes maintain single vision when one eye’s image is shifted by a prism. Placing a base-out prism over the right eye temporarily displaces that eye’s image outward, so the brain must adjust to keep the two eyes aligned. A brief outward drift of the other eye followed by quick re-fixation shows that the vergence system can re-establish alignment and fuse the images, which is a normal, healthy response. There isn’t lingering diplopia or a persistent suppression pattern, so this transient disconjugate movement is consistent with normal binocular function. If there were true suppression or persistent diplopia, the eye movements or perception wouldn’t normalize with re-fixation in this way.