Certified Ophthalmic Medical Technologist (COMT) Practice Exam

What phenomenon is involved when a patient with acute left esotropia shows movement in the opposite eye during prism alternate cover testing?

1. Convergence insufficiency

2. Primary/secondary deviation

3. Suppression

4. Heterotropia

The correct answer is: Primary/secondary deviation

The phenomenon involved in this scenario is best understood through the concepts of primary and secondary deviation. In the case of acute left esotropia, the left eye is turned inward, and when performing a prism alternate cover test, the movement in the opposite eye (the right eye) during the test indicates that there may be a difference in muscle function or neural control between the two eyes. Primary deviation refers to the deviation that occurs when the non-fixating eye (the left eye, in this case) is tested while the fixing eye (the right eye) is covered. Secondary deviation occurs when the fixing eye is covered, and the amount of deviation can be greater than the primary deviation due to the increased effort required by the muscles of the fixing eye, in this case, the right eye. This increased effort can sometimes lead to compensatory movements of the right eye. Therefore, the presence of movement in the opposite eye during the test illustrates the difference between how each eye is functioning in response to the coverage and the misalignment, making this concept crucial for understanding their behaviors in the presence of strabismus.