Certified Ophthalmic Medical Technologist (COMT) Practice Exam

Fusional divergence is measured using which type of prisms?

1. BO (base out)

2. BI (base in)

3. Vertical prisms

4. None of the above

The correct answer is: BI (base in)

Fusional divergence is the ability of the eyes to turn outward in response to visual stimuli, such as the distance between objects. This ability is typically assessed in clinical settings to evaluate a patient's overall binocular vision and their capacity to maintain single vision during activities that require divergent gaze. Base-in prisms are used in this measurement because they simulate the convergence of the eyes. When base-in prisms are introduced, the patient needs to diverge their eyes to compensate for the induced convergence, which allows the clinician to measure the maximum amount of divergence that can be achieved before double vision (diplopia) occurs. This assessment is crucial in identifying any discrepancies in the patient's binocular vision capabilities and determining potential treatment strategies, such as prisms or vision therapy. By using base-out prisms, one would be measuring fusional convergence instead. Vertical prisms, on the other hand, would address misalignment on the vertical plane and would not provide the information needed for assessing fusional divergence specifically. Hence, base-in prisms are the correct choice for evaluating this specific aspect of binocular vision.