Certified Ophthalmic Medical Technologist (COMT) Practice Exam

If there are 3D base up (BU) right eye (OD) and 2D base up (BU) left eye (OS), what is the net prismatic effect?

1. 2D BU OD

2. 1D BU OD

3. 3D BU OS

4. 5D base up

The correct answer is: 1D BU OD

To determine the net prismatic effect from the given prisms in each eye, it is essential first to understand how prism diopters relate to each other, especially when they have the same base direction. In this scenario, the right eye has a 3D base up prism, and the left eye has a 2D base up prism. When calculating the net effect, you can add the magnitude of the prisms together since they both direct light upward (BU). 1. For the right eye, the prismatic effect is 3D BU. 2. For the left eye, the prismatic effect is 2D BU. By adding these together: 3D (from the right eye) + 2D (from the left eye) results in a total of 5D base up. This total indicates how much deviation in visual direction results from both prisms. The critical point here is recognizing that while the total effect is 5D BU, the question seeks the net prismatic effect with respect to a specific eye and its orientation. When a net prismatic effect is being labeled as per a single eye's perspective, it often defaults to how much the effect in the right eye translates into an equivalent in the left eye