Certified Ophthalmic Medical Technologist (COMT) Practice Exam

When neutralizing -2.00 +1.00 X 85 in plus cylinder, where will the thin mires focus?

1. -1.00

2. -2.00

3. +1.00

4. 0.00

The correct answer is: -2.00

In plus cylinder notation, the values refer to the power of the lens in different meridians. When you have a prescription such as -2.00 +1.00 x 85, it means that there is a base power of -2.00 diopters with an additional 1.00 diopter of plus power at an axis of 85 degrees. To determine where the thin mires will focus when neutralizing the prescription, you consider the net effect of combining the two powers. The starting point of -2.00 diopters represents a myopic condition, and when you add +1.00 diopter to it, the overall focal point decreases in myopia, resulting in a focus that approaches a less negative value. This results in a net power of -1.00 diopters at the specific meridian designated by the plus cylinder. However, when evaluating where the thin mires focus, the focus will align at the power that directly neutralizes the net effect of the entire lens system. Since the overall prescription includes a -2.00 diopter base with a supplementary +1.00 adjustment, the mires indicate where the -2.00 power predominates, especially if the testing setup is in relation to