Certified Ophthalmic Medical Technologist (COMT) Practice Exam

If a patient with simple hyperopic astigmatism requires +0.75 D of cylindrical power at axis 90, where should a +1.50 D cylindrical lens be set?

1. At axis 0

2. At axis 90

3. At axis 45 or 135

4. At axis 180

The correct answer is: At axis 45 or 135

In the case of simple hyperopic astigmatism, the eye has two different powers along two perpendicular meridians, with the condition resulting in blurred vision. When correcting hyperopic astigmatism, the cylindrical lens is used to enhance vision by addressing the difference in power between these meridians. When a patient requires +0.75 D of cylindrical power at axis 90, it indicates that this axis is aligned with the patient's steep meridian where the refractive error is greatest. To add +1.50 D cylindrical power, the new cylindrical lens needs to be positioned in a way that it can provide the correct cylindrical power along the axes. Setting the +1.50 D lens at axis 45 or 135 effectively introduces the necessary cylindrical power that contributes to the overall correction prescribed. This orientation takes advantage of the fact that placing a cylindrical lens at 45 degrees (which is perpendicular to the 90-degree axis of the existing prescription) will provide the additional power needed to address the astigmatic component more efficiently. Thus, positioning the lens at either of these axes allows it to work in harmony with the existing prescription to optimize visual clarity for the patient. By setting the cylindrical lens in this manner, we ensure that the