American Board of Opticianry (ABO) Practice Test

Which type of lenses can correct an eye that requires a different correction in different meridians?

1. the total power of the lens

2. an eye which requires a different correction in different meridians can be corrected with cylinder lenses

3. the speed of light in air divided by the speed of light in the material

4. a biconvex lens

The correct answer is: an eye which requires a different correction in different meridians can be corrected with cylinder lenses

The reason why cylinder lenses are the correct choice for addressing an eye that requires a different correction in different meridians lies in their inherent design to manage astigmatism. Astigmatism occurs when the eye's cornea is irregularly shaped, resulting in light being focused at multiple points or in different directions, creating blurred vision. Cylinder lenses are specifically designed with different curved surfaces that have different powers: one meridian has a spherical power, while the other is more curved in one direction. This allows for precise correction dependent on the specific orientation of the astigmatism, which enables the lens to effectively target the varying refractive errors across different meridians in the eye. By utilizing cylinder lenses, optometrists can provide a tailored solution for patients whose vision issues cannot be adequately corrected with spherical lenses alone. In contrast, options related to total power calculations, the propagation of light, or biconvex lens types do not directly address the need for differing corrections across meridians.