What is an A-Scan primarily used to measure?

An A-Scan is primarily used to measure the length of the eye, specifically the axial length, which is critical for calculating the appropriate intraocular lens (IOL) power needed for cataract surgery. By accurately determining the length of the eye, ophthalmologists can select an IOL that helps achieve the desired refractive outcome, ultimately improving the patient's vision.

This measurement is essential because the axial length directly impacts how light is focused on the retina. Without an accurate A-Scan measurement, there is a risk of postoperative refractive errors, leading to suboptimal visual results. The other options, while important in ophthalmology, relate to different aspects of eye health and diagnostics and are not the primary function of an A-Scan.