What does the Snellen Chart primarily test?

The Snellen Chart is primarily used to assess visual acuity, which is the clarity or sharpness of vision. This chart features letters of different sizes arranged in rows, where a person is asked to read the smallest letters they can see at a standard distance, usually 20 feet. The results provide a numerical measurement, commonly expressed as a fraction (e.g., 20/20), indicating how well a person can see compared to a typical individual at that distance.

When a person has 20/20 vision, it means they can see at 20 feet what a person with normal vision can also see at that distance. Lower visual acuity measurements such as 20/40 suggest that the person sees at 20 feet what a person with normal vision sees at 40 feet, indicating compromised vision.

This measurement is distinct from other visual tests such as those for color perception, which evaluate a person's ability to distinguish colors; intraocular pressure assessments, which measure the fluid pressure inside the eye and are crucial for diagnosing conditions like glaucoma; and tests for peripheral vision, which examine the ability to see objects outside of one’s direct line of sight. Each of these tests evaluates different aspects of vision and eye health, highlighting the specialized role of