What is the primary purpose of a Snellen eye chart?

The primary purpose of a Snellen eye chart is to measure visual acuity. This type of chart is standardized and typically presents letters or symbols in varying sizes, allowing healthcare professionals to determine the smallest size of letters an individual can read at a standardized distance, usually 20 feet. The results provide a quantitative measure of the clarity or sharpness of vision, commonly expressed as a fraction (for example, 20/20 vision).

By using the Snellen eye chart, practitioners can assess whether a person has normal vision or if there are issues that might require prescription glasses, contact lenses, or further examination by an eye care specialist. The other options pertain to different aspects of vision and visual function but are not the primary focus of the Snellen chart.