Snellenruutuja

Snellenruutuja, often translated as Snellen chart or E-chart, is a visual acuity test used by eye care professionals to determine the sharpness of a person's vision. Developed by Dutch ophthalmologist Herman Snellen in the 1860s, the chart consists of rows of letters, numbers, or symbols that progressively decrease in size from top to bottom. The individual being tested is asked to read the smallest line they can clearly distinguish from a standardized distance. This distance is typically 20 feet (or 6 meters) in a well-lit room.

The results of a Snellen chart test are expressed as a fraction, such as 20/20. The top number represents the distance at which the patient is able to read a particular line, while the bottom number indicates the distance at which a person with normal vision could read that same line. For example, a reading of 20/20 means the person can see at 20 feet what a person with normal vision can see at 20 feet. A reading of 20/40 means the person can see at 20 feet what a person with normal vision can see at 40 feet, indicating poorer vision. Conversely, a reading like 20/15 suggests better than average vision.

Variations of the Snellen chart exist for different purposes. The "E" chart, also known as a tumbling E chart, is used for individuals who cannot read or for young children who are unable to identify letters. In this version, only the letter "E" is used, oriented in different directions, and the patient must indicate the direction the "E" is facing. Snellenruutuja remains a fundamental tool in optometry and ophthalmology for assessing visual acuity and detecting potential vision problems.