Snellenasteikkoon

Snellenasteikkoon is a term that refers to the Snellen chart, a widely used tool for measuring visual acuity. It is named after Dutch ophthalmologist Herman Snellen, who developed it in the 1860s. The chart consists of rows of letters of decreasing size, printed in a standardized font. Individuals are typically asked to read the letters from a specific distance, usually 20 feet (6 meters).

Visual acuity is commonly expressed as a fraction, such as 20/20. The top number represents the distance at which the test is conducted, and the bottom number indicates the distance at which a person with normal vision can read the same line of letters. Therefore, 20/20 vision means that a person can see at 20 feet what a person with normal vision can see at 20 feet. A score of 20/40 means that the person can only see at 20 feet what a person with normal vision can see at 40 feet, indicating poorer vision.

The Snellen chart is a fundamental part of routine eye examinations conducted by optometrists and ophthalmologists. It helps in diagnosing refractive errors like myopia (nearsightedness), hyperopia (farsightedness), and astigmatism, as well as other eye conditions that may affect vision. While the Snellen chart remains a standard, variations and more sophisticated visual acuity tests exist for more detailed assessments.

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