Snellen Chart:
The Snellen chart, named after Dutch ophthalmologist Hermann Snellen, is a visual acuity chart used to measure a person’s distance visual acuity. It consists of multiple rows of letters, usually in capital form, which decrease in size as you move down the chart. The Snellen chart is widely utilized for testing visual clarity and determining the effectiveness of glasses or contact lenses.
Components of a Snellen Chart:
- Row: Each row of the Snellen chart consists of a set of characters, typically letters.
- Letter Size: The size of letters decreases as you move from the top row to the bottom row, with the top row typically representing 20/200 visual acuity and the bottom row representing 20/10 visual acuity.
- 20/20 Visual Acuity: The measurement of normal visual acuity, where a person can read the letters on the 20/20 line from a distance of 20 feet.
- Distance: The Snellen chart is designed to be viewed from a standardized distance, usually 20 feet or 6 meters.
- Visual Acuity: Visual acuity is a measure of the eye’s ability to perceive fine details and is expressed as a ratio, with the distance at which a person with normal vision can read a specific line serving as the numerator and the distance at which the chart is viewed serving as the denominator.