Enter the diopter value into the calculator to determine the equivalent Snellen acuity.
Diopter To Snellen Conversion Formula
The following formula is used to convert diopter (D) to Snellen acuity:
Snellen Acuity = 1 / (D * 0.25 + 1)
Variables:
- D is the diopter value
- Snellen Acuity is the visual acuity based on the Snellen chart
To convert diopter to Snellen acuity, divide 1 by the sum of the diopter value multiplied by 0.25 and 1. The result is then typically rounded to the nearest whole number and expressed as a fraction with 20 as the numerator, which represents the standard viewing distance of 20 feet.
What is Diopter?
A diopter is a unit of measurement for the optical power of a lens or curved mirror. It is the reciprocal of the focal length measured in meters. In the context of vision correction, it is used to describe the refractive power of eyeglasses or contact lenses needed to correct a person’s vision.
What is Snellen Acuity?
Snellen acuity is a measure of visual acuity, which is the clarity or sharpness of vision. It is typically represented by a fraction, such as 20/20, where the first number indicates the distance at which a person can clearly see a letter that the average person can see at the second number’s distance. The Snellen chart is commonly used to test and express visual acuity.
How to Calculate Snellen Acuity from Diopter?
The following steps outline how to convert diopter to Snellen acuity:
- First, determine the diopter value (D).
- Next, use the formula Snellen Acuity = 1 / (D * 0.25 + 1).
- Finally, calculate the Snellen Acuity and express it as a fraction with 20 as the numerator.
- After inserting the diopter value and calculating the result, check your answer with the calculator above.
Example Problem :
Use the following variable as an example problem to test your knowledge.
Diopter value (D) = -2.00