1. What is a Visual Acuity Calculator?

Definition: This calculator determines visual acuity as a Snellen fraction based on test distance and letter distance.

Purpose: It helps eye care professionals and researchers quantify visual acuity in the standard Snellen format (e.g., 20/20 vision).

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( VA \) — Visual Acuity (Snellen fraction)
• \( Test\ Distance \) — Distance from patient to chart (feet)
• \( Letter\ Distance \) — Distance at which letter subtends 5 arcminutes (feet)

Explanation: The ratio compares the test distance to the reference distance where the smallest identifiable letter would be clearly visible to someone with normal vision.

3. Importance of Visual Acuity Measurement

Details: Visual acuity assessment is fundamental in eye examinations, driver's license requirements, and occupational vision standards.

4. Using the Calculator

Tips: Enter the test distance (typically 20 feet) and the letter distance (the number under the smallest line the patient can read). Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What does 20/20 vision mean?
A: It means you can see at 20 feet what a person with normal vision can see at 20 feet.

Q2: What if my test distance isn't 20 feet?
A: The calculator works for any distance. Just enter your actual test distance.

Q3: How do I find the letter distance?
A: This is typically printed next to each line of letters on a Snellen chart (e.g., 20, 30, 40, etc.).

Q4: What about metric measurements?
A: Convert meters to feet (1m = 3.28084ft) before entering values, as Snellen fractions traditionally use feet.

Q5: What does 20/40 vision indicate?
A: You see at 20 feet what a person with normal vision sees at 40 feet - indicating reduced acuity.