1. What is a Visual Acuity Calculator?

Definition: This calculator determines visual acuity as a Snellen fraction by comparing test distance to letter distance.

Purpose: It helps eye care professionals and researchers quantify vision clarity using the standard Snellen notation.

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 minutes of arc (feet)

Explanation: The ratio compares how far the patient is from the chart versus how far a person with normal vision would be to see the same letters.

3. Importance of Visual Acuity Measurement

Details: Standardized visual acuity measurement is crucial for diagnosing vision problems, prescribing corrective lenses, and monitoring eye health.

4. Using the Calculator

Tips: Enter the test distance (typically 20 ft) and the letter distance (the number under the line of letters on the eye chart). 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 sees at 20 feet.

Q2: What if my result is 20/40?
A: This means you must be at 20 feet to see what someone with normal vision sees at 40 feet.

Q3: What's the standard test distance?
A: In the US, 20 feet is standard, while 6 meters is used in many other countries.

Q4: How is letter distance determined?
A: It's based on the size of letters that subtend 5 minutes of arc at the specified distance.

Q5: Can I use meters instead of feet?
A: Yes, as long as both distances use the same unit, the ratio will be correct.