Visual Acuity Converter
Convert between Snellen (feet/meters), Decimal, and LogMAR visual acuity formats. Assess legal blindness status and driving eligibility based on vision measurements.
Calculate Visual Acuity Conversions
Normal vision is 20/20
Conversion Results
Visual Acuity Reference Guide
| Snellen (Feet) | Snellen (Meters) | Decimal | LogMAR | Classification |
|---|---|---|---|---|
| 20/10 | 6/3 | 2.0 | -0.30 | Excellent |
| 20/20 | 6/6 | 1.0 | 0.00 | Normal |
| 20/40 | 6/12 | 0.5 | 0.30 | Mild Impairment |
| 20/60 | 6/18 | 0.33 | 0.48 | Moderate Impairment |
| 20/80 | 6/24 | 0.25 | 0.60 | Moderate Impairment |
| 20/200 | 6/60 | 0.10 | 1.00 | Legal Blindness |
| 20/400 | 6/120 | 0.05 | 1.30 | Profound Impairment |
Important Notes:
- Legal blindness in the US: 20/200 or worse in better eye with best correction, or visual field <20°
- Driving requirements vary by state/country, typically 20/40 or better
- LogMAR is preferred for research (0.00 = normal, positive = worse, negative = better)
- These conversions assume best corrected visual acuity
Driving Vision Requirements
| Visual Acuity | Driving Status | Notes |
|---|---|---|
| 20/20 to 20/40 | Unrestricted | Meets requirements in all jurisdictions |
| 20/50 to 20/70 | Restricted | May require daylight only, speed limits, or area restrictions |
| 20/80 to 20/100 | Severely Restricted | May require bioptic telescopes in some states |
| Worse than 20/100 | Not Eligible | Generally does not meet minimum requirements |
Understanding Visual Acuity Measurements
What is Visual Acuity?
Visual acuity is a measure of the spatial resolution of the visual system – essentially, how well you can see fine details. It's typically measured using a standardized eye chart at a specific distance.
Snellen Notation
The Snellen fraction (e.g., 20/20) represents testing distance over the distance at which a normal eye can read the same line:
- 20/20: Normal vision – you can read at 20 feet what a normal eye can read at 20 feet
- 20/40: You can read at 20 feet what a normal eye can read at 40 feet (worse vision)
- 20/10: You can read at 20 feet what a normal eye can read at only 10 feet (better vision)
Decimal Acuity
Decimal acuity is simply the Snellen numerator divided by the denominator. 20/20 = 1.0, 20/40 = 0.5, etc. Values greater than 1.0 indicate better than average vision.
LogMAR System
LogMAR (Logarithm of the Minimum Angle of Resolution) is the preferred method in clinical research because it provides a more linear scale:
- 0.00: Normal vision (20/20)
- Positive values: Worse than normal (0.30 = 20/40, 1.00 = 20/200)
- Negative values: Better than normal (-0.30 = 20/10)
Legal Blindness
In the United States, legal blindness is defined as:
- Visual acuity of 20/200 or worse in the better eye with best correction, OR
- Visual field restriction to 20 degrees or less (tunnel vision)
Legal blindness qualifies individuals for certain benefits and accommodations, but many legally blind people retain useful vision.
Clinical Applications
Visual acuity testing is essential for:
- Routine vision screening and comprehensive eye examinations
- Monitoring progression of eye diseases (cataracts, macular degeneration, glaucoma)
- Assessing effectiveness of refractive correction (glasses/contacts)
- Determining eligibility for vision rehabilitation services
- Legal documentation for disability benefits or driving privileges
Frequently Asked Questions
What does 20/20 vision really mean?
20/20 vision means you can see at 20 feet what a person with normal vision can see at 20 feet. It's considered "normal" vision, but not necessarily perfect – some people naturally have 20/15 or even 20/10 vision. 20/20 specifically refers to clarity at a distance and doesn't account for peripheral vision, depth perception, eye coordination, or color vision.
Can you drive with 20/40 vision?
Yes, 20/40 vision typically meets the minimum requirement for an unrestricted driver's license in most US states and many countries. However, requirements vary by jurisdiction – some states require 20/40 in at least one eye, while others require 20/40 in both eyes or a combined standard. Always check your local DMV requirements.
What's the difference between Snellen feet and meters?
Snellen feet (20/20) is used primarily in the United States, while Snellen meters (6/6) is the international standard. They measure the same thing at different distances: 20 feet equals approximately 6 meters. A 20/20 measurement in feet is equivalent to 6/6 in meters.
Why is LogMAR preferred in research studies?
LogMAR provides a logarithmic scale that better represents equal steps in visual acuity loss. In Snellen notation, the difference between 20/20 and 20/40 seems similar to 20/40 and 20/80, but they're not equivalent changes. LogMAR's linear scale (0.0, 0.3, 0.6) makes statistical analysis more accurate and allows for letter-by-letter scoring on standardized charts like ETDRS.
If I'm legally blind, does that mean I can't see anything?
No, legal blindness is a legal definition for benefit eligibility, not a medical description of total blindness. Someone who is legally blind (20/200 or worse) may still have substantial usable vision, including the ability to read large print, navigate familiar environments, or use assistive devices. Complete blindness (no light perception) is relatively rare among those classified as legally blind.
Can visual acuity improve naturally or does it only get worse?
Visual acuity can improve in certain situations: after proper refractive correction (glasses/contacts), following cataract surgery, after treatment of certain eye conditions, or during childhood visual development. However, uncorrected refractive errors and many eye diseases do tend to worsen over time. Regular eye exams are important for maintaining optimal vision.
What's the best possible human vision?
While 20/20 is considered "normal," many people naturally have better vision. 20/15 or 20/10 vision is not uncommon, especially in younger individuals. The theoretical limit of human visual acuity is around 20/8 to 20/5, though this is extremely rare. Some birds of prey have even better visual acuity, equivalent to 20/4 or better in human terms.
How accurate is visual acuity testing?
Visual acuity testing is generally reliable but can be affected by factors like lighting conditions, chart type and calibration, testing distance, patient cooperation, and whether pupils are dilated. Standardized charts (like ETDRS) provide the most consistent results. Results can vary slightly between tests, which is why eye care professionals often test multiple times or use different methods to confirm measurements.
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