When you receive an eye exam in South Korea, your visual acuity is recorded on a decimal scale rather than the fraction format common in the United States. A score of 1.0 on a Korean eye chart directly equals 20/20 vision in the US standard. Understanding how these numbers map across borders helps you interpret your medical records or buy corrective lenses abroad without confusion.
While the US relies on fractional notation like 20/40, South Korea uses a clean decimal system where 1.0 represents standard sharp vision. If your exam report lists numbers like 0.5 or 1.2, you're looking at a decimal measurement. Converting these values requires a simple mathematical calculation or a direct reference guide.
The Mechanics of Visual Acuity Scales
Visual acuity measures the sharpness of your vision at a standardized distance. The system you grew up with shapes how you expect your results to look.
The US Snellen scale uses a fraction. The top number represents the testing distance in feet, usually 20 feet. The bottom number represents the distance at which a person with standard vision can read the same line. If you have 20/40 vision, you can see at 20 feet what a person with normal vision can see at 40 feet.
South Korea uses a decimal scale instead of a fraction. You divide the numerator by the denominator of the equivalent Snellen fraction to find the decimal score. For example, dividing 20 by 20 gives you 1.0. Dividing 20 by 40 gives you 0.5. This single decimal number makes record-keeping concise.
Korean Decimal to US Snellen Conversion Table
Translating your Korean eye exam results into the US standard is straightforward once you have a reference point. Here is how standard decimal measurements match up against US foot measurements and metric equivalents.
- A decimal score of 2.0 equals 20/10 in the US and 6/3 in metric. This indicates exceptional visual clarity.
- A decimal score of 1.5 equals 20/13 in the US and 6/4 in metric.
- A decimal score of 1.2 equals 20/17 in the US and 6/5 in metric.
- A decimal score of 1.0 equals 20/20 in the US and 6/6 in metric, which is the baseline standard.
- A decimal score of 0.8 equals 20/25 in the US and 6/7.5 in metric.
- A decimal score of 0.5 equals 20/40 in the US and 6/12 in metric, which is often the driving threshold in many regions.
- A decimal score of 0.1 equals 20/200 in the US and 6/60 in metric, marking the legal blindness threshold under Social Security Administration guidelines.
Why South Korea Uses Decimal Scoring
Medical infrastructure in South Korea adopted the decimal system for efficiency and global alignment with metric-using nations. Optometrists and ophthalmologists can quickly plot patient progress on charts without dealing with fractional math.
Korean eye charts often feature hangul characters alongside numbers or standard Landolt rings, but the scoring math remains identical to European decimal charts. If you move between clinics in Seoul and Los Angeles, your doctor will instantly recognize that a 1.0 means normal vision, even if they write prescriptions using American Academy of Ophthalmology standards.
Common Mistakes When Converting Vision Scales
People often misinterpret decimal scores by confusing visual acuity with prescription strength. Your visual acuity score on a chart doesn't tell you the diopter power needed for your contact lenses.
Another frequent error is assuming that higher numbers on a decimal chart always mean better vision. While 1.5 or 2.0 represent sharper-than-average sight, numbers below 1.0 mean your eyes require correction. Don't try to calculate your astigmatism axis using a visual acuity conversion chart. Acuity charts only measure crispness, not the shape of your cornea.
Frequently Asked Questions
Is 1.5 vision on a Korean chart better than 20/20?
Yes. A decimal score of 1.5 translates to roughly 20/13 in the US system. This means you can read letters from 20 feet away that a person with standard vision would need to stand 13 feet away to read.
Do Korean eye exams use different letters than US exams?
Korean eye charts often use hangul letters designed with uniform stroke widths that mimic the optical properties of standard Snellen optotypes. Some clinics also use numbers or Landolt broken rings to test patients of all ages.
Can I use my Korean eyeglass prescription directly in the US?
Your optical prescription for glasses uses diopters, cylinder, and axis measurements, which are universal across both countries. However, your visual acuity score on the chart is just a diagnostic metric and isn't used directly to grind lenses.
What is considered legal blindness on the Korean scale?
Legal blindness in the US is defined as 20/200 or worse in the better eye with best correction. On the Korean decimal scale, this exact threshold is 0.1.
