R R

Why Can Visual Acuity Test Results Differ Between Eye Exams?

Visual acuity test results can differ because chart choice, vision correction, and repeat testing can affect the score. In a comparison of 773 eyes from 413 retinal-trial participants, standardized research testing produced scores averaging 6.1 letters better than routine Snellen testing. The measurements came from different visits and testing procedures, so the difference doesn't prove that eyesight improved or that the chart alone caused the change.

Link to This Resource Page

Provide a valuable resource to your clients or customers by linking to this resource page. Just place the following link on your website.

To display this...

Why Can Visual Acuity Test Results Differ Between Eye Exams?

Visual acuity test results can differ because chart choice, vision correction, and repeat testing can affect the score. In a comparison of 773 eyes from 413 retinal-trial participants, standardized research testing produced scores averaging 6.1 letters better than routine Snellen testing. The measurements came from different visits and testing procedures, so the difference doesn't prove that eyesight improved or that the chart alone caused the change.

read more about visual acuity ...

Copy this HTML:

Copy HTML Copied!

How Much Can Repeat Visual Acuity Measurements Vary?

Repeat measurements can vary even in patients with stable eye disease. Testing of 40 eyes from 40 patients found 95% tolerance limits for change of ?0.14 logMAR with ETDRS charts and ?0.18 logMAR with Snellen charts. These limits describe repeat-test variation in that sample. They aren't universal cutoffs for deciding whether vision has changed, and they don't explain the cause of a different result in an individual patient.

Can Snellen and ETDRS Testing Produce Different Scores?

Yes, Snellen and ETDRS testing can produce different scores, especially in eyes with poorer starting acuity. Snellen is the familiar letter chart, while ETDRS refers to standardized research testing. In the retinal-trial comparison, eyes starting at 20/25 or better averaged 1.9 letters better with ETDRS testing; eyes starting at 20/160 or worse averaged 12.6 letters better. But a separate comparison in patients with stable eye disease found similar average results across charts. Different populations and testing procedures mean there isn't one fixed adjustment that makes the scores interchangeable.

Can Pinhole Testing Match Vision After Refraction?

Pinhole testing can approximate vision after refraction in some patients, but it doesn't always match. The test involves reading a chart through a small opening; refraction checks which lenses provide the clearest vision. Among 204 eyes from 104 adults aged at least 50, pinhole scores averaged 0.4 letters better than best-corrected scores. In a separate comparison of 209 eyes from 110 participants with diabetes, pinhole scores had a median difference of four letters worse than scores after manual refraction. These findings don't establish that pinhole testing can replace refraction for everyone.

Does a Different Score Always Mean Your Vision Has Changed?

No, a different score doesn't automatically mean your eyesight has improved or worsened. Before comparing results, check whether both tests measured the same eye with the same type of vision correction and testing method. A score without glasses or contacts measures uncorrected acuity; best-corrected acuity measures vision with the best possible lens prescription. Those results answer different questions. A changed score can still reflect a vision problem, so an eye care professional should interpret it alongside your symptoms and examination findings.

Learn More About Visual Acuity Test Results

What Does logMAR Mean on an Eye Test Report?

logMAR stands for the logarithm of the minimum angle of resolution, a scale for recording visual acuity. Lower values indicate sharper measured vision.

Does a Faster Eye Chart Test Give a Less Accurate Result?

Not necessarily. In the stable-eye-disease comparison, average reading times were 18.67 seconds for Snellen and 34.65 seconds for ETDRS, while average acuity results were similar.

Can Practice Affect an Eye Chart Result?

Yes. Repeated testing produced a small practice effect in the stable-eye-disease comparison, greatest with Snellen and smallest with ETDRS.

When to See Your Doctor

Arrange an eye exam for persistent blur, gradually worsening sharpness, or difficulty reading or seeing at night. Seek emergency eye care for sudden partial or complete vision loss, a curtain-like shadow, or sudden blurred vision with eye pain. Don't assume these symptoms come from ordinary test variation.

References

Eye. Accuracy of pinhole visual acuity at an urban Indian hospital. https://pmc.ncbi.nlm.nih.gov/articles/PMC6367369/. Published October 19, 2018. Accessed November 4, 2026.

Eye. Comparison of the ETDRS logMAR, ?compact reduced logMar' and Snellen charts in routine clinical practice. https://pubmed.ncbi.nlm.nih.gov/19557025/. Published June 26, 2009. Accessed November 4, 2026.

MedlinePlus. Visual acuity test. https://medlineplus.gov/ency/article/003396.htm. Reviewed January 20, 2025. Accessed November 4, 2026.

MedlinePlus. Vision problems. https://medlineplus.gov/ency/article/003029.htm. Reviewed August 5, 2024. Accessed November 4, 2026.

Ophthalmology. Visual acuity testing using autorefraction or pinhole occluder compared with a manual protocol refraction in individuals with diabetes. https://pubmed.ncbi.nlm.nih.gov/20947171/. Published October 14, 2010. Accessed November 4, 2026.

Ophthalmology Retina. Visual Acuity Variability: Comparing Discrepancies between Snellen and ETDRS Measurements among Subjects Entering Prospective Trials. https://pubmed.ncbi.nlm.nih.gov/32595096/. Published April 23, 2020. Accessed November 4, 2026.