Visionworks.info
Understand Your Vision
Independent educational vision tools, eye tests, prescription explainers, and eye-health guides. Learn how common vision numbers work — and why a real eye exam still matters.
Featured eye tests
Educational screenings to explore acuity, near vision, astigmatism cues, and color discrimination.
Visual Acuity Test
Educational on-screen eye chart to explore Snellen-style acuity lines — not a clinical examination.
Near Vision Test
Explore near reading clarity with an educational near-vision chart and learn why working distance matters.
Astigmatism Test
An educational astigmatism dial/line pattern to explore uneven blur — not a clinical cylinder measurement.
Color Vision Test
Educational color-vision plates and comparisons to learn about color discrimination — not a clinical diagnosis.
Prescription tools
Decode glasses prescription fields, explore PD, ADD, and frame measurements in plain language.
Pupillary Distance
Learn what PD means, explore single vs dual PD, and practice educational measurement concepts for glasses fitting.
Prescription Decoder
Paste or enter OD/OS sphere, cylinder, axis, ADD, prism, and PD to get plain-English educational explanations.
Reading ADD Explainer
Learn what ADD means for progressive, bifocal, and reading lenses — educational ranges only, not a prescription.
Frame Size
Decode eye size, bridge, and temple measurements such as 52□18 140 and learn how frame fit works.
Calculators
Educational calculators for diopters, viewing distance, and lens estimates — always labeled as learning aids.
Snellen Converter
Convert between Snellen 20/xx, metric 6/xx, decimal acuity, and logMAR for learning — not diagnosis.
Screen Distance
Estimate ergonomic viewing-distance ranges for monitors and TVs based on size — educational comfort guidance.
Reading Distance
Relate reading distance to diopters educationally (D ≈ 1/f) and understand near-work ergonomics.
Diopter Calculator
Calculate diopters from focal distance and explore optical power concepts without false acuity conversion claims.
Lens Thickness Estimator
Rough educational estimates of lens edge/center thickness from power, index, and eye size — labeled estimate only.
20/20 Vision Explorer
Interactively explore what 20/20 and other acuity notations mean — clarity concepts without false prescription mapping.
Learn about eyesight
Start with clear hubs for vision basics, common conditions, symptoms, and prescription fields.
Vision-number explorer
See what common acuity notations like 20/20 and 20/40 mean — and what they do not tell you.
Acuity numbers describe how well you can resolve detail under test conditions. They are not a full description of eye health, peripheral vision, color vision, binocular function, or disease risk. Use the explorer to build intuition, then confirm concerns with an eye-care professional.
Popular questions
Recent guides
Fresh explainers from the Visionworks.info library.
How to Read a Glasses Prescription
Decode OD, OS, SPH, CYL, AXIS, ADD, prism, and PD on a glasses prescription with careful educational definitions — not a substitute for your clinician.
Eye Chart Limitations: Home and Online Charts
Home printouts and online eye charts rarely match clinical calibration. Browser zoom, pixel density, distance, and lighting can invalidate comparisons to clinic acuity.
Snellen Chart Explained
The Snellen chart is a classic visual acuity design using letter sizes tied to fractions like 20/20. Learn what the numbers mean and where Snellen fits among modern charts.
Eye Chart Guide: How Vision Charts Work
Eye charts estimate visual acuity using standardized letter sizes at a known distance. Learn Snellen basics, testing conditions, and clinic versus home chart differences.
Can You Get Glasses Without an Eye Exam?
U.S. context: glasses require a valid prescription from a licensed examiner. OTC readers are different. FTC Eyeglass Rule education covers prescription release — not legal advice.
Optometrist vs Ophthalmologist: What’s the Difference?
Optometrists (OD) and ophthalmologists (MD/DO) both provide eye care with different training pathways. Opticians fit eyewear but do not perform medical eye exams.
Why online vision tests have limits
Browser-based vision tools can help you learn vocabulary and notice patterns, but they are not a comprehensive eye examination. Screen pixel density, brightness, ambient lighting, viewing distance, glare, device color settings, and testing technique all change results.
- Online tools do not measure eye health inside the eye (retina, optic nerve, pressure, or disease screening).
- They cannot reliably prescribe glasses or contact lenses.
- Children, adults with sudden changes, and anyone with trauma or severe symptoms need professional evaluation.
- A “normal” online result never rules out eye disease.
Use these tools to prepare for appointments and understand terms — then rely on an optometrist or ophthalmologist for diagnosis and treatment.
Methodology & sources
We research from authoritative organizations and label content as editorially researched — not physician-reviewed unless that is true.
Preferred references include the National Eye Institute, American Academy of Ophthalmology, American Optometric Association, FDA/FTC consumer materials where relevant, and other primary sources. See each page’s Sources section for citations.
Frequently asked questions
No. Visionworks.info is an independent informational website. It is not affiliated with, endorsed by, or operated by Visionworks retail optical stores, VSP Vision, or any optical retailer.
No. Our tools are educational. They cannot replace a comprehensive eye examination by an optometrist or ophthalmologist, and they do not diagnose disease or prescribe lenses.
20/20 is a common Snellen-style reference for high-contrast distance letter acuity. It does not mean perfect eye health or perfect vision in all conditions. Explore our acuity library and 20/20 vision tool to learn more.
Not reliably for an individual. Prescription diopters and visual acuity measure different things. Our sphere and acuity pages explain why one-to-one converters are misleading.
OD is the right eye, OS the left eye, SPH is spherical power, CYL and AXIS describe astigmatic correction. Use the prescription decoder and field encyclopedia for plain-English explanations.
Pupillary distance helps center lenses correctly. Dual PD is often preferred for progressives. Prefer professional measurement when possible — see our PD guides.
Seek urgent or emergency care for sudden vision loss, a curtain or shadow over vision, new flashes with many floaters, severe eye pain, chemical exposure, or eye trauma.
We editorially research authoritative sources such as NEI/NIH, AAO, AOA, FDA, FTC, CDC, and MedlinePlus. We do not invent physician reviewers. See our editorial policy and source lists on articles/tools.