Online Tool Store
Astigmatism Test Chart
An on-screen sunburst dial and parallel-line chart for a quick, informational astigmatism screening, checking whether radial lines and meridians appear evenly sharp across your field of view.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Sunburst Dial & Optical Astigmatism Chart
Test one eye at a time from approximately 2 to 3 feet (arm's length) from your screen.
Numbers represent clock hours / meridians (1 to 12). If some spokes appear noticeably darker, thicker, or sharper than others, astigmatism may be present along that axis.
How to Perform the Test:
- If you normally wear contact lenses or glasses for distance, keep them on.
- Sit back comfortably approximately 2 to 3 feet (arm's length) from your screen.
- Cover your Left Eye with your palm (do not press on your eyeball) and observe the chart with your Right Eye.
- Do all radial lines / bars look equally black, uniform, and sharp? Or are some lines darker and bolder while others look blurred or grey?
- Switch eyes: cover your Right Eye and repeat for your Left Eye.
How it works
- Position yourself approximately 2 to 3 feet (about arm\'s length) away from your display screen.
- Cover one eye with your hand and look directly at the white center focal dot of the sunburst wheel.
- Examine whether all 36 radial spokes look uniformly black and sharp, or if certain clock positions (e.g. 12 to 6, or 3 to 9) stand out with greater contrast.
- Switch to the Parallel Line chart to verify horizontal (180°), vertical (90°), and diagonal (45°/135°) meridian consistency.
FAQ
What is astigmatism and what causes it?
Astigmatism is a very common refractive error caused by an imperfect, asymmetrical curvature of the cornea or lens (shaped more like a football than a basketball), causing light to focus at multiple points rather than a single focal point on the retina.
How does a sunburst clock dial test indicate astigmatism?
Because light rays focus unevenly across meridians, someone with uncorrected astigmatism will perceive lines along one specific axis as significantly darker, sharper, or thicker, while perpendicular lines appear blurry, faded, or double.
Should I keep my prescription glasses or contacts on during the test?
If you wear corrective lenses intended to correct astigmatism (toric lenses or cylinder prescriptions), wearing them tests whether your current prescription is still accurate. If you remove them, the chart tests your raw uncorrected visual acuity.
Does this test diagnose eye disease?
No. This is an informational screening chart. Only an optometrist or ophthalmologist using a phoropter, keratometer, or corneal topographer can formally diagnose and measure cylinder and axis prescriptions.
How we compare
| Feature | Online Tool Store | Low-res image scans | Printed paper chart |
|---|---|---|---|
| High-resolution vector SVG rendering | ✓ | ✗ (Pixelated) | ✓ |
| Dual mode (Sunburst Dial + Parallel Blocks) | ✓ | ✗ | ✗ |
| High-contrast darkroom display background | ✓ | ✗ | ✗ |