Vision Tools and Eye Prescription Calculators
Understand common vision measurements, prescription notation, and visual examples. Each tool explains its method and limits so you can use the result in the right context.
Choose a vision tool
Calculators perform notation or unit conversions. The decoder explains terminology, while the blur illustration demonstrates a generic graphic effect rather than a clinical prediction.
Astigmatism Blur Illustration
Explore a generic, non-clinical example of how a directional blur effect changes text and lights.
Open simulatorEye Prescription Decoder
Learn what SPH, CYL, AXIS, ADD, and common prescription abbreviations mean without interpreting your clinical needs.
Decode the fieldsCylinder Transposition Calculator
Convert an eyeglass prescription between plus-cylinder and minus-cylinder notation with a transparent calculation.
Transpose a prescriptionVisual Acuity Converter
Convert common Snellen, decimal, and logMAR visual-acuity formats and see the nearest standard chart value.
Convert visual acuityWhat these tools can and cannot tell you
These tools organize information and perform standard mathematical conversions. They cannot diagnose an eye condition, verify whether a prescription is correct, reproduce exactly how another person sees, or replace an eye examination. Ask an optometrist or ophthalmologist about symptoms, prescription changes, or treatment decisions.
Continue with a screening or guide
Astigmatism screening
Compare each eye with a guided screen-based check and review neutral observations.
Start the screeningAstigmatism dial test
Use a focused fan chart and learn what a repeatable directional difference may mean.
Open the dial testAccuracy and limitations
Understand what an online eye screening can reasonably show and what affects it.
Read the guide