Pupilla learning lab
Lensometer Simulator
Read a finished spectacle lens on a manual lensometer: close the doubled American Cross mires on the power drum, find the axis on the unbroken thin line, take the cylinder as the difference of two readings, and watch Prentice's Rule put prism on the reticle rings.
- Free in your browser
- English & Arabic
- Education & training
Your first practice session
- Place a virtual lens and focus the first set of target lines.
- Read the second focus and determine cylinder from the difference.
- Identify the axis, then inspect prism and decentration.
Common mistakes to avoid
- Reading power before the target is focused.
- Confusing cylinder axis with the meridian of cylinder power.
For education and training only. Pupilla is not a medical device and must not be used for diagnosis or treatment decisions.
Understand the principles
Refractive errors and astigmatism: myopia, hyperopia and Sturm's conoid
A refractive error means light from a distant object does not focus on the retina when accommodation is relaxed. In myopia the focus falls in front of the retina and is corrected with minus (concave) lenses; in hyperopia it falls behind the retina and is corrected with plus (convex) lenses. In astigmatism the eye has different power in two meridians, so a point of light forms two focal lines separated by the interval of Sturm (Sturm's conoid); a cylindrical lens at the right axis brings both lines together on the retina.
Questions about this simulator
What can I practise with the Lensometer Simulator?
Read a finished spectacle lens on a manual lensometer: close the doubled American Cross mires on the power drum, find the axis on the unbroken thin line, take the cylinder as the difference of two readings, and watch Prentice's Rule put prism on the reticle rings.
Do I need to install software or create an account?
Open the simulator free in a modern browser without installation. An account enables supported saved progress and results; coverage varies by module.
Can I use a phone or tablet?
You can access it in modern phone and tablet browsers. A larger screen gives diagrams and controls more space; performance depends on the device and browser.
Does this replace clinical training or patient diagnosis?
For education and training only. Pupilla is not a medical device and must not be used for diagnosis or treatment decisions.
References & further learning
Sources for the teaching principles. Listing a source does not imply its institution endorses or validates this simulator.