Pupilla learning lab
Refraction Simulator
Change axial length, corneal curvature and astigmatism, then correct them with sphere, cylinder and axis trial lenses and watch Sturm's conoid collapse onto the retina.
- Free in your browser
- English & Arabic
- Education & training
Your first practice session
- Change one eye parameter and predict where light will focus.
- Add sphere correction, then explore cylinder power and axis.
- Compare the corrected focal pattern with the starting model.
Common mistakes to avoid
- Changing several parameters before explaining any of them.
- Treating spherical equivalent as a complete astigmatic correction.
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.
Streak retinoscopy: with motion, against motion and neutralization
Streak retinoscopy measures refractive error objectively by watching the red reflex in the pupil as you sweep a streak of light across it. If the reflex moves in the same direction as the streak ("with motion"), add plus lenses; if it moves the opposite way ("against motion"), add minus lenses. At neutralization the pupil fills with light and shows no motion. The neutralizing lens minus the dioptric value of your working distance — for example 1.50 D at 67 cm — is the refractive error in that meridian.
Questions about this simulator
What can I practise with the Refraction Simulator?
Change axial length, corneal curvature and astigmatism, then correct them with sphere, cylinder and axis trial lenses and watch Sturm's conoid collapse onto the retina.
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.