Pupilla learning lab
Cover Test Simulator
Practise cover–uncover and alternate cover testing on a virtual patient. Compare tropias and phorias, observe refixation and explore prism neutralization.
- Free in your browser
- English & Arabic
- Education & training
This workflow uses the shared Eye Exam Simulator. The button opens the existing examination tools.
Your first practice session
- Start with esotropia and watch the uncovered eye.
- Alternate the cover and describe the direction of refixation.
- Compare with a phoria and explain the difference.
Common mistakes to avoid
- Watching the covered eye instead of the uncovered eye.
- Treating alternate cover testing as a test of manifest deviation alone.
For education and training only. Pupilla is not a medical device and must not be used for diagnosis or treatment decisions.
Understand the principles
The cover test: cover–uncover, alternate cover and prism cover test
The cover test detects and measures strabismus. In the cover–uncover test you cover one eye and watch the other: if the uncovered eye moves to take up fixation, there is a manifest deviation (a tropia). If no tropia is seen but the covered eye moves back into line when the cover is removed, there is a latent deviation (a phoria). The alternate cover test breaks fusion to reveal the total deviation, and adding prisms until the movement stops (the prism cover test) measures it in prism dioptres.
Hirschberg and Krimsky tests: measuring strabismus with the corneal light reflex
The Hirschberg test estimates strabismus from where a penlight's reflection sits on each cornea: a reflex displaced temporally means esotropia, nasally means exotropia, downward means hypertropia and upward means hypotropia. Each millimeter of decentration is traditionally counted as about 7 degrees, or 15 prism dioptres, although photographic studies suggest closer to 21 prism dioptres per millimeter. The Krimsky test measures the angle more precisely by placing prisms in front of an eye until the corneal reflexes are symmetric in both eyes.
Try a virtual patient
Teaching examples in the exam simulator. Observe and explain the signs before comparing cases.
Questions about this simulator
What can I practise with the Cover Test Simulator?
Practise cover–uncover and alternate cover testing on a virtual patient. Compare tropias and phorias, observe refixation and explore prism neutralization.
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.