This simulator models the eye's cornea and lens as a combined imaging system that must focus light exactly onto the retina. Explore how a normal eye accommodates for any object distance, and see exactly what goes wrong — and how corrective lenses fix it — in myopia and hyperopia.
• A cross-section diagram of the eye with cornea, lens, and retina, plus an external object and traced focusing rays. • Three live controls: object distance (near to far), eye condition (normal, myopic, or hyperopic), and an optional corrective lens (diverging or converging). • A live readout showing exactly where the focus point lands relative to the retina, and whether the resulting image is sharp or blurred. • Five preset scenarios: a normal eye, uncorrected and corrected myopia, and uncorrected and corrected hyperopia.
The ciliary muscles reshape the eye's lens continuously, increasing its curvature (and optical power) as an object moves closer, and relaxing it for distant objects. This process, called accommodation, is what lets a normal (emmetropic) eye keep images sharply focused on the retina across a wide range of distances — right up to its near point, beyond which the lens simply cannot curve any further.
Myopia (nearsightedness) occurs when the eyeball is too long relative to its focusing power (or the cornea/lens too strong), so images focus in front of the retina — a diverging (concave) corrective lens spreads the incoming rays slightly before the cornea, pushing the focus back onto the retina. Hyperopia (farsightedness) is the opposite: the eyeball is too short relative to its focusing power, so images would focus behind the retina — a converging (convex) corrective lens adds focusing power to pull the image forward onto the retina.
Accommodation is the process by which the ciliary muscles reshape the eye's lens — increasing curvature for near objects, relaxing it for far ones — so the eye can keep images focused on the retina across a range of distances.
Myopia occurs when the eyeball is too long, or the cornea and lens too strong, for the eye's own geometry — light focuses in front of the retina instead of on it, blurring distant objects most.
Hyperopia occurs when the eyeball is too short relative to the eye's focusing power — light would focus behind the retina, blurring near objects most.
Myopia has too much focusing power already, so a diverging (concave) lens reduces it, pushing the focus point back onto the retina. Hyperopia has too little focusing power, so a converging (convex) lens adds power, pulling the focus point forward onto the retina.