Why doesn’t “Suggest correction” fix near objects too?

Real eyes accommodate (change P_eye) for near vision. This page keeps P_eye fixed except via presets and glasses — it is a teaching cartoon, not a clinical refraction.

Powers are in the same abstract 1/sim units as Simple Eye Model. Relate to diopters only after choosing a physical scale for the reduced eye length.

Eye: Myopia & Hyperopia

Reduced eye + glasses; retina blur cue; presets and suggested ΔP.

About this model

A one-lens reduced eye uses the thin-lens equation 1/v = P_eye + P_glasses − 1/u with the retina at fixed v_retina. Myopia corresponds to too much refractive power (or an effectively long axial length): for distant objects the image forms in front of the retina (v < v_retina). Hyperopia corresponds to too little power: the image would lie behind the retina (v > v_retina) for distant light. Spherical corrective lenses add paraxial power at the spectacle plane in this toy model. The “E” uses canvas blur as a qualitative defocus indicator, not point-spread optics.

Who it's for: Pairs with Simple Eye Model; good before discussing astigmatism and accommodation limits.

Key terms

myopia
hyperopia
refractive power
corrective lens
reduced eye

How it works

Same paraxial reduced eye as Simple Eye Model: 1/v = P_eye + P_glasses − 1/u with fixed retina at v_retina = 2.35 (sim units). Myopia (too much P_eye or effectively long axis): distant objects form in front of the retina (v too small). Hyperopia: v too large — the focus would lie behind the retina. Corrective lenses shift P_total; diverging (negative ΔP) helps myopia, converging helps hyperopia. The E on the retina uses blur as a crude defocus cue — not wave optics.

Key equations

1/v = P_eye + ΔP − 1/u

Distant (u → ∞): need P_eye + ΔP ≈ 1/v_retina for sharp retina image

Frequently asked questions

Why doesn’t “Suggest correction” fix near objects too?: Real eyes accommodate (change P_eye) for near vision. This page keeps P_eye fixed except via presets and glasses — it is a teaching cartoon, not a clinical refraction.
Are diopters shown?: Powers are in the same abstract 1/sim units as Simple Eye Model. Relate to diopters only after choosing a physical scale for the reduced eye length.

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