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

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.