Applications: II. Our eyes and eyeglasses

• Eyes: an optical system that can form a real, virtual and reduced size image on the retina

• Multiple refractors: cornea, the lens and some fluids (total power: 60 diopters, lens only: 20 diopters)

• the lens can vary its focal length (20-24 diopters) (eyes like an auto-focus camera) (auto-focusing property decreases with age)

• eye problems:

- myopia (nearsightedness): clear images formed in front of the retina, corrected by eyeglasses with diverging lenses)

- hyperopia (farsightedness): clear images are formed behind the retina, corrected by eyeglasses with converging lenses)

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