The Eye and Accommodation

Light enters through the cornea, the clear curved surface at the front of the eye, which does most of the bending needed to focus it. That light then passes through the pupil and the lens, which fine-tunes the focus, before landing on the retina at the back of the eye. Because light rays cross as they bend, the image that forms on the retina is upside down and reversed left-right; the brain flips it back during processing so what you perceive matches the world.

The lens adjusts its shape through accommodation, controlled by the ciliary muscles. To focus on something near, the ciliary muscles contract, letting the lens thicken and curve more, which bends light more sharply. To focus on something far, those muscles relax and the lens flattens, bending light less. This constant reshaping keeps the focal point sitting exactly on the retina regardless of distance.

Nearsightedness, or myopia, is not a retinal problem — the retina itself works fine and can still detect light normally. The issue is structural: usually the eyeball is slightly too long front-to-back, or the cornea is too curved, so light from distant objects bends too much and converges to a focal point in front of the retina instead of directly on it. By the time that light reaches the retina it has already crossed and spread back out, producing a blurred image. Near objects still focus correctly because less bending is needed to land their focal point on the shorter distance to the retina, which is why nearsighted eyes often see close-up just fine.