How the Eye Works

Diagram of the eye

Ocular Anatomy

A camera works by focusing light through a lens system onto film to capture a sharp picture. The eye, like a camera, has a lens system—the cornea and lens. This focuses light onto the retina, a light-sensitive tissue that lines the back of the eye. Signals from the retina are sent through the optic nerve to the brain, where they are interpreted as the images we see.

What Is a Refractive Error?
Refractive errors exist when the eye’s curvature is poorly matched to the length of the eye. This means that light rays cannot focus properly on the retina.

Your vision-correction treatment will be tailored to your specific refractive issues, including nearsightedness, farsightedness and astigmatism. Vision correction surgeries either change the shape of the front surface of the eye or add a lens to improve the focus.

Please read on to learn more detail about common issues with vision.

Myopia (Nearsightedness)
Myopia is the most common refractive error. Being nearsighted means you can see close objects clearly, but distant objects appear blurry—or maybe aren’t even distinguishable. With myopia, either the eye is too long or the cornea is too steep. This causes light rays entering the eye to fall in front of the retina instead of directly on it. Myopia is often inherited. It usually begins in childhood and then stabilizes in the late teens or early adulthood. Corrective eyeglasses or contact lenses have traditionally been prescribed to make the light rays focus directly onto the retina.

Hyperopia (Farsightedness)
Farsighted patients can focus on distant objects, but close-up objects are blurry. This happens when the eye is unusually short or the cornea is too flat. As a result, light rays are not yet focused when they hit the retina. In young people, the natural lens can sometimes correct this focusing issue. But with aging, the natural lens loses this ability, and the vision become blurry. This is why many hyperopic patients are unaware of their condition even into their 20s or 30s.

When the curve of the cornea, and sometimes the lens, is unevenly shaped—curved a bit like a football—astigmatism occurs. Almost everyone has some degree of astigmatism. For some people, the uneven curve causes light rays to focus on many points in the eye. This distorts both close and far vision.

This is the very common, age-related loss of the ability to focus close-up. A young eye’s lens is soft and flexible, so it can change shape easily. This enables the eye to focus on objects both near and far away. As people enter their 40s, the lens becomes begins losing flexibility and can’t focus on close-up objects. Initially the blurring is worse in dim light. (A common discovery is the inability to read a restaurant menu!) Later, people find that the fine print in newspapers, magazines and phone books is blurry and hard to read. Near vision is usually corrected with reading or bifocal glasses.

Refractive surgery or contact lenses can be used to correct one eye for near vision and one eye for distance. This is called monovision. This requires a careful screening process to determine if you are a good candidate.

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