Background

Use this activity to explore common refractive errors and how corrections help correct them. In this acitivity, we will examine both myopia (nearsightedness) and hyperopia (farsightedness).

Myopia

Myopia is a common form of mild visual impairment, often called nearsightedness because people with myopia can focus well on near objects but faraway objects appear blurry. With myopia, the eye tends to be too long from front to back for the lens. The process of accommodation does not make the lens thin enough to focus the light from more distant objects onto the retina. Because these distant objects are being focused in front of the retina instead of onto it, the objects appear blurry. To correct the problem, the lens must be weakened. To weaken the lens, a diverging or negative artificial lens is used, that is, a concave lens. A diverging lens is wider at the edges than at the middle. As a result, light is spreading out even more after the light has passed through the lens than before.

Hyperopia

Hyperopia is also a common form of mild visual impairment, often called farsightedness because people with hyperopia can focus well on faraway objects but near objects may appear blurry. With hyperopia, the eye tends to be too short for the lens. The process of accommodation does not make the lens thick enough to focus on the light from more close objects onto the retina. Because these close objects are being focused behind of the retina instead of on it, the objects will appear blurry. Distant objects, however, are seen just fine. As with myopia, eyeglasses can be fitted that will allow the near objects to be imaged on the retinae. In this case, to strengthen the lens, a converging or positive artificial lens is used, that is, as convex lens. A converging lens is wider in the middle than at the edge like the lens of our eye. This lens adds more focusing power to the eye.

If you wear glass or contacts, check the prescription for your classes. You will see either a plus (+) or minus (-) in front of a number for the correction for each eye. These signs on the number tell you the type of lens you have, which indicates whether hyperopia or myopia is being corrected. The number refers to the strength of the correction. The larger the number the stronger the correction needed.

Instructions

Full Screen Mode

To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.

Illustration Tab

Settings

Below is a list of the ways that you can alter the illustration. The settings include the following:

Eye is: select the refractive error: Emmetropic is normal, Myopic is nearsighted, and Hyperopic is farsighted.
Add Lens: add or remove a lens: None is no lens, Convex is a converging lens, and Concave is a diverging lens.
Turn Light On: turn on and off the light.
Light Position: moves the light closer or farther from the eye.

Reset

Pressing this button restores the settings to their default values.