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Related Links: 1. Eyecare Glossary 2. All About Vision |
How the Eye Works
Emmetropia
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The normal eye functions as a sphere to precisely focus light on the retina.
This is called emmetropia. Clear vision is possible as the cornea, lens and retina work together perfectly. Light rays enter the eye through the cornea (clear, front surface of the eye), pass through the lens, and are focused on the retina.
(Schematic) Artist's idea of how the eye looks, with labels pointing to the cornea, iris, lens, retina, fovia, and optic nerve. |
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Myopia
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Myopia (nearsightedness) occurs when light rays are focused in front of the retina, instead of directly on the retina. Myopia is found when a cornea is too steep or the eye is too long. When light is not focused directly on the retina, images appear blurred. Glasses or contact lenses are needed to move the light's focus to the retina and provide a clear image.
(Schematic) Artist's idea of how a myopic eye looks, with light passing through the lens but falling short of the retina. |
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Hyperopia
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Hyperopia (farsightedness) occurs when light rays focus behind the retina. Most people who are farsighted are not aware of it when they are young. The natural accommodating (focusing) power of the eyes often compensates for farsightedness until adulthood or sometimes until the forties or fifties. Eventually glasses or contacts are needed to focus images clearly on the retina. (Schematic) Artist's idea of how a hyperopic eye looks with the light focusing on a point further away than the retina. |
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Astigmatism
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Astigmatism occurs when light rays are focused at more than one point on the retina. With astigmatism, the curvature of the cornea and/or lens is not the same in all directions. Like a football, the curves of the eye may be steep in one direction and less steep in the other. A person may have astigmatism along with myopia or hyperopia. Glasses or contact lenses are needed to focus the light equally on the retina and provide a clear image. (Schematic) Artist's idea of how an astigmatic eye looks. |
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Presbyopia
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Presbyopia occurs when the eye's natural focusing ability (accommodation) becomes insufficient. The eye can no longer readjust its focus from distance to near objects. It is part of the natural aging process. Before the onset of presbyopia, the human lens has the ability to flex, adjust its optical power, and change focus. This ability declines throughout life and usually becomes apparent in the mid 40's.
(Schematic) Artist's idea of how a presbyopic eye looks. |
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Presbyopic individuals with previously normal vision require reading glasses to view near objects, while those that are also nearsighted or farsighted require bifocals for clear viewing at far and near distances. The most common way to treat presbyopia is with bifocal or multifocal/progressive glasses or contact lenses.
People who are nearsighted often notice that they can read fine print comfortably without corrective lenses well past the age of 40. Although nearsightedness individuals still require corrective lenses for distance, they can take off their lenses to see for near. Removing glasses or contact lenses to read often becomes inconvenient and most nearsighted individuals eventually wear bifocal or progressive/multifocal glasses or contact lenses.
Bifocal lenses allow the user to view distant objects through the top portion of their lens, and to view near objects (with additional power and magnification) through the bottom portion of their lenses. Multifocal or progressive lenses provide sharp vision at all distances by progressively adding magnification to the lens. Also, multifocal/progressive lenses don't have a line separating the distance and near prescriptions, which many find cosmetically more pleasing than standard bifocal lenses. Additionally, there are many visual and functional advantages to multifocal/progressive lenses. The opticians at Encore will be happy to discuss multifocal options based on your prescription, lifestyle and occupational requirements.
Contact lens wearers also have many presbyopia options, including bifocal or multifocal contact lenses and monovision. Drs. Bridgewater and Chrisagis are experienced fitting all of these options and deciding how to best address your specific needs.