With a healthy eye, light rays entering the eye are focused directly on the retina to form a sharp image, which is then sent to the brain via the optic nerve, resulting in a visual image.
When the eye’s dimensions are not well-aligned, the light rays are not correctly focused. This results in a refractive error such as near-sightedness, farsightedness and astigmatism (an irregular curvature of the cornea). Refractive errors are very widespread and affect people of all ages.
The eye functions on a similar principle to an old fashioned camera. Your iris or coloured portion of your eye acts as the shutter regulating the amount of light. The cornea or clear dome covering your iris, combined with your lens behind the iris are the lenses that focus the light onto your retina at the back of your eye. This simulates the film of a camera sending images to the brain.
In a generally healthy eye that does not need glasses or contact lenses to see clearly, light enters the eye and are focused directly on the retina to form a sharp image, which is then sent to the brain via the optic nerve, resulting in a visual image.
Sometimes the dimensions of the eye do not align. This causes the light rays to not correctly focus on the back of the retina. This results in what is known as a refractive error. Refractive errors include, near-sightedness, farsightedness and astigmatism (an irregular curvature of the cornea). Refractive errors are extremely common and affect humans of all ages.
In myopia, the cornea, lens or both are too strong for the size of your eye, causing light rays to be focused in front of the retina. You will have clear close up vision but objects in the distance are blurred.
In hypermetropia, the cornea and lens are too weak for the size of your eye therefore, light rays are not focused before they reach the retina. Typically, your near vision blurs first and then your distance at a later stage.
Astigmatism is a refractive error due to the cornea not being perfectly spherical which causes an asymmetric blur. Having astigmatism is quite common and some directions in an image are more out of focus than others. Your cornea is shaped more like a football rather than a soccer ball. As a result, light is focused at different locations and the image doesn’t focus to a point. If you have astigmatism you may also have myopia or hypermetropia.
Part of the aging process is that everyone develops presbyopia at some point. Anyone considering laser eye or vision correction surgery should be aware of its impact. Presbyopia is a gradual loss of the ability to focus on near objects. When you are young, the natural lens of the eye is soft and has the ability to change shape when focusing. As you age the eye loses flexibility and cannot shift its focus that well and strongly anymore. Presbyopia can develop from around 40 years of age onward and people who may have had perfect vision will find it increasingly difficult to focus on close-up tasks. One might need multiple glasses to see at various distances once presbyopia sets in.
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