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In order to understand how a cataract affects the eye, it is first important to understand how the eye naturally works, and the factors that affect clear vision. One or more of the vision conditions mentioned here may play a role in an individual’s vision and cataract treatment options.
Normal Vision
The cornea and lens focus a sharp image onto the retina along the back wall of the eye. This focused image is sent to the brain via the optic nerve and is perceived by the patient as a sharp image.
Nearsightedness
The cornea is too curved or the eye is too long, casting a fuzzy image onto the retina by focusing light in front of it. This causes a blurry image of objects that are far away from the viewer.
Farsightedness
The cornea is too flat or the eye is too short, casting a fuzzy image onto the retina by focusing light in back of it. This causes a blurry image of objects that are near to the viewer. Patients with higher degrees of farsightedness have blurring of objects at both near and far to the viewer.
Astigmatism
Astigmatism is typically the result of a cornea that is elongated and not perfectly spherical, which casts a distorted image onto the retina. This causes a blurry image of objects that are both near and far to the viewer. Astigmatism often occurs in combination with other refractive errors such as nearsightedness or farsightedness.
Presbyopia
The youthful human lens is able to flex (accommodate) generating “zoom” power for up-close reading vision. As we age, a natural hardening of the lens results in loss of accommodation and is the first step in cataract development. The loss of accommodation is referred to as presbyopia and requires the use of reading glasses or a transition into bifocals/trifocals for some patients to achieve their full range of vision. Most patients recognize these changes in their mid-40s.
