Common Vision Conditions
How Our Eyes Work
The eye is a tiny organ that measures about an inch long and weighs about 1/4 of an ounce. It is part of a complex system that translates light into images. Light enters our eye through the cornea and into the pupil. The pupil is the black hole in the middle of the iris, the colored part of the eye. Behind the iris is the natural lens. It focuses the light onto the retina, the inside layer of the eye. The retina contains cells that are sensitive to light. This allows an image to be projected on them. The image is then converted into electrical impulses that are sent to the brain through the optic nerve at the back of the eye.
All of this happens continuously and instantly to give us clear vision at near, intermediate and far distances. But, our eyes don’t always work perfectly. Their exact size and shape affect how well they focus light. These differences can cause some of us to have refractive errors such as myopia, hyperopia, or astigmatism. In addition, over time, we all lose our ability to focus on near objects. This is a refractive condition known as presbyopia.
Presbyopia is the clinical term for near vision loss that most of us begin to notice in our 40s and 50s. It happens because our natural lens is losing its elasticity and ability to adjust its shape. This causes the image of near objects to form behind the retina, making our near vision blurry.
Myopia is the most common refractive error. Experts estimate that more than 40% of Americans have myopia, also known as nearsightedness. This occurs primarily because the eye is too long. The image of distant objects forms in front of the retina, making these objects blurry.
Hyperopia, or farsightedness, is a refractive error that occurs primarily because the eye is too short. As a result, the image of near objects forms behind the retina and makes these objects blurry.
Astigmatism occurs when light coming into the eye focuses inconsistently. This can cause objects to look stretched or distorted. Astigmatism occurs when the cornea, the outer layer of the eye, has an irregular oval shape. People with astigmatism may also have other refractive errors.