Doctors define legal blindness as 20/200 vision or worse. The numbers mean that someone with perfect 20/20 vision can see objects from 200 feet; someone with 20/200 vision can only see objects from 20 feet. Some eye conditions may cause temporary loss of vision in one or both eyes. Knowing some of the causes for temporary blindness may help a person understand her condition, as well as determine the best treatments to restore vision.
A natural lens sits inside the eye, near the front. The lens focuses light on the back of the eye, playing a significant role in how well a person can see. With age, the lens turns hard and yellow, limiting the focusing capabilities of the lens, a condition called a cataract. In the early stages, a person will require prescription changes to make up for the changes to the lens. Eventually, the cataract will cause significant vision changes that an eye glass prescription cannot correct. A person with cataracts will struggle to read, watch television or perform other daily tasks. If left untreated, cataracts may lead to blindness in the affected eye, and this accounts for 48 percent of all cases of blindness worldwide, says the World Health Organization. Surgical removal of the cataract will restore vision in most patients, as long as the eye has overall good health.
The back of the eye has a lining called the retina. This sensitive layer of tissue relays visual information to the optic nerve, which then sends the information to the brain. A retinal detachment occurs when the retina pulls away from the back of the eye. Since the tissue can no longer transmit visual cues, the person will see a dark “curtain” over a section of the vision. The black area may take up a small portion of the vision, or, if a full detachment occurs, most of vision may appear black. A person with a detachment must seek immediate treatment to prevent permanent loss. Prompt surgical reattachment may return most of a person’s lost vision, says MayoClinic.com.
People with diabetes have a greater risk of certain eye disease. One condition, diabetic retinopathy, causes new blood vessels to grow on the retina, the back lining of the eye. These abnormal vessels are fragile, and often break and leak fluid. If the bleeding occurs above the retinal layer, the blood may mix with the vitreous, the jelly-like substance that fills the back of the eye. Significant bleeding may cloud vision, causing vision loss. Eye doctors use lasers to stop the growth and bleeding of these new vessels. However, if the bleeding clouds the vitreous, the patient cannot see out of the eye and the doctor cannot into the eye. If this occurs, the doctor may need to begin treatment with a vitrectomy, a procedure that removes the cloudy vitreous and replaces this with a clear liquid, says the American Optometric Association. This will clear vision, and further laser treatment will work to prevent additional bleeds.