Learn more about Ophthalmic diagnosis, care, and treatments with this comprehensive encyclopedia.
Legal BlindnessLegal blindness is a baseline measurement of vision loss that qualifies for benefits. Most government agencies and healthcare institutions agree it refers to a central visual acuity of 20/200 or less in the better eye with the best possible correction, and/or a visual field of 20 degrees or less.
Legal blindness always requires both eyes meet the minimum measurement; there is no such thing as “legal blindness in one eye.”
Legal blindness should not be confused with “blindness” which is generally understood to mean an inability to differentiate light from dark or see at all. Most people who qualify for legal blindness have varying degrees of usable vision.
LensThe lens is a dense, transparent structure made of proteins, located just behind the iris and pupil. Its curvature and density cause light waves to bend as they travel through the lens. After passing through the lens, the light waves converge and project an inverted image on the retina. The retina changes the light waves to electric impulses that then travel along the optic nerve to the brain. This entire series of events results in a visual and understandable representation of light and color.
The lens also changes shape in order to focus on objects at various distances. The older one becomes, the stiffer and more inflexible the lens becomes. Oftentimes, the lens becomes so stiff that it cannot change its shape sufficiently to accommodate both images of objects up close and far away. This is why the need for bifocals or reading glasses are common as people age.
New, thin layers continually grow over old layers of the lens. These layers of cells grow inward from the edges but never form in the center of the lens. If the cells at the center of the lens grow cloudy, cataracts develop. Natural lenses can be replaced with artificial lenses in a relatively fast and easy surgical procedure, making cataracts an easily treatable disease.
Laser PhotocoagulationLaser photocoagulation is a treatment most often used for diabetic retinopathy that uses a laser to seal leaking blood vessels. During later stages of diabetic retinopathy, abnormal blood vessels grow in response to damage within the retina. These new capillaries are weak and will often break, leak, or burst. When this happens, sudden and severe vision loss can occur.
During laser photocoagulation, a laser is used to direct intense, focused rays of light through the transparent structures of the eye to the retina. The laser will burn, or coagulate, the tissues around the abnormal blood vessels, destroying the blood vessels and scarring the tissues so that new blood vessel growth cannot occur. The laser is not directed toward the macula, the area responsible for clear, distinct, straight-ahead vision, as it would destroy sight. Vision is preserved using this procedure but is not restored.
Treatment is usually a short, painless, and relatively easy process, done in the doctor’s office, and does not require hospitalization.
Laser photocoagulation is sometimes used to treat type 2 neovascularization and central serous chorioretinopathy, as well as for detached retinas.
The image below shows how laser light is focused on to specific areas of the retina using a "contact lens" held by the doctor.