National Eye Institute

Cataract
A clouding of the lens of the eye.

Diabetes
Diabetes is a chronic disease in which blood sugar levels are above normal. Complications may lead to vision loss.

Diabetic eye disease
A group of eye problems that people with diabetes may face as a complication of diabetes.

Diabetic retinopathy
Damage to the blood vessels in the retina due to diabetes.

Dilated eye exam
An eye examination where drops are placed in your eyes to widen, or dilate, the pupils. The eye care professional uses a special magnifying lens to examine the retina and optic nerve for signs of damage and other eye problems. After the exam, your closeup vision may remain blurred for several hours.

Focal laser treatment
A laser surgery treatment where an ophthalmologist places up to several hundred small laser burns in the areas of retinal leakage surrounding the macula.

Glaucoma
An increase in the fluid pressure inside the eye that leads to optic nerve damage and loss of vision.

Macula
Small central area of the retina; area of acute central vision.

Macular edema
When fluid leaks into the center of the macula, the part of the eye where sharp, straight-ahead vision occurs. The fluid makes the macula swell, blurring vision.

Mild nonproliferative retinopathy
The first stage of diabetic retinopathy where small areas of balloon-like swelling (microaneurysms) occur in the tiny blood vessels of the retina.

Moderate nonproliferative retinopathy
The second stage of diabetic retinopathy where blood vessels that nourish the retina are blocked.

Optic nerve
Largest sensory nerve of the eye; carries impulses for sight from the retina to the brain.

Proliferative retinopathy
The fourth stage of diabetic retinopathy where signals sent by the retina for nourishment trigger the growth of new blood vessels. These new blood vessels are abnormal and fragile. They grow along the retina and the surface of the clear vitreous gel that fills the inside of the eye. By themselves, these blood vessels do not cause symptoms or vision loss. However, they have thin, fragile walls. If they leak blood, severe vision loss and even blindness can occur.

Scatter laser surgery
A laser surgery treatment where an ophthalmologist places 1,000 to 2,000 laser burns in the areas of the retina away from the macula, causing the abnormal blood vessels to shrink.

Severe nonproliferative retinopathy
The third stage of diabetic retinopathy where many more blood vessels are blocked, depriving several areas of the retina of blood supply. These areas of the retina send signals to the body to grow new blood vessels for nourishment.

Tonometry
An instrument that measures the pressure inside your eye. Numbing drops may be applied to your eye during this test.

Type 1 diabetes
Formerly called juvenile diabetes or insulin-dependent diabetes, is usually first diagnosed in children, teenagers, or young adults. In this form of diabetes, the beta cells of the pancreas no longer make insulin because the body's immune system has attacked and destroyed them.

Type 2 diabetes
Formerly called adult-onset diabetes or noninsulin-dependent diabetes, is the most common form of diabetes. People can develop type 2 diabetes at any age-even during childhood. This form of diabetes usually begins with insulin resistance, a condition in which fat, muscle, and liver cells do not use insulin properly. At first, the pancreas keeps up with the added demand by producing more insulin. In time, however, it loses the ability to secrete enough insulin in response to meals.

Visual acuity test
An eye chart test that measures how well you see at various distances.

Vitrectomy
A surgical treatment where an ophthalmologist removes the vitreous gel and replaces it with a salt solution.

Vitreous gel
Transparent, colorless mass that fills the rear two-thirds of the eyeball, between the lens and the retina.