This study, conducted at the NIH Clinical Center and the University of Wisconsin University, will compare measurements obtained using older and newer models of a machine called an optical coherence tomography (OCT) scanner. This instrument uses a beam of light to measure the thickness of the retina, the light-sensitive inner lining of the back of the eye. OCT measurements will be done in multicenter clinical trials of new treatments for disorders that cause vision loss, such as macular edema. Because some centers in these studies will use the older OCT model and some the newer one, it is necessary to determine whether the two models give comparable results.

People 18 years of age and older in the following categories may be eligible for this study:

• People with diabetes, with or without macular edema;
• People with other retinal disease, such as uveitis or vein occlusion in the retina;
• People with no history of eye disease who have a normal retina.

Participants will have the following tests and procedures:

• Eye examination to assess vision and eye pressure and to evaluate the retina. The pupils are dilated with drops for this examination.
• Stereoscopic color fundus photography to examine the back of the eye. Eye drops are used to enlarge the size of the pupils to allow for a through examination and photographs of the eye using a special camera that flashes a bright light into the eye.
• OCT to measure retinal thickness. For this procedure, the subject sits in front of a small screen and looks at a target in the center of the screen while a dim red light moves across the subject's retina. This test is done first with one model of the OCT scanner, then the other. Finally, the test is repeated in both eyes with whichever model was used first.

Patients who are being treated for macular edema will repeat the same tests at their 3-month visits.