An ophthalmoscope is an instrument that enables a doctor to examine the inside of your eye. The instrument has an angled mirror, various lenses, and a light source. With it, a doctor can see the vitreous humor (the jellylike substance in the eye), the retina, the optic nerve, and the retinal veins and arteries. Ophthalmoscopy is painless.
Ophthalmoscopy is useful to detect not only changes in the retina due to eye disease but also changes due to certain diseases affecting other parts of the body. For instance, it is useful to detect the changes that occur in the retinal blood vessels in people with high blood pressure, arteriosclerosis, and diabetes mellitus. Ophthalmoscopy can also be used to diagnose elevated pressure within the brain, which results in a swelling (pushing-out) of the normally cupped optic disk (papilledema). Tumors on the retina can be seen with ophthalmoscopy. Macular degeneration can be diagnosed with ophthalmoscopy as well.