Many cases of diabetic retinopathy do not show symptoms until the disease has progressed, and can be detected only during an eye exam.

The ophthalmologist is likely to review a medical history and perform a physical examination concentrating on the patient’s eyes. Symptoms related to the eyes or vision problems will be of particular interest, as well as a history of the patient’s range of glucose (blood sugar) levels.

The patient’s visual acuity will be tested, and intraocular pressure (fluid pressure in the eye) will be measured. The eyes will be dilated during the exam. Eyedrops are placed in the eyes to enlarge the pupils and allow the physician to examine more of the inside of the eye. An instrument called an ophthalmoscope or funduscope is used to examine the retina. 

The physician will look for the following symptoms in making a diagnosis:

• Blood vessels that leak
• Hemorrhage of the retina
• Swollen retina
• Fatty deposits (exudates) in the retina
• Damage to nerve fibers
• Changes in blood vessels
• Microaneurysms
• New blood vessels (neovascularization)
• Vitreous hemorrhage
• Formation of scar tissue and possible detachment of the retina

Sometimes a physician will use fluorescein angiography to check for leaky blood vessels. In this test, a dye is injected into a vein in the patient’s arm. When the dye travels to the retina, it fills the blood vessels, which appear white when photographed with blue light.