Ophthalmoscopy, or funduscopy, is a medical test where the interior surface of the eye (the "fundus") is examined using an ophthalmoscope (also known as a funduscope) which consists of a single high magnification lens and a light source. It is routinely performed as part of a regular eyesight examination, but is regularly performed when a patient is suffering from a severe headache to check ocular pressure and in patients with diabetes mellitus to check for deterioration of the retina.