ophthalmoscope

n. instrument used to see the interior of the eye; device used in eye examinations

The ophthalmoscope is an instrument used to examine the eye. Its use is crucial in determining the health of the retina and the vitreous humor. In patients with headaches, the finding of swollen optic discs, or papilledema, on ophthalmoscopy is a key sign, as this indicates raised intracranial pressure (ICP) which could be due to hydrocephalus, benign intracranial hypertension (aka pseudotumor cerebri) or brain tumor, amongst other conditions. Cupped optic discs are seen in glaucoma.
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Ophthalmoscope /oph·thal·mo·scope/ an instrument containing a perforated mirror and lenses used to examine the interior of the eye. [more]Ophthalmoscope - Community and Resources

Noun
1. medical instrument for examining the retina of the eye
(hypernym) medical instrument
(hyponym) orthoscope

(n.)
An instrument for viewing the interior of the eye, particularly the retina. Light is thrown into the eye by a mirror (usually concave) and the interior is then examined with or without the aid of a lens.