A mains electricity (AC-powered), ophthalmic instrument designed to examine the interior of the eye allowing the examiner to clearly see a wide angle, stereoscopic impression of the details of the fundus (retina) and other structures. It typically consists of a main light to illuminate the interior of the eyeball, a system of lenses and filters and an illuminator beam to eliminate reflexes. Also called a binocular indirect ophthalmoscope (BIO), it produces images that better overcome large refractive errors and subtle colour differences. It can be mounted on a headband or spectacle frames and the power is run through a transformer to reduce this to low-voltage.
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