keratoscope

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keratoscope (Placido's disc) (ke-ră-toh-skohp) n. an instrument for detecting abnormal curvature of the cornea. It consists of a black disc marked with concentric white rings. The examiner looks at the reflection of the rings in the patient's cornea; a cornea that is abnormally curved (for example in keratoconus) or scarred reflects distorted rings.