An optical instrument or recording device designed to measure and document the refractive properties of lenses or the eye's optical characteristics.
From Greek 'diopter' (optical power) + '-graph' (that which writes or records), combining optical measurement terminology with the idea of visual recording.
A dioptograph is essentially an early ancestor of modern automated eye-testing machines—instead of the phoropter you use at the optometrist where you click lenses, this historical device would automatically record refractive data.
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