Opsiometer

Part of speech: noun

Definitions

1. An instrument used to measure the degree of ocular deviation or eye misalignment
2. A device that quantifies eye movement in relation to certain stimuli
3. A tool designed for evaluating the alignment of the eyes in clinical settings

Etymology: Its parts are two Ancient Greek elements: "opsis", meaning sight or appearance, and "metron", measure. The second element is the one in "thermometer" and "speedometer", and it turns a name for what is being measured into a name for the instrument. Here that is the eye's deviation from its intended line of sight, the misalignment behind a squint or double vision. "Opsis" comes from the Greek root for seeing, which also gives English "optic" and "optical". So the name amounts to "sight-measure," a tool named for the faculty it tests. French forms the parallel "opsiomètre" on the same Greek base.

Synonyms: optometer, vision tester, eye tester