ˌ ̷ ̷ˌthalˈmäməd.ə(r), -_thəl- noun
Etymology: International Scientific Vocabulary ophthalm- + -meter
: an instrument for measuring the eye ; specifically : an instrument for measuring the size of a reflected image on the convex surface of the cornea of the eye by which its principal meridians and the presence and amount of astigmatism may be determined