Is it farther or further?
keratoscopy ker·a·tos·co·py (kěr'ə-tŏs'kə-pē)
Examination of the anterior surface of the cornea to determine the character and amount of corneal astigmatism.
keratoscope ker·a·to·scope (kěr'ə-tō-skōp')
An instrument marked with lines or circles for use in examining the curvature of the cornea. Also called Placido's disk.