To designate and describe parts of letters and other characters, many terms are borrowed from architecture or from human and animal anatomy. We are even speaking of type design anatomy.

In Latin type design, the eye refers to the ratio between the x-height and the other guidelines (ascenders and descenders).

A typeface is suited for text usage if it has a ratio slightly bigger between its eye to its ascenders and descenders, as this enhances the legibility of the letters.