The dual meaning ofĀ kerato-Ā reflects its etymology: the Greek rootĀ kerasĀ (āhornā) was applied to the cornea because early anatomists recognized its tough, horn-like consistency ā the cornea is indeed an avascular, dense, fibrous tissue similar in feel to compressed horn. In ophthalmology,Ā kerato-Ā refers specifically to the cornea ā the clear, dome-shaped anterior surface of the eye responsible for about two-thirds of the eyeās total refractive power. In dermatology and histology,Ā kerato-Ā refers toĀ keratin, the fibrous structural protein that is the primary component of the epidermis (outer skin), hair shafts, fingernails, toenails, and animal horns/hooves. Because keratin-producing cells (keratinocytes) make up ~90% of all epidermal cells, theĀ kerato-Ā root is extremely productive in dermatological terminology as well. Context is everything ā if you seeĀ kerato-Ā in an ophthalmology note, it refers to the cornea; if you see it in a dermatology note, it almost certainly refers to keratin or horny skin tissue.
In the eye, the cornea gets its name from Medieval LatinĀ cornea telaĀ (āhorny web/sheathā), directly referencing its horn-like texture. It is the transparent, avascular anterior layer covering the iris and pupil, responsible for approximately 65-75% of the eyeās refractive power.