fibrous tunic of eyeball fibrous tunic of eyeball the sclera and cornea form the fibrous tunic of the bulb of the eye; the sclera is opaque, and constitutes the posterior five-sixths of the tunic; the cornea is transparent, and forms the anterior sixth. fibrous tunic of eyeballhorizontal section of the eyeball. (cornea labeled at top, sclera labeled at center right.)detailsidentifierslatintunica fibrosa bulbi, tunica fibrosa oculita98a15.2.02.001ta26743fma58102anatomical terminology the term "corneosclera" is also used to describe the sclera and cornea together.