Medical Terminology Simplified

Fibrous Tunic

11–2 The fibrous tunicis the outer layer of the eyeball. It consists of the posterior

opaque (1) scleraand the anterior transparent (2) cornea. The sclera is the white

part of the eyeball. It is composed of tightly bound elastic and collagenous fibers,

which give shape to the eyeball and protect its inner structures. The sclera is avascular

but does contain sensory receptors for pain. At the junction of the sclera and cornea

is an opening known as the canal of Schlemm.A fluid called aqueous humor drains

into this sinus. The cornea is transparent and convex to permit the passage and cause

refraction (bending) of incoming lightwaves. The optic nerve exits through the

sclera at the posterior portion of the eyeball.

Observe the location of the outer layer of the eyeball (fibrous tunic) as you label the

sclera and cornea in Figure 11–1.

Frame 11–1to Frame 11–2

Eyes • CHAPTER 11 511511

(2)

(5)

(8)

(4)

(1)

(3)

(6)

(9)

(10)

(7)

(11)

Figure 11-1Eye structures.