The Globe

The eye has three layers or coats, three compartments and contains three fluids (Figure 2.2).

1. The three coats of the eye are as follows:

(a) Outer fibrous layer:

• lamina cribrosa.

(b) Middle vascular layer ("uveal tract"):

• ciliary body - consisting of the pars plicata and pars plana

(c) Inner nervous layer:

• pigment epithelium of the retina

• retinal photoreceptors

• retinal neurons.

2. The three compartments of the eye are as follows:

(a) Anterior chamber - the space between the cornea and the iris diaphragm.

(b) Posterior chamber - the triangular space between the iris anteriorly, the lens and zonule posteriorly, and the ciliary body.

(c) Vitreous chamber - the space behind the lens and zonule.

3. The three intraocular fluids are as follows:

(a) Aqueous humour - a watery, optically clear solution of water and electrolytes similar to tissue fluids except that aqueous humour has a low protein content normally.

(b) Vitreous humour - a transparent gel consisting of a three-dimensional

Figure 2.1. Surface anatomy.O

Figure 2.1. Surface anatomy.O

network of collagen fibres with the interspaces filled with polymerised hyaluronic acid molecules and water. It fills the space between the posterior surface of the lens, ciliary body and retina.

(c) Blood - in addition to its usual functions, blood contributes to the maintenance of intraocular pressure. Most of the blood within the eye is in the choroid. The choroidal blood flow represents the largest blood flow per unit tissue in the body. The degree of desaturation of efferent choroidal blood is relatively small and indicates that the choroidal vasculature has functions beyond retinal nutrition. It might be that the choroid serves as a heat exchanger for the retina, which absorbs energy as light strikes the retinal pigment epithelium.

Clinically, the eye can be considered to be composed of two segments:

1. Anterior segment - all structures from (and including) the lens forward.

2. Posterior segment - all structures posterior to the lens.

0 0

Post a comment