The Special Senses

Page
5

Optic nerve

Posterior pole

Fovea centralis

Macula lutea

Retina

Choroid

Sclera

Ora serrata

(a) Diagrammatic view. The vitreous humor is illustrated only in the bottom part of the eyeball.

Ciliary body

Ciliary zonule

(suspensory

ligament)

Cornea

Iris

Anterior pole

Pupil

Anterior

segment (contains

aqueous humor)

Lens

Scleral venous

sinus

Posterior segment

(contains vitreous humor)

Slide 34

Internal Chambers and Fluids

Posterior segment contains vitreous humor that:

Transmits light

Supports the posterior surface of the lens

Holds the neural retina firmly against the pigmented layer

Contributes to intraocular pressure

Anterior segment is composed of two chambers

Anterior chamber—between the cornea and the iris

Posterior chamber—between the iris and the lens

Slide 35

Internal Chambers and Fluids

Anterior segment contains aqueous humor

Plasma like fluid continuously filtered from capillaries of the ciliary processes

Drains via the scleral venous sinus (canal of Schlemm) at the sclera-cornea junction

Supplies nutrients and oxygen mainly to the lens and cornea but also to the retina, and removes wastes

Glaucoma: compression of the retina and optic nerve if drainage of aqueous humor is blocked

Slide 36

Figure 15.8

Sclera

Bulbar

conjunctiva

Scleral venous

sinus

Posterior

chamber

Anterior

chamber

Anterior

segment

(contains

aqueous

humor)

Corneal-

scleral junction

Cornea

Cornea

Corneal epithelium

Corneal endothelium

Aqueous humor

Iris

Lens

Lens epithelium

Lens

Posterior

segment

(contains

vitreous

humor)

Ciliary zonule

(suspensory

ligament)

Ciliary

processes

Ciliary

muscle

Ciliary body

1

Aqueous humor is

formed by filtration

from the capillaries in

the ciliary processes.

2

Aqueous humor flows from the

posterior chamber through the

pupil into the anterior chamber.

Some also flows through the

vitreous humor (not shown).

3

Aqueous humor is reabsorbed

into the venous blood by the

scleral venous sinus.

1

2

3

Slide 37

Lens

Biconvex, transparent, flexible, elastic, and avascular

Allows precise focusing of light on the retina

Cells of lens epithelium differentiate into lens fibers that form the bulk of the lens

Lens fibers—cells filled with the transparent protein crystallin

Lens becomes denser, more convex, and less elastic with age