The Lens, Aqueous, And The Anterior Chamber Angle Of The Eye
The eye has many components. Among its parts are the lens, aqueous humor and the anterior chamber angle of the eye. The properties and characteristics of each parts can be viewed in a large scale using a teaching microscope.
THE LENS
Seen in a eaching microscope, the lens is biconvex, avascular, colorless and almost completely transparent structure, about 4 mm thick and 9 mm in diameter. It is suspended behind the iris by the zonule, which connects it with the ciliary body. Anterior to the lens is the aqueous; posterior to it, the vitreous. The lens capsule is a semipermeable membrane (slightly more permeable than a capil¬lary wall) that will admit water and electrolytes.
A subcapsular epithelium is present anteriorly as seen in a teaching microscope. The lens nucleus is harder than the cor¬tex. With age, subepithelial lamellar fibers are continuously produced, so that the lens gradually becomes larger and less elastic throughout life. The nucleus and cortex are made up of long concentric lamellae. The suture lines formed by the end-to-end joining of these lamellar fibers are Y-shaped when viewed with the slit¬lamp. When viewed and seen in a teaching microscope, the Y is upright anteriorly and in¬verted posteriorly.
Each lamellar fiber contains a flattened nucleus. These nuclei are evident microscopically in the periph¬eral portion of the lens near the equator and are contin¬uous with the subcapsular epithelium.
The lens is held in place by a suspensory ligament known as the zonule (zonule of Zinn), which is composed of numerous fibrils that arise from the surface of the ciliary body and insert into the lens equator.
The lens consists of about 65% water, about 35% protein (the highest protein content of any tissue of the body), and a trace of minerals common to other body tissues. Potassium is more concentrated in the lens than in most tissues. Ascorbic acid and glutathione are pre¬sent in both oxidized and reduced forms.
There are no pain fibers, blood vessels, or nerves in the lens.
THE AQUEOUS
Aqueous humor is produced by the ciliary body. Enter¬ing the posterior chamber, it passes through the pupil into the anterior chamber and then pe¬ripherally toward the anterior chamber angle.
THE ANTERIOR CHAMBER ANGLE
The anterior chamber angle lies at the junction of the peripheral cornea and the root of the iris. Its main anatomic features when seen in a teaching microscope are Schwalbe’s line, the trabecular meshwork (which over¬lies Schlemm’s canal), and the scleral spur.
Schwalbe’s line, when seen in a teaching microscope, marks the termination of the corneal endothelium. The trabecular meshwork is triangular in cross-section, with its base directed toward the ciliary body. It is composed of perforated sheets of collagen and elastic tissue, forming a filter with decreasing pore size as the canal of Schlemm is approached. The inter¬nal portion of the meshwork, facing the anterior cham¬ber, is known as the uveal meshwork; the external por¬tion, adjacent to the canal of Schlemm, is called the corneoscleral meshwork. The longitudinal fibers of the ciliary muscle insert into the trabecular meshwork. The scleral spur is an inward extension of the sclera between the ciliary body and Schlemm’s canal, to which the iris and ciliary body are attached. Efferent channels from Schlemm’s canal (about 30 collector channels and about 12 aqueous veins) communicate with the episcle¬ral venous system. Read more on this subject
