Cavities and chambers of the eyeball


The eyeball contains an anterior cavity and a posterior cavity, segregated by the interior lens and the associated lens capsule. The anterior cavity is then segregated once again into two distinct chambers, the anterior chamber and the posterior chamber, by the iris. Between the iris and the cornea, the anterior chamber can be located. Alternatively, between the iris and the suspensory ligament and the lens, the posterior chamber can be located. Both chambers are fluid filled (a watery substance known as aqueous humor) and are connected at the pupil. Aqueous humor is perpetually produced, which maintains intraocular pressure of 12 mmHg in both the anterior and posterior chambers. The avascular lens and the cornea also receive the necessary fluids and oxygenation from the aqueous humor. The vascular epithelium of the ciliary body is believed to secrete approximately 5.5 milliliters of aqueous humor in a 24 hour period. It drains from the eyeball from the scleral venous sinus after receiving the fluid from the anterior chamber. The fluid enters the anterior chamber after passing through the fluid. The fluid’s final destination is the bloodstream, where it mixes with other waste fluids until it is finally excreted from the body. Where the iris meets the cornea, the scleral venous sinus (or the canal of Schlemm) can be located.

A transparent jelly-like fluid known as vitreous humor is found in the large posterior cavity. This substance is responsible for assisting in maintaining the appropriate intraocular pressure, retaining the shape of the eyeball, and presses the retina against the choroid. The vitreous humor does not undergo continuous production but was originally formed in the embryonic stage. As the human body grows, an adjustment in the amount of vitreous humor takes effect.


Cavities and chambers of the eyeball
Image: Cavities And Chambers Of The Eyeball


The Eyeball’s Functional Purpose

The eyeball is the vessel which transmits the basics of sight. Its basic function is to focus rays of light for the purpose of stimulating the photoreceptors of the retina. This requires five basic processes to come into play. First, the light rays must transmit through the transparent media of the eyeball. Second, media of various densities refract the light. The lens must then accommodate in order to properly focus the light rays. The iris then constricts the pupil in a regulatory manner to adjust the light to an appropriate degree, which then flows into the posterior cavity. Finally, the eyeballs must experience convergence to maintain visual acuity. When one or more of these basic functions fails, the likely result is at least partial visual impairment.


When light enters the eye, it must first pass through 4 transparent media before they can reach the photoreceptors for proper stimulation. The light rays initially pass through the cornea before they pass through the aqueous humor, then the lens, and finally the vitreous humor. The cornea and the lens are considered solid transparent media, created by avascular protein fibers which are packed remarkably close together. The out layer of the cornea is covered by an extra thin transparent membrane which is really a continuation of the conjunctiva. The aqueous humor is a fluid media and the vitreous humor is a mix, creating a jelly like media that remains transparent.


By definition, refraction means to bend the light. When light rays are refracted, they are able to transmit from one media at an oblique angle before reaching a different media, resulting in variation of optical density. The aqueous humor and the vitreous humor provide minimal refraction. The main refracting media remains the convex cornea, providing the greatest refraction. The light rays travel through the lens, which is designed to refine the refraction. In fact, the lens is the only refractive media which is able to adjust its shape to provide ultimate refraction angles. The refraction of light rays is then able to define the refraction so intensively that the images appear upside-down on the surface of the retina. The visual cortex of the occipital lobe receives the impulses of images and is able to interpret them in the right side up manner that the image presents.


Lens accommodation refers to the lens’ ability to alter its shape in order to refine the refraction. Ciliary muscle contract, which enables adjustments of the lens shape. This helps to bring the image into a clear image for the retina. The biconvex lens of the eye is makes various adjustments for any image which is viewed from less than 20 feet away. When the smooth muscle fibers of the ciliary body contract, the lens relaxes and thickens in response to the relaxation of the suspensory ligament. This creates a thicker lens which in turn creates a more convex lens, necessary for the viewing of objects close to the eye.


Parasympathetic impulses cause constriction of the pupil. In reality, the pupillary constrictor muscle receive the simulation, which means the iris is responsible for closing in around the pupil rather than the pupil growing or shrinking. Pupillary constriction is relied upon for two vital reasons in receiving vision. The initial responsibility of pupillary constriction reduces the amount of light that can reach the posterior cavity. It also protects the retina from damage as the result of bright light or a sudden flooding of light. A small pupil prevents an overload of light from reaching the posterior cavity by means of the periphery of the lens. Without this mechanism in effect, the retina would not be able to achieve focused vision. Autonomic constriction of the pupillary muscles occurs in conjunction with the accommodation of the lens for optimal visual acuity.


When visual stimulation of a close object is necessary, the eyes converge. This means that the eyeballs each rotate medially. This is the phenomenon that can explain why peeking at the tip of one’s nose creates a cross-eyed effect. Convergence occurs so that each retina will be allotted the same amount of light when focusing in on an object that is close at hand.


The eyes are responsible for transducing energy derived from the electromagnetic spectrum to create and send impulses to the brain for interpretation. Visible light ranges between 400 and 700 nanometers. The infrared segment of the spectrum includes light of higher wavelengths is not discerned by the eye as anything other than heat when viewed at the appropriate angles. Ultraviolet light is created using more energy than light and thus, with its shorter wavelength, is filtered out by the lens’ yellow filter. Should a human have their lenses removed but not replaced with any form of prosthesis is likely to visually witness ultraviolet rays, just as insects such as honeybees can.
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