The human eye is very unique, if we compare it with a camera. It gives us the ability to see things in three dimensional picture. Inspite of this, our vision has its own limitations. We cannot see all the wavelengthes of the light spectrum. What can we see is limited to the visible region of the light spectrum. We cannot see light in the ultra-violet or the infra red regions of the spectrum. Examples are CO2 LASER which we can feel but do not see. this LASER is in the infra red region.
The structure of the human is complicated and the substructure of the eye that processes the light data that is received to it and transforms it to electrical signals is called the RETINA. In some diseases of the eye the retina becomes detached from the other structure (The choroid) that normally holds the retina causing visual disturbances and blindness.
The light received on the retina is focused through the lens. The lens is attached to a muscle that is called the ciliary muscle. Contraction or relaxation of this muscle adjusts the lens so that it focus the light on the retina.
The structure or anatomy of the eye is as follows:
The outer layer of the eyeball is called the cornea. This structure covers the iris and the pupil. It is continuous with the white of the eye ( the sclera) which covers all the other parts of the eyeball. The cornea does not have blood supply so its nutrition comes from glucose who is in the aquous humor. This fluid is found in the anterior and posterior spaces of the eye and these anterior and posterior spaces are separated with the iris and the ciliary muscle. They both contain the aquous humor. This fluid is responsible mostly for the intraocular pressure of the eye which is normally in the range between 10-20 mmHg. The cornea is transparent and the light that passes through it is slightly refracted.
The iris is a pigmented structure that has a lot of melanin pigment that is produced by melanocytes that are found in the iris. The degree of melanin concetration in the iris determines the color of the eyes. Brown to black eyes mean that the iris has a lot of melanin pigment while blue to green eyes mean that the iris does not have much melanin. The iris is continuous with the ciliary muscle and the choroid. The ciliary body which contains the ciliary muscle secretes the aquous humor.
The choroid is rich in blood supply. it is pigmented like the iris and appear brown in color due to the high concentration of melanin in this layer. The cornea is in turn continuous with the white of the eye or the sclera. The sclera does not have blood supply or cells. It is composed of connective tissue thats why its injury does not heal quickly.
The pathology of the eye can be either infectious or non infectious. Infectious diseases can be caused with bacteria or viruses or fungi. The non infectious diseases can be a manifestation of other systemic diseases such as occurs in sarcoidosis which causes a simultaneous inflammation of the iris and the ciliary body. The name of this disease is iridocyclitis. Two intestinal diseases have manifestations in the eye as well in the form of iritis. These are ulcerative colitis and crohn disease.
Cararact or inability for light to penetrate the lens is a condition in which the lens is unable for some reason to let the light pass through it. This condition can progress to loss of vision due to the irreversible damage that happens to the lens. This is so because the lens does not have inherent blood supply and relies on diffuseable glucose for its energy sources. The glucose comes from the aquous humor.
Glaucoma is another eye disease and is defined as an increase in the intraocular pressure of the eye. The eye have two types of fluids. These are the aquous humour and the vitrious body. The aquous humor is found in the anterior space of the eye while the vitreous body is found in the posterior part of the eye. They are separated by the lens and the ciliary body. The vitreous body is jellylike in structure.
The intraocular pressure is determined primarily by the aquous humour and partly by the vitreous body. The aquous humour is continually changed and is kept at a constant volume. An interruption to this dynamic mechanism of the aquous humour such as a blockage can lead to intraocular pressure and subsequently can lead to glaucoma. This in turn can cause loss of vision