Parts of an eye. 1) Our paired eyes are located in sockets of the skull called orbits. A brief account of the structure and function of the human eye is given in the following section.
The adult human eyeball is nearly a spherical structure. The wall of the eyeball is composed of three layers. The external layer is composed of dense connective tissue and is called the sclera.
The anterior portion of this layer is called the cornea. The middle layer choroid contains many blood vessels and looks bluish in color.
The choroid layer is thin over the posterior two-thirds of the eyeball, but it becomes thick in the interior part to form the ciliary body.
The ciliary body itself continues to form a pigmented and opaque structure called the iris, which is the visible colored portion of the eye.
The eyeball contains a transparent crystalline lens held in place by ligaments attached to the ciliary body. In front of the lens, the aperture surrounded by the iris is called the pupil.
The diameter of the pupil is regulated by the muscle fibers of the iris. The inner layer is the retina, and it contains three layers of cells- from inside to outside - ganglion cells, bipolar cells, and photoreceptor cells.
There are two types of photoreceptor cells, namely, rods and cones. These cells contain the light-sensitive protein called the photopigments.
The daylight vision and color vision are functions of the rods. The rods contain a purplish red protein called the rhodopsin or visual purple, which contains vitamin A.
There are three types of cones in the human eye that possess their own characteristics of photopigment that's respond to red, green, and blue light. The sensation of different colors is produced by various combinations of these cones and their photopigments.
When these cones are stimulated equally, A sensation of white light is produced. The optic nerves leave the eye, and the retinal blood vessels enter it at A point medical to and slightly above the posterior pole of the eyeball.
Photoreceptor cells are not present in that region. Hence, it is called the blind spot at the posterior pole of the eye lateral to the blind spot, a yellowish pigmented spot called macula lutea with A central pit called the fovea.
The fovea is A thinned-out portion of the retina where only the cones are densely packed. It is the point where the visual acuity(resolution)is the greatest.
The space between the cornea and the lens is called the aqueous chamber and contains a thin watery fluid called aqueous humor.
The space between the lens and the retina is called the vitreous chamber and is filled with a transparent gel called the vitreous humor.
2) Mechanism of vision.
The light rays are visible wavelength focussed on the retina through the cornea, and the lens generates potential in rods and cones.
As mentioned earlier, the photosensitive compound in the human eyes is composed of opis and retinal from opsin resulting in changes in the structure of the opsin.
This causes membrane permeability changes.
Very knowledgeable
You must be logged in to post a comment.