What I've researched so far.
What I've researched so far.
I've found some really good information about the eye in general which I felt like sharing with you. Here goes:
The human eye is the organ which gives us the sense of sight, allowing us to learn more about the surrounding world than we do with any of the other four senses. We use our eyes in almost every activity we perform, whether reading, working, watching television, writing a letter, driving a car, and in countless other ways. Most people probably would agree that sight is the sense they value more than all the rest.
The eye allows us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect or emit. The eye is able to see in bright light or in dim light, but it cannot see objects when light is absent.
process of vision
Light waves from an object (such as a tree) enter the eye first through the cornea, which is the clear dome at the front of the eye. The light then progresses through the pupil, the circular opening in the center of the colored iris. Next, the light passes through the crystalline lens, which is located immediately behind the iris and the pupil.
Initially, the light waves are bent or converged first by the cornea, and then further by the crystalline lens, to a nodal point (N) located immediately behind the back surface of the lens. At that point, the image becomes reversed (turned backwards) and inverted (turned upside-down).
The light continues through the vitreous humor, the clear gel that makes up about 80% of the eye?s volume, and then, ideally, back to a clear focus on the retina behind the vitreous. The small central area of the retina is the macula, which provides the best vision of any location in the retina. If the eye is considered to be a type of camera, the retina is equivalent to the film inside of the camera, registering the tiny photons of light which interact with it.
Within the layers of the retina, light impulses are changed into electrical signals and then sent through the optic nerve, along the visual pathway, to the occipital cortex at the posterior or back of the brain. Here, the electrical signals are interpreted or ?seen? by the brain as a visual image. When the light entering the eyes is bright enough, the pupils will constrict (get smaller), due to the pupillary light response.
Actually, then, we do not ?see? with our eyes but, rather, with our brains. Our eyes merely are the beginnings of the visual process.
myopia, hyperopia, astigmatism
If the incoming light from a far away object focuses before it gets to the back of the eye, that eye?s refractive error is called ?myopia? (nearsightedness). If incoming light from something far away has not focused by the time it reaches the back of the eye, that eye?s refractive error is ?hyperopia? (farsightedness).
In the case of ?astigmatism,? one or more surfaces of the cornea or lens (the eye structures which focus incoming light) are not spherical (shaped like the side of a basketball) but, rather, are cylindrical or toric (shaped more like the side of a football). As a result, there is no distinct point of focus inside the eye but, rather, a smeared or spread-out focus. Astigmatism is the most common refractive error.
presbyopia (?after 40? vision)
After age 40, and most noticeably after age 45, the human eye is affected by presbyopia, which results in greater difficulty maintaining a clear focus at a near distance with an eye which sees clearly at a far away distance (the latter being with or without the aid of glasses or contact lenses or following a LASIK procedure). This is due to a lessening of flexibility of the crystalline lens, as well as to a weakening of the ciliary muscles which control lens focusing, both attributable to the aging process.
eye growth
The average newborn?s eyeball is about 18 millimeters in diameter, from front to back (axial length); it grows slightly to a length of approximately 19½ millimeters as an infant; and it continues to grow gradually to a length of about 24-25 millimeters, or about 1 inch, in adulthood. (A ping-pong ball is about 1½ inch in diameter, which makes the average adult eyeball about 2/3 the size of a ping-pong ball.) The eyeball is set in a protective cone-shaped cavity in the skull called the ?orbit? or ?socket.?
extraocular muscles
The orbit is surrounded by layers of soft, fatty tissue which protect the eye and enable it to turn easily. Three pairs of extraocular muscles regulate the motion of each eye: the medial/lateral rectus muscles, the superior/inferior rectus muscles, and the superior/inferior oblique muscles.
eye structures
Among the most important components of the human eye are the cornea, conjunctiva, iris, crystalline lens, vitreous humor, retina, macula, optic nerve, and extraocular muscles.
Hope you've found it useful whether you have or not an eye conditon. Take care.
Débora
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