Laser Eye Surgery

Many people who have eye damage always seek what the best cure system. The result of many cure model still don’t make satisfactory yet. If you're looking for an alternative option to glasses or contact lenses, laser eye surgery could be the ideal solution. Laser eye surgery is an eye treatment that has given millions of people freedom from the need to wear glasses and contact lenses.

LASIK or Lasik is a type of refractive surgery for correcting myopia, hyperopia, and astigmatism. LASIK is performed by ophthalmologists using a laser The procedure is generally preferred to photorefractive keratectomy, PRK, (also called ASA, Advanced Surface Ablation) because it requires less time for the patient's recovery, and the patient feels less pain overall. However, there are instances where a PRK/ASA procedure is medically justified as being a better alternative to LASIK

Many patients choose LASIK as an alternative to wearing corrective eyeglasses or contact lenses. This technology have been apply by the Colombia-based Spanish ophthalmologist Jose Barraquer, who, around 1950 in his clinic in Bogotá, Colombia, developed the first microkeratome, and developed the technique used to cut thin flaps in the cornea and alter its shape, in a procedure he called keratomileusis. Stephan Schaller assisted in this landmark procedure. Barraquer also researched the question of how much of the cornea had to be left unaltered to provide stable long-term results.

This technology then improve and other country also interest to this technology. Russia in the 1970s by Svyatoslav Fyodorov, and PRK (photorefractive keratectomy), developed in 1983 at Columbia University by Dr. Steven Trokel, who in addition published an article in the American Journal of Ophthalmology in 1983 outlining the potential benefits of using the Excimer laser in refractive surgeries. (RK is a procedure in which radial corneal cuts are made, typically using a micrometer diamond knife, and is completely different from LASIK).

In the United Stated this technique use on June 20, 1989. "Method for modifying corneal curvature," encompassing the surgical procedure in which a flap is cut in the cornea and pulled back to expose the corneal bed. The exposed surface is then ablated to the desired shape with an Excimer laser, after which the flap is replaced.

LASIK surgery may need of one day be replaced by intrastromal ablation via all-femtosecond correction (like Femtosecond Lenticule Extraction, FLIVC, or IntraCOR), or other techniques that avoid weakening the cornea with large incisions and deliver less energy to surrounding tissues. The 20/10 FEMTEC laser has recently been used for incision-less ablation on several hundred human eyes and achieved very successful results for presbyopia, with trials ongoing for myopia and other disorders.

Myopia or Nearsightedness

Myopia, or nearsightedness, is an error of refraction in the eye that causes objects more than a short distance away to appear blurred. It usually result from the cornea of the eye being too far from the retina, so that images are focused in front of the retina.

The error can be corrected for by concave Eye Diseases or by contact lenses, severe cases of myopia are sometimes treated by a controversial surgical distortion of the cornea known as radial keratotomy.

Many thousand people are suffer of this eye error, nearsightedness make people difficult to see something in distance such as highway sign, or object in a distance, but can see for close object and can work easily for close object like sewing.

To correct this error people can use a eye glasses or contact lens, but currently the technology have improved using eye laser surgery. The kind of this surgery as follows:
PRK is laser eye surgery that removes a layer of corneal tissue, which flattens the cornea and allows light rays to focus closer to or even on the retina.

LASIK is the most common refractive procedure a flap is cut through the top of the cornea, a laser removes some corneal tissue, and then the flap is dropped back into place.

Many Kind of Animals Eyes

Animals eyes are classified vary on this world. Eyes are an organ that base on the light come different each others, there are about 32 kind on animals world, that principally different work. The most complete of eyes like a camera that can absorb of wide spectrum like on primate such as monkey and human.

Eyes model of many animals is vary, and for human all eyes is located in the fronts that sometime have a blind spot area that cannot be seen. If we lay 2 same drawing of cat or other drawing with a distance of about 15 cm, then locate in front about one arm, close one of your eyes then move that drawing close to eyes slowly, on certain distance then one of the drawing will lost.

Octopus eye is an example of better eyes structure than primate in, the blood vessel located before the light recipient. So the octopus eye design is better than the human eye!

Our eyes are an advance design because can use as camera SLR and autofocus, auto exposure (fast adapt from dark to light by opening the diaphragm). If on the insect eyes they cannot adapt vastly and fish eyes just fixed focus like plastic camera and dog eyes are color blind.

Human eyes are stereoscopic (can suspect the distance from sight), using comparison software can compare the parallax distance and this technology still don’t imitate by human equipment.

The Retina

Retina is a delicate servos membrane, upon the surface of which the images of external objects are received. Its outer surface is in contact which the choroid; its inner with the vitreous body. Behind it is continuous with the optic nerve; it is gradually diminishes in thickness from behind forward; and, in front, extends nearly as far as the ciliary body, where it appears to terminate is a jagged margin, the ora scrrata. Here the nervous tissues of the retina end, a thin prolongation of the membrane extends forward over the back of the ciliary processes and iris, forming the parts ciliaris retinae and parts iridiae retina, already referred to. This forward prolongation consists of the pigmentary layer of the retina together with a stratum of columnar epithelium.

The retina is soft, semi transparent, and of a purple tint in the fresh state, owing to the presence of a coloring material named rhodopsin or visual purple; but it soon becomes eluded, opaque and bleached when exposed to sunlight. Exactly in the center of the posterior park of the retina, corresponding to the axis of the eye, and at a point in the fresh state, owing to the presence of a coloring material named rhodopsin or visual purple; but it soon becomes clouded, opaque and bleached when exposed to sunlight. Exactly in the center of the posterior part of the retina, corresponding to the exist of the eye, and at a point in which the sense of vision is most perfect is an oval yellowish spot, called, after its discover, the yellow spot or macula lutea of Sommering , having a central depression, the fovea centralis.

The retina in the situation of the fovea centralis is exceedingly thin, and the dark color of the choroid is distinetly seen through it; so that it presents more the appearance of a foramen, and hence the name “foramen of Sommering” at first given to it. It exist only in man, the quadrumana and some suarian reptiles. About one-eight of an inch to the inner side of the yellow spot is the point of entrance of the optic nerve (porus opticus); here the nervous substance is slightly raised so as to form an eminence (colliculus nervi optivi); the arteria centralis retinae pierce its centre. That is the only part of the surface of the retina from which the power of vision is absent, and is termed the “blind spot.”

If the membrane damage than our eyes need use an aid tools like glass or contact lense, right now people don't need use this glass if use current technology by laser surgery LASIK.

The Sclerotic and Cornea

The sclerotic and cornea form the external tunic of the eyeball; they are essentially fibrous in eye structure, the sclerotic being opaque, and forming the posterior five sixths of the globe; the cornea, which forms the remaining sixth, being transparent.

The sclerotic has received its name from its extreme density and hardness; it is a firm, unyielding, fibrous membrane, serving to maintain the form of the globe. It is much thicker behind than front. Its external surface is of a white color, and is in contact with the inner surface of the capsule of Tenon; it is quite smooth, except at the points where the Rocti and Obliqui muscles are in the whitness and brilliancy of the front of the eyeball. Its inner surface is stained of a brown color, marked by grooves, in which are lodged the ciliary nerves and vessels; this is loosely connected by an exceedingly fine cellular tissue (lamina fusca) with the outer surface of the choroids, an extensive lymph-space (perichoroidal) intervening between the sclerotic and choroids. Behind it is pierced by the optic nerve, and is continuous with its fibrous sheath, which is derived from the dura mater. At the point where the optic nerve passes through the sclerotic, this tunic forms a thin cribriform lamina (the lamina cribrosa); the minute orifices in this region serve for the transmission of the nervous filaments, and the fibrous septa dividing them from one another are continuous with the membranous processes which separate the bundles of nerve-fibres. One of these openings larger than the rest, occupies the center of the lamella; it transmits the arteria centralis retinae to the interior of the eyeball. Around the eribriform lamella are numerous small apertures for the margin of the cornea and the entrance of the optic nerve are four or five large apertures, for the transmission with that of the cornea by direct continuity of tissue, but the opaque sclerotic slightly overlaps the outer surface of the transparent cornea.

Chinese Eye Test

If you cannot decipher anything, then try pulling the corner of your eyes as if you were Chinese or try to look this sentence from left side or right side of your computer.

if you don't see anything its mean you already blind, he he he 

Eye as a Camera

Light is excluded or permitted to enter by the eyelids. The equivalent of the camera shutter. Once admitted, the amount of light is further regulated by a variable opening, the pupil, which is like the aperture of a camera. The diameter of the pupil is controlled by the expansion and contraction of muscles in the iris. If a bright light is shone into the eye, the pupil immediately constricts. This is the light reflex, the purpose of which is to protect the retina from too intense illumination. As time passes, the retina adapts to the new level of light and the pupil returns to its original size.

Light ray are focused by a lens system composed of the cornea and crystalline lens, and an inverted image in projected in the retina. To prevent the blurring of images by internal reflection, the inner walls of the camera, the choroid layer, are painted black. The process by which the lens focuses on external objects is called accommodation. When a distant object is viewed, the lens is fairly flat. As the object moves nearer, the lens increasingly thickness, or curves outward. Lens shape is controlled by the ciliary body. A blurred image elicits reflected impulses to the ciliary body that promote contraction or relaxation until the image is sharp.

The description of how eye work as camera that cornea is the transparent, curved front layer of the eye. The pupil, behind the cornea, is a hole in the colored membrane called the iris. Tiny muscles in the iris change the size of the pupil – like the aperture of a camera – to control the amount of light getting into the eye. There is a small, powerful lens behind the pupil which changes shape based on the pull of muscles in the eye. Like a camera lens, the lens in the eye focuses incoming images from the outside world (incidentally, cataract surgery removes this lens and replaces it with a clear artificial one).

Adult Human Eye

Adult human eye is a hollow globe with a diameter of approximately 2.5 cm (1 in). The wall of the globe is composed of three coats. The outer coat, called the fibros funic, supplies the basic support of the eye and gives it shape. The fibrous funic is divided into the cornea, which is the transparent, exposed membrane in front of the lens, and the sciera, the firm, while coat of the eye to which is attached the muscles that move the eyeball. The middle, or vascular, coat is composed of three regions. The choroids layer is pigmented black and carries blood vessels to and from the eye. In mammals (animals eye) other than humans, it has an iridescent layer that increases the retina’s sensitivity to low-intensity light. The ciliary’s body consists of a ring-shaped muscle, which can change the lens shape, and chiliary processes to which the lens is attached. The iris, which contains an opening, the pupil, is colored and has a sphincter and a dilator muscle, called a contractile diaphragm. The innermost coat is the retina, which lies behind the lens. It contains the optic disk, or blind spot, which is the junction of nerve fibers passing to the brain. The retina also contains rods and cones, light sensitive cells. The lens is a biconcave, transparent eye structure.

The eye is composed of three membrane layers. The outer white layer, or sclera, helps the eye keep its spherical shape. The transparent part of the sclera, or cornea, is protected by conjunctiva. The middle layer, the choroids, supplies the eye with blood. The iris, which is colored, and ciliary body, which holds the lens in position, are part of this layer. The inner layer, or retina, receive light and sends nervous message to the brain by way of the optic nerve. The fovea or focal point, and blindspot are located on the inner surface. The aqueous humor, a fluid and vitreous, a jelly, fill the cavities of the eye.

Eye Evolution

At least three times during evolution, eyes with lenses have developed independently in animals eyes as widely different as insects, mollusks, and vertebrates. Fish move the whole lens closer to the retina when focusing on distant objects. Mammals, including humans, have evolved a more complex method of focusing by changing the curvature of the lens, flattening it for close objects, thickening it for distant ones. Predatory birds have an effective strategy of keeping the prey in focus while sweeping down on it; instead of adjusting the lens, they quickly change cornea, which is a transparent membrane covering the lens and also supporting the eyeball.

Another essential refinement, color perception, also evolved independently several times. Among mammals only humans, primates, and a few other species can recognize colors clearly. Birds, on the other hand, have a color perception superior to that of humans. Among insects, honeybees can be trained to distinguish colors, but they are color blind to red. Similar training experiments have shown that at least some teleosts, or bony fish, can discriminate colors, but elasmobranches, such as sharks, cannot.

Finally, evolution resulted in the gradual, development of binocular vision, the shifting of the eyes position from the side of the head to the front; this permitted that fusion of the images in each separate eye into a single, three dimensional image in the brain.

Glaucoma

Glaucoma is an eye disease in which the optic nerve is damage as a result of an imbalance between the production and draining of the watery fluid produced by cells behind the lens of the eye. Glaucoma is a major cause of blindness.

The normal eye continually produces a fluid that flows into the anterior chamber of the eyeball and eventually drains through tiny channels between the cornea and iris. A number of different disease processes can cause these channels to become blocked. The fluid pressure then builds within the eyeball and over a period of months or years, can damage the optic nerve. This condition, called chronic open angle glaucoma, is the most common form of the disease, the risk of its onset increases from middle age onward. No paint is involved, and the loss of peripheral vision is so gradual that it may go unnoticed for a long time.

A less common condition, called acute narrow angle glaucoma, results from a sudden and complete blockage of the drainage channels due to abnormal eye structure, injury to the eye, certain drugs, or systemic disorders such as diabetes. The risk of its onset also increases after middle age. The onset, sometimes preceded by preliminary attacks, is marked by pain, eye redness, blurred vision, and haziness of the cornea. Only one eye is usually affected at a time, but the other is likely to be affected later. Predisposition to both forms of glaucoma tends to run in families.

The peripheral vision lost in undetected chronic glaucoma cannot be restored. For this reason, regular examinations by an ophthalmologist are recommended for its early detection, especially after the age of 40. Chronic glaucoma is treated by drugs that increase fluid outflow or decrease fluid production. If drugs do not check the condition, surgery may be recommended to open drainage channels. Such surgery is essential following an attack of acute glaucoma, in order to prevent visual impairment. Drug therapies and modern surgical techniques, including the use of laser beams, have shown a high rate of success in treating the disease.

Eye Structure

For maintain the eyes human must enough of Vitamin A. Vitamin A has the structure of one-half molecule of beta-carotene, a pigment found in almost all plants. It cannot be made by animals and must be present in the food or be made from plant carotene seems to be responsible for the growth toward light, and it also plays a role in photosynthesis, the process by which sun light and water are combined to produce organic nutrients. Remarkably, evolution has adapted this almost universal plant pigment to animal vision.

The eyes of vertebrates differ in some details, yet they are all build to a common plan. More is known about the human eye than about that of any other vertebrate, and it may therefore serve as an example. There are many different between animals eye and human eye.

Protecting the eyeball is a bony socket called the orbit. Each eye is suspended within its orbit and is surrounded by a cushion of fat and blood vessels and motor and sensory nerves, including the optic nerve. These are six small muscle attached to each eye to allow coordinated movement of the pair. The eyelids provide some protection in the front and also serve to keep the cornea lubricated by spreading the tear fluid with each blink, as well as an only fluid produced by Meibomian gland in the lid. The tear fluid is produced by the lacrimal glands near the outer portion of each eyebrow and is collected and drained through tiny canals within the upper and lower lids near the nose. The tears eventually flow into the nasal passages and are swallowed.

Eye in Invertebrates

The light receptors of many invertebrates do not form definite images; the simply register light or dark or the direction of a source of light. The simplest such animal eyes are the light sensitive patches found on the flagella, or limblike projections, of the protozoan Euglena and the eyes pots of certain flatworms called planaria. Some organisms that have evolved true eyes have also retained simple photoreceptors of this type. Examples are the so called ocelli found in the lobsters and in the brain area under the skull; these organism can perceive light even when their true eyes have been removed.

Detection of Light
Despite the variety of types of eyes, the chemical process that transforms light into nerve impulses in the eyes is basically similar in all land vertebrates and marine fish, and in some insects. In 1967 George Wald of Harvard shared a Nobel Prize for physiology or medicine for discovering the details of the first step, which occurs in the retina or ommatidium.

The substances in the retina that detect light are called photosensitive, or visual, pigments. The major pigment in the eye is rhodopsin, or visual purple, which is composed of two distinct parts; a protein molecule called opsin, and a molecule made from vitamin A called retinene. When light strikes rhodopsin, the opsin portion, this leads, through a cascade of chemical reactions, to nerve impulse that relay visual information to the animal’s brain.

In the dark, and with the aid of chemical energy obtained from metabolism, retinene and opsin are recombined and rhodopsin is reconstituted. In very intense light, visual purple may be split faster than it can be reconstituted. Vision may then become impaired, for example, as in so called snow blindness. Vision many be similarly impaired if vitamin A is deficient I supply, and a shortage of retinene results in so-called night blindness.

Animals Eye

Almost all animals can perceive and respond to light, but eyes are as varied as the animals that posses them.

Eyes that form definite images are found only in some mollusks, mainly squids, octopuses and cuttlefish; in a few worm; in most arthropods, including insects, spiders, lobster, and most crabs; and in vertebrates. Except for most insects, these animals have eyes that are similar in structure and function to a camera. The eye uses a single Lens to focus a picture on a surface of densely packed cells called photoreceptors. The receptor surface, called the retina, functions like a piece of film. An external object is pictured on the retina like the points of newspaper photograph. The picture later received in the Brain, however is not the same simple point by point image. Exactly what this picture is remains unknown, but perception is a process that takes place in the brain not in the eye. Information from the eye, like the piece of a puzzle, is analyzed in the brain and fitted into meaningful forms.

Most insect eyes are built on an entirely different principle from the described above and are called compound eyes. Thousands of densely packed lenses are spread like a honeycomb over a spherical surface so that a mosaic image is formed. Each lens is associated with relatively few receptor cells, and the entire unit is called an ommatidium. No structure, therefore, is strictly analogous to the retina of other animals. What kind of image this arrangement conveys to the insect depends on the complexity of the structure.

Eyes Color

Human have different of eyes color, eyes color is a polygenic phenotypic character that determine by pigment that available on the eye’s iris. Human and animals also have different this kind of eye color, there are blue, brown, gray, green and may others.

Eye color is genetic that are complicated involve why the eye have certain of color. Usually blue color is determine by multiple genes. The genetics of eye color are so complex that almost any parent child combination of eye color can occur. Chromosome on this eye genetically is take from both of their parent chromosome that sometime create of new color combination.

There are different contain that causes a color on the eye, in human eyes, these variation in color are attributed to varying ratios of eumelanin that is produced by melanocytes in the iris. Animals eye have more vary of eyes color like in bird, brightly color are largely determined by other pigments, such as pteridines, purines, and carotenoids.

Color variations among different irides are typically attributed to the melanin content within the iris stroma. The density of cells within the stroma affects how much light is absorbed by the underlying pigment epithelium.

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• The eye and eyeball