Human Anatomy – Eyes

Like a camera, the eye gathers light, focuses it, and then transmits it through a lens to build a picture of its environment. In other words, the eye gives you the sense of sight.

While a camera creates pictures on film or sensor, the eye builds images on a layer of light-sensitive tissue called retina. It transforms light, as it passes through the eye, into electrical signals. These signals are delivered back and forth to the brain via the optic nerve, thereby creating vision.

Just how much light enters the eye is controlled by the iris, the colored circle in the eye. At the center of the iris is the dark circle known as the pupil, which widens and narrows to control the amount of light going in. Behind the pupil and iris is the lens, which focuses light inside the eye.

There is a clear, protective dome over the iris called the cornea. It is there, like the lens inside the eye, to help focus light. Besides the cornea, the surface of the eye is covered by a transparent tissue layer called the conjunctiva.

Much of the eye contains a transparent substance named the vitreous. The white of the eye is called the sclera.

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Eye diseases and conditions

Many people’s eye problems consist of no more than difficulty reading small print or trouble seeing near and faraway objects. Others have lost their eyesight altogether.

Doctors refer to vision loss in general as visual impairment. Blindness, then, is visual impairment of the highest degree, but there is such a thing as legal blindness. Legally blind individuals are those who need to stand at least 20 feet close to the object to see it clearly.

Many conditions lead to eyesight loss. Cataract is one, a condition characterized by the clouding of the lens, throwing light out of focus in the back of the eye. Glaucoma is another, a disease that raises pressure in the eye, damaging the optic nerve.

Aging also leads to vision loss. The macula, the sensitive area at the center of the retina, can degenerate with old age, leading to central vision loss.

Diabetes is just as infamous for its negative effects on vision. High blood sugar can bring about retinopathy or damage to the eyes’ blood vessels. Even worse, diabetes can spark a medical emergency, causing the retina to come off the eye.

Many people suffer from vision defects due to refractive errors in the eye. In astigmatism, for example, the eye could not properly focus light into the retina.

Myopia is a very common refractive error in the eye. Myopic persons are nearsighted; they could not see an object well from a distance. Nearsightedness occurs when the eyeball becomes too long for its lens.

Conversely, hyperopia is farsightedness. Hyperopic people are not able to see objects when they are near. In this condition, the eye’s muscles have either weakened or the eyeball has become too short for its lens.

Children are known to develop a condition called amblyopia, wherein one eye has poorer vision than the other. The eye with defective vision is known in common parlance as “lazy eye.”

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Individuals who complain of seeing double should seek a doctor as soon as possible. Diplopia or double vision is an urgent eyesight problem with underlying conditions.

Yet another common eye condition among people is strabismus. This is a condition in which the eyes are not aligned, pointing in different directions. People have several informal names for strabismus, including “squint eye” and “crossed eye.”

Scotoma is what doctors call the condition wherein the visual field has a dark or blind spot. Hypertension and multiple sclerosis are known to cause this eye defect.

Bacteria have to do with some eye infections, like red bumps on the eyelid called styes. A stye is similar to a chalazion, a cyst in the eyelid caused by a blocked oil-manufacturing gland. Chalazions aren’t caused by bacteria however.

Eyes are very open to inflammation. The conjunctiva alone can be easily inflamed by viruses, bacteria and allergies, setting off conjunctivitis (aka pinkeye or sore eye). In fact, the conjunctiva could grow a pterygium or thick mass, weakening vision.

Inflammation of the cornea is called keratitis. This happens when bacteria, amoeba or viruses infect a corneal abrasion.

Inflammation of the retina is known as retinitis. Viruses often cause this but it may be hereditary in origin.

Viruses may also cause inflammation of the iris, called iritis or uveitis. Iritis may also be caused by bacteria or an overactive immune system.

Optic neuritis, or the inflammation of the optic nerve, is often caused by an overactive immune system too. This condition can progress into loss of vision in the affected eye.

Inflammation of the eyelids is known as blepharitis.

Individuals who could not cry tears or secrete sufficient amounts of them are said to have dry eyes. A dry eye often has underlying conditions, e.g. Sjogren’s syndrome, lupus, and scleroderma.

There are still many more eye disorders and conditions. Notwithstanding, all but trauma could put out an eye, soft as it is. The area around the cornea is known to bleed (hyphema) due to trauma.

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Treating eye conditions

Glasses and contact lenses can be customized to correct astigmatism, myopia and hyperopia. After a refraction, an ophthalmologist or optometrist can order a suitable eyeglass prescription for the patient.

But for a more permanent solution, patients may submit to a surgical procedure called laser assisted in situ keratomileusis (LASIK). LASIK is done by creating a flap in the cornea and using laser to reshape its surface.

LASIK is similar to LASEK (laser epithelial keratomileusis), only that the latter does not create flaps. A LASEK surgeon removes the upper tissue of the cornea. Photorefractive keratectomy (PRK) is the precedent of LASEK.

Apart from LASIK, LASEK and PRK, there is another way to treat nearsightedness: radial keratotomy. However, this procedure has become obsolete.

Laser can also be used to congeal leaking blood vessels in the retina. This procedure is called laser photocoagulation, and it is always used to treat diabetic retinopathy.

In treating cataracts, an ophthalmologist performs surgery. He or she removes the cataract and replaces it with artificial lens.

Ophthalmologists recommend eye drops or artificial tears to treat irritated eyes. However, Cyclosporine eye drops are best for dry eye resulting from keratoconjunctivitis sicca.

Tests for eye conditions

Healthy lifestyle has it that adults should regularly have their eyes examined. A regular eye exam usually includes a slit lamp examination, which can identify a wide gamut of eye problems.

Almost always, ophthalmologists use a visual acuity test to measure a person’s vision from various distances. It typically involves reading a Snellen chart.

A fundoscopic exam can check for problems in the retina. It is done by widening the pupil with dilating drops and shining radiant light into it, revealing the inner eye. Ophthalmologists also diagnose retina problems by using a variation of angiography called fluorescein angiography.

To diagnose glaucoma, ophthalmologists use tonometry, which checks for intraocular pressure in the eye.

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1 Response

  1. anubhav says:

    I have a personal experience of a repeated red eye leading to weakening of muscles that has eventually made me wear spectacles. Not taking precautions early on meant that the infection became widespread and caused some sort of a ballooning in the vascular supply.

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