We use our eyes in virtually everything we do and depend on our vision perhaps more than any other sense we have. Sight is the most precious of the five senses, and many people fear blindness more than any other disability.
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 give off. The eye is able to see in dim light or bright light, but it cannot see objects when light is absent. The eye changes light rays into electrical signals then sends them to the brain, which interprets these electrical signals as visual images.
The eye is set in a protective cone-shaped cavity in the skull called the orbit or socket and measures approximately one inch in diameter. The orbit is surrounded by layers of soft, fatty tissue which protect the eye and enable it to turn easily. Six muscles regulate the motion of the eye. Among the more important parts of the human eye are the iris, cornea, lens, retina, conjunctiva, macula, and the optic nerve.
Cornea The cornea is sometimes referred to as the "window of the eye." It provides most of the focusing power when light enters your eye. The cornea is composed of 5 layers of tissue. The outer layer (the epithelium) is the eye's protective layer. This layer is made up of highly regenerative cells that have the ability to grow back within 3 days, and therefore, allow for fast healing of superficial injuries. Most of the inner layers provide strength to the eye. The laser vision correction procedure is performed on this part of the eye.
Lens The lens is the clear structure located behind the pupil. Its primary function is to provide fine-tuning for focusing and reading. The lens performs this function by altering its shape to become thinner or thicker as necessary. Between the ages of 40 and 50, the lens becomes less flexible and presbyopia sets in. As people reach their 60's or 70's, the lens sometimes becomes cloudy and hard (cataract formation), preventing light from entering the eye.
Pupil The pupil is the 'black circle' that you see in people's eyes. The primary function of the pupil is to control the amount of light entering the eye. When you are in a bright environment, the pupil becomes smaller to allow less light through. When it is dark, the pupil expands to allow more light to reach the back of the eye.
Iris This is the colored part you see in people's eyes (i.e. blue/green/brown/hazel). The primary function of the iris is to control the size of the pupil. This is achieved through contraction or expansion of the muscles of the iris.
Vitreous Body This is the clear 'gel like' substance located inside the eye's cavity. Its purpose is to provide a spherical shape to the eye. The vitreous may develop small clumps known as 'floaters,' which are more common in nearsighted people than in the rest of the population.
Optic Nerve The optic nerve carries images from the retina to the brain.
Retina The retina consists of fine nerve tissue which lines the inside wall of the eyes and acts like the film in a camera. Its primary function is to transmit images to the brain. When your vision is perfect, the light rays coming into your eye focus precisely on this part of the eye.
Sclera This is the 'white part' that we see in people's eyes. The sclera's purpose is to provide structure, strength and protection to the eye.
Visual Acuity: What is 20/20 Vision? Visual acuity is only one in a series of factors that evaluate one's vision.20/20 vision is a term used to express normal visual acuity (the clarity or sharpness of vision) measured at a distance of 20 feet. If you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance. If you have 20/100 vision, it means that you must be as close as 20 feet to see what a person with normal vision can see at 100 feet.
20/20 does not necessarily mean perfect vision. 20/20 vision only indicates the sharpness or clarity of vision at a distance. There are other important vision skills, including peripheral awareness or side vision, eye coordination, depth perception, focusing ability and color vision that contribute to your overall visual ability.
Some people can see well at a distance, but are unable to bring nearer objects into focus. This condition can be caused by hyperopia (farsightedness) or presbyopia (loss of focusing ability). Others can see items that are close, but cannot see those far away. This condition may be caused by myopia (nearsightedness).
A comprehensive eye examination by a doctor of optometry can diagnose those causes, if any, that are affecting your ability to see well. In most cases, your optometrist can prescribe glasses, contact lenses or a vision therapy program that will help improve your vision. If the reduced vision is due to an eye disease, the use of ocular medication or other treatment may be used.
Common Eye Problems and Diseases:
Age Related Macular Degeneration AMD is the leading cause of blindness in older Americans. It results from a breakdown of the most sensitive part of the retina called the macula. There are many new and exciting treatments for this condition, but prevention remains the best possible treatment. If you have a family history of AMD, the doctors can tell you what to do to protect yourself from this devastating condition.
Itchy, red, swollen, tearing eyes often mean eye allergies. Most commonly, eye allergies are treated with eye drops. A new and more convenient once daily eye drop is expected to be available early in 2007.
Amblyopia (Lazy Eye) Amblyopia develops in young children and can mean permanent visual dysfunction if not diagnosed and treated early in life. We recommend a comprehensive eye examination for all children before entering Kindergarten at around age 4 to evaluate for signs of this potentially sight threatening condition. If found early, many patients with Amblyopia can be very successfully treated.
Astigmatism This form of visual blurring results from distortion in the shape of the cornea. It is correctable with eyeglasses, contact lenses, or refractive surgery.
Blepharitis Inflammation of the eyelids can cause chronic eye irritation, dry eye, tearing, foreign body sensation, and crusty debris. There are effective treatments for this dermatological condition of the eye lids.
Cataracts and Cataract Surgery If you live long enough, you are likely to develop cataracts, which cause blurred vision. Fortunately, cataract removal is a routine procedure. A cataract is a clouding of the natural lens of the eye. There are also some new and exciting cataract implants which can restore vision at both far and near following cataract surgery.
Color (Deficiency) "Blindness" Color deficiency is usually genetically inherited and can be very mild or severe. There are tests available to determine the extent of your color deficiency, but no treatment exists to restore color perception.
Conjunctivitis (Pink Eye) Conjunctivitis is an infection of the outer covering of the eye. Typical symptoms are burning and stinging, tearing, itching and discharge from the eyes. Treatment with antibiotic eyedrops usually clears this infection quickly. Conjunctivitis can be very contagious so you should seek treatment immediately if you think you have this condition.
Diabetic Retinopathy Diabetes can cause retinal degradation that can be sight-threatening. Diabetic patients, regardless of age or severity of disease, should receive a dilated eye examination at least yearly to look for this potential problem. If found, there are many effective treatments to keep the retinas healthy and prevent vision loss.
Dry Eye Syndrome Dry eyes are a very common condition and can be seen in men and women of all ages. There are many potential problems ranging from blurred vision, ocular discomfort, and chronic ocular infections. Artificial tear drops, tear duct plugs, prescription Restasis, and nutritional supplements can help restore eye moisture. This condition also causes problems with contact lens wear, but there are many new contact lens options for dry eye patients.
Floaters or Spots As we age, many of us develop floaters or dark spots in the fluid of the eye. We often see them passing by our vision and they seem to move with the eyes. They are commonly seen against a light colored background. They're usually harmless, but they can also be signs of a serious problem, such as a detached retina. It is very important to be examined immediately should you see floaters especially if accompanied by bright flashing lights or shadows in your field of vision.
Glaucoma Glaucoma is a disease where the nerve of the eye becomes damaged. The result of a damaged optic nerve is a diminishing field of vision and if left untreated, can lead to blindness. A series of tests done in the office can determine if you are at risk for developing this potentially sight threatening disease.
Higher-Order Aberrations (HOAs) If severe enough, vision errors known as higher-order aberrations (HOAs) can cause symptoms such as night vision problems, glare, or double images. There are contact lenses designed to reduce this effect and Custom or Wavefront guided Laser eye surgery can also be used to treat this condition.
Hyperopia (Farsightedness) If you're hyperopic, you may see better from a distance than up close, or your vision may be blurred at all distances. Treatment options include eyeglasses, contact lenses, and Laser eye surgery.
Keratoconus Keratoconus is a degenerative disorder of the cornea or outer covering of the eye. The result is a rapid increase in eyeglass prescription which cannot be corrected with eyeglasses alone. Special contact lenses can help people with thinning, bulging corneas to see better. Ultimately, surgery is necessary for most patients with keratoconus. Corneal transplant surgery is the main treatment, but recently surgeons have begun using Intacs for keratoconus. Intacs are implantable corneal rings which were originally marketed for correction of mild myopia but are now used mostly to correct the poor vision caused by keratoconus.
Macular Degeneration (AMD) An estimated 13 million Americans have signs of this sight-threatening disease, the world's number one cause of blindness. But medical researchers are working on it — find out about FDA-approved macular degeneration treatments, as well as macular degeneration treatments still in development and the Lucentis vs. Avastin treatment debate. Also catch up on macular degeneration news and read our FAQs and Eye Doctor Q&A on macular degeneration.
If you are nearsighted, you see very well at close distances when your glasses are off. There are many treatments available including eyeglasses, contact lenses, and Lasik laser vision correction
Presbyopia is a condition where we cannot see at close distances and affects everyone as we age. Between ages 40-60 almost everyone will need reading glasses.