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Human EyeEye Care

The eye is an organ which collects light and turns it into electronic messages which are sent to the brain. The brain then turns those signals into a picture for you to see. Since we have two eyes, two pictures are usually created. These two offset pictures allow us to have depth of vision (primarily at near). Most of our depth of vision comes from judging the relative size of the objects we see. Therefore, if we lose the vision in one eye, we can continue to do most everything we could do before.

Anatomy of the Eye

  • Cornea - clear window in front of the pupil and the iris which allows light into the eye.
  • Optic Nerve - cable-like structure which carries vision from the retina to the brain.
  • Retina - the delicate layer of tissue in the back of the eye that collects the light that enters your eye.Diagram of the Eye
  • Vitreous - the clear gel like substance that fills the space in the eye between the lens and the retina.
  • Sclera - the outside wall of the eyeball.
  • Lens - clear structure, which sits behind the iris and focuses light onto the retina.
  • Pupil - the dark central opening in the middle of the iris.
  • Iris - colored part of the eye, behind the cornea and in front of the lens. Muscles in the iris control the size of the pupil to adjust the amount of light entering the eye.
  • Macula - the specialized area in the retina which allows us to see fine details.

(Diagram courtesy of Peter Mallen, Harvard University.)


Contact Lenses

From left to right, images display contact lens insertion, courtesy of Alcon)

Inserting Contact Lenses 1 Inserting Contact Lenses 2 Removing Contact Lenses 4 Inserting Contact Lenses 3 Removing Contact Lenses 2

Reasons to Consider Contact Lenses:

  • Contact lenses move with your eye, allow a natural field of view, have no frames to obstruct your vision and greatly reduce distortions.
  • They do not fog up, like glasses, nor do they get splattered by mud or rain.
    Contact lenses do not get in the way of your activities.
  • Many people feel they look better in contact lenses.
    Contact lenses, compared to eyeglasses, generally offer better sight.

Interactive Eye Test (This link takes you to a self-administered vision test.)

Eye Infections, Diseases and Disorders

Factors That Can Lead to Eye Problems:

  • Aging: Advancing age is the single most important risk factor for Dry Eye. Dry Eye Syndromes affects 75% of people over the age of 65.
  • Women: Hormonal changes brought on by pregnancy, lactation, oral contraceptives, menstruation, and post menopause
  • Disease: Several diseases result in side effects of Dry Eye Syndrome: Rheumatoid Arthritis, Diabetes, Thyroid Abnormality, Asthma, Cataracts, Glaucoma, Lupus
  • Medications: Certain medications can decrease the body's ability to produce lubricating tears: Antidepressants, Decongestants, Antihistamines, Blood Pressure Medication, Oral Contraceptives, Diuretics, Ulcer Medication, Tranquilizers, Beta Blockers.
  • Contact Lenses: Dry Eye is the leading cause of contact lens discomfort or intolerance. Soft contacts in particular, rapidly evaporate the tears from the eye, causing irritation, protein deposits, infection, and pain.
  • Environmental Conditions: Exposure to Smoke, Fluorescent Lights, Air Pollution, Wind, Heaters, Air Conditioning, and Dry Climates, can increase tear evaporation.
  • Computer Users: Computer users spend hours staring at their terminal ignoring their normal blinking process which is a vital function of tear production.

" Pink Eye" (Conjunctivitis)

Pink eye occurs when there is an inflammation of the membrane that lines the eye and the inner eyelids. Pink eye can be caused by an infection or an allergy. It may also happen if dust or an irritating chemical (like perfume or hair spray) touch the eye directly.

Symptoms

  • red, itchy eyes with a discharge that may be either clear, watery or cloudy and sticky
  • eyes may be watery
  • nose may itch
  • eyelids may look swollen

Dry Eye

TeardropDry eye is caused by the moisture level in the eye is maintained by the balance of tear production and tear loss through drainage and evaporation. When this balance is not sustained, dry spots appear on the eye's surface and cause irritation.

  • Dry Eye Syndrome can damage tissue and possibly scar the cornea of the eye, leading to irreversible, sight threatening conditions.
  • Dry Eye Syndrome is the leading cause of contact lens intolerance or discomfort. Contacts can cause tears to evaporate from the eyes causing irritation, protein deposits, infection and pain.

Eye Glasses"Nearsightedness" (Myopia)

Myopia, also known as nearsightedness, is a refractive error caused by an eyeball that is too long to focus light on the retina or a cornea which is too steeply curved. In these cases light focuses instead in front of the retina.

Glaucoma

Vision without GlaucomaGlaucoma occurs as a condition when increased fluid pressure is inside the eye. This damages the optic nerve causing partial vision loss and eventually blindness. Glaucoma explains causes, incidents, risk factors, symptoms, treatment and expectations of this disease.

The pictures to the right show the difference of vision between a normal (top) and vision of a person who is characterized by glaucoma (lower).
(Courtesy of the National Eye Institute.)

Facts on Glaucoma

  • Vision With GlaucomaGlaucoma affects an estimated three million people in the United States, and an estimated 300,000 new cases are diagnosed each year.
  • Glaucoma is a leading cause of blindness in the United States. Each year, approximately 5,400 Americans go blind from glaucoma
  • Glaucoma generally attacks side or peripheral vision first, therefore it is possible to have 20-20 eyesight and still have glaucoma
  • Glaucoma is actually a group of eye illnesses characterized by damage to the optic nerve. The most common type of glaucoma are is the open angle glaucoma, which happens to people over the age of 59. However, there are types of glaucoma which affect infants and children.
  • Glaucoma is five times more likely to affect African Americans than whites. It also strikes African Americans earlier. By age 70, one in 10 African Americans, compared with one in 50 whites, develops the disease.
  • The warning signs of glaucoma include:
    • Blurred vision or "halos" around lights
    • Problems focusing on objects
    • Difficulty adjusting eyes in dark places
    • Frequent change of eyeglasses which doesn't help
    • Loss of peripheral vision
    • Aching or discomfort around the eyes.

Astigmatism

Astigmatism results from variation or irregularities in the curvature of the cornea or the lens. In the astigmatic eye, the variations in the curvature of the cornea prevent all the light rays of a source from focusing at a single point, thus causing blurred vision.

Symptoms:

  • Blurred vision, both near and distant
  • Eye strain, headaches
  • Frequent squinting may occur as a result of eye strain and headache

Cross Eyes DiagramCross Eyes (Strabismus)

Cross eyes occur when there is a misalignment or lack of coordination between the two eyes. Generally with this condition, the two eyes point in different directions. The misalignment is a result of a failure of eye muscles to work together properly. It is usually diagnosed in childhood but can occur later in life. Cross eyes often worsen when eye muscles are tired – for example, late in the day, in bright sunshine, or during the course of an illness.If untreated, cross eyes are likely to worsen with age.

Symptoms:

  • misaligned eyes and uncoordinated eye movements, either constant or intermittent
  • squinting
  • tilting head to look at things
  • frequent eye movements
  • headache
  • rubbing of eyes
  • double vision

References and Resources

Aetna Intelihealth
Eye Search
National Eye Institute