HOW YOUR EYE WORKS
The human eye works in a manner similar to a camera. Light passes through the cornea and the lens, which focus the light onto the retina. The retina, which can be compared to the film in a camera, contains photosensitive cells that translate the light into an electrical charge, rather like a negative. The charges then pass through the optic nerve to the brain, where they are turned into the images we see.
Diagram from EyeMDLink
THE ANATOMY OF THE EYE
THE ANTERIOR CHAMBER is the portion of the eye located in front of the iris.
THE POSTERIOR CHAMBER is the portion of the eye located behind the iris.
THE CORNEA is the outer “window” of the eye. It is the primary focusing element of the eye. The outer layer of the cornea is known as the epithelium, which protects the eye. The epithelium is composed of transparent cells which regenerate quickly.
THE AQUEOUS HUMOR is a clear, fluid substance that circulates througout the front part of the eye behind the cornea. It maintains a constant pressure inside of the eye.
THE IRIS is the colored part of the eye. It assists the eye in adapting to changing light conditions by dilating or constricting the pupil to allow more or less light to pass through the eye.
THE LENS focuses light that passes through the eye. The lens can change its shape to focus on near, intermediate and distant objects.
THE CILIARY BODY is the structure which secretes the aqueous humor within the eye. The ciliary body also contains the ciliary muscle, which is responsible for changing the shape of the lens.
THE ZONULES are fibers which suspend the lens inside of the eye.
THE SCLERA is the white part of the eye. It is composed of strong tissues that protect the inner structure of the eye.
THE RETINA is a thin, light-sensitive tissue lining the back of the eye. Here, the retina’s photoreceptor cells translate light into electrical pulses and send them to the brain, where they become images.
THE MACULA is the center portion of the retina. It contains a high concentration of photoreceptor cells which convert light into nerve signals. Due to this high concentration of photoreceptor cells, the macula is responsible for the sharpness of our vision and our ability to see fine details.
THE OPTIC NERVE carries visual information from the eye to the brain.
THE CHOROID is a layer of blood vessels behind the retina. The choroid supplies oxygen and nutrients to the outer layer of the retina.
THE VITREOUS HUMOR is a gel substance which fills the posterior chamber of the eye.
EYE CONDITIONS
Amblyopia (Lazy Eye)
Amblyopia is a condition in which the central vision in one eye does not develop properly. Typically, amblyopia affects 2-3% of the population. Development of amblyopia often occurs in childhood and can occur as a result of several factors including crossed eyes, large differences in prescription, cataracts and low hanging upper eyelids. If left untreated, amblyopia can lead to permanent vision problems.
Symptoms include squinting or completely closing one eye in order to see, poor visual acuity, straining eyes and headaches.
Treatment options include vision therapy, patching one eye, eye drops, correcting prescriptions for nearsightedness or farsightedness, and surgery.
Astigmatism
Astigmatism occurs when the cornea of the eye is misshapen. Normal corneas are spherical. In patients with astigmatism, the corneas are shaped in a manner similar to a football. Thus, light cannot focus correctly onto the retina, causing multiple focusing points in the field of vision.
Symptoms include blurry vision and double vision. Contact lens wearers may notice that their lenses turn upon blinking.
Toric corrective lenses can alleviate symptoms of astigmatism. However, LASIK laser vision correction can permanently reshape the cornea, so no corrective lenses are needed.
Blepharitis
Blepharitis is a regular inflammation of the eyelid. The condition causes the upper and lower eyelids to become coated with oily particles and bacteria near the bottom of the eyelashes.
Symptoms include eye irritation, itching, redness, stinging and burning, and the appearance of dandruff around the eyelashes.
To treat blepharitis, use warm compresses to loosen debris and dilute oils around the eye. Eyelid scrubs can also alleviate symptoms. To make an eyelid scrub, mix one part baby shampoo with one part water in your hand and use a cotton swab to gently scrub the eyelashes for 15 seconds. Other treatments include a prescription antibiotic ointment and prescription steroid eye drops to relieve discomfort and inflammation.
Cataracts
Cataracts occur when the natural lens of the eye become cloudy. The clouding of the lens can occur for various reasons including exposure to UV rays, exposure to environmental pollutants, use of certain medications and the aging process.
Symptoms of cataracts include visual changes which create difficulty in performing daily tasks, halos around lights, difficulty driving at night, foggy vision, and dull colors.
New glasses or bifocals may treat cataracts in their early stages. For more advanced cataracts, lens replacement surgery may be an option. In lens replacement surgery, the natural lens of the eye is removed and replaced with an artificial intraocular lens (IOL). To read more about cataract treatment options at Carolina Vision Center, visit the link below.
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Chalazion
A chalazion (pronounced kuh-LAY-zee-un) is the enlargement of the meibomian gland, the oil-producing gland in the eyelid. The chalazion forms when the gland opening becomes clogged with oil secretions.
Symptoms include the appearance of a red, swollen and tender cyst near the eyelid, and sometimes blurry vision.
Warm compresses can help to clear the clogged gland. Other treatments include a prescription antibiotic ointment to relieve discomfort and inflammation, cortisone steroid injections, or surgical removal.
Conjunctivitis
Conjunctivitis is commonly known as pink eye. It is the inflammation of the thin, clear membrane over the white part of the eye, called the sclera. Pink eye is highly contagious, and can cause bothersome redness and itching.
There are multiple versions of conjunctivitis, and while the symptoms are similar, there are varying degrees of severity. Viral conjunctivitis usually affects only one eye and causes excessive watering and a light discharge. Bacterial conjunctivitis affects both eyes and causes heavy discharge. Allergic conjunctivitis causes itching, redness and tearing in both eyes and sometimes affects the nose. Giant papillary conjunctivitis usually affects both eyes and causes contact lens intolerance, itching, heavy discharge, tearing, and red cysts on the underside of the lid.
The best treatment for conjunctivitis is prevention. Wash your hands frequently and avoiding rubbing your eyes. Do not share washcloths, towels or pillowcases with others, and wash these items frequently. Do not share eye drops or cosmetics. If you are a contact lens wearer, keep contact lenses well-maintained. When pink eye develops, remove contact lenses. Cold compresses may alleviate the itching and burning symptoms. Some forms of pink eye may be treated with homeopathic or antibiotic eye drops.
Diabetic Retinopathy
Diabetic retinopathy occurs in patients with diabetes. When blood sugar levels become too high, the blood vessels in the back of the eye become damaged due to small leaks and the growth of new blood vessels. Advanced stages of diabetic retinopathy can lead to retinal detachment and permanent blindness.
Symptoms may be sparse in the early stages of the condition. As the condition progresses, symptoms include small shadows or “floaters” in your field of vision, difficulty reading, decreased near vision, and double vision.
The best treatment for diabetic retinopathy is prevention. If you are a diabetic, maintain normal blood sugar levels through a combination of diet, exercise and medication. Check your blood sugar often, and schedule annual eye exams so that your ophthalmologist can detect the condition as soon as it develops. If diabetic retinopathy develops, the condition can be treated with a painless laser treatment called laser photocoagulation, which closes off leaks in the blood vessels and hinders new blood vessel growth.
Dry Eye is a lack of moisture and lubrication in the eye. Dry Eye can be caused by a number of factors including contact lens wear, environmental allergens, dry climate, extended computer use and use of certain medications. Dry Eye may also be a symptom of systemic diseases such as lupus, rheumatoid arthritis and rosacea.
Symptoms include regular ocular dryness, scratchiness, burning, excessive watering and discharge.
Dry Eye is usually treated with the use of artificial tears, including the prescription eye drop Restasis. Dry Eye may also be treated on a nutritional basis. If you experience symptoms of dry eye, increase your intake of antioxidants and Omega-3 fatty acids by consuming fruits, vegetables, nuts, and cold water fish. Carolina Vision Center also offers HydroEye, a nutritional supplement clinically proven to alleviate symptoms of Dry Eye.
Floaters and Flashers
Floaters are spots or shadows that pass through your field of vision. Flashers are brief bursts of light, sometimes referred to as “seeing stars.” They are created by tiny gatherings of cells inside the clear fluid that fills the inner portion of your eye.
Symptoms include small specks, clouds, strands, webs or bursts of light that pass through your field of vision.
Most floaters and flashers are harmless and do not require treatment. However, if new floaters and flashers develop or if these visual distortions occur often and affect your visual acuity, you may have early stages of a serious condition called diabetic retinopathy. In that case, see your ophthalmologist as soon as possible.
Glaucoma is the leading cause of blindness in America, especially within the elderly population. Glaucoma affects the optic nerve, which sends images from our eyes to our brain. In our eyes, a clear liquid called aqueous humor circulates and flows through a drainage system. If the drainage system becomes blocked, aqueous humor builds up and creates pressure on the optic nerve. If too much pressure builds on the optic nerve, the nerve can be destroyed and blindness can occur. There are two types of glaucoma. Open-angle glaucoma can develop as we age because our eye’s drainage system becomes less efficient. Closed-angle glaucoma develops when the iris (the colored part of our eye) is located too close to the drainage system, causing the eye’s fluid pressure to increase.
Open-angle glaucoma has no symptoms in its early stage. When the condition advances, you may notice blank spots in your vision. Closed-angle glaucoma does have symptoms including blurred vision, severe eye pain, headaches, rainbow halos around lights, nausea and vomiting.
Regular glaucoma screenings are imperative to detect both types of glaucoma in their earliest stages. If you are diagnosed with glaucoma, eye drops can prevent further damage. A procedure called Selective Laser Trabeculoplasty is a laser treatment that works by stimulating and rejuvenating the body’s own tissue and cells to increase drainage in the eye and lower pressure.
Hyperopia
Hyperopia is the clinical term for farsightedness. Hyperopia occurs when the cornea of the eye is too flat. Thus, light passes through the eye at in incorrect angle and causes images at close proximity to appear blurry.
Symptoms of hyperopia include blurry near vision.
Hyperopia can be treated with glasses or contact lenses. However, there are treatment options that can reduce or even eliminate dependence on glasses and contacts. LASIK laser vision correction can correct hyperopia by steepening the angle of the cornea. Another procedure called Conductive Keratoplasty (CK) uses radiofrequency to steepen the cornea an thus reduce dependence on corrective lenses.
Keratoconus
Keratoconus (pronounced KER-uh-toh-KONE-us) means “cone-shaped cornea.” This is an uncommon condition in which the dome-like cornea becomes thin and develops a cone-like bulge. The altered cornea distorts vision. Some researchers believe that keratoconus is a genetic condition.
Symptoms include blurry vision, light sensitivity, glare, mild eye irritation, and frequent changes in your refractive prescription.
Keratoconus can be treated in its early stages with glasses. As the condition progresses, rigid contact lenses may be prescribed in order to allow the eye to reflect light evenly. In its late stages, corneal transplants may be necessary.
Macular Degeneration
Macular Degeneration is a leading cause of vision loss, especially among the elderly population. The condition occurs with the degeneration of the macula, the part of the retina responsible for the crisp, central vision needed for tasks such as reading or driving. There are two types of macular degeneration. Dry macular degeneration is the more common form of the condition, and it is caused by the aging or thinning of the macular tissue. Wet macular degeneration affects the eye’s vascular system. In this form of the condition, new blood vessels form beneath the retina and leak blood into the eye, causing permanent damage to light-sensitive cells. While both forms of macular degeneration can lead to vision loss, wet macular degeneration is more likely to cause irreversible blindness. Risk factors for macular degeneration include aging, smoking, use of certain medications, high blood pressure, obesity, and lighter eye color. Macular degeneration also tends to be genetic, and the condition occurs more often in female patients and caucasian patients.
Symptoms of both forms of macular degeneration include a gradual and painless loss of central vision and unusually distorted vision.
Regular eye exams can detect macular degeneration before the condition progresses. If you are at risk for macular degeneration, check your vision often with a device called an Amsler Grid. An Amsler Grid is a series of black lines arranged into a graph pattern. If the lines on the grid appear wavy, broken or distorted in any way, visit your optometrist or ophthalmologist immediately. Currently, there are no FDA approved treatments for dry macular degeneration. For wet macular degeneration, treatments aimed at preventing the growth of new blood vessels include Lucentis and Macugen. Nutritionally based vision care and increasing one’s intake of antioxidants, especially lutein and zeaxanthin, may be effective in preventing the progression of the condition.
Myopia
Myopia is the clinical term for nearsightedness. Myopia occurs when the cornea of the eye is too steep. Thus, light passes through the eye at an incorrect angle and causes images at a distance to appear blurry.
Symptoms of myopia include blurry distance vision.
Myopia can be treated with glasses or contact lenses. However, there are other, more permanent treatment options. LASIK laser vision correction can correct myopia by flattening the angle of the cornea, thus reducing or even eliminating dependence on corrrective lenses.
Ophthalmic Migraine
Ophthalmic migraines are characterized by visual distortions such as colored lights or flashes, prolonged blurring in one eye, lines, “shimmering” and vision loss in one eye. Migraines may be accompanied by a severe pounding headache, sensitivity to light and sound, and nausea. Migraines are caused by a change in serotonin levels in the brain, which causes blood vessels to constrict and flow of oxygen to the brain to decrease. Hormonal changes and stress can also cause the on-set of migraines.
Symptoms include vision loss or blurry vision in one eye, lights and flashes, sensitivity to light and sound, severe headache and nausea.
Over-the-counter anti-inflammatory medications such as aspirin or ibuprofen can reduce symptoms. Preventative medications may be prescribed for patients when symptoms occur often and interfere with one’s daily activities.
Pinguecula and Pterygium
Pinguecula (pronounced pin-GWEK-yoo-la) is a yellow patch or growth on the conjunctiva (the clear membrane that covers the white part of the eye), typically on the side closest to the nose. It is similar to a callus on the skin, resulting in protein, fat and/or calcium deposits. A Pterygium (pronounced ter-IJ-ee-um) is a growth of tissue on the conjunctiva that extends over the cornea.
Pinguecula or Pterygium may cause redness or inflammation, blurred vision, irritation, dryness, itching, burning, and a sensation of a foreign object in the eye.
In most cases, no treatment is needed. The pinguecula and the pterygium may vanish with no treatment. If eyes become red and irritated, eyedrops or ointments may be necessary. If a large growth affects vision or causes extreme discomfort, the growth may be surgically removed.
Ptosis
Ptosis is the clinical term for drooping of the eyelid. Typically, only the upper eyelid of one or both eyes is affected. Sometimes, the droop may not be noticeable. Other times, the droop may cover the entire pupil and create vision problems. Congenital ptosis is present from birth, but the condition can also develop due to aging, disease or injury. Ptosis can also develop following eye surgery.
Symptoms may include the physical drooping of the eyelid, accompanied by diminished visual acuity.
The best treatment for ptosis is surgery. The surgeon will tighten the eyelid muscles to improve both vision and physical appearance. Individuals born with congenital ptosis must have treatment in order for their vision to develop properly. If left untreated, ptosis may lead to amblyopia (lazy eye).
Strabismus
Strabismus is a condition commonly known as “crossed eyes.” With this condition, the eye do not look toward the same object. As one eye moves, the other eye points in another direction. This disorder can lead to amblyopia (lazy eye). Unequal function of the eye muscles on one side of the eye or paralysis of the ocular muscle can cause strabismus. The condition often develops in children with moderate to high levels of uncorrected hyperopia (farsightedness). Infants may appear to have crossed eyes due to undeveloped vision. However, if the condition does not disappear as the child ages, treatment may be necessary.
Symptoms include crossed eyes, eyes which point in different directions, and the onset of lazy eye.
Patients affected by strabismus may require vision therapy including eye patches or visual exercises, glasses to assist in proper focusing, eye drops, and in some cases, surgery to help realign the eyes.
Sty
A sty is an inflammation or infection causes by blockages in the oil-producing glands in the eyelid. When the gland is blocked, oil builds up and creates a painful lump under the skin. Often, bacteria can infect the lump as well. Gland blockage can be caused by a number of factors including build-up of cosmetics in the eye area, improper hygiene, stress, hormonal changes, and other inflammatory eye conditions such as blepharitis.
Symptoms may include a lump on the eyelid, swelling, tenderness, pain, redness, burning, blurry vision and/or discharge.
To self-treat a sty, use warm compresses several times per day and keep your eyes closed as much as possible. Discontinue use of eye cosmetics and contact lenses. Clean the eye area gently but thoroughly with a mixture of baby shampoo and water. See a doctor for treatment if your eye area becomes swollen, if your vision becomes distorted, or if you experience pain, bleeding or fever. Your doctor may prescribe an antibiotic to relieve infection and pain medication to alleviate discomfort.
Subconjunctival Hemorrhage
A subconjunctival hemorrhage is a “bruise” on the eye which occurs when blood vessels under the conjunctiva (the clear membrane covering the white part of the eye) break and cause blood to leak onto the white part of the eye. This condition is commonly caused by coughing, sneezing, eye strain, eye trauma or similar actions that would raise the blood pressure in the eye. Less frequent causes of subconjunctival hemorrhage include diabetes, high blood pressure, blood clotting disorders, and consumption of excessive amounts of aspirin or blood thinners.
A subconjunctival hemorrhage usually appears as a painless brown or red spot on the white part of the eye.
Usually, no treatment is required. The bruising usually vanishes within several days. However, individuals who have recurring subconjunctival hemorrhages should consider an eye examination to determine the cause of the condition.
Vision 101 is intended to provide general information regarding vision care and certain ocular conditions. Consult a vision care professional if you suspect that your vision is affected by any of the above conditions or any other ocular conditions. The information provided here is not intended to advise any particular medical treatment or to prevent or cure any specific medical condition.