How Does Nearsightedness Develop in Children?

ScienceDaily (Mar. 1, 2012) - Myopia (Nearsightedness) develops in children when the lens stops compensating for continued growth of the eye, according to a study in the March issue of Optometry and Vision Science, official journal of the American Academy of Optometry.

The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.

Using detailed information on eye growth and vision changes in children over time, the new research shows "decoupling" of lens adaptation from eye growth about a year before myopia occurs. Donald O. Mutti, OD, PhD, of The Ohio State University College of Optometry, is lead author of the new study.

Growth Imbalance Leads to Myopia…

The researchers analyzed repeated measurements of vision and eye growth performed over several years in children aged 6 to 14. The study focused on the growth of the two key parts of the eye affecting normal vision: the cornea, the transparent front part that lets light into the eye; and the lens, located behind the cornea, which focuses light rays on the retina at the back of the eye.

Myopia or Nearsightedness -- difficulty seeing objects at a distance -- develops in about 34% of American children as they grow. Vision professionals and scientists typically think of myopia as a problem occurring when the eyeball becomes too long (front to back) for the optical power of the cornea and lens.

However, it has been unclear how this imbalance develops in children who previously had normal vision. To answer this question, Dr. Mutti and colleagues compared changes in eye growth for children who developed myopia at different ages versus those whose vision remained normal.

They found that, in children without myopia, the lens grew thinner and flatter to maintain normal vision as the eye grew. This adaptation maintained a normal balance between the optical power of the lens and the increasing length of the eyeball. From age nine months to nine years, eyeball length increased by an average of three millimeters.

...As Lens Stops Responding to Increasing Eye Length

However, in children who developed myopia, the lens stopped changing in response to eye growth. Nearsightedness developed not just because of increases in the length of the eyeball, but rather because the optical power of the lens no longer changed as the eye grew.

The imbalance occurred rather suddenly: about one year before the children became Nearsighted. For at least five years after the development of myopia, the eye kept becoming longer but the lens stopped flattening and thinning.

In contrast to the lens, changes in corneal growth showed little or no relation to the development of myopia. The cornea is responsible for about two-thirds of the optical power of the eye, and the lens for the remaining one-third.

The study provides vision professionals with an important new piece of information on why some children develop myopia. However, what's still unclear is why the lens suddenly stops adapting to continued growth of the eye. More research will be needed to answer that question -- one possibility is that an abnormally thick ciliary muscle within the eye forms a mechanical restriction preventing the stretching that thins and flattens the lens as the eye continues to grow.

http://www.sciencedaily.com/releases/2012/03/120301113258.htm

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The above story is reprinted from materials provided by Wolters Kluwer Health: Lippincott Williams & Wilkins, via Newswise.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

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Contact Lenses Provide Extended Pain Relief to Laser Eye Surgery Patients

Contact Lenses

Provide Extended Pain Relief to Laser Eye Surgery Patients

Scientists are reporting development of Contact lenses that could provide a continuous supply of anesthetic medication to the eyes of patients who undergo laser eye surgery -- an advance that could relieve patients of the burden of repeatedly placing drops of medicine into their eyes every few hours for several days.Their report appears in ACS' journal Langmuir

.

Anuj Chauhan and colleagues explain that more than 1 million laser eye correction procedures are performed each year in the U.S. The surgery enables most patients to see clearly without eye glasses or Contact lenses. The procedure known as LASIK is the most common type of laser eye surgery, but complications can develop if the patient undergoes trauma or is hit very hard at any time after the procedure. Photorefractive keratectomy (PRK) doesn't have this complication, and that's why it is preferred for athletes and those in the military. A downside to PRK, however, is a longer period of pain after surgery. To ease their pain, PRK patients place drops of several medications, including anesthetics, into their eyes every few hours, which can interfere with daily life and increase the risk of drug overdose. PRK patients receive a special "bandage Contact lens" after surgery to help the outer layer of the eye heal.

The researchers tested whether anesthetics loaded onto this type of lens could release the drugs over time automatically. They found that adding vitamin E to the lenses extended the time of release of three commonly used anesthetics from just under two hours to up to an entire day -- or a few days in some instances. The vitamin E acts as a barrier, keeping the anesthetics on the eye, right where they are needed. The researchers say that, in the future, these lenses could serve as bandage Contact lenses after PRK surgery while also delivering necessary pain medications.

The authors acknowledge funding from the University of Florida.

http://www.sciencedaily.com/releases/2012/01/120118112001.htm

The above story is reprinted from materials provided by American Chemical Society.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

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Eye Allergies

 

Eye Allergies often are hereditary, and occur due to processes associated with other types of allergic responses.

When an allergic reaction takes place, your eyes may be overreacting to a substance perceived as harmful, even though it may not be. These substances are called allergens.

For example, dust that is harmless to most people can cause excessive production of tears and mucus in eyes of overly sensitive, allergic individuals.

Allergies can trigger other problems, such as conjunctivitis (pink eye) and asthma. Combined nasal and eye Allergies create a condition known as rhinoconjunctivitis.

About 30 percent to 50 percent of U.S. residents have allergy symptoms. And about 75 percent of those symptoms affect the eyes.*

Allergy Symptoms and Signs

Common signs of Allergies include:

• Red, swollen or itchy eyes
• Runny nose
• Sneezing and coughing
• Itchy nose, mouth or throat
• Headache from sinus congestion

Beyond more obvious symptoms, you also may feel fatigued and could suffer from lack of sleep.

What Causes Eye Allergies?

Many allergens are in the air, where they come in contact with your eyes and nose. Airborne allergens include pollen, mold, dust and pet dander.

Other causes of Allergies, such as certain foods or bee stings, do not typically affect the eyes the way airborne allergens do. Adverse reactions to certain cosmetics or drugs such as antibiotic eye drops also may cause eye Allergies.

Some people actually are allergic to the preservatives in eye drops such as those used to lubricate dry eyes. In this case, you may need to use a preservative-free brand.

General Eye Allergy Treatment

Avoidance. The most common "treatment" is to avoid what's causing your eye allergy. Itchy eyes? Keep your home free of pet dander and dust and keep pets off the furniture. Stay inside with the air conditioner on when a lot of pollen is in the air. Use high quality furnace filters that trap common allergens and replace the filters frequently.

Make sure you wear wraparound sunglasses to help shield your eyes from allergens, and drive with your windows closed during allergy season.

Medications. If you're not sure what's causing your eye Allergies, or you're not having any luck avoiding them, your next step probably will be medication to alleviate the symptoms.

Over-the-counter and prescription medications each have their advantages; for example, over-the-counter products often are less expensive, while prescription ones usually are stronger and may be more effective.

Eye drops are available as simple eye washes, or they may have one or more active ingredients such as antihistamines, decongestants or mast cell stabilizers that inhibit inflammation. Antihistamines relieve many symptoms caused by airborne allergens, such as itchy, watery eyes, runny nose and sneezing. Decongestants help shrink swollen nasal passages for easier breathing.

Relief for Watery, Itchy Eyes

Common causes of excessively watery eyes are allergies and dry eye syndrome — two very different problems.

With allergies, your body's release of histamine causes your eyes to water, just as it may cause your nose to run.

It may seem illogical that dry eye syndrome could cause watery eyes. But sometimes an underlying dry eye condition stimulates your tear glands to overproduce the watery component of your eye's tears as a protective response, leading to watery eyes.

Decongestants clear up redness. They contain vasoconstrictors, which make the blood vessels in your eyes smaller, lessening the apparent redness. They treat a symptom but not the cause of eye allergies.

In fact, with extended use, the blood vessels can become dependent on the vasoconstrictor to stay small. When you discontinue the eye drops, the vessels actually get bigger than they were in the beginning. This process is called rebound hyperemia, and the result is that your red eyes could worsen over time.

Some products have ingredients that act as mast cell stabilizers, which alleviate redness and swelling. Mast cell stabilizers are similar to antihistamines. But while antihistamines are known for their immediate relief, mast cell stabilizers are known for their long-lasting relief.

Eye Allergy News

Have Fall Allergies? You Might Not Want To Live in One of These Cities

October 2011 — Is your town one of the top 100 most challenging in the country for fall allergies? Check the new list compiled by the Asthma and Allergy Foundation of America.

Knoxville, Tenn. is number one this year, joining other pollen-ridden southern and midwestern cities. The next four on the list are: Dayton, Ohio; McAllen, Texas; Jackson, Miss.; and Oklahoma City.

It's not just pollen that's causing the problem. Indoor allergens such as dust mites, pet dander and mold also trigger allergic reactions in the fall.

Please click here for the top 100 U.S. cities for fall allergies.

Also, take a look at today's pollen count map.

Antihistamines, decongestants and mast cell stabilizers are available in pill form, but pills don't work as quickly as eye drops or gels to bring eye relief.

Nonsteroidal anti-inflammatory drug (NSAID) eye drops may be prescribed to decrease swelling, inflammation and other symptoms associated with seasonal allergic conjunctivitis, also called hay fever.

Prescription corticosteroid eye drops also may provide similar, quick relief. However, steroids have been associated with side effects such as increased inner eye pressure (intraocular pressure) leading to glaucoma and damage to optic nerve.

Steroids also have been known to cause the eye's natural lens to become cloudy, producing cataracts.

Check the product label or insert for a list of side effects of over-the-counter medications. For prescription medication, ask your doctor. In some cases, combinations of medications may be used.

You may benefit from immunotherapy, in which an allergy specialist injects you with small amounts of the allergen to help you gradually build up immunity.

Eye Allergies and Contact Lenses

Even if you are generally a successful contact lens wearer, allergy season can make your contacts uncomfortable. Airborne allergens can get on your lenses, causing discomfort. Allergens also can stimulate the excessive production of natural substances in your tears, which can bind to your contacts and cause blur and additional discomfort. Pollen maps can help you determine when allergens are present.

Ask your eye doctor about eye drops that can help relieve your symptoms and keep your contact lenses clean. Certain drops can discolor or damage certain lenses, so it makes sense to ask first before trying out a new brand.

Another alternative is daily disposable contact lenses, which are discarded nightly. Because you replace them so frequently, these types of lenses are unlikely to develop irritating deposits that can build up over time and cause or heighten allergy-related discomfort.

By Gina White, with updates by Marilyn Haddrill; reviewed by Vance Thompson, MD

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