Tag Archives: American Academy of Ophthalmology

Presbyopia

Definition:
Presbyopia (Greek word “presbys”, meaning “old person”) describes the condition where the eye exhibits a progressively diminished ability to focus on near objects with age. Presbyopia’s exact mechanisms are not known with certainty, however, the research evidence most strongly supports a loss of elasticity of the crystalline lens, although changes in the lens’s curvature from continual growth and loss of power of the ciliary muscles (the muscles that bend and straighten the lens) have also been postulated as its cause.

………CLICK & SEE THE PICTURES

Similar to grey hair and wrinkles, presbyopia is a symptom caused by the natural course of aging presbyopia is the gradual loss of your eyes’ ability to focus actively on nearby objects — is a not-so-subtle reminder that you’ve reached middle age. A natural, often annoying part of aging, presbyopia usually develops after age 40.The first symptoms (described below) are usually first noticed between the ages of 40-50. The ability to focus on near objects declines throughout life, from an accommodation of about 20 dioptres (ability to focus at 50 mm away) in a child to 10 dioptres at 25 (100 mm) and leveling off at 0.5 to 1 dioptre at age 60 (ability to focus down to 1-2 meters only).

Symptoms
The first symptoms most people notice are difficulty reading fine print, particularly in low light conditions, eyestrain when reading for long periods, blur at near or momentarily blurred vision when transitioning between viewing distances. Many advanced presbyopes complain that their arms have become “too short” to hold reading material at a comfortable distance.

Presbyopia, like other focus defects, becomes much less noticeable in bright sunlight. This is a result of the iris closing to a smaller diameter. As with any lens, increasing the focal ratio of the lens increases depth of field by reducing the level of blur of out-of-focus objects (compare the effect of aperture on depth of field in photography).

A delayed onset of seeking correction for presbyopia has been found among those with certain professions and those with miotic pupils. In particular, farmers and housewives seek correction later, whereas service workers and construction workers seek eyesight correction earlier.

Focusing mechanism of the eye:
In optics, the closest point at which an object can be brought into focus by the eye is called the eye’s near point. A standard near point distance of 25 cm is typically assumed in the design of optical instruments, and in characterizing optical devices such as magnifying glasses.

There is some confusion in articles and even textbooks over how the focusing mechanism of the eye actually works. In the classic book, ‘Eye and Brain’ by Gregory, for example, the lens is said to be suspended by a membrane, the ‘zonula’, which holds it under tension. The tension is released, by contraction of the ciliary muscle, to allow the lens to fatten, for close vision. This would seem to imply that the ciliary muscle, which is outside the zonula must be circumferential, contracting like a sphincter, to slacken the tension of the zonula pulling outwards on the lens. This is consistent with the fact that our eyes seem to be in the ‘relaxed’ state when focusing at infinity, and also explains why no amount of effort seems to enable a myopic person to see further away. Many texts, though, describe the ‘ciliary muscles’ (which seem more likely to be just elastic ligaments and not under any form of nervous control) as pulling the lens taut in order to focus at close range. This has the counterintuitive effect of steepening the lens centrally (increasing its power) and flattening peripherally.

Presbyopia and the ‘payoff’ for the nearsighted
Many people with myopia are able to read comfortably without eyeglasses or contact lenses even after age 40. However, their myopia does not disappear and the long-distance visual challenges will remain. Myopes with astigmatism will find near vision better though not perfect without glasses or contact lenses once presbyopia sets in, but the greater the amount of astigmatism the poorer their uncorrected near vision. Myopes considering refractive surgery are advised that surgically correcting their nearsightedness may actually be a disadvantage after the age of 40 when the eyes become presbyopic and lose their ability to accommodate or change focus because they will then need to use glasses for reading. A surgical technique offered is to create a “reading eye” and a “distance vision eye”, a technique commonly used in contact lens practice, known as monovision. Monovision can be created with contact lenses or spectacles so candidates for this procedure can determine if they are prepared to have their corneas reshaped by surgery to cause this effect permanently.

Causes:
Presbyopia is caused by an age-related process. This is different from astigmatism, nearsightedness and farsightedness, which are related to the shape of the eyeball and caused by genetic factors, disease or trauma. Presbyopia is generally believed to stem from a gradual loss of flexibility in the natural lens inside your eye.

These age-related changes occur within the proteins in the lens, making the lens harder and less elastic with the years. Age-related changes also take place in the muscle fibers surrounding the lens. With less elasticity, the eye has a harder time focusing up close. Other, less popular theories exist as well.

Most experts agree that presbyopia is caused by a hardening of your lens, which in turn develops with aging. As your lens becomes less flexible, it can no longer change shape, and close-up images appear out of focus.

Tests and diagnosis:
Presbyopia is diagnosed by a basic eye exam. This exam is generally administered by either an ophthalmologist or an optometrist. An ophthalmologist, who has a doctor of medicine (M.D.) degree, is a specialist trained to diagnose and manage eye disorders, including those that may require either medical or surgical treatment. An optometrist, who has a doctor of optometry (O.D.) degree, can perform many of the same services as an ophthalmologist, such as evaluating your vision, prescribing corrective lenses and diagnosing common eye disorders. In some states, optometrists also treat selected eye disorders with drugs. However, an optometrist may refer you to an ophthalmologist for more complex eye problems and for surgical procedures.

A complete eye examination involves a series of tests. Your eye doctor may use odd-looking instruments, aim bright lights directly at your eyes and request that you look through an array of lenses. Each test is necessary and allows your doctor to evaluate a different aspect of your vision.

According to the American Academy of Ophthalmology, if you don’t wear glasses or contacts, have no symptoms of eye trouble and are at a low risk of developing eye disease, you should have your eyes examined at the following intervals:

*Every five to 10 years under age 40
*Every two to four years between ages 40 and 64
*Every one to two years beginning at age 65

However, if you wear glasses or contacts, have your eyes checked more often. And if you notice any problems with your vision, schedule an appointment with your eye doctor as soon as possible, even if you’ve recently had an eye exam. Blurred vision may suggest you need a prescription change or have another eye problem that may need evaluation and treatment.

Treatment:
Presbyopia is not routinely curable – though tentative steps toward a possible cure suggest that this may be possible – but the loss of focusing ability can be compensated for by corrective lenses including eyeglasses or contact lenses. In subjects with other refractory problems, convex lenses are used. In some cases, the addition of bifocals to an existing lens prescription is sufficient. As the ability to change focus worsens, the prescription needs to be changed accordingly.

In order to reduce the need for bifocals or reading glasses, some people choose contact lenses to correct one eye for near and one eye for far with a method called “monovision”. Monovision sometimes interferes with depth perception. There are also newer bifocal or multifocal contact lenses that attempt to correct both near and far vision with the same lens.

Controversially, eye exercises have been quoted as a way to delay the onset of presbyopia, but there is no evidence that they work.

Nutrition
At least one scientific study reported that taking lutein supplements or otherwise increasing the amount of lutein in the diet resulted in an improvement in visual acuity, while another study suggested that lutein supplementation might slow aging of the lens. Lutein is found naturally in both the lens of the eye and the macula, the central area of the retina.

The goal of treatment is to compensate for the inability of your eyes to focus on nearby objects. Treatment options include wearing corrective lenses, undergoing refractive surgery or getting lens implants.

Corrective lenses
If you had good, uncorrected vision before developing presbyopia, you may be able to use nonprescription reading glasses. But check with your eye doctor about what’s right for you.

Reading glasses sold over-the-counter are labeled on a scale that corresponds to the degree of magnification (power). The least powerful are labeled +1.00, and the most powerful +3.00. When purchasing reading glasses, try out a few different powers until you find the magnification that allows you to read comfortably. Test each pair on printed material held about 14 to 16 inches in front of your face.

You’ll need prescription lenses for presbyopia if over-the-counter glasses are inadequate or if you already wear corrective lenses for nearsightedness, farsightedness or astigmatism. Your choices include:

Prescription reading glasses. If you have no other vision problems, you can have prescription lenses for reading only.

Bifocals. These glasses come in two styles — those with a visible horizontal line and those without a line (progressive bifocals). When you look through progressive bifocals at eye level, the lenses correct your distance vision. This correction gradually changes to reading correction at the bottom.

Trifocals. These glasses have corrections for close work, middle-distance vision — such as for computer screens — and distance vision. Trifocals can have visible lines or progressive lenses.

Bifocal contacts. Bifocal contact lenses, like bifocal glasses, provide distance and close-up correction on each contact. The bottom, reading portion of the lens is weighted to keep the lens correctly positioned on your eye. These are frequently difficult to fit and often do not provide altogether satisfactory visual results.

Monovision contacts. With monovision contacts, you wear a contact lens for distance vision in your dominant eye and a contact lens for close-up vision in your nondominant eye. Your dominant eye is generally the one you use when you’re aiming a camera to take a picture.

Modified monovision. With this option, you wear a bifocal contact lens in your nondominant eye and a contact lens set for distance in your dominant eye. You use both eyes for distance and one eye for reading. Your brain learns which lens to favor — depending on whether you’re viewing things close up or far away — so you don’t have to consciously make the choice of which eye to use.

Refractive surgery:-
Refractive surgery changes the shape of your cornea. For presbyopia, this treatment — equivalent to wearing monovision contact lenses — may be used to improve close-up vision in the nondominant eye. The American Academy of Ophthalmology recommends that people try monovision contacts to determine if they can adjust to this kind of correction before considering refractive surgery.

Most refractive surgical procedures were developed to correct nearsightedness, farsightedness and astigmatism. Few studies have been published about the long-term effectiveness of monovision refractive surgery for people with presbyopia, but some evidence suggests that the surgery may help some people with presbyopia reduce their dependence on corrective lenses. Eventually, though, many people who have had refractive surgery will still need corrective lenses for reading.

Refractive surgical procedures include the following:

Conductive keratoplasty (CK). This procedure uses radio frequency energy to apply heat to very tiny spots around the cornea. The degree of change in the cornea’s curvature depends on the number and spacing of the spots, as well as the way in which the corneal tissue heals after the treatment. The results of CK are variable and unstable in many people.

New surgical options to treat presbyopia are being researched and are already available in many countries. One example is Refractec Inc.’s conductive keratoplasty, or NearVision CK treatment, which uses radio waves to create more curvature in the cornea for a higher “plus” prescription to improve near vision. The method was FDA-approved for the temporary reduction of presbyopia in April 2004. (In 2002 it had been approved for mild farsightedness.) Click to read more about how CK works.
…………………….CLICK & SEE

The eye’s lens stiffens with age, so it is less able to focus when you view something up close. The result is blurred near vision. (Illustration: Varilux).
A highly experimental treatment is a soft, elastic polymer gel that researchers say would be injected into the capsular bag, the cavity that contains the natural lens. In theory, the gel would replace the natural lens and serve as a new, more elastic lens. Experiments also have centered on laser treatment of the eye’s hardened lens to increase flexibility and improve focus.

With the recent introduction of presbyopia-correcting intraocular lenses, some people undergoing cataract surgery may be able to achieve clear vision at all distances. Also, an elective procedure known as refractive lens exchange may enable you to replace your eye’s natural lens with an artificial one using presbyopia-correcting lenses.

Other methods are being researched as well. Click to read more about surgical options for presbyopia.

Laser-assisted in-situ keratomileusis (LASIK). With this procedure, your eye surgeon uses a laser or an instrument called a keratome to make a thin, hinged flap in your cornea. Your surgeon then uses an excimer laser to remove inner layers of your cornea to steepen its domed shape. An excimer laser differs from other lasers in that it doesn’t produce heat.

Laser epithelial keratomileusis (LASEK). Instead of creating a flap in the cornea, the surgeon creates a flap only in the cornea’s thin protective cover (epithelium). Your surgeon will use an excimer laser to reshape the cornea’s outer layers and steepen its curvature and then reposition the epithelial flap.

Photorefractive keratectomy (PRK). This procedure is similar to LASEK, except the surgeon removes the epithelium. It will grow back naturally, conforming to your cornea’s new shape.

Lens implants
Another procedure used by some ophthalmologists involves removal of your clear natural lens and replacement with a synthetic lens inside your eye (intraocular lens implant). The synthetic lens implant is designed to allow your eye to see things both near and at a distance. However, synthetic lens implants haven’t been entirely satisfactory; recipients have experienced problems with glare and blurring. In addition, this surgery carries with it the same risks associated with cataract surgery, such as inflammation, infection, bleeding and glaucoma.

.
Lifestyle modification and home remedies:
Although you can’t prevent presbyopia, you can help protect your eyes and your vision. Follow these steps:

Have your eyes checked. Regardless of how well you see, have your eyes checked regularly for problems.
Control chronic health conditions. Certain conditions, such as diabetes and high blood pressure, can affect your vision if you don’t receive proper treatment.

Recognize symptoms. Sudden loss of vision in one eye, sudden hazy or blurred vision, flashes of light, black spots, or halos or rainbows around lights may signal a serious medical problem, such as acute glaucoma or stroke, or some other treatable retinal condition, such as a retinal tear or retinal detachment. Talk to your doctor if you experience any of these symptoms.

Protect your eyes from the sun. Wear sunglasses that block ultraviolet (UV) radiation. This is especially important if you spend long hours in the sun or are taking a prescription medication that increases your sensitivity to UV radiation.

Eat healthy foods. Try to eat plenty of fruits and leafy greens and other vegetables; these foods generally contain high levels of antioxidants as well as vitamin A and beta carotene. They’re also vital to maintaining healthy vision.
Use the right glasses. The right glasses optimize your vision. Having regular exams will ensure that your eyeglass prescription is correct.
Use good lighting. Turn up the light for better vision.

Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose.
Resources:
http://en.wikipedia.org/wiki/Presbyopia
http://www.allaboutvision.com/conditions/presbyopia.htm
MayoClinic.com

Advertisements

New Anti-Cancer Compound Found

A marine compound discovered off the coast of Key Largo in Florida inhibits cancer cell growth in lab tests and is likely to prompt the development of effective new drugs.

The University of Florida (UF)-patented compound, largazole, is derived from cyanobacteria that grow on coral reefs. It is being described as one of the most promising finds since the college’s marine lab was established three years ago.

The molecule’s natural chemical structure and its ability to inhibit cancer cell growth were first described in the Journal of American Chemical Society in February, and the lab synthesis and description of the molecular basis for its anti-cancer activity appeared on July 2.

“It’s exciting because we’ve found a compound in nature that may one day surpass a currently marketed drug or could become the structural template for rationally designed drugs with improved selectivity,” said Hendrik Luesch, assistant professor in UF’s Department of Medicinal Chemistry and the study’s principal investigator.

Largazole, discovered and named by Luesch for its Florida location and structural features, seeks out a family of enzymes called histone deacetylase, or HDAC. Overactivity of certain HDACs has been associated with several cancers such as prostate and colon tumours, and inhibition of HDACs can activate tumour-suppressor genes that have been silenced in these cancers.

Although scientists have been probing the depths of the ocean for marine products since the early 1960s, many pharmaceutical companies lost interest before researchers could deliver useful compounds because natural products were considered too costly and time-consuming to research and develop.

Many common medications, from pain relievers to cholesterol-reducing statins, stem from natural products that grow on the earth, but there is literally an ocean of compounds yet to be discovered in our seas.

Only 14 natural marine products developed are in clinical trials today, Luesch said, and one drug recently approved in Europe is the first-ever marine-derived anti-cancer agent.

“Marine study is in its infancy”, said William Fenical, professor of oceanography and pharmaceutical sciences at the University of California, San Diego. “The ocean is a genetically distinct environment and the single, most diverse source of new molecules to be discovered”.

HDACs are already targeted by a drug approved for cutaneous T-cell lymphoma manufactured by the global pharmaceutical company Merck & Co. Inc. However, UF’s compound does not inhibit all HDACs equally, meaning a largazole-based drug might result in improved therapies and fewer side effects, Luesch said.

Luesch said that, within the next few months, he plans to study whether largazole reduces or prevents tumour growth in mice. Luesch has several other anti-tumour natural products from Atlantic and Pacific cyanobacteria in the pipeline.

These results were presented on Thursday at an international natural products scientific meeting in Athens.

Sources: The Times Of Imdia

Zemanta Pixie

Tips for a Safe Holi

Every year there are several cases of eye-injury owing to uncontrolled Holi celebrations. Consultant Eye Surgeon Dr Anand Shroff provides some tips on how to protect your eyes and the measures to take should an injury occur.

Girl at Holi Phagwa

Girl at Holi Phagwa (Photo credit: Wikipedia)

From time immemorial, man has been attracted to colours. Dry Holi colours known as ‘gulal’ and wet colours or ‘rang’ were originally prepared naturally from flowers and vegetables. However with time, in the quest of more long-lasting and strong colours, chemical and artificial colours are being used. These chemicals pose serious risks to our body and eyes.

The eyes especially are extremely susceptible during Holi because of their strategic place in the body and also because of the use of toxic materials in colours these days. The synthetic colours used during Holi are known to cause eye irritation and allergies, and even temporary blindness besides bronchial asthma and skin infections.

Some of these colours have been shown to possess cancerous properties. Considering the toxicity of synthetic colours, some institutions and organisations have now come forward to make people aware of the use of eco-friendly natural colours along with the resurrection of old traditional vegetable-based Holi colours. Hence, herbal ‘gulals’ are now commercially available in the market.

Some Safety Tips :-
Ensure that your eyes remain protected at all times. Use sunglasses to protect your eyes from coloured water.

Use a hat or cap to protect your hair from being coloured with strong chemical dyes.

Apply a thick layer of coconut oil on your body and hair so that the colour doesn’t stick and it can be washed off easily later. While washing off the colour, use lukewarm water and keep your eyes tightly closed.

If you are travelling, keep the car windows tightly shut. Better still, avoid travelling on this day.

Ensure that only non-toxic colours are used by younger children.

What to do?
In case the chemicals make contact with your eyes and skin, taking certain these measures helps to avoid permanent damage. If the injury is serious or the symptoms such as irritation of eyes and skin, pain, swelling, photophobia (sensitivity to light), persist, see a doctor at the earliest.

Wash eyes with room temperature with clean water.

Remove contaminated clothing and wash exposed skin area thoroughly with soap and water.

Visit an eye specialist immediately if you have suffered an eye injury with a high-speed balloon or stone as severe injury can cause rupturing of the eyeball or even a retinal detachment.

Do not attempt to clean the eye immediately as the water may be contaminated and cause further infection. Instead shut the eye and rush to the nearest hospital.

Avoid inhaling the powders as this affects the respiratory tract causing irritation, cough, difficulty in breathing, and even bronchitis.

If someone is experiencing prolonged breathlessness, move him/ her towards a source of fresh air, and administer oxygen if possible.

Encourage your friends to play a safe Holi this year!

Sources:The Times Of India

Enhanced by Zemanta

How to Get the Calcium We Need

Adults who shrug off their calcium needs miss out on protective benefits — against broken bones, heart attacks, and cancer.

Calcium, the body’s most abundant mineral, plays a critical role in bone health, but it does much more than that. Calcium permits cells to divide, regulates muscle contraction and relaxation, keeps the heart beating and the brain working, plays an important role in the movement of protein and nutrients inside cells, helps control blood pressure, and is essential for blood clotting. Calcium also seems to protect against heart attacks and certain types of cancers.

“We evolved from the ocean, and the ocean is a high-calcium bath,” says Michael Holick, M.D., Ph.D., professor of medicine, dermatology, and physiology at Boston University Medical Center. “Living organisms used calcium for all types of purposes because it was readily available. But now that we’re on land, the lack of calcium in our environment poses a serious risk.”

The body maintains its blood calcium level at any expense, Holick says. So if you’re not absorbing enough calcium from what you eat to satisfy your body’s requirement, you’ll steal it from your bones.

In effect, the body uses its bones as a calcium bank.
“It constantly takes calcium from the bone and supplies it to the blood to make sure that all of these essential functions can continue,” explains Bernard P. Halloran, Ph.D., professor of medicine at the University of California San Francisco.

When you eat a piece of cheese, drink a glass of milk, or take a calcium supplement, the calcium is digested in the intestine, where vitamin D stimulates its absorption.
It then travels through the body in your blood, where it. s constantly deposited and withdrawn from bone. “It’s as if we put a thousand dollars worth of calcium into the bone each day and remove a thousand dollars worth each day,” says Halloran. “The bone stays in a steady state, but a amount of calcium goes in and out of it.” This ensures that the body always has a source of calcium when it needs it..…click & see

We are Never Too Old
Many adults shrug off the need for adequate calcium and feel it’s not necessary since they’re no longer building bone, a process that ends at about age 30. “But if you continue to consume an inadequate amount of calcium, you’ll gradually erode your skeleton to the point where, one morning, you’ll break a bone when you get out of bed,” warns Halloran.

According to one researcher, if adults simply added one more glass of milk and a cup of yogurt a day, and either walked or participated in some other form of weight-bearing exercise for 30 minutes a day, they could substantially reduce the incidence of broken bones resulting from osteoporosis.

Because vitamin D plays a role in the body’s absorption of calcium, consuming a sufficient amount is also crucially important and simple. Milk has been fortified with vitamin D, so if you drink milk you’re getting enough. And, since your body makes vitamin D when exposed to the sun’s rays, 15 to 30 minutes of sunlight on your face and hands two to three times a week will take care of it. If you don’t drink milk and the weather is gloomy, take a multivitamin that includes vitamin D. But never use supplements of this single vitamin unless your doctor recommends them; too much vitamin D can be toxic.

Good Sources of Calcium
Although the optimal amount of calcium isn’t known, “enough” according to the Food and Nutrition Board of the National Academy of Sciences. Institute of Medicine, is 1,200 milligrams (mg) a day for adults over 50. The most readily available form of calcium is in dairy products.

But  we can get calcium from many other foods as well. Tofu, if prepared with calcium sulfate, is an outstanding source. Just one-quarter of a block gives you a substantial 553 mg. Don’t like tofu? Try whizzing it in a blender with some milk or juice, fresh fruit, and a bit of honey to make a nourishing and delicious smoothie. Leafy green vegetables, calcium-fortified fruit juices, canned sardines, and canned salmon with bones are all good sources. Even carrots and green peas contain calcium. To up your consumption of calcium in a way you won’t even notice, add dry milk to soups or sauces. Just one-quarter cup of dry milk provides 375 mg of calcium.

Debunking Myths
“Milk is a poor source.” Some people believe that drinking milk is not a good way to get calcium because the protein in it carries away the calcium in urine. “Here’s the story,” says Holick. “The body metabolizes the sulfur amino acids in protein and releases sulfuric acid. And that acid, which is excreted in urine, takes calcium along with it.” So it does have a marginal effect on bones. However, if you get enough calcium in your diet, you can more than offset any loss.

“Coffee saps calcium.” A while back, reports warned that drinking caffeinated coffee would leach calcium from bones. “But a nicely done study shows that the amount of calcium in the milk you put into your coffee is enough to make up for the minuscule amount of calcium lost,” Holick says.

“Calcium causes kidney stones.” In the past, people whose risk of kidney stones was high were told to limit the amount of calcium they ate because the stones are made from calcium salts. But current thinking has it that calcium from food actually decreases the risk of kidney stones.

The most important message about calcium is also the simplest: Make sure you get an adequate amount. You don’t have to count milligrams with every bite, but learn which foods are rich in calcium and make them a regular part of your diet. And, to guarantee that the calcium you eat becomes available to your body, get sufficient vitamin D, via the sun or in a multivitamin tablet.

How much calcium is in … ?
Both men and women over age 50 should be eating 1,200 mg of calcium a day. The chart below shows the calcium content of some common foods:-

Food………………….Amount…………………..Calcium
Yogurt..…………………….1 8-oz container……………….. 400
Low-fat milk..…………1 8-oz.glass………………………… 300 mg
Calcium-fortified juice…1 8-oz.glass………………….300 mg
Swiss cheese..…………1 1-oz.slice…………………………… 270 mg
Sardines with bones.……3 oz……………………………….200 mg
Broccoli….……………….1 cup………………………………………75 mg
Green beans.…………..1 cup………………………………………60 mg
Orange………………..1pce…………………………………………….50 mg

From New Choices (Reader’s Digest)