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.

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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.

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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.
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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.

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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

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