Vision & Refractive Errors (and LASIK)

Vision and Refractive Errors

Computer Screens

Complaints of eye discomfort and fatigue are becoming more common as the use of computer screens increases. While it is true that computer screens can cause eyestrain, there is no convincing evidence that they can harm the eyes.

Some people fear that computer screens emit damaging ultraviolet (UV) light or radiation. The amount of UV light emitted by computer screens is a fraction of what is emitted from a fluorescent light. Radiation levels from computer screens are so low that a lifetime of exposure will not damage the eyes. After prolonged use of a computer screen, black and white objects may appear colored, but this is not a sign of eye damage.

Symptoms of eyestrain are eye irritation (red, watery, or dry eyes), eye fatigue (tired, aching heaviness of the eyelids or forehead), difficulty in focusing, and headaches. However, eyestrain does not result in permanent eye damage.

Eyestrain, backache, and muscle spasms may improve with proper arrangement of the computer screen and seating area. The Occupational Safety and Health Administration (OSHA) provides helpful suggestions on workstation arrangement.

It is important to wear appropriate eyeglasses adjusted for the distance between the eyes and the computer screen. Most computer users prefer to position the screen farther from where they normally read. Prescription eyeglasses should be adjusted accordingly.

Take periodic rest breaks. Using a computer requires unchanging body, head, and eye positions that can be fatiguing. Lubricate the eyes by blinking frequently or using artificial tears (lubricating eyedrops).  Keep workstations clean to minimize eye irritation from dust.

Minimize light glare by adjusting office lights or using hoods or filters on the video screen. Standard office lighting is too bright for comfortable computer screen viewing.

Refractive Errors

Refractive errors occur when light does not focus properly on the retina because of the shape of the eye. The resulting image is blurred. Common refractive errors are myopia (nearsightedness), hyperopia (farsightedness), astigmatism (distorted vision), and presbyopia (aging eyes).

Emmetropia

An emmetropic eye is of normal length, has a cornea that is perfectly shaped and allows light to focus crisply on the retina without the aid of glasses or contact lenses.  Objects are clear at all distances.

Emmetropia (light focused on the retina):

Myopia


A myopic eye is longer than a normal eye or has a cornea that is too steep, causing light rays to focus in front of the retina instead of on it. With myopia, close objects appear clear, but distant ones appear blurred.

Myopia:


Hyperopia

A hyperopic eye is shorter than normal or has a cornea that is too flat. The light rays focus beyond the retina instead of on it. Distant objects may appear clear, but close ones appear blurred.

Hyperopia: 

Astigmatism

The cornea of an astigmatic eye is curved unevenly. Images focus in front of and beyond the retina, causing both close and distant objects to appear blurry.

Astigmatism:  

Presbyopia


Presbyopia refers to the hardening of the lens that occurs with age. After the age of 40, the lens becomes more rigid and cannot change shape as easily to accommodate near objects. This makes reading and other tasks performed at close range difficult. Presbyopia can occur in combination with any of the other three refractive errors.  Often, inexpensive over-the-counter reading glasses alone will help with this condition.

Refractive errors are usually corrected with eyeglasses or contact lenses. Sometimes surgery is needed or desirable.


Laser Surgery of the Eye

The word laser is an acronym for Light Amplification by Stimulated Emission of Radiation. A laser is a concentrated beam of light, created when an electrical current passes through a special material. Used in eye surgery since the 1970s, the laser is popular for its unparalleled degree of precision and predictability. Lasers are being used for an increasing variety of eye diseases.

A laser's specific wavelength allows energy to be absorbed in selected tissues and not damage surrounding tissues. The laser beam is so precise it can cut notches in a strand of human hair without breaking it.

Thermal lasers convert light to heat. This type of laser seals blood vessels and destroys abnormal tissues. Photoablative lasers cut or sculpt tissue and are used to remove tissue, changing the shape and surface of the eye.

For diabetics with diabetic retinopathy, lasers (pan retinal photocoagulation or focal grids) can preserve vision, sometimes for many years. In treating diabetic retinopathy, the laser light seals leaking blood vessels in the retina, the light-sensitive layer of cells lining the back of the eye. Lasers also treat unusual retinal disorders, including blood vessel problems and tumors.

Also used to treat glaucoma, lasers (peripheral iridotomies) can create a new passage through the iris to relieve eye pressure.  Lasers in glaucoma (argon or selective laser trabeculoplasty) may also improve drainage through the trabecular meshwork in the eye, thereby lowering the overall pressure.

Although lasers do not remove cataracts, they may one day. Right now, they open the posterior capsule (Yag capsulotomy), which often becomes cloudy after cataract surgery, restoring vision in a matter of hours.

More recently, the excimer laser has received a great deal of attention as a tool for permanently correcting refractive errors such as nearsightedness, farsightedness, and astigmatism. Refractive laser surgery can decrease or eliminate the need for eyeglasses and contact lenses by reshaping the cornea.


LASIK with the Microkeratome

Until recently, if you were one of the millions of people with a refractive error, eyeglasses and contact lenses were the only options for correcting vision. But with the development of refractive surgery, some people with myopia (nearsightedness), hyperopia (farsightedness), or astigmatism (a cornea with unequal curves) can have their vision improved surgically.

Laser-assisted in situ keratomileusis
(LASIK) is a refractive procedure that uses a microkeratome cutting device to create a flap in the cornea and a laser to permanently reshape the cornea. The reshaped cornea helps focus light directly onto the retina to produce clearer vision.

LASIK is usually performed as an outpatient procedure using topical anesthesia with eyedrops. The procedure itself generally takes about 15 minutes. The surgeon creates a flap in the cornea with a microkeratome. The flap is lifted to the side, and the cool beam of the excimer laser is used to remove a thin layer of corneal tissue. The flap is folded back to its normal position and sealed without sutures. The removal of corneal tissue permanently reshapes the cornea.

A clear shield is used to protect the flap for the first day and night after surgery. The vision is usually slightly cloudy immediately after the procedure but clears rapidly, often within just a few hours. Your vision should be clear by the next day. Healing after surgery is often less painful than with other methods of refractive surgery because the laser removes tissue from the inside of the cornea and not the surface. Antibiotic and steroid eyedrops are used several times a day for the first week, along with rewetting drops. After the first week, you should need to use only the rewetting eyedrops.

Some people experience poor night vision after LASIK. The surgery also may result in undercorrection or overcorrection, which can often be improved with a second surgery. More rare and serious complications include a dislocated flap, epithelial ingrowth, and inflammation or infection underneath the flap. Most complications can be managed without any loss of vision. Permanent vision loss is very rare.

The ideal candidate for LASIK has a stable refractive error, has adequate corneal thickness and a normal corneal shape, is free of eye disease, is at least 18 years old, and is willing to accept the potential risks, complications, and side effects of LASIK.


LASIK With the Femtosecond Laser

This is a procedure where the laser cuts the flap instead of the microkeratome.  The surgeon creates a flap in the cornea with a special laser called a femtosecond laser. Tiny, quick pulses of laser light are applied to your cornea, creating microscopic bubbles at a specific depth and position within your cornea. The cool beam of a second laser, called an excimer laser, is then used to remove a thin layer of corneal tissue. The flap is folded back to its normal position and sealed without sutures. The removal of corneal tissue permanently reshapes the cornea.

Healing is essentially the same for both types of LASIK.


Wavefront-Guided Laser Surgery

Wavefront-guided LASIK is an enhanced version of LASIK. It uses a special device to precisely measure the eye's unique irregularities and variations as well as your need for corrective lenses. This procedure has been compared to taking a fingerprint of the eye. You may benefit from this customized approach.

Wavefront measuring devices, called analyzers or aberrometers, create a precise map of the eye. It is very detailed and records subtle distortions in your eye's visual system. Using this map, the excimer laser can be programmed to correct for these measured distortions, giving you clearer vision than was possible before with conventional treatments.


Photorefractive Keratectomy (PRK)

Photorefractive keratectomy (PRK) is one of several refractive surgery procedures used by ophthalmologists to permanently change the shape of the cornea to improve the way it focuses light on the retina.

PRK is an outpatient procedure performed with topical anesthetic eyedrops. It takes only about 15 minutes. The corneal reshaping is similar to LASIK and is performed with an excimer laser, but there is no flap creation.  Instead, the epithelium or outer cell layer of the cornea is completely removed and allowed to heal after the corneal reshaping. 

Immediately following surgery, the eye is patched or a bandage contact lens is placed on the eye. Vision is blurry for several days following PRK. It may take a month or longer to achieve your best vision. You may need to use medicated eyedrops for up to three months.  Though healing is longer than from LASIK, the overall cornea will be stronger as there are no flaps made.  There is no risk of late flap complications with PRK simply because there is no flap.

Possible complications of PRK surgery include undercorrection, overcorrection, poor night vision, and corneal scarring. Permanent vision loss is very rare. To be a candidate for the procedure you must have a stable and appropriate refractive error, be free of eye disease, be at least 18 years old, and be willing to accept the potential risks, complications, and side effects of PRK.

Recycling Eyeglasses

The World Health Organization estimates that corrective lenses can improve the eyesight of one-fourth of the world's population. Unfortunately, for many people a pair of eyeglasses is both unaffordable and unobtainable. The donation of old but useful eyeglasses to the needy in the US and abroad can help solve this problem.

The Lions Clubs International and local Lions Clubs conduct eyeglass-recycling programs. Used glasses are cleaned, repaired, and classified by prescription, then distributed free to needy people in developing countries around the world.

Contact a local Lions Club or call Lions Club International at 630.571.5466 to find a local recycling center. Chapters collect the used prescription eyeglasses, reading glasses, and even sunglasses, and then package and ship them to the centers.

Community services for the visually impaired often have names of those needing glasses. Donating your eyeglasses to any charitable organization will improve the eyesight of those in need.