FAQs 
Definitions
Definitions
ANESTHESIA FOR CATARACT SURGERY
The standard cataract surgery anesthetic is a local anesthetic that blocks the optic nerve. The anesthesia is administered by injection and is painless. The patient is awake during surgery but may be sedated. The eye is immobilized. A new topical anesthetic is now being used by a small number of ophthalmologists.
APHAKIA
The absence of the eye's natural crystalline lens, usually after cataract removal. APHAKIC SPECTACLES Thick, plus-powered eyeglasses that were once the standard correction for optical power following extraction of cataract. The glasses were cumbersome and greatly distorted peripheral vision. Today, an intraocular lens (IOL) is implanted in the eye after the cataract is removed.
ASTIGMATISM
Astigmatism is blurry vision produced by football-shaped corneas which are too steep in one place and too flat in another. Astigmatic corneas focus light in two different places in the eye, making both near and distance vision a problem.
ASTIGMATIC KERATOTOMY (AK)
Astigmatic Keratotomy (AK) is similar to Radial Keratotomy (RK) in that it is incisional surgery, but the calculated surgical incisions are made traverse to the cornea. AK may be performed in conjunction to RK.
AUTOMATED LAMELLAR KERATOPLASTY (ALK)
ALK is a refractive surgery technique for low to moderate myopia. In the procedure, the ophthalmologist places an instrument called an automated microkeratome on the eye which removes, in a shaving motion, a thin layer of cornea only microns thick. An even thinner layer of cornea underneath this top cap is removed, and the top cap is replaced. The procedure does not require sutures.
BINOCULAR COORDINATION
One of the more important visual skills is the ability to coordinate the two eyes together. A child is born with two eyes, but he must learn to team them together. Some children learn to do this properly while others do not. For example, some children develop a problem known as exophoria, which is a tendency for the eyes to deviate in an outward direction. This is not the same as a condition known as exotropia where the eye actually can be seen to be in an outward position.
CATARACT
An opacity or clouding of the crystalline lens that may prevent a clear image from forming on the retina. The cataractous lens may require surgical removal if visual loss becomes significant, with lost optical power replaced with an intraocular lens.
CORNEA
The transparent front segment of the eye that covers the iris, pupil and anterior chamber, providing most of the eye's optical power.
CRYSTALLINE LENS
The natural lens of the eye, located behind the pupil, which helps bring rays of light to focus on the retina. The original state of the lens is transparent, but the lens becomes cloudy with age.
DIOPTER (dy-ahp-tur)
A measurement of the degree to which light converges or diverges; also of lens refractive power. Equal to the reciprocal of the focal length of a lens (in meters), e.g., a 2-diopter lens brings parallel rays of light to a focus at half a meter.
EMMETROPIA (em-uh-TROP-pee-uh)
Refractive condition in which no refractive error is present and distant images are focused sharply on the retina with no need for corrective lenses.
EXCIMER LASER
The excimer laser produces an ultraviolet beam of light which is emitted in pulses. Each pulse removes 1/4000 millimeter of tissue from the surface of the cornea. It would take about 200 pulses from an excimer laser just to cut a human hair in half. The excimer laser has been used in industry since 1971 and has been used in ophthalmic surgery since 1983. Approval of the excimer laser procedure was based on clinical trials of more than 1600 eyes together with safety information through three years of follow-up. The studies using the 6mm treatment zone found that of the 341 eyes at six months, 95% were corrected to 20/40 or better without spectacles or contact lenses, and 66% to 20/20 or better without spectacles or contact lenses. In 23 out of 340 eyes (6.8%), the best vision that can be achieved with spectacles declined by 2 or more lines from preop; none was worse than 20/40. The clinical trials showed the following transient complications: pain (24-48 hours), corneal swelling, double vision, feeling something in the eye, shadow images, light sensitivity, tearing and pupil enlargement. These problems lasted up to several weeks. The clinical trials using the 6mm treatment zone showed the following adverse events occurred in at least 1.0% of the patients within 6 months post-treatment: night vision difficulty (1.0%); elevation of intraocular pressure (1.8%); hazy cornea affecting vision (2.3%); overcorrection or became farsighted (5.0%); undercorrection or still nearsighted (5.6%); loss of the best vision that can be achieved with glasses (6.8%); mild halo (9.7%); and, minor glare (10.0%).
EXTRACAPSULAR CATARACT EXTRACTION
A cataract surgical procedure which removes the cataractous lens but leaves the rear lens capsule intact.
FUNCTIONAL VISUAL DISABILITY
The degree to which a visual error interferes with a person's ability to perform normal daily activities, such as reading, driving at night, or performing hobbies.
HYPEROPIA
Also known as farsightedness, hyperopia is a refractive error caused by an eyeball that is too short to focus light on the retina. Light strikes the retina before it can come to a sharp focus.
INTRAOCULAR LENS (IOL)
A plastic lens that may be surgically implanted to replace the natural lens of the eye. There are numerous styles of IOLs, including foldable IOLs and multifocal IOLs.
IRIS
Pigmented tissue that lies behind the cornea that gives color to the eye (e.g., blue eyes) and controls the amount of light entering the eye by varying the size of the black pupillary opening.
LASER ASSISTED IN-SITU KERATOMILEUSIS (LASIK)
Laser Assisted In Situ Keratomileusis, or LASIK, combines PRK with elements of ALK. LASIK is considered effective for all levels of myopia, including high myopia up to -20 diopters. The ophthalmologist uses the automated microkeratome to shave off a thin, hinged layer of the cornea. The surgeon then uses the excimer laser to vaporize a thin layer of the underlying cornea, and the top flap is restored to its place.LASIK is the newest refractive procedure and therefore there is little hard data on its outcomes. However, many refractive surgeons believe LASIK holds the most promise for patients with moderate to high myopia.
MICRON (MY-kron)
A unit of length equal to one-millionth of a meter. MYOPIA Also known as nearsightedness, myopia is a refractive error caused by an eyeball that is too long to focus light on the retina or a cornea which is too steeply curved. In these cases light focuses instead in front of the retina
OPHTHALMOLOGIST
A physician specializing in refractive, medical, and surgical treatment of eye diseases and disorders.
OPTOMETRIST
Non-medical professional trained to prescribe eyeglasses or contact lenses, examine eyes, and detect eye disease.
PERK STUDY
The Prospective Evaluation of Refractive Keratotomy Study, a multicenter study of radial keratotomy outcomes funded by the National Eye Institute. Ten-year results of radial keratotomy patients who had the surgery in 1983 were published in Archives of Ophthalmology in October 1994. The study found that seven out of ten patients who had the operation on both eyes no longer wore or required corrective lenses ten years after surgery, and 85% of patients saw 20/40 or better without glasses. It concluded that RK is a "reasonably safe operation" that can "effectively reduce but not eliminate myopia." The study also found that 43% of patients experienced a hyperopic shift following surgery over the ten-year period. These patients typically experienced an improvement in their vision as their refractive error moved closer to 20/20. It is for this reason that ophthalmic surgeons will often intentionally undercorrect their patients, then monitor the rate of healing before performing a follow-up enhancement procedure if necessary. However, patients whose vision had achieved full correction or near full correction through surgery and who experience a hyperopic shift could become farsighted and need to wear glasses.
PHACOEMULSIFICATION (fay-koh-ee-mul-sih-fih-KAY-shun)
A cataract surgical procedure which uses an ultrasonic vibration to shatter and break up a cataract, making it easier to remove. The vibration is delivered by an irrigation-aspiration instrument. In a survey of ASCRS members in 1994, 86% preferred the phacoemulsification cataract removal technique over the extracapsular cataract extraction technique. The technique was invented by Charles D. Kelman, M.D., and was first published in 1967.
POSTERIOR CAPSULAR OPACIFICATION (PCO)
Opacification of the posterior lens capsule, sometimes called "secondary cataract," is often a consequence of modern cataract surgery. It occurs when a thin membrane of tissue grows over the remaining capsule following cataract surgery, and can develop in as many as half of all cases between several months and several years after surgery. PCO is treated using the YAG laser on an outpatient basis.
PHOTOREFRACTIVE KERATECTOMY (PRK)
A surgical technique employing an excimer laser to reshape the surface of the cornea and thereby reducing nearsightedness. The laser is controlled by a computer which determines for each patient treated the location, number of pulses, and surface area to be impacted by the laser light beam, based on that individual patient's vision and correction needs.
PRESBYOPIA
Also called "old age vision," presbyopia occurs as the lens of the eye ages and becomes less elastic and able to accommodate. Usually becomes significant after age 45 and is often signaled by the need for bifocals.
PUPIL
The variable-sized, black circular opening in the center of the iris that controls the amount of light that enters the eye.
RADIAL KERATOTOMY (RK)
A surgical technique employing radial incisions made in the periphery of the cornea to allow the central cornea to flatten, reducing its optical power and thereby nearsightedness.
RETINA
The thin lining at the back of the eye that converts images from the eye's optical system into electronical impulses sent along the optic nerve for transmission to the brain.
SCLERAL INCISION
The external white of the eye through which an incision is made during a cataract operation that uses a scleral incision.
YAG LASER
The YAG laser is a surgical instrument that emits a short pulsed, high energy light beam that can be precisely focused by computer to cut, vaporize, or fragment tissue. The YAG laser is used to treat posterior capsular opacification, a clouding of the remaining capsular tissue that develops postoperatively in as many as half of cataract removal operations. The tissue is vaporized with carefully controlled pulses of the YAG laser, and the surgery is performed on an outpatient basis.
Courtesy of Eyeglass House
Definitions
PLEASE NOTE: The information contained herein is intended to be educational and is not intended in any way as a substitute for medical advice and care from qualified, licensed vision care providers.
ANESTHESIA FOR CATARACT SURGERY
The standard cataract surgery anesthetic is a local anesthetic that blocks the optic nerve. The anesthesia is administered by injection and is painless. The patient is awake during surgery but may be sedated. The eye is immobilized. A new topical anesthetic is now being used by a small number of ophthalmologists.
APHAKIA
The absence of the eye's natural crystalline lens, usually after cataract removal. APHAKIC SPECTACLES Thick, plus-powered eyeglasses that were once the standard correction for optical power following extraction of cataract. The glasses were cumbersome and greatly distorted peripheral vision. Today, an intraocular lens (IOL) is implanted in the eye after the cataract is removed.
ASTIGMATISM
Astigmatism is blurry vision produced by football-shaped corneas which are too steep in one place and too flat in another. Astigmatic corneas focus light in two different places in the eye, making both near and distance vision a problem.
ASTIGMATIC KERATOTOMY (AK)
Astigmatic Keratotomy (AK) is similar to Radial Keratotomy (RK) in that it is incisional surgery, but the calculated surgical incisions are made traverse to the cornea. AK may be performed in conjunction to RK.
AUTOMATED LAMELLAR KERATOPLASTY (ALK)
ALK is a refractive surgery technique for low to moderate myopia. In the procedure, the ophthalmologist places an instrument called an automated microkeratome on the eye which removes, in a shaving motion, a thin layer of cornea only microns thick. An even thinner layer of cornea underneath this top cap is removed, and the top cap is replaced. The procedure does not require sutures.
BINOCULAR COORDINATION
One of the more important visual skills is the ability to coordinate the two eyes together. A child is born with two eyes, but he must learn to team them together. Some children learn to do this properly while others do not. For example, some children develop a problem known as exophoria, which is a tendency for the eyes to deviate in an outward direction. This is not the same as a condition known as exotropia where the eye actually can be seen to be in an outward position.
CATARACT
An opacity or clouding of the crystalline lens that may prevent a clear image from forming on the retina. The cataractous lens may require surgical removal if visual loss becomes significant, with lost optical power replaced with an intraocular lens.
CORNEA
The transparent front segment of the eye that covers the iris, pupil and anterior chamber, providing most of the eye's optical power.
CRYSTALLINE LENS
The natural lens of the eye, located behind the pupil, which helps bring rays of light to focus on the retina. The original state of the lens is transparent, but the lens becomes cloudy with age.
DIOPTER (dy-ahp-tur)
A measurement of the degree to which light converges or diverges; also of lens refractive power. Equal to the reciprocal of the focal length of a lens (in meters), e.g., a 2-diopter lens brings parallel rays of light to a focus at half a meter.
EMMETROPIA (em-uh-TROP-pee-uh)
Refractive condition in which no refractive error is present and distant images are focused sharply on the retina with no need for corrective lenses.
EXCIMER LASER
The excimer laser produces an ultraviolet beam of light which is emitted in pulses. Each pulse removes 1/4000 millimeter of tissue from the surface of the cornea. It would take about 200 pulses from an excimer laser just to cut a human hair in half. The excimer laser has been used in industry since 1971 and has been used in ophthalmic surgery since 1983. Approval of the excimer laser procedure was based on clinical trials of more than 1600 eyes together with safety information through three years of follow-up. The studies using the 6mm treatment zone found that of the 341 eyes at six months, 95% were corrected to 20/40 or better without spectacles or contact lenses, and 66% to 20/20 or better without spectacles or contact lenses. In 23 out of 340 eyes (6.8%), the best vision that can be achieved with spectacles declined by 2 or more lines from preop; none was worse than 20/40. The clinical trials showed the following transient complications: pain (24-48 hours), corneal swelling, double vision, feeling something in the eye, shadow images, light sensitivity, tearing and pupil enlargement. These problems lasted up to several weeks. The clinical trials using the 6mm treatment zone showed the following adverse events occurred in at least 1.0% of the patients within 6 months post-treatment: night vision difficulty (1.0%); elevation of intraocular pressure (1.8%); hazy cornea affecting vision (2.3%); overcorrection or became farsighted (5.0%); undercorrection or still nearsighted (5.6%); loss of the best vision that can be achieved with glasses (6.8%); mild halo (9.7%); and, minor glare (10.0%).
EXTRACAPSULAR CATARACT EXTRACTION
A cataract surgical procedure which removes the cataractous lens but leaves the rear lens capsule intact.
FUNCTIONAL VISUAL DISABILITY
The degree to which a visual error interferes with a person's ability to perform normal daily activities, such as reading, driving at night, or performing hobbies.
HYPEROPIA
Also known as farsightedness, hyperopia is a refractive error caused by an eyeball that is too short to focus light on the retina. Light strikes the retina before it can come to a sharp focus.
INTRAOCULAR LENS (IOL)
A plastic lens that may be surgically implanted to replace the natural lens of the eye. There are numerous styles of IOLs, including foldable IOLs and multifocal IOLs.
IRIS
Pigmented tissue that lies behind the cornea that gives color to the eye (e.g., blue eyes) and controls the amount of light entering the eye by varying the size of the black pupillary opening.
LASER ASSISTED IN-SITU KERATOMILEUSIS (LASIK)
Laser Assisted In Situ Keratomileusis, or LASIK, combines PRK with elements of ALK. LASIK is considered effective for all levels of myopia, including high myopia up to -20 diopters. The ophthalmologist uses the automated microkeratome to shave off a thin, hinged layer of the cornea. The surgeon then uses the excimer laser to vaporize a thin layer of the underlying cornea, and the top flap is restored to its place.LASIK is the newest refractive procedure and therefore there is little hard data on its outcomes. However, many refractive surgeons believe LASIK holds the most promise for patients with moderate to high myopia.
MICRON (MY-kron)
A unit of length equal to one-millionth of a meter. MYOPIA Also known as nearsightedness, myopia is a refractive error caused by an eyeball that is too long to focus light on the retina or a cornea which is too steeply curved. In these cases light focuses instead in front of the retina
OPHTHALMOLOGIST
A physician specializing in refractive, medical, and surgical treatment of eye diseases and disorders.
OPTOMETRIST
Non-medical professional trained to prescribe eyeglasses or contact lenses, examine eyes, and detect eye disease.
PERK STUDY
The Prospective Evaluation of Refractive Keratotomy Study, a multicenter study of radial keratotomy outcomes funded by the National Eye Institute. Ten-year results of radial keratotomy patients who had the surgery in 1983 were published in Archives of Ophthalmology in October 1994. The study found that seven out of ten patients who had the operation on both eyes no longer wore or required corrective lenses ten years after surgery, and 85% of patients saw 20/40 or better without glasses. It concluded that RK is a "reasonably safe operation" that can "effectively reduce but not eliminate myopia." The study also found that 43% of patients experienced a hyperopic shift following surgery over the ten-year period. These patients typically experienced an improvement in their vision as their refractive error moved closer to 20/20. It is for this reason that ophthalmic surgeons will often intentionally undercorrect their patients, then monitor the rate of healing before performing a follow-up enhancement procedure if necessary. However, patients whose vision had achieved full correction or near full correction through surgery and who experience a hyperopic shift could become farsighted and need to wear glasses.
PHACOEMULSIFICATION (fay-koh-ee-mul-sih-fih-KAY-shun)
A cataract surgical procedure which uses an ultrasonic vibration to shatter and break up a cataract, making it easier to remove. The vibration is delivered by an irrigation-aspiration instrument. In a survey of ASCRS members in 1994, 86% preferred the phacoemulsification cataract removal technique over the extracapsular cataract extraction technique. The technique was invented by Charles D. Kelman, M.D., and was first published in 1967.
POSTERIOR CAPSULAR OPACIFICATION (PCO)
Opacification of the posterior lens capsule, sometimes called "secondary cataract," is often a consequence of modern cataract surgery. It occurs when a thin membrane of tissue grows over the remaining capsule following cataract surgery, and can develop in as many as half of all cases between several months and several years after surgery. PCO is treated using the YAG laser on an outpatient basis.
PHOTOREFRACTIVE KERATECTOMY (PRK)
A surgical technique employing an excimer laser to reshape the surface of the cornea and thereby reducing nearsightedness. The laser is controlled by a computer which determines for each patient treated the location, number of pulses, and surface area to be impacted by the laser light beam, based on that individual patient's vision and correction needs.
PRESBYOPIA
Also called "old age vision," presbyopia occurs as the lens of the eye ages and becomes less elastic and able to accommodate. Usually becomes significant after age 45 and is often signaled by the need for bifocals.
PUPIL
The variable-sized, black circular opening in the center of the iris that controls the amount of light that enters the eye.
RADIAL KERATOTOMY (RK)
A surgical technique employing radial incisions made in the periphery of the cornea to allow the central cornea to flatten, reducing its optical power and thereby nearsightedness.
RETINA
The thin lining at the back of the eye that converts images from the eye's optical system into electronical impulses sent along the optic nerve for transmission to the brain.
SCLERAL INCISION
The external white of the eye through which an incision is made during a cataract operation that uses a scleral incision.
YAG LASER
The YAG laser is a surgical instrument that emits a short pulsed, high energy light beam that can be precisely focused by computer to cut, vaporize, or fragment tissue. The YAG laser is used to treat posterior capsular opacification, a clouding of the remaining capsular tissue that develops postoperatively in as many as half of cataract removal operations. The tissue is vaporized with carefully controlled pulses of the YAG laser, and the surgery is performed on an outpatient basis.
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Courtesy of Eyeglass House
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