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INTACS
Correction of nearsightedness

INTACS™ are very thin plastic prescription inserts for the correction of mild nearsightedness (myopia), a condition that affects over 20 million adult Americans. In contrast to other surgical procedures for reshaping the cornea of the eye, the inserts reshape the curvature of the cornea by the placing within the rim of the cornea two clear prescription inserts made of a plastic, called polymethylmethacrylate or PMMA. PMMA is very well tolerated by the body (biocompatible) and has been used in contact lenses and cataract surgery for over 50 years. They can be removed or replaced if vision needs to be changed

Anatomy and Physiology

  • There are two eyes. The eyes lie in bony casings within the skull called orbits. Each eye is globular in shape and about one inch in diameter
  • Light entering the front of the eye passes through the cornea, anterior (front) chamber, iris, lens and vitreous and finally is focused on the retina, the film of the eye. (Figures 1 and 2))
Figure 1 - Cross-sectional anatomy of the eye. See text for descriptionsFigure 2 - Normal eye. An object is focused on the retina
  • The cornea is a curved, highly transparent tissue that separates air from clear fluid in the anterior chamber of the eye, which lies between the cornea and lens. The cornea is approximately 0.5 mm. thick. It is comparable in size to a contact lens
  • The lens is a firm gel-like transparent tissue that is almost eight millimeters (one-third inch) in diameter and biconvex in shape, that is, thicker in the center than at the edge. A thin transparent capsule surrounds the lens
  • The iris is in front of the lens and consists of a circular pigmented muscle that gives the eye its color. The iris acts like the diaphragm of a camera and adjusts the amount of light that enters the eye through the hole in its center called the pupil. Light then passes through the vitreous, a clear gel-like material that fills the center of the eye, onto the retina
  • The retina is the film of the eye. It is a true extension of the brain and is composed of special nerve cells sensitive to light
  • The optic nerve is formed from these nerve cells and carries the light image entering the eye to the brain
  • In the normal eye with perfect vision, the light rays enter the eye and are focused precisely on the retina. In this situation, a clear image is sent to the brain
  • The cornea provides about 75 percent of the eye's focusing or refractive power. The natural lens inside the eye provides the remaining focusing power. The shape, or curvature, of the cornea determines how well you see and how "in focus" an image is when it reaches the retina
  • Nearly all of the light that reaches the retina must pass through the central area of the cornea or the "optical zone"

In the normal eye with perfect vision, the light rays enter the eye and are focused precisely on the retina. In this situation, a clear image is sent to the brain. The cornea provides about 75 percent of the eye's focusing or refractive power. The natural lens inside the eye provides the remaining focusing power. The shape, or curvature, of the cornea determines how well you see and how "in focus" an image is when it reaches the retina. Nearly all of the light that reaches the retina must pass through the central area of the cornea or the "optical zone".

Pathology

  • While some people with mild nearsightedness can function without their glasses or contact lenses in certain situations, most rely on corrective lenses everyday. In the United States, INTACS inserts are indicated for the correction of mild nearsightedness
  • Nearsightedness occurs when the cornea has a steeper curve than normal or the length of the eyeball from front to back is too long. In either situation distant light entering the eye focuses in front of the retina. (Figure 3)
Figure 3 - Nearsighted eye. A distant object is focused in front of the retina causing a blurred image
  • People with nearsightedness see nearby objects clearly, but distant objects appear blurry
  • The degree of nearsightedness is measured in negative (-) diopters. INTACS are available for the correction of -1.00 to -3.00 diopters of nearsightedness in persons who have no more than 1 diopter of astigmatism. (Astigmatism is a condition in which the curvature of the eye is irregular. This irregularity causes the light rays entering the eye to come to different points of focus. The result is blurred vision.)

History and Examination

  • A general eye exam is given by the ophthalmologist (eye specialist). The ophthalmologist also inquires about overall health and medical history
  • The following tests are typically conducted to determine if a patient is a good candidate for any refractive surgery, including INTACS inserts:
    1. General history. This allows the physician to determine if refractive surgery is an option. Questions include general medical history, ophthalmic history and current medications
    2. Dilated exam (Ophthalmoscopy). The patient's eyes are dilated with drops placed in the eye (cycloplegic) and the ophthalmologist examines the vitreous and retina. The patient is asked to look at a point in the room, and the doctor shines a bright light in the eye
    3. Manifest and Cycloplegic Refraction. This measures the patient's prescription for eyeglasses. The manifest refraction is completed first and the cycloplegic refraction is completed after the use of eye drops to dilate the pupil
    4. Slit Lamp Exam. A slit lamp is a special type of microscope. The ophthalmologist is able to examine the cornea and also determine if the tear film is adequate. Additionally, the doctor exams the eyelids to assure they are free of any infections that may compromise the surgical outcome
    5. Keratometry. The curvature (shape) of the cornea is measured
    6. Tonometry. The intraocular (inside the eye) pressure of the eye is measured. This is particularly important in patients with glaucoma in which the intraocular pressure is above normal
    7. Topography. This "maps" the cornea to give more precise information about its curvature and surface
    8. Visual Acuity Testing. Uncorrected and best-corrected (with lenses) vision is tested using standard eye charts

Important: If contact lenses are worn, it is very important to stop wearing them 2-3 weeks before the preoperative examination per the doctor's instructions. Failure to do this may produce poor results.

Indications and Contraindications

  • Candidates for the inserts must
    1. Be at least 21 years of age
    2. Have healthy eyes that are free from disease or corneal abnormality (for example: scarring or infection)
    3. Have nearsightedness between -1.00 to -3.00 diopters with no more than 1.00 diopter of astigmatism
    4. Have documented evidence of stable vision for at least one year (minor fluctuations may not disqualify candidate)
  • INTAC inserts should NOT be placed if
    1. There is an autoimmune or immunodeficiency diseases (for example: lupus, rheumatoid arthritis, AIDS)
    2. Pregnant or nursing
    3. Known conditions of the eye that may increase the likelihood of future problems
    4. Taking prescription medications, such as isotretinoin (Accutane ); amiodarone (Cordarone ); sumatriptan (Imitrex ) that may affect corneal healing or your vision. You should discuss all medications you take, even over-the-counter medications, with your eye doctor
  • Discuss with your doctor if
    1. An insulin dependent diabetes or have other medical conditions that affect wound healing
    2. Have had a Herpes infection in of the eyes

Note: INTACS do NOT eliminate the need for reading glasses. The need for reading glasses is caused by a natural condition of aging called presbyopia. Between ages 40 and 50, the lens of the eye loses its ability to focus on objects at close range. This is when many people begin to rely on reading glasses. No refractive surgery currently available can prevent the changes that cause presbyopia or correct this condition. However, because INTACS can be removed or replaced, they may provide other options as vision changes occur with age

Surgical Procedure

  • INTACS are inserted in a brief outpatient procedure by an ophthalmologist
  • They cannot be felt, are no more visible than a contact lens and require no maintenance. Because the optical zone is crucial for clear vision, the inserts are designed to be placed at the outer edge of the cornea and away from the optical zone
  • The inserts are placed in the periphery of the cornea and reshape the cornea by flattening it just enough to allow light rays entering the eye to focus on the retina.
  • The procedure usually takes only 15 minutes per eye but plan on at least an hour for the visit
  • Typically, a mild oral sedative is given before the procedure. The patient is positioned comfortably, facing up, on a surgical table or reclining chair. The face is covered with a surgical drape exposing only the surgical eye
  • Anesthetic drops are used to numb the eye, which is held open throughout the procedure to prevent blinking.
  • A single, small opening is made in the cornea (Figure 4)
  • To stabilize the eye, a centering guide is placed on the surface of the cornea for one to two minutes. Patients may experience some discomfort (typically a pressure sensation) during this part of the procedure (Figure 5)
  • The cornea has several layers to it, like a pad of paper. These layers are called the stroma. Making a place for the INTACS inserts within the stroma is like separating two pages just enough to create a space
  • While the eye is stabilized, two semicircular tunnels are made in the cornea. The inserts are placed in these tunnels. The inserts are placed within the layers of the cornea at approximately a two-thirds depth (Figure 6)
  • After the second INTACS segment is placed, the small opening in the cornea is closed
    Figure 4 - A small incision is made in the outer layer of the cornea. Courtesy KeraVision, Inc
    Figure 5 - The eye is stabilized with centering guide. Courtesy KeraVision, Inc
    Figure 6 - Two INTACS segments are placed within the intrastromal tunnels. Courtesy Keravision, Inc

 

Complications

  • Infection- this occurred in 0.2% of patients
  • Shallow placement of the INTACS inserts has occurred in 0.2% of patients
  • Temporary loss of 2 lines of best corrected vision occurs in 0.2% of patients
  • Anterior chamber perforation during placement of the INTACS has occurred in 0.4% of patients
  • Overcorrection of nearsightedness
  • Undercorrection
  • Reduction in sensation of the central portion of the cornea
  • Difficulty with night vision
  • Irregularity of the cornea causing astigmatism
  • Blurred vision
  • Double vision
  • Corneal blood vessels
  • Halos of light
  • Glare
  • Fluctuating distance vision
  • If the results of the procedure are not satisfactory, the inserts can be removed or replaced. In the small number of cases where INTACS were removed, patients' vision returned to levels seen before surgery by 3 months following removal, in most cases. All patients were able to be corrected with glasses to 20/20 or better following the removal of the inserts.

If the results of the procedure are not satisfactory, Intacs can be removed or replaced. In the small number of cases where Intacs were removed, patients' vision returned to levels seen before surgery by 3 months following removal, in most cases. All patients were able to be corrected with glasses to 20/20 or better following the removal of the inserts.

Care after Surgery

  • Antibiotic eye drops may be prescribed. The ophthalmologist may prescribe steroid drops for the first week or two following the procedure to decrease any irritation and redness. All medicines should be taken as directed
  • To prevent accidental rubbing of the eyes during sleep, the patient may be instructed to wear a clear shield at night in the first few weeks after surgery
  • Eyes are examined the day following the procedure. If there are no complications, a typical follow-up schedule is one week, one month, three months, six months and one year
  • Most patients see an improvement in vision the day after surgery, though vision may fluctuate during the initial healing process
  • In clinical studies, 97% of patients saw 20/40 or better with INTACS; 74% saw 20/20 or better-the standard for good vision, and 53% saw 20/16 or better-a level that exceeds the standard for good vision(Figure 7)
Figure 7 - Nearsighted vision as corrected with inserted INTACS segments. Courtesy KeraVision, Inc

INTACS™ is a registered trademarks of KeraVision,Inc Accutane┬« is a registered trademark of Roche Pharmaceuticals. Cordarone┬« is a registered trademark of Wyeth-Ayerst Laboratories. Imitrex┬« is a registered trademark of Glaxo-Wellcome, Inc.