May 25, 2004

Advances in vision correction

By Norma J. Levingston, O.D.
Special to the Times

This month, we continue our discussion of vision-correction alternatives. Last month, we reviewed PRK, Laser Vision Correction (LASIK), wavefront LASIK and IntraLASIK.

Intacs
Intacs are the first FDA-approved non-laser surgical treatment designed especially for people with mild nearsightedness (1-3 diopters of myopia correction). Intacs are made of polymethylmethacrylate (PMMA), which is the same polymer that has been safely used in eyes for nearly 50 years in procedures to correct cataracts.

Intacs are two small, clear crescent shaped pieces that are inserted into the cornea. During surgery, a tunnel is created between the layers of the stroma (the middle layer of the cornea). The tunnel is made outside the central optical zone of the eye, but still within the cornea.

The surgeon chooses the appropriate ring thickness (the thicker the ring, the more flattening, and the more vision correction achieved). The two crescents are inserted in the tunnel and the procedure is done.

Intacs are designed for long-term vision correction but can be removed if necessary. Intacs can be replaced with different size implants or removed for good. If they are removed permanently, vision tends to return to the way it was within three months.

Many people find Intacs advantageous over LASIK and other refractive procedures because they do not remove any corneal tissue. Intacs allow patients to consider other options down the road since they are reversible. Intacs can also be used as a treatment for keratoconnus (thin, steep corneas).

Corneal Refractive Therapy (CRT)
Corneal Refractive Therapy (CRT) is a new FDA-approved procedure in which patients wear a uniquely designed, oxygen-permeable contact lens during sleep to reshape the cornea. During the day, patients enjoy the benefits of functional vision without eyeglasses or contact lenses.

Unlike LASIK, CRT is a non-surgical therapy. CRT is safe and reversible, so if a patient’s prescription changes or if you wish to discontinue the process, the eyes will return to their normal shape. Patients are choosing CRT as an alternative to vision correction surgery.

Candidates for CRT have some or all of the following criteria:
- Low to moderately high myopia
- Patients who desire to go spectacle or contact lens free throughout their daily lives
- Patients who are adverse to surgery
- Patients under the legal age approved for refractive surgery
- Athletes
- All techniques to alter the focusing ability of the eye discussed previously have involved reshaping the cornea in some form. The remainder of the techniques will involve the lens of the eye.

Clear Lensectomy
A cataract is a clouding of the natural lens in the eye. Treatment of cataract involved removing this clouded lens and replacing it with an artificial lens called a lens implant. Exactly the same operation can be done when the lens is not clouded in order to change the power of the lens as a way to correct nearsightedness or farsightedness. This is called Refractive Lens Replacement of Clear Lensectomy.

Clear Lensectomy is considered a reasonable surgical choice at this time for extremely high farsightedness and nearsightedness. This procedure is less likely to produce side effects such as starbursts, glare, halos and decreased night vision than any of the corneal refractive procedures.

P-IOL
Phakic Intraocular Lens (P-IOL) represents a new approach in the surgical correction of significant amounts of nearsightedness. The P-IOL is a tiny plastic lens that is placed inside the eye in front of the natural crystalline lens to provide additional refractive change.

Unlike the IOLs used in cataract surgery, the P-IOL is placed between the clear cornea and the iris. This unique design eliminates the need to remove the human lens and corrects nearsightedness while preserving the natural ability of the eye to focus on distant as well as near objects.

Over the last few months, we have discussed the vision correction alternatives available other than eyeglasses and daytime contact lenses. Some of the alternatives are permanent and some are reversible. Some of the alternatives involve altering the cornea and some involve altering the lens.

Most of the alternatives are FDA-approved for people 18 years of age and up. CRT can be used to treat children under the age of 18 years. It goes without saying that each procedure is dependent upon the skill and expertise of the treating doctor.

The desire to be free of eyeglasses or contact lens can now be fulfilled for most individuals.

Dr. Levingston, a past president of the National Optometric Association, has practiced in the Evergreen area since 1982. She is available for questions or consultation at Evergreen Valley Optometry; 3257 South White Road (at Aborn); San Jose, CA 95148; phone: (408) 238-9696; e-mail: eyedoc1@direcway.com.