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May 28, 2006
LASIK Bioptics
CRS Today May 2006
The concept of bioptics was first described by Roberto Zaldivar, MD,1 when he performed LASIK to correct residual refractive error in eyes that had received phakic IOLs. Dr. Zaldivar found that the bioptics procedure was an effective and predictable method for correcting residual error in patients who had extreme preoperative myopia of up to -35.00D. In 1994, José Güell, MD, described his concept of adjustable refractive surgery2; he performed LASIK to correct residual ametropia after different types of intraocular surgeries, including implantation surgeries for IOLs and phakic IOLs, penetrating keratoplasties, and corneal refractive surgeries such as PRK and radial and arcuate keratotomy.3 Currently, ophthalmologists use the term bioptics when techniques for IOL implantation are followed by a procedure involving excimer laser corneal ablation such as LASIK, Epi-LASIK, or PRK.4-9 The advantage of placing the IOL first is the improvement in the patient's quality of vision. Using corneal refractive surgical techniques, such as LASIK, as a secondary enhancement tool improves the accuracy of the final refractive outcome.
Potential candidates for a planned bioptics procedure include patients who wish to minimize their dependence on corrective eyewear after lens surgery. If a patient desires a presbyopia-correcting IOL and has more than 0.75D of residual postoperative astigmatism with a healthy cornea, he may be a good candidate for a planned bioptics procedure. Most available excimer lasers can effectively treat up to 5.00D of astigmatism. For higher levels, the surgeon may use a combination of limbal relaxing incisions with bioptics to effectively fine-tune the refractive outcome.
Timing of Flap Creation
One of the biggest questions when performing a planned LASIK bioptics procedure is when to create the LASIK flap. One may cut the flap 1 to 2 weeks in advance or at the time of the intraocular surgery.2,3 Cutting the flap prior to placing the IOL avoids the possible risks related to a microkeratome use in eyes that contain an IOL. The major potential risk of using a microkeratome in an eye with an IOL is corneal endothelial damage.
Creating the flap before the intraocular procedure allows the earlier correction of residual ametropia (4 to 6 weeks after the intraocular surgery). The surgeon can simply lift the LASIK flap instead of risking potential complications due to the increased IOP secondary to placing a microkeratome suction ring on these eyes. A potential disadvantage of creating the flap before the intraocular procedure is the increased risk of epithelial ingrowth after lifting the flap for the enhancement procedure.
Another technique is to perform the bioptics procedure in a sequential fashion. After the IOL surgery, the eye is allowed to heal, and the refraction is permitted to stabilize for at least 3 months prior to the LASIK enhancement.1,4-6 The advantage of this approach is that it avoids having to lift the flap on the eye, thus minimizing the incidence of epithelial ingrowth and other potential flap-related complications, such as diffuse lamellar keratitis, for these patients. There is a difference between cutting a new flap after the intraocular procedure and lifting a previously created flap in terms of the risk of epithelial ingrowth. This risk is higher with a relifted versus freshly cut flap. This sequential method is the only option for patients awaiting advanced surface ablation.
Posted by aman at May 28, 2006 11:08 PM