Archive for the ‘Phakic Implants for High Refractive Errors’ Category

Phakic Implants for High Refractive Errors

Friday, January 21st, 2011

Dr Raymond Stein of the Bochner Eye Institute wrote the following clinical update. We hope you find it of interest.

Phakic implants are used in vision correction for high refractive errors that cannot be treated by laser vision correction. Over the past 13 years we have been inserting the Implantable Contact Lens (ICL), a posterior chamber phakic implant made by Starr Surgical. Clinical outcomes for high myopia and astigmatism have generally been excellent with 95% of eyes achieving 20/30 or better uncorrected vision. The main indications are refractive errors that are too high for laser vision correction. In general patients are candidates for a phakic implant if they have myopia greater than 10 D or hyperopia greater than 5 D.  Astigmatism can be treated up to 6 D. Patients must have a satisfactory depth of the anterior chamber (distance between the corneal endothelium and the crystalline lens) of greater or equal to 2.8 mm. Most of the high myopes will qualify unlike the high hyperopes. Patients should also have a pupil size of 7 mm or less.

Another surgical option, which patients need to know about in the informed consent, is a refractive lens exchange. Our preference is not to perform a lens exchange for high myopia because of the increased risk of retinal tears and detachment.  This is not the case with the treatment of high hyperopia, which is associated with a minimal retinal risk.

In patients that are good candidates for the ICL, a refraction is performed, the limbal white-to-white distance is measured to determine the length of the implant, and two small YAG laser iridotomies are performed to reduce the risk of elevated intraocular pressure from papillary block. The implant is custom ordered from Switzerland.

The surgical procedure is relatively easy for patients.  At the Bochner Eye Institute we perform this procedure in our sterile operating room approved by the Ontario College of Physicians and Surgeons. Under topical anesthesia a 2.8 mm limbal incision is constructed. Intraocular xylcaine is injected to numb the contents of the eye. After the implant has been carefully folded into a cartridge it is injected into the anterior chamber where it gradually unfolds. Using a specialized instrument the haptics are gently placed behind the iris. Miochol is then injected to constrict the pupil.  Intraocular Vancomycin is injected to prevent infection. The patient is then checked one hour postoperatively to be sure the intraocular pressure is normal. Follow-up examinations are usually 1 day, 1 week, 1 month, and 3 months.

Complications are rare. The main risk is inducing a cataract (1%). If patients are not satisfied with their level of uncorrected vision then laser vision correction can be performed. We have not had a case of infection over the past 13 years.

Specialized indications for the ICL include patients with keratoconus and those following radial keratotomy. In keratoconus patients if they have satisfactory best-corrected spectacle acuity (20/40 or better) then consideration can be given to the ICL. Patients may require an Intracorneal ring to reduce the degree of irregular astigmatism prior to a phakic implant. In the situation following radial keratotomy if patients have developed a hyperopic shift then this can be corrected by the ICL. Unlike a natural hyperope the post-RK eyes were previously myopic and usually have a satisfactory anterior chamber depth.