refractive iols
LASIK Versus Refractive Lens Implants
How to incorporate new refractive lens technology in a co-management relationship.
GREGORY PAMEL, M.D., & JORDAN KASSALOW, O.D., New York, N.Y.

Co-management of vision correction procedures has fostered mutually beneficial relationships between optometrists and ophthalmologists. The advent of phakic, multifocal and accommodating intraocular lens implants broadens co-management opportunities. We can now work together to provide patients, impaired by the highest levels of refractive error, sight restorative surgery.

There are several critical stages in the co-management relationship. First, determine which procedure is optimal for each patient. After counseling the patient extensively, you and the surgeon must decide which procedure is optimal. Second, complete a thorough preoperative work-up. The operative procedure is then performed, and lastly, you must provide postoperative care. Being knowledgeable about new lens technologies and understanding the respective roles of the optometrist and ophthalmologist throughout this process can help patients achieve the best possible outcome.

Lens implants vs. LASIK

Not all patients are candidates for lens implantation, just as not all patients are candidates for LASIK. Parameters like refractive error, age, presence of cataract, corneal thickness and shape all impact whether one procedure or the other is appropriate for a particular patient. There are also patients who may be candidates for either LASIK or IOL implantation. Patients fall into four categories when making the determination about which refractive procedure is optimal for each patient.

• LASIK candidates. Pre-presbyopic patients with refractive errors of less than -8.00D of myopia or less than +4.00D of hyperopia, are generally good candidates for LASIK surgery. These patients must have healthy corneas with appropriate thickness in relation to the refractive error, normal corneal topography, normal tear film and the absence of significant medical conditions like diabetes, collagen vascular diseases and pregnancy. Wavefront-optimized and wavefront-guided treatments provide excellent visual results in this group of patients.

• Phakic lens candidates. We prefer phakic lens implants in myopic patients with errors of -10.00D or more. The ablation profile in LASIK can lead to an increase in higher-order aberrations with subsequent glare and night vision problems for this group.

These lenses are also a good option for patients with refractive errors as low as -5.00D in whom LASIK is contraindicated due to insufficient corneal thickness, irregular astigmatism or profound dry eyes.

• Multifocal/accommodating lens candidates. Presbyopic patients, including patients with early cataracts, may prefer the multifocal or accommodating lens implants because they can achieve good distance and near vision. Although monovision LASIK is an option, it is often unacceptable because depth perception is compromised.

These implants are ideal for high hyperopes (+4D or greater) who are most interested in eliminating their dependency on distance and reading glasses. However, patients with myopia above -6.00D are at a higher risk for retinal detachment after cataract or refractive lens exchange. Counsel patients about the additional risk appropriately.

• Candidates for both procedures. Myopic patients who fall between -5.00D and -10.00D with sufficient corneal thickness and normal topography may be candidates for either procedure.

For this group, it is imperative to discuss options with the patient to determine which is the best procedure. Considerations include age, range of myopia, amount of astigmatism, endothelial cell count and anterior chamber depth.

Pre-op work-up

Co-managing doctors must agree on the division of labor when performing the pre-operative tests. Unlike LASIK, which is typically performed bilaterally, IOLs are implanted one eye at a time. Depending on surgeon and patient preference, there may be a one to four week interval between procedures for the first and second eyes. During this interval, patients may need to wear a contact lens in the untreated eye to minimize anisometropia or aniseikonia. In our case, Dr. Kasslaow performs all pre-operative tests with the exception of the anterior chamber depth, endothelial cell count, A-scan and IOL calculation.

No matter what the choice for correction, a thorough and precise preoperative work-up must be performed. Critical tests include: a careful dry and wet refraction; pupil size measurement; keratometry; IOP measurement and dilated fundus exam. The refraction is the most important part of the preoperative work in these patients. Young, highly myopic patients can easily accommodate more minus in their prescription. Take care to measure the refraction both with contact lenses in (over-refraction) and after lenses have been kept out for the appropriate time (one week for soft lenses, two weeks for gas permeable). In addition, for highly myopic refractions, keep the vertex distance constant to ensure accuracy. A full cycloplegic refraction should be performed as well.

Calculating the lens implant parameters is a critical step in achieving optimal results with lens implants. To calculate phakic lens implant power, refraction is the critical value. Since this procedure is additive — nothing is removed from the eye — the axial length does not have to be measured. Keratometry measurements and anterior chamber depth measurements are necessary to calculate the implant using the Van Der Heijde formula. However, these values are significantly less important than the measured refractions. Use immersion A-scan to eliminate the effect of corneal compression seen when using a contact probe to measure anterior chamber depth.

When calculating IOL values for younger patients, target slight hyperopia in anticipation of continued myopic progression with age. For presbyopic patients over age 40, target slight myopia to reduce reading spectacle dependence. Pre-op cylinder should be less than or equal to 0.50D for implantation.

For either multifocal or accommodating implants, it's important to get a very accurate A-scan using either immersion A-scan technique or non-contact biometry. Pupil size should be a minimum of 2.5mm in those patients receiving a multifocal lens, because smaller pupils will marginalize the multifocality of the implant. Uncorrected astigmatism should be no greater than 0.5D postoperatively. Counsel patients on the importance of implanting both eyes to achieve the near-vision benefit.

Address astigmatism with patients preoperatively, since residual postoperative astigmatism will interfere with the effect of phakic, accommodating or multifocal implants and reduce visual acuity. Phakic IOLs do not correct astigmatism, but can reduce it if the incision is well-placed on the axis of astigma- tism. Most patients have with-the-rule astigmatism, which makes it convenient for the surgeon to operate at 12 o'clock location. Astigmatism can also be managed at the time of surgery or postoperatively with limbal or corneal relaxing incisions.

Post-op care

After the implant procedure is complete, close post-op management is key. We see our patients at: day one, one week, three weeks, one month, three months, six months, one year and then on an annual basis. In our office, Dr. Pamel sees the patient on day one. He checks the incision, the suture where indicated, the IOL placement and checks for infections or abnormal intraocular inflammation. He then tests the patient's visual acuity and performs a refraction. He also reviews the proper dosage of medications. Typically, patients will benefit from a fourth generation fluoroquinolone, an NSAID and a steroid q.i.d. for one week. After one week, discontinue the antibiotic and NSAID and taper steroid by one drop per week for three weeks.

The optometrist, Dr. Kassalow, sees patients for the one-week visit. He measures visual acuity, performs a refraction, checks the IOP, examines the anterior chamber reaction, checks sutures and the incision, ensures the IOL placement is optimal and prescribes medication based on the clinical findings.

At the two-week point, it's back to the M.D. to schedule the procedure for the second eye. If all is normal, the patient will undergo the second procedure at the one-month point. The post-op management schedule for the second eye repeats that of the first.

After the sutures are removed from the second eye, the patient will see the O.D. at three and six months. At 12 months, the phakic IOL patient will return to the surgeon for an endothelial cell count.

Some patients may require additional procedures to attain optimal vision. The most common reason for enhancement is residual ammetropia or progression of myopia following surgery. High myopes are likely to become more myopic. LASIK or LASEK can successfully treat small myopic refractive errors in these patients. We wait a minimum of three to six months before performing enhancements in these patients.

Throughout the last ten years, the limitations of LASIK as a refractive procedure have become more apparent. The availability of new lens implants offers eye care providers new technologies to support the co-management relationship in surgical cases. These implants may prove a better modality to treat patients who are outside the treatment range or have contraindications for LASIK.

Intraocular Lens Implants

Phakic Lens Implant. The Verisyse lens implant (Advanced Medical Optics, (AMO)) is a phakic lens implant designed to treat myopia ranging from -5.00D to -20.00D. Approximately three million people in the United States have myopia above -6.00D. The Verisyse is a rigid PMMA lens available in a 6mm optic, in powers from -5.00D to -15.00D, and in a 5mm optic in powers over -15.00D to -20.00D. Because it is a rigid lens implant, it requires placement through either a 5.2mm- or 6.2mm-incision, which requires closure with one suture. A critical distance of at least 1.5mm from the corneal endothelium after implantation is necessary to avoid excessive endothelial cell loss. Endothelial cell counts must be taken preoperatively and age adjusted to determine if enough cells are present. Anterior chamber depth must be greater than 3.2mm preoperatively, which is common in highly myopic patients. Accommodating Lens Implants. The crystalens (Eyeonics Inc.) is the first pseudoaccommodating implant (below) approved by the FDA. It is designed to correct distance, intermediate and near vision through movement of the optic via a hinged design. The implant requires the removal of the natural crystalline lens (through a 3.5mm-scleral tunnel incision) as in cataract surgery. The lens is designed with two hinges attached to the optic, which allows the lens to move from a posterior vaulted position to correct distance vision, to an anterior vaulted position to correct near vision. Multifocal Lens Implants. Two new multifocal lens implants, the AcrySof ReSTOR (Alcon Laboratories) and ReZoom (AMO) were recently approved in March 2005. These implants are designed using a series of concentric rings to provide distance, intermediate and near vision. The ReSTOR (above) lens employs apodized diffractive technology, which uses apodization, diffraction and refraction. The refractive optics are in the outer half of the lens, which provides for good night vision when the pupil enlarges. The diffractive optics, located in the central 3.6mm of the lens, consist of ring elements that are equally divided between distance and near vision. ReSTOR's apodized diffractive optic reduces the incidence of glare and halos after implantation. The near vision add measures 4.00D in the spectacle plane.   The ReZoom (left) is a three-piece acrylic implant with Balanced View Optics technology. This involves a refractive, distance-dominant, multifocal optic with five optical zones designed to optimize light distribution on the retina in varying lighting conditions and pupil sizes. The near-vision add measures 2.80D in the spectacle plane. Zones 1, 3 and 5 are distant-dominant; zones 2 and 4 are near-dominant. Aspheric transitions between zones provide good intermediate vision.

Dr. Pamel (www.nyclasik.com) is board certified in ophthalmology, specializing in corneal, LASIK and cataract surgery. He also serves as an attending surgeon at Manhattan Eye, Ear and Throat Hospital. Dr. Pamel was a principal investigator for the Verisyse phakic IOL clinical trials.

Dr. Kassalow specialized in contact lenses, and has a strong interest in primary care and public health. He is director of the River Blindness programs at Helen Keller International. He is also a consultant to the World Health Organization and is a member of the Council on Foreign Relations.