Article Date: 11/1/2002

Technology
A New Era of Refractive Technologies
Recent advances in technology have opened the gateways to providing patients with alternative treatments. See what's available now.
BY J. JAMES THIMONS, O.D., F.A.A.O., Fairfield, Conn.

The new millennium has ushered in a wave of advances in refractive surgery and related technologies. These advances involve thermal therapy, incisional procedures, refractive intraocular lenses (IOLs) and software applications and have given us a wealth of choices.

But while the advancements give us a range of choices that are unequaled in the history of our profession, they also present significant challenges in deciding the best alternatives for our patients and how each technology fits in our treatment armamentarium. We'll take a look at some of these options and explain how to best apply them.

The new LTK

One of the newest entries into the arena of refractive surgery is conductive keratoplasty, a radiowave system designed to treat mild to moderate hyperopia (+1.00D to 3.00D) with up to 1.00D of astigmatism. The system, manufactured by Refractec, Inc., has recently received FDA approval and is now available to use for primary therapy of hyperopia and hyperopic astigmatism as well as the treatment of consecutive hyperopia after refractive or cataract surgery.

This technology is the second generation of thermal therapy and follows on the heals of laser thermal keratoplasty (LTK), which has been available for the past several years. As with all thermal corneal procedures, the real test of its success will be its ability to produce stable results without regression (all previous techniques have been less than completely successful).

What the clinical results say. The data from the Phase III clinical trials were encouraging compared to other options in this arena. The average preoperative refractive error was +1.97D sphere and ±0.37D cylinder with the average equivalent sphere at +1.79D. The average preoperative uncorrected visual acuity (UCVA) was >20/40 80%.

The treatment nomogram uses concentric points of thermal energy in a ring fashion at 6-, 7- and/or 8-mm zones, depending on desired total correction from +0.75D to +3.00D.

The six-month postoperative data shows that compared to VISX's Star 3 and Alcon's LadarVision lasers and the Sunrise LTK system, the Refractec therapy was superior for both patients who achieved 20/20 UCVA (54% vs. 21%, 38% and 37%, respectively) and patients who had 20/40 or greater UCVA (96% vs. 78%, 88% and 78%).

Regression analysis of the data shows that the Refractec system requires less initial over-correction than laser to achieve the same final result at two years and is more stable at the 24 month data point.

Beating old standards. The Achilles heel of all thermal treatments previously attempted has been the inability to maintain a stable corneal surface and therefore provide a lasting refractive correction. While lasers have continued to improve in this regard and can correct significantly greater levels of hyperopia and astigmatism, the clinical trials of the Refractec system seem to support a marked improvement at the lower levels of hyperopic therapy. This is accompanied by a relative level of portability and a marked decrease in initial cost, which makes conductive keratoplasty a technology to watch in the future.

Solving problems with IOLs

Another category of refractive technology that has made significant inroads is the use of phakic IOLs such as Ophtec's Artisan, Bausch & Lomb's (B&L's) NuVita and Staar Surgical Systems' ICL. These lenses, while still under FDA review, have rekindled interest in the use of intraocular procedures to solve the refractive problems of patients who have higher levels of myopic and hyperopic correction (up to 10.00D of hyperopia and 8.00D to 24.00D of myopia).

IOL advantages. The advantage that IOLs bring is the ability to achieve superior optical outcomes in the higher refractive range compared to laser-assisted in situ keratomileusis (LASIK).

This advantage is offset by the increased risk associated with IOL implantation and their long-term use.

The flip side. The complications are not dissimilar to traditional cataract surgery and involve such concerns as corneal decompensation, pigmentary dispersion, glaucoma and the risk of intraocular issues such as retinal detachment and infection. The position of the lens is either in the anterior chamber (AC), as with traditional AC lenses, or in a unique placement anterior to the lens and posterior to the iris.

All of these lenses require exceptional surgical technique and it's unlikely that the general ophthalmologist will use them initially. Typically, they'll be the domain of the refractive or refractive/cataract specialist.

In conjunction with these lenses, LASIK has been used postoperatively to correct residual refractive error. This technique is called Bi-Optic therapy and gives the clinician a remarkable ability to titrate final refractive outcomes in these patients to levels that were unheard of even a few years ago.

Seeking an alternative

While phakic IOLs are a viable alternative for younger patients who have residual accommodative capacity, the PreLex System (presbyopic lens exchange) is a consideration for presbyopic hyperopes who are not good laser candidates.

This system uses the Array IOL (by Allergan) to provide a multifocal refractive correction that typically gives patients good distance UCVA and reasonable uncorrected near visual acuity (UCNVA), which you can supplement by prescribing a reading prescription.

PreLex pros and cons. The advantages of this system are its ability to maintain the prolate shape of the cornea and to effectively eliminate the risk of regression seen in laser treatment of higher levels of hyperopia.

The disadvantages of the system are the loss of contrast function seen in some patients and a nomogram that's not as predictable as that typically seen in lower refractive error patients undergoing cataract surgery. This lens system has been used more commonly with hyperopes but hasn't shared the same success with myopes or patients who have significant astigmatism (>1.25D).

Welcoming wavefront

Making lasers better has been the primary focus of the industry over the past five years and these efforts are beginning to yield some success. Certainly the most talked about aspect in this arena is the concept of customized ablations. This solution has been approached in several ways by different manufacturers including B&L, VISX and Alcon.

Each company has approached the process from a different perspective but all are using the concepts involved in wavefront technology and the application of Zernicke Polynomials to measure the impact of the procedure on the patient's visual function. The device used to measure the aberration of the visual system is termed an aberrometer.

Today's wavefront sensors. The four current wavefront sensors are the Tscherning, Ray-Tracing, Resolving and Shack-Hartmann. Each analyzes the visual system using a pattern of light rays that pass into the eye and subsequently are captured upon their exit and analyzed for change.

This gives the system the ability to identify the abnormalities and use the information to develop a treatment protocol that, unlike current laser treatments, is capable of individualizing the laser therapy to address specific variations of the ocular surface and other refractive elements of the eye.

Wavefronts of the future. Last month, Alcon became the first company to receive FDA approval for customized LASIK surgery using an excimer laser (the LADARVision 4000) and a wavefront measuring device (the LADARWave). B&L and VISX are working toward the release of their own systems. All three currently have these technologies available outside the United States. B&L has developed Zyoptics, Alcon has Custom Cornea and VISX has WaveScan technology.

The initial application of these systems outside the United States has been in individuals who've undergone refractive surgery and have suffered less-than-desirable outcomes. The other group is patients who have previously not been considered candidates because of irregular corneas or mild corneal disease.

Recent work has been directed toward the treatment of more typical refractive errors and it's anticipated that as these companies release the technology in the United States, all of these applications will be available for clinicians to access.

The technology this concept brings to the field may have broader applications at the primary care level in that it's able to analyze the refractive system at a level far beyond any available instrumentation.

Primary care use for wavefront in the future? Wavefront technology may some day help the primary care clinician design spectacle and contact lens corrections at levels of sophistication that revolutionize eye care.

An improved microkeratome

The final new technology that warrants mention is intrastromal corneal photodisruption with the femtosecond laser. This system, developed by Kurtz and Juasez in conjunction with IntraLase, uses plasma-mediated ablation to produce extremely precise corneal flaps by controlling the depth without significant elevation of IOP.

This is a major advantage over current microkeratomes in that they're unable to consistently produce uniform cap thickness, which can significantly impact the quality of the surgical outcome of LASIK.

Looking at a bright future

With all the options I've mentioned, you should be able to satisfy all of your patients, no matter what their condition. Whether setting up or extending your referral network, these advances will make a huge difference to your patients and your practice.

Dr. Thimons is from Ophthalmic Consultants, a multi-specialty surgical practice, and TLC Laser Center in Fairfield, Conn. He's also Optometric Management's clinical director.

 


Optometric Management, Issue: November 2002