AAO refractive pre-meetings focus on LASIK, LASEK

LASIK results are improving with active eye trackers. LASEK may provide better results with wavefront-guided ablation. Other options seem far off in development.

NEW ORLEANS — LASIK and a renewed interest in surface ablation were the primary topics of interest at the refractive pre-meetings before the American Academy of Ophthalmology here. Nonlaser options for hyperopia correction such as conductive keratoplasty drew some interest, but other options seemed far down the development pipeline, beyond imminent clinical use.

As in years past, in this column I present highlights of the discussions at the meetings, held by the International Society of Refractive Surgery and the Refractive Surgery Interest Group. After looking at both programs, I decided to spend most of my time at the ISRS Fall Refractive Symposium. That 2-day program was packed with sessions of interest, and I had to choose carefully to get a good sampling of what is new in refractive surgery.

First day ISRS

On its opening morning, the ISRS meeting had three sessions I wanted to attend: Thermokeratoplasty and Non-excimer Lasers, covering laser thermokeratoplasty using both the Sunrise (holmium) and Rodenstock (diode) lasers, the IntraLase femtosecond laser and conductive keratoplasty using the Refractec Viewpoint CK system; Laser Delivery and Profile Debate, covering eye trackers, treatment zones sizes and results obtained with several laser systems using new eye trackers; and the latest version of Catch the Wave, with presentations by most of the refractive laser companies describing the latest versions of their lasers and diagnostics.

The late morning sessions covered the use of LASIK for correcting hyperopia with and without astigmatism. There was also a session on microkeratomes, with nine speakers discussing their favorite keratomes.

The early afternoon session featured a discussion on refractive IOLs, where several speakers debated the merits of phakic IOLs; a session on a new laser-adjustable IOL; and a session titled Worst Case/Best Save Video Grandrounds, which included several presentations on laser epithelial keratomileusis (LASEK).

The late afternoon included a discussion of LASIK complications and a session titled Diagnostic Wavefront/Optical Aberrations, at which the question was asked: Is wavefront measurement necessary, or is topographical measurement enough? The various wavefront measurement systems — Shack-Hartmann aberrometry (Alcon, Asclepion-Meditec, Bausch & Lomb and Visx), ray tracing (Tracey), scanning slit refractometer (Nidek) and Tscherning (WaveLight and Schwind) — were compared with corneal mapping using AstraMax (LaserSight), Orbscan (Bausch & Lomb) and other topographers.

Second day ISRS

On the second day, one early morning session, entitled Wavefront Technology and Custom Ablation, included a face-off of the various laser systems and their approaches to wavefront-guided custom ablations. and a second section on topography versus wavefront. Another early morning session covered refractive implantable devices, including Intacs, intracorneal implants for hyperopia (the Anamed PermaVision lens), Ferrara intracorneal rings and IOLs for hyperopia.

One late morning session, titled Presbyopia Correction, included discussions of scleral bands (Presby Corp.), laser ablation (SurgiLight), anterior sclerotomy, myopic LASIK for monovision, LTK for monovision and two accommodating IOLs (C&C Vision’s AT-45 and the 1CU from HumanOptics). A second session again covered LASIK complications.

The afternoon sessions included one on management issues, Re-inventing Yourself as a Refractive Surgeon: What it Takes in 2001; and a session on LASIK Enhancement and Lamellar Surgery.

The RSIG meeting program covered a number of the same topics, including LASIK techniques and complications; photorefractive keratectomy and intracorneal implants; presbyopia; surgical correction of hyperopia; IOLs in refractive surgery; and refractive lasers and aberrometers.

Overview

This article is organized to include the latest information by type of correction. It covers mainly laser approaches but also includes nonlaser techniques under development such as inlays (PermaVision from Anamed) and heated tips (ViewPoint CK from Refractec) for hyperopia, and accommodating IOLs and surgical techniques (Presby Corp.) for presbyopia.

Included in the laser discussions are excimer-based procedures as well as those being done with holmium (Sunrise LTK), erbium (SurgiLight’s presbyopia reversal) and femtosecond devices (IntraLase’s microkeratome replacement today and possible refractive application in the future).

Current myopia correction

According to the latest survey data from MarketScope (2001 Survey of Refractive Surgeons, August 30, 2001), nearly 94% of ophthalmologists surveyed are using standard or “classic” LASIK to correct low myopia (up to 3 D), almost 99% use LASIK for moderate myopia (up to 5 D) and 91% use it for high myopia (greater than 7 D). The rest use phakic IOLs (5%) or some other technique. The percentages are just as high for correcting myopia with astigmatism.

Thus the question to be answered at this year’s meetings was, Is there anything coming along that might replace classic LASIK?

There were some answers. Eye trackers are leading to some spectacular results with LASIK. The laser systems with improved eye trackers seem to be obtaining excellent results. As noted in my earlier article on customized ablation (Ocular Surgery News, January 1, 2002, AAO report: LASEK, customized ablation draw interest), the reported results for two of these laser systems, the Visx Star S3 with ActiveTrak and the WaveLight Allegretto, also with an active infrared tracker, compare very well with initial results obtained in the wavefront customized ablation trials reported to date.

Use of eye trackers leads to better centration, no decentration, and the ability to place blend zones where they add to better quality vision through reduction of glare and halos in night vision.

Future myopia correction

The next question is how much better results will be with either wavefront or corneal topographers added to excimer systems. That answer was not as clear.

Two companies have topography systems combined with their wavefront devices: Bausch & Lomb’s Zyoptix Zywave wavefront along with its Orbscan topographer and Nidek’s Navex OPD-Scan, which combines topography with retinoscopy to measure total eye aberrations.

LaserSight has developed its AstraMax stereotopography system, which is linked to their new CIPTA software to provide oblate corneal ablations. Only Alcon and Visx do not have a built-in topographer.

I was not able to obtain clinical data on these systems, but presentations at the meeting suggested that all were providing improved results when compared to classic LASIK.

All the laser manufacturers now have some sort of active eye trackers, and all but LaserSight have working wavefront devices. So far, only the Asclepion, Schwind, WaveLight and Alcon systems are directly linked to their lasers. But all companies have plans to do that and, with the systems in use today, it is a simple task to perform the wavefront analysis, copy it to a disk and place the disc into the laser to perform the ablation.

Alcon and B&L, with their international data, appear to be in the lead of U.S. clinical trials for custom ablations, with Visx about 6 to 8 months behind. All other companies are still in the planning stages.

So the real question is, if classic LASIK with improved laser systems is working well, do we need wavefront? That answer is not clear.

Wavefront-guided ablations will be used to correct previous complications including decentered ablation, uncleared central islands and irregular astigmatism. It is expected to improve the quality of vision (especially for people suffering from poor night vision) minimize induced aberrations and correct higher-order aberrations such as third-order aberrations coma and trefoil.

But there is the question of how much higher-order aberrations should be corrected. This was related in my earlier customized ablation article but bears repeating. In a study of Navy “top gun” pilots, a comparison of higher-order aberrations showed that pilots with 20/12.5 acuity had some degree of coma, while those with normal 20/20 acuities had less coma. Would we turn 20/12.5 pilots into 20/20 pilots if we corrected their higher-order aberrations?

Early answers are ambiguous. There appears to be a lot of work ahead before wavefront-guided ablations become the norm.

Coleman Kraff, MD, said at the meeting that some surgeons are achieving excellent results with wavefront-guided ablations, but others have not yet hit their marks. In order for wavefront-guided ablations to provide minimized individual aberrations, the eye must be accurately registered between the capture of the diagnosis and the treatment, preferably in three axes.

One last point. Again, this was mentioned previously but bears repeating. LASIK, even with wavefront, gives more aberrations rather than fewer. In Marguerite McDonald’s study of wavefront-guided PRK versus LASIK last year, her PRK patients routinely had better acuities than her LASIK patients.

This is part of impetus for LASEK. But the results reported to date for LASEK have been mixed. Some surgeons report excellent results, while others report problems; the alcohol solution used to lift the epithelium causes cell death, haze and regression.

But Dr. McDonald has done it again. In her Binkhorst lecture, she described what she calls “gel-assisted LASEK.” Using hydroxypropylcellulose gel, she found she could “stiffen” the epithelium and lift it from its stromal bed, then cut it into quadrants that can be lifted outward away from the ablation zone, allowing PRK to be performed on the stroma.

Again using the gel, she was able to push the epithelium quadrants back onto the cornea. Using a bandage contact lens, she could then get re-epithelialization without cell loss. She believes that this modified, flap-free LASEK is a safer alternative to LASIK.

Other refractive alternatives

What lies beyond LASIK and LASEK for myopia? At present, not much.

IntraLase, with its femtosecond laser to perform intrastromal ablation — the removal of tissue within the stroma by making two passes at different levels — is still a way off. Previous attempts to do this by both Intelligent Surgical Lasers with their picosecond laser in the 1990s and Phoenix Laser Systems with a Q-switched YAG back in the late 1980s were unsuccessful.

It seems only early experiments have been performed, and it will probably be some time before human trials are conducted. The company strategy is first to establish the device for use as a microkeratome alternative, then seek approval to treat presbyopia, and finally go after myopia approval.

As for the solid-state laser from Q-Vis, after speaking to company representatives at the meeting, they appear to be far from establishing a beachhead in the United States. The company is just starting phase 3 clinical trials, so it is at least 12 to 18 months away from filing for premarket approval.

There is also the question of whether carcinogenesis is caused by the 213-nm wavelength. As we recall from the early days of excimer refractive surgery, that question was raised when J.T. Lin first proposed using a solid-state quintupled YAG operating at 213 nm. I’m not sure the question was ever resolved.

As for other surgical approaches, clear lens extraction does not seem to be an alternative to corneal refractive surgery in young people, especially low to moderate myopes.

There is another fly in the ointment for refractive surgery in general. CIBA Vision and Bausch & Lomb both recently had extended-wear contact lenses approved. These could prove to be viable alternatives to surgery.

Back in the mid-1970s, when the first extended-wear lenses became available, they took the public by storm. Some may recall the CooperVision television ad that proclaimed, “I can see beyond my bedcovers!”

As you may also recall, corneal ulcers and other problems soon stopped that generation of lenses in their tracks. But these new lenses are truly oxygen-permeable and have probably overcome all of those earlier problems. I advise you to watch carefully how well they are accepted.

Current correction of hyperopia

According to the MarketScope survey of refractive surgeons, almost 90% of surgeons choose LASIK for correction of low or moderate hyperopia, with or without astigmatism. Only about 8% of surgeons use the Sunrise LTK system. About 1% still use PRK. A few use some other undefined means: 4% for low hyperopia and 16% for moderate hyperopia. For high hyperopia correction, 20% of surgeons turn to phakic IOLs, while 21% still use LASIK and 63% choose some other means.

The 2001 ISRS Leaming Survey of Trends in Refractive Surgery in the United States had similar findings. For +1 D hyperopes, 70% of survey respondents said they would choose LASIK, and 17% said they would use either LTK or CK. For +3 D hyperopes, 84% chose LASIK, and only 2% said they would use LTK or clear lens extraction (CLE). For +5 hyperopes, 29% chose LASIK, 39% said their choice was CLE and 30% said they would wait for something else.

The results for all laser systems for correcting hyperopia appear to provide comparable results, which seem to be acceptable.

The two laser systems approved for hyperopia, LADARVision and Star S3, with their working eye tracker systems, are achieving good results for hyperopia and hyperopia with astigmatism. The feeling is that these systems are giving better results than those same systems without the eye tracker.

For that reason, few ophthalmologists appear to be interested in trying the Sunrise LTK system, which apparently has fallen out of favor. There was however, much interest in the Refractec ViewPoint CK system, especially at its low price of $45,000 for the unit and approximately $100 to $150 for the disposable tips, one used for each eye.

Future correction of hyperopia

The only other new means for correcting hyperopia on the horizon is the Anamed PermaVision Lens. This 78% water hydrogel lenticle, which has the same refractive index as the cornea and is only 30 µm to 60 µm thick, appears to provide adequate fluid and nutrient flow to keep the cornea healthy. It is used for correcting from +1 to +6 D of hyperopia by opening a flap in the cornea, inserting the lens and closing the flap.

In an international clinical study of the lens in 60 patients, the mean starting spherical manifest spherical equivalent was +3.52 D. Of 14 patients examined after 6 months, the mean spherical equivalent was reduced to +0.58 D. Immediately postop, the patients were about 0.5 D myopic, and they drifted to plano over 2 to 3 weeks.

An inversion problem with insertion of the lens has apparently been overcome with the use of a new delivery system. The company has received CE approval for marketing in Europe. U.S. clinical trials are expected to begin by the end of this year.

Current correction of presbyopia

In an ISRS presentation, John Hunkeler listed a bevy of options for the correction of presbyopia. He said three ways of tackling the problem are the monovision, pseudo-accommodation and multifocal vision approaches. Among the surgical options are monovision LASIK, multifocal corneal ablation, monovision with LTK or CK, scleral relaxing incisions, scleral expansion bands, laser scleral ablation and lens exchange using the Array multifocal IOL or an accommodating IOL.

Of all the options other than LASIK monovision, probably the insertion of the Array multifocal IOL has had the best results to date. The jury is still out on the accommodating IOLs in development now by at least three manufacturers: C&C Vision’s AT-45 CrystaLens, the Human Optics 1CU and an un named lens under development by Quest Vision.

Future correction of presbyopia

Of the non-monovision surgical options, scleral relaxing incisions do not work. This approach, in which the sclera is cut in an RK-like fashion, quickly regresses and leaves the patient with no change in near vision. Scleral expansion bands do seem to provide some near vision ability for about 70% of patients to date. Laser scleral ablation — which appears barbaric when witnessed — has had good results in some doctors’ hands, but others have not fared as well. More trials are needed with these techniques to see if they will really work in the nonspecialist’s hands.