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What’s ahead for 2009 - Advanced technology and ideas move glaucoma treatment, refractive surgery and cornea transplants to better, less invasive procedures

As soon as an ophthalmic procedure gains traction with the community, another more advanced technique or technology as already begun to challenge it. Sometimes the challenger is a natural progression of the more established technology, and sometimes it arises from a different set of ideals and theories altogether.

 

This evolution of technology is not limited to any one specialty of ophthalmology either. Rather, it can be found in every aspect of ophthalmology.

Collagen crosslinking coming to America

Corneal collagen crosslinking (CXL) has been under investigation since 1998, and it was developed by Theo Seiler, M.D., Ph.D., professor, University of Zurich, Zurich, Switzerland, while he was at the University of Dresden, Dresden, Germany.

 

CXL involves instilling drops of riboflavin onto the eye over a period of 30 minutes to saturate the cornea. Then the physician continues adding riboflavin drops for another 30 minutes while exposing the eye to ultra violet (UV) light. The interaction of the light and riboflavin forms chemical bonds, or crosslinks, between the collagen molecules making the cornea stiffer. As a result, the corneal collagen tissue is stronger and can more uniformly retain its natural curved shape rather than bow forward into the cone-like shape that usually is indicative of ectasia or keratoconus. 

 

At the American Academy of Ophthalmology (AAO) annual meeting last month in Atlanta, R. Doyle Stulting, M.D., Ph.D., professor of ophthalmology, Emory University, Atlanta, presented the six-month post-op data of the Food and Drug Administration (FDA) trials. Dr. Stulting is the principal investigator in the FDA trials.

 

So far, the study includes 109 patients with keratoconus and 96 with ectasia, Dr. Stulting said. The early results show there is no change in maximum K readings until about six months post-operatively when there is significant flattening of the cornea. At the three-month point, there is about a 2/3 D difference between the controls and test group of keratoconus patients, but at six months, this becomes 2 D of difference. The findings were the same in the ectasia groups, though there was a steepening at one month. The cornea also thins significantly (about 23 and 31 microns for keratoconus and ectasia, respectively).

 

In Europe, 99% of patients treated by CXL have remained stable, said Eric D. Donnenfeld, M.D., co-chairman of cornea, Nassau University Medical Center, East Meadow, N.Y., who also is an investigator in the ongoing trials.

 

“Collagen crosslinking halts the progression of ectactic corneal disease for both ectasia following LASIK and keratoconus,” Dr. Donnenfeld declared.

 

Prospective study in the United States will close recruitment in March, he said. The one-year data will not be available until March 2010, so the earliest this procedure could be approved by the FDA would be in 2011.

Lasers fight for superiority in glaucoma treatment

Even as glaucoma experts argue over which laser treatment is best in glaucoma therapy, argon laser trabeculoplasty (ALT) or selective laser trabeculoplasty (SLT), a new laser treatment is emerging, micropulse laser trabeculoplasty (MLT).

 

“Historically there have been a lot of different lasers that have been fired at the trabecular meshwork (TM),” said Andrew G. Iwach, M.D., associate clinical professor, University of California, San Francisco. The goal has been to achieve the pressure lowering effect while not causing damage to the TM by using different wavelengths and energy pulse characteristics. For example, ALT uses a 0.1 second pulse whereas SLT uses only a 3 nanosecond pulse. MLT utilizes a 0.3 millisecond pulse.

 

Dr. Iwach said MLT is similar to SLT except for the energy wavelength and pulse profile, which is much longer pulse delivered over a shorter microburst over an extended period of time. The micropulse width allows less time for the laser-induced heat to spread to adjacent tissues, which results in confining the thermal rise to the TM tissue.

 

So far, Dr. Iwach has tested MLT on 26 eyes that were headed to surgery. “We wanted to see how it would do in the worst case scenario,” he said. And even in those eyes, some did very well, but it is early whereas SLT has a track record.

 

There is only one published MLT study, which is out of Italy, and Dr. Iwach illustrated how much in its infancy MLT is by pointing out that the power settings and spot size used in that study differ from what he used in his own study.

 

“Ultimately, does one do better than the other? Ask me in a year or so,” Dr. Iwach said. “We have some early data, and this is how it all develops.”

Cornea donor tissue will become a relic

The evolution of a procedure is perhaps the most dramatic in cornea transplants. As recently as 10 to 15 years ago, patients with endothelial dysfunction had only one option, full-thickness penetrating keratoplasty (PKP).

 

But then Gerrit Melles, M.D., Ph.D., Netherlands Institute for Innovative Ocular Surgery, the Netherlands, introduced the world to deep lamellar endothelial keratoplasty (DLEK), but it was an arduous procedure, said Mark S. Gorovoy, M.D., Fort Myers, Fla., and it eventually gave way to another of Dr. Melles’ innovations, Descemet’s stripping endothelial keratoplasty (DSEK) in which Dr. Melles stripped Descemet’s membrane from the recipient to provide a bed to stick the donor tissue directly onto the posterior surface. This eliminated the recipient stromal dissection from the endothelial keratoplasty procedure.

 

At the ASCRS annual meeting in Washington, D.C., in 2005, Dr. Gorovoy introduced his own evolution of the procedure, Descemet’s stripping automated endothelial keratoplasty (DSAEK). What Dr. Gorovoy did was to adapt its shape by cutting the donor tissue with a mechanical microkeratome, hence the “automated” part of DSAEK.

 

The dislocation rate with DSAEK is not totally resolved, but it is down to the 5-6% range, which is acceptable, Dr. Gorovoy said. During the learning curve, physicians were reporting 30% dislocation rates, but with skills developed over time, it is conceivable for the physician to be operating in the 5% to 10% range. The primary failure rate should be around 1%, and Dr. Gorovoy recently reported a 200-case series in which he achieved 0% primary failures, but it is another area that demonstrates the procedure’s learning curve.

 

But as DSAEK is solidifying its position, a new procedure is being developed, however, that could supplant DSAEK. Also developed by Dr. Melles, Descemet’s membrane endothelial keratoplasty (DMEK) requires the physician to replace the stripped area with a donor Descemet’s membrane, so the physician would be replacing Descemet’s with Descemet’s.

 

Theoretically, this should provide better vision in a quicker period, Dr. Gorovoy said. The downside is that it is challenging to get the donor tissue without damaging it and getting it to stick in the eye.
Dr. Gorovoy said he thinks DSAEK is the solution for transplants, but he added that DMEK has potential, though it is too early to tell how effective DMEK will be in the long-term as the procedure is improved.

 

“I think the ultimate solution is not to solve these problems with any surgery and genetically have engineered endothelial cells that can just repopulate the surface of the cornea,” Dr. Gorovoy said acknowledging that this is far off.

 

Editors’ note: Dr. Stulting has financial interests with Peschke Meditrade (Huenenberg, Switzerland). Dr. Donnenfeld has no financial interests related to his comments. Dr. Iwach has financial interests with Iridex (Mountain View, Calif.) and Lumenis (Santa Clara, Calif.). Dr. Gorovoy has financial interests with Harvey Precision Instruments (Rotonda, Calif.).

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EyeWorld | by David Laber EyeWorld Staff Writer