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Non-penetrating glaucoma surgery needs better wound healing control, surgeon says
More targeted, less cytotoxic drugs are needed to control wound healing, enhance filtration and achieve lower IOP levels.
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NANTES, France — Wound healing is the key issue to improve the results of non-penetrating glaucoma surgery, according to Philippe Sourdille, MD, who is in practice here.
“If we can modulate wound healing as to keep the decompression chamber for a longer time, we should be able to guarantee a better filtration and lower IOP levels,” he said.
In non-penetrating surgery the main source of intraocular pressure (IOP) lowering is sub-conjunctival filtration. This can be combined with other mechanisms, such as uveal absorption and intrascleral filtration. All these phenomena rely on a well-functioning decompression chamber, Dr. Sourdille said.
“Still, the decompression chamber may become shallower, or may close, even if you have used implants or drugs. It’s a basic phenomenon of surgery: the tissue you have removed naturally tends to be replaced by something. Consequently, filtration becomes less efficient,” he said.
This slower, more delicate filtration procedure accounts for the absence of IOP below 10 mm Hg.
“We are confronted with the fact that 20% to 30% of our cases still need some form of medical treatment after surgery, and that even this is sometimes insufficient to achieve a sufficiently low IOP,” he said.
Lower IOP levels
An average level of IOP between 17 mm Hg and 20 mm Hg is, in Dr. Sourdille’s opinion, too high to be safe.
“IOP should be below 15 mm Hg, ideally between 10 mm Hg and 12 mm Hg to guarantee that at least 90% to 95% of the patients will not suffer from visual field deterioration for many years,” he said.
The use of mitomycin C can improve the results of non-penetrating surgery by giving a better wound healing control and lowering the IOP 2 mm Hg to 3 mm Hg more, he said. However, he added that mitomycin C is well known for its medium- to long-term complications.
“Several studies have been aimed at finding the ideal drug to modulate wound healing and have the right amount of filtration. The current drugs can be used with non-penetrating surgery, especially in cases of low-tension glaucoma, reoperation, young adults or congenital glaucoma. However, we know we are going to have iatrogenic complications due to the use of these drugs,” he said.
Research should now be aimed at finding more targeted drugs, like anti-TGF ß, but less cytotoxic and more effective in modulating wound healing.
“Eventually, we should be able to take patients off drugs, because the burden of using drops once or twice a day for 30 years, with a significant percentage of patients suffering at different levels from this therapy, is not economically correct, and it is something the patient would be happy to get rid of,” he said.
Diagnosis and surgical improvements
Dr. Sourdille said that efforts should also be directed to an early evaluation of glaucoma. Too often, he said, surgery is performed at an advanced stage of the disease.
“This means that very often, even if we lower the pressure, we are unable to halt the enemy. We should focus more on early diagnosis, when the course of the disease can still be reversed,” he said.
Current diagnostic tools are only at the anatomic stage, when ganglion cells are already dead.
“More clinical research should be carried out on what we call the ‘functional stage’ of the disease. At that stage the suffering of ganglion cells could be diagnosed before their degeneration becomes irreversible,” he added.
When asked to comment on the technical advances of non-penetrating surgery, Dr. Sourdille remarked that the surgical technique has not changed a great deal in the past 2 to 3 years.
“An alternative has been the use of lasers,” he said. “The erbium laser replaces the knife in the ab-externo approach, with the laser beam performing the tissue ablation. Still, because the probe has to be held by the surgeon, I consider this a different knife, not a different approach.
“With the excimer laser, the machine has a more prominent role. With the excimer being delivered from the outside, we can reach the pre-descemetic level and Schlemm’s canal. More recently, in addition to this, we have developed an ab-interno approach, with the probe again being held by the surgeon’s hands,” he explained.
Whatever the surgical approach is, the rationale of using laser is that it could make surgery easier, more reproducible and less surgeon-dependent, Dr. Sourdille said.
Finally, he commented on the results of recent studies comparing non-penetrating surgery and trabeculectomy.
“Something that comes out very clearly is that non-penetrating surgery has a much lower rate of complications than trabeculectomy. However, because we are still confronted with a significant number of failures in terms of IOP lowering, we must still work at improving the technique,” he added.
For Your Information:
- Philippe Sourdille, MD, can be reached at Clinique Sourdille, 3 Place Anatole France, F-44000 Nantes, France; (33) 251-83-32-00; fax: (33) 251-83-87-19; e-mail: philippe.sourdille@wanadoo.fr.