An optic nerve which is damaged, most often following too high pressure inside the eye. And a field of vision that narrows, from the periphery to the center. This is the definition of glaucoma, for which 1.5 million French people are currently monitored or treated.
Medications, lasers or surgery allow the majority of them to stabilize the disease at the stage where it was discovered. But for 10 to 15 percent of sufferers, glaucoma continues to worsen and can lead to blindness. Hence all-out research to protect the optic nerve.
“No treatment directly aimed at the regeneration of these nerve fibers has yet proven its effectiveness in humans,” warns Professor Christophe Baudouin, of the Quinze-Vingts-Institut de la vision hospital, “but there are has made many advances in the control of intraocular pressure. This neuroprotection strategy has largely demonstrated its effectiveness.
Silent for years, glaucoma is, in most cases, linked to problems with defective evacuation of aqueous humor. Continuously secreted by glands located near the lens, it accumulates inside the eye, increases pressure and destroys the nerve cells of the optic nerve. To remedy this, once the diagnosis has been made, “we have four therapeutic families, a fifth currently the subject of clinical trials,” continues the professor.
Some medications reduce the secretion of aqueous humor, others facilitate its flow outside the eye through a drainage system called the “trabecular meshwork”. With one exception, they are administered as eye drops. However, except for surgery, these are prescribed for life. In view of their potential deleterious effects on the ocular surface - dryness, irritation, inflammation - the recent development of preservative-free formulas has constituted a formidable advance. And when they prove insufficient, we resort to laser or surgical interventions, the technique of which has also progressed.
“The laser makes it possible to remove the blockage by creating a small orifice in the iris, for so-called “closed angle” glaucoma,” explains Professor Baudouin. It can also improve the functioning of the trabecular meshwork for open-angle glaucoma, which is the most common. These objectives are also those of surgery, in patients whose disease is not stabilized by eye drops or lasers. “Over the past ten years, it has become less risky, thanks to so-called minimally invasive procedures based on the implantation of microdrains to evacuate aqueous humor,” adds the ophthalmologist. However, there remain patients for whom all these therapies are not enough. Hence the exploration of other avenues targeting the optic nerve more directly.
“A few years ago, I would have told you that I hoped to obtain good results with stem cell injections,” recognizes Christophe Baudouin. “But preclinical trials have shown the high variability of responses to this treatment, and especially its dangerousness for the eye.” Another option considered: the use of gene therapy, to produce a neuroprotective protein in the eye.
Finally, we are also considering intervening in the visual cortex, by stimulating genetically modified neurons to be activated by ultrasound, hence the name “sonogenetic therapy”. Currently, these treatments are only tested in animals. But scientists are hopeful of achieving human trials in the near future.