Increasingly Common as the Population Ages but Treatment Has Never Been Better!
By Elma Chang, M.D. and Reay Brown, M.D.
Three million people in the U.S have glaucoma – an asymptomatic, blinding eye disease. At least 1 million of these victims don’t even know they have it, which is why glaucoma is called the “Thief in the Night.†Detecting glaucoma is one of the main reasons we recommend an eye exam every 1 or 2 years, even for people who feel like they are seeing very well.
The fluid inside the eye has a natural circulation designed to achieve a normal internal pressure. Normal pressure should be defined as any pressure that does not cause optic nerve damage with a corresponding visual field defect. Using this argument, the previously accepted thought that a patient cannot have glaucoma if the eye pressure is below 21 is false. In the same way, if a patient has an eye pressure above 21 but no coexisting optic nerve damage, the patient is diagnosed with ocular hypertension and not glaucoma.
In a patient where it has been established that the optic nerve has thinning that corresponds with a visual field loss, visual fields are obtained on an annual basis. Peripheral vision is slowly – and imperceptibly – lost. If undetected and untreated, the eye may become totally blind. Since glaucoma is usually bilateral, patients too often present with blindness in one eye and advanced visual loss in the other. However, this progressive damage can be slowed or stopped completely by treatments that reduce the eye pressure to a normal level.
Fortunately, we have many excellent treatments for glaucoma. Eye drops are usually the first line of treatment. These lower pressure by enhancing outflow and reducing the fluid production. The next step is laser treatment – a very safe and effective option that is performed in the office and only takes a few minutes.
Cataract surgery has been found to be a very effective intervention for lowering eye pressure even though its main goal is to improve vision. We also have several devices (iStent, CyPass, and Xen implants) that we can place at the time of cataract surgery, and these have been breakthroughs in glaucoma treatment. Patients who need further pressure lowering will receive a trabeculectomy or a tube-shunt.
Medications – Both Now and the Future
Eye drops that decrease fluid production are beta-blockers (timolol maleate, Betimol, Timoptic), adrenergic agonists (brimonidine, Alphagan) or topical and oral carbonic anhydrase inhibitors (dorzolamide, Azopt, acetazolamide, Diamox). Medicines that promote outflow are cholinergic agonists (Pilocarpine), adrenergic agonists and prostaglandin analogs (latanoprost, Lumigan, Travatan, and Xalatan).
Rhopressa is a newer topical medication that is awaiting final FDA approval and will be available soon. It acts via rhokinase inhibition. This has been found to increase both aqueous outflow through the trabecular meshwork and reduce episcleral venous pressure.
Newer Delivery Systems
Eye drops require that patients use them once or twice daily. Compliance has been a major obstacle in treating glaucoma patients. Studies have shown that as many as 80 percent of patients forget to take their eye drops. Sustained drug delivery devices may be one key to improving compliance.
One device is a ring that is placed under the upper and lower lids. Another device is placed in the tear punctum in the lower lid. These devices are in studies and have shown good results.in reducing intraocular pressure (IOP) for up to 6 months.
Other studies have examined the use of particulate drug delivery systems or injectable formulations such as microspheres, liposomes and nanospheres/nanoparticles. This involves trapping the drug in the nanocarrier matrix and releasing the bioactive agent in a controlled fashion after administration.
It is impossible to know which of these technologies will emerge as the best option, but it is clear that longer duration treatments are a critical unmet need. We will continue to see rapid improvement in these technologies.
Laser Surgery
Laser surgery has traditionally been used as an intermediate step between topical therapy and incisional surgery. Laser therapy can increase outflow of fluid through the trabecular meshwork (laser trabeculoplasty) or decrease aqueous production from the ciliary body (diode laser cyclophotocoagulation). Laser trabeculoplasty can easily be performed in the office setting.
The Micropulse laser is a newer laser technology that seeks to improve the safety of the traditional diode cyclophotocoagulation while preserving the pressure-lowering.
Cataract Surgery with MIGS
One of the major recent advances in glaucoma treatment has been the discovery that cataract surgery lowers pressure and that the magnitude of pressure reduction was proportional to the pre-op intraocular pressure. In other words, cataract surgery is also a glaucoma operation that lowers pressure best in patients who need it the most.
There are 3.5 million cataract operations each year in the U.S., and studies show that as many as 20 percent of these patients have a concurrent diagnosis of glaucoma. So, this is all very good news for glaucoma patients.
Cataract and glaucoma are also linked because the two new devices that have been approved for glaucoma treatment – the iStent and CyPass – are restricted for use only at the time of cataract surgery. They can be used “off-label†as stand-alone procedures, but insurance coverage is more uncertain.
The iStent (Image 1) and CyPass (Image 2) are the first devices in the category of micro-incisional glaucoma surgery or MIGS. MIGS is a revolution in glaucoma treatment. MIGS approaches are much safer than conventional glaucoma surgery.
One of the key differences between MIGS and traditional glaucoma surgeries is the approach to the eye’s outflow system. Specifically, an ab interno approach is used in MIGS where the surgeon is able to access the trabecular meshwork (iStent) or suprachoroidal space (CyPass) via a corneal incision. Previously, the outflow system was approached via an ab externo approach, which meant that the outflow system was accessible only after resecting back conjuntival and scleral tissues.
There are many new approaches in the MIGS category. These include the ability to thread a catheter in the space behind the trabecular meshwork (canaloplasty) and then pull the catheter through the meshwork and creating an opening in the trabecular meshwork (goniotomy). A similar goniotomy effect can be achieved with several new technologies – the Trabectome, the Kahook blade and the Trab360 device.
Incisional Surgeries – Now and What’s on the Horizon
In some cases, treatment with eye drops, laser, cataract surgery and MIGS may not be enough to halt glaucoma damage. The next step is a trabeculectomy or a tube implant. These procedures create a pathway – essentially a hole – from inside the eye to a bleb (a fluid-filled bump) on the ocular surface. This can achieve profound pressure reduction but has a greater risk of infection, IOP being too low for clear vision, double vision and failure.
Finally, the newest device to achieve FDA approval is the Xen gel implant. This device is also implanted ab interno via a corneal incision. It is a newer and less invasive way to perform the trabeculectomy. The goal is to implant a gel-like Xen material in the subconjunctival space. The implant itself maintains a passageway between the anterior chamber and the subconjunctival space. The hope is that this will be safer than a traditional trabeculectomy but just as effective in lowering IOP.
The pace of innovation in glaucoma treatment is accelerating – both for topical therapy and for surgery. Most glaucoma surgeons still perform traditional glaucoma surgeries (trabeculectomies and tube implantations), but the acceptance of MIGS devices and technology is growing.
Our practice has been involved with some of the research that led to the development of the iStent and with the studies that led to the approval of the CyPass. We believe that MIGS is fundamentally changing the glaucoma treatment paradigm with surgical approaches becoming more common.
But these innovations are just the beginning. We have never had so many outstanding options for treating glaucoma and tailoring the approach to each patient. No one should ever become blind from glaucoma.
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