Glaucoma Tomorrow
The functionality of IOP-lowering drainage devices may be greatly increased in the near future due to the work of Dr. Lee and his team, who have begun using magnetic technologies to keep these devices from being clogged and adjust flow resistance.
By Todd Farley
One of the most effective means of treating glaucoma is through the use of drainage devices that help reduce intraocular pressure (IOP). Although the devices have a tendency to clog, researchers seem to have found a way to ameliorate that problem through the use of new magnetic technologies.
It’s estimated that as many as 3 million Americans — and 60 million people around the world — suffer from glaucoma, although half of those may not yet be aware of their condition. The World Health Organization lists glaucoma as the second leading cause of blindness around the globe, with approximately 120,000 Americans having already lost their sight to it.
Glaucoma Mechanics
“Glaucoma is an eye disease that is characterized by increasing intraocular pressure,” says Dr. Hyowon “Hugh” Lee, an assistant professor at Purdue University’s Weldon School of Biomedical Engineering and a researcher at the Birck Nanotechnology Center. “Intraocular pressure is the pressure inside the eye, and too much can damage the optic nerve and eventually cause blindness.”
The IOP that characterizes glaucoma results when there is too much fluid in the eye. Normally this fluid (called “aqueous humor”) flows through the eye and drains out of the trabecular meshwork, a tissue found where the iris and the cornea meet. If too much of this fluid is produced, however, or if it does not properly drain from the eye, pressure increases and damage to the optic nerve can occur. The optic nerve transmits images from the eye to the brain. Glaucoma can cause blind spots in the peripheral or central vision; in more advanced stages, “tunnel vision” can result. Untreated glaucoma frequently leads to blindness, while as many as 15% of people who do treat their disease still lose sight in at least one eye over the years.
Risk factors for glaucoma include age (being more than 60 years old) and genetics (a family history of the disease), but it also seems to adversely affect African-Americans, Asians, and Hispanics. Certain physical conditions such as diabetes, heart disease, high blood pressure, and sickle cell anemia also seem to increase the likelihood one will get glaucoma, as does the long-term use of corticosteroid medications (especially eyedrops).
IOP-lowering Treatments
The effects of glaucoma cannot be reversed, so vision lost to the disease is lost forever. Neither is there a cure for it. Fortunately, treatments are available that help to mitigate glaucoma’s effects. These include eyedrops and oral treatments to help reduce IOP, as well as various surgical procedures aimed at keeping that pressure down. Surgical options include laser trabeculoplasty (done in an ophthalmologist’s office, with the doctor using a laser to unclog the trabecular meshwork); filtering surgery (which removes part of the trabecular meshwork); and MIGS surgery (a minimally invasive surgical procedure done expressly to reduce pressure in the eye). Another surgical option for the treatment of glaucoma that has become increasingly popular is the insertion of drainage tubes in the eyes. These devices are shunts that help to channel away the extra fluid that can lead to increased IOP.
“If it is detected early enough, there are some pharmacological treatments for glaucoma that can potentially keep the pressure lowered for a while,” Dr. Lee says, “but there are some patients that do not respond to the drugs any more. or those people, surgical intervention is required, and in recent years the drainage device has been one of the more popular choices for those non-pharmaceutically responding patients.”
The drainage devices surgically implanted into the eyes of glaucoma patients to help drain the aqueous humor are very, very small. “The tube itself is tiny,” Dr. Lee says, “only about 200 microns in diameter and just a few millimeters long. Still, it is large enough that it can be seen with the naked eye.”
Small or not, once implanted these drainage devices normally prove beneficial in helping to keep down IOP in glaucoma patients. The only issue is that over time the efficiency of these devices can waver, as Dr. Lee explains.
Problems with Drainage Devices
“Again, what happens in glaucoma is that the natural drainage pathway for the liquid in your eye gets blocked somehow, and these drainage devices end up providing a new pathway for the fluid to exit out,” he says. “The problem is that once we have paved a new pathway or conduit for the fluid to flow out it, needs to remain open; but with these conventional glaucoma drainage devices that doesn’t always happen.”
Frequently the build-up of a proteinaceous film (sometimes called “microbial sludge”) in these drainage devices can stop the aqueous humor from flowing through them and out of the eye, rendering the devices virtually useless and necessitating their replacement. In fact, within5 years of implantation as many as one-third of traditional drainage devices need to be replaced for that reason.
“The problem is that the reliability of these drainage devices is not always perfect,” Dr. Lee says, “which requires patients to undergo revision surgery to remove and replace the failed devices. Obviously if you have a critical disease like glaucoma where an increased period of IOP can damage your vision, it’s vital that the device you use to treat the disease maintains functionality.”
New Tech to Prevent Clogging of Drainage Devices
Fortunately, the functionality of such devices may be greatly increased in the near future due to the work of Dr. Lee and his team, who have begun using magnetic technologies to keep those glaucoma drainage devices from being clogged.
“Because of this occlusion problem, or blockage problem, in the tube, we fabricated these micro-scale devices and integrated them into the lumen of the tubes,” Dr. Lee says. “The micro-scale devices vibrate on demand, allowing us to clear out the proteinaceous film that gets deposited in the device as the fluid travels through the tube and out of the eye. This allows us to periodically ‘clean the pipe,’ if you will, so that it remains free of any kind of obstruction.”
Keeping a drainage device free of “any kind of obstruction” means it will never need to be replaced, saving patients from the trouble and risks that come from additional surgeries. Doing so also helps provide patients with a long-term solution to the long-term problem of glaucoma.
“We have expertise in creating these micro-scale actuators, which basically means some sort of mechanism to move,” Dr. Lee says. “They are powered using externally applied magnets so that when we apply the magnetic field, we can cause them to vibrate at certain amplitudes, within a certain range of motion, or at certain speeds.”
As Dr. Lee imagines it, that would mean in the near future glaucoma patients with drainage devices could keep using those devices forever, never needing to repair or replace them, based only on some sort of cleaning session using a hand-held magnet. “We’d have an external electromagnet,” he says, “and then we could apply a specific amount of magnetic strength and frequency to be able to vibrate the actuators and clean the devices as we want to.”
While Dr. Lee is confident in the efficiency of his actuators, he hasn’t developed a protocol to optimize their use. “We have not yet determined the optimum frequency to use on a drainage device. Given that it takes a while for proteinaceous film to occlude it, we have not yet determined how often it might need to be cleaned,” he explains. “We envision that it might work best using an approach like the dentist takes, maybe visits every 6 months to prophylactically remove those depositions of film.”
That’s not the only method Dr. Lee imagines working, though. “We can certainly create in-home devices, too. Maybe this is something that one would want to do every few days at home, for 20 minutes or so. We had very good results in the study when using the actuator for only 5 minutes, so maybe it would work best if it was akin to brushing your teeth before bed every day.”
Adjusting Flow Resistance
The promising results of Dr. Lee’s study were released in the November 2018 issue of Microsystems and Nanotechnology,1 but the abilities of his actuators to keep traditional glaucoma drainage devices clean and functional is not the only exciting news in it. In addition, the study revealed that these new magnetically controlled actuators can adjust “flow resistance” to control the amount of fluid coursing through the drainage tubes.
“The resistance of the flow can be characterized by the amount of obstructions in the tube,” Dr. Lee explains. “We can vary the amount of resistance by deflecting the flow or causing more drag on the fluid. This is an ongoing piece of work, but we can actually cause the actuators to stand up to cause the fluid to slow down, or we can remove all the obstructions and leave a free pathway for the fluid to flow.”
While an impressive bit of technology unto itself, this ability to adjust flow resistance in traditional glaucoma drainage devices also means future ophthalmologists will be able to deliver treatment on an individual basis.
“The device we envision is actually one that has the capability to be tailored to different patients,” Dr. Lee says, “so we’ll have an array of actuators that can be tuned to different signals. This is a way to personalize the treatment, because everyone has a different level of pressure in the eye. For patients with high IOP and more extreme cases, you want to be able to really allow the drainage to flow very, very fast, but if someone has low pressure then you might want to control how much fluid exits out.”
What’s Next
So far, the exciting results of the study have been done on bench top only, showing proof of concept, but after patenting the technology Dr. Lee and his team are starting in vivo evaluation in rats and mice. While not yet at the point to test his hypothesis on humans, Dr. Lee looks forward to that happening one day soon.
“We need additional funding to continue this work, which we think has a great deal of promise and could one day be translated into clinics,” Dr. Lee concludes. “But getting biomedical devices, and especially advanced biomedical devices, into the marketplace takes some time and effort. We’re working to validate our approach and we hope to continue this work and get it to patients soon.”
References
1. Park H, Raffiee AH, John SWM, Ardekani AM, Lee H. Towards smart self-clearing glaucoma drainage device. Microsystems & Nanoengineering. 2018. DOI: 10.1038/s41378–018–0032–3.
