The ability to consistently monitor a patient’s intraocular pressure (IOP) could lead to significantly improved patient outcomes — and it is something of a Holy Grail in glaucoma management.
Glaucoma is associated with IOP that gradually increases over time, and by the time the patient presents with more serious symptoms (like intense eye pain, headaches, and blurred vision), the damage has been done.
It’s no small wonder that glaucoma is often described as the “silent thief of sight.” However, it is not a condition that strikes without warning… we just often fail to notice.
As such, monitoring increases in IOP is crucially important — and so too is finding a method that can consistently monitor changes in IOP.
The gold standard in IOP monitoring
Currently, Goldmann applanation tonometry (GAT) is regarded as the gold standard for in-clinic IOP measurements, but it’s not without drawbacks. The requirement for routine clinic visits remains a significant burden, especially in areas with limited facilities, and for the elderly and infirm. Handheld devices have also been developed like I-Care Home, but these have their limitations, too, such as requiring the patient to remain awake.
This is an important point — as the ideal way to understand a patient’s IOP is to measure it constantly over 24 hours — so naturally, a handheld device is limited as it can only work while the patient is awake. As such, finding a way to measure IOP during sleep is a major area of research at the moment, and one possible method uses highly adapted contact lenses. And yes, this does tend to contradict the conventional wisdom about the nocturnal wearing of contact lenses, but it’s permissible in this case.
Good news from Hoosier Country
According to a group of researchers based primarily at Purdue University (Indiana, USA), the lenses used to monitor IOP at night are much softer than usual and use ophthalmic silicone hydrogels. Such lenses can seamlessly fit a variety of corneal shapes and sizes without significant safety concerns for those even with glaucoma, other ocular diseases, or post-incisional surgeries.
The challenge in making them effective at monitoring IOP is that they need to include a wireless tonometer due to the high temperatures and corrosive chemicals required for microfabrication production. That’s to say nothing of the discomfort a patient might experience while wearing such a device in their eye during sleep, regardless of how soft the lenses are.
In a study called Smart Soft Contact Lenses for Continuous 24-hour Monitoring of Intraocular Pressure in Glaucoma Care,* researchers look into this issue and offer a potential solution, a “soft, thin and stretchable ocular tonometer [that] is built upon various commercial brands of soft contact lenses,” called smart soft contact lenses (SSCL). They hope that this new design will offer all the key functions, such as lens power, biocompatibility, softness, transparency, wettability, and oxygen transmissibility — without sacrificing efficacy. The lenses are also designed to match nearly any cornea shape and with low-cost production, SSCLs can be disposed of after multiple uses.
Can smart lenses bear the GAT?
To understand the efficacy of SSCLs, the researchers carried out a set of in vivo evaluations in rabbit, dog, and human eyes (from normal to hypertension) to confirm superior measurement accuracy, within-subject repeatability, and user comfort. They compared the results with those taken from more conventional lens-based tonometers. The results taken from the trials involving humans were the most interesting.
The IOP of the participants under postural changes was monitored in real-time with the SSCL as compared to control measurements with both the iCare Home and the Triggerfish lens at time-matched points. The researchers found that the results of the SSCL were closer to those of the GAT over the iCare Home, and that the SSCL had a high level of measurement accuracy. In an interesting sub-conclusion, unlike the Triggerfish lens, the SSCL did not produce any residual heat.
So it might not be long until we have an easy-to-use and effective tool to measure IOP in glaucoma patients. The researchers behind the study go even further: They believe that the SSCL could also be tailored for other chronic ocular diseases, such as cataract and age-related macular degeneration.
Time will tell if it will enjoy similar levels of efficacy… and that’s a development we look forward to reporting on.
*Zhang J, Kim K, Kim HJ, et al. Smart Soft Contact lenses for Continuous 24-hour Monitoring of Intraocular Pressure in Glaucoma Care. Nat Commun. 2022;13:5518.
Editor’s Note: This article was first published in COOKIE magazine Issue 10.