By Dr. Benjamin Caplan, MD | Board-Certified Family Physician, CMO at CED Clinic | Evidence Watch
A University of Minnesota survey found that roughly 1 in 6 eye clinic patients had used marijuana within the past month, and nearly half of glaucoma patients expressed interest in using it for their condition. Because cannabis can transiently lower intraocular pressure, undisclosed use before an eye exam may produce misleadingly normal pressure readings, potentially delaying glaucoma diagnosis or masking inadequate treatment.
Nearly 1 in 6 Eye Clinic Patients Report Recent Marijuana Use, Raising Concerns About Glaucoma Diagnosis Accuracy
A small but clinically suggestive survey at the University of Minnesota finds widespread patient interest in cannabis for glaucoma alongside significant knowledge gaps and underappreciated measurement risks, pointing toward a practical need for pre-exam cannabis screening protocols in ophthalmology settings.
#72
Strong Clinical Relevance
Directly addresses an actionable clinical blind spot at the intersection of cannabis use and ophthalmologic measurement accuracy, though evidence strength is limited by small sample size.
Intraocular Pressure
Patient Screening
Ophthalmology
Survey Research
Intraocular pressure measurement is the single most important quantitative tool in glaucoma diagnosis and management. Cannabis is well established as a transient IOP-lowering agent, yet ophthalmology clinics do not routinely ask patients about recent marijuana use before tonometry. As cannabis legalization accelerates across U.S. states, the proportion of patients arriving for eye exams with pharmacologically lowered IOP is likely growing in ways that clinicians have not systematically accounted for. Without pre-exam screening, clinicians risk making diagnostic and treatment decisions based on artificially reassuring pressure readings.
Glaucoma remains the leading cause of irreversible blindness worldwide, and IOP measurement is central to its detection and monitoring. Marijuana’s capacity to lower IOP by 25 to 30 percent for 3 to 4 hours has been recognized since the 1970s, yet no ophthalmologic society recommends it as a treatment due to the short duration of effect, the requirement for near-continuous dosing, and potential adverse effects. What has received far less attention is the confounding problem: patients who use cannabis before arriving for an eye exam may present with artificially lowered IOP that masks disease progression or delays initial diagnosis. This cross-sectional survey, conducted at four University of Minnesota eye clinics, sought to quantify how common recent cannabis use is among ophthalmic patients and to characterize patient attitudes toward marijuana as a glaucoma treatment.
Among 134 surveyed patients, 15.7% reported marijuana use within the past month, 8.2% described themselves as regular users, and 4.5% reported daily use. Among the subset of glaucoma patients, 44.2% expressed interest in using marijuana for their condition. Notably, patients who had used marijuana within 24 hours of their exam were significantly more likely to know it lowers IOP (p=0.02), raising the possibility that some users are self-medicating in ways that directly confound the very measurements clinicians rely on. Beliefs that marijuana is effective, lowers IOP, and has fewer side effects than standard medications were significantly associated with interest in use (p values ranging from 0.011 to 0.016). These findings, however, come from a small convenience sample at a single academic center without objective IOP or biomarker validation, and the authors appropriately note that larger, multi-center studies with biological confirmation are needed before these prevalence estimates can be generalized.
This study names a problem I have seen hiding in plain sight for years. The idea that a significant fraction of eye clinic patients are walking through the door with pharmacologically altered intraocular pressure, and that nobody is asking about it, should concern every ophthalmologist who depends on tonometry for clinical decision-making. The 44% interest rate among glaucoma patients is not surprising to me; patients hear that marijuana lowers eye pressure and reasonably wonder why their doctors are not prescribing it. What this paper gets right is connecting the dots between that patient curiosity and the real risk of measurement artifact. What it cannot yet prove, given the small sample, is how often this actually changes a clinical outcome.
In my practice, I discuss cannabis use openly with every patient, including those managing glaucoma. I explain that while THC does transiently lower IOP, the effect is too short-lived and the dosing requirements too demanding to replace standard therapy. More importantly, I emphasize that undisclosed use before eye appointments can actually work against the patient by making their pressure appear better controlled than it truly is. The clinical fix here is simple: ask the question before you take the measurement.
This study sits at the very beginning of a research arc that links cannabis prevalence data to actual clinical outcomes in ophthalmology. We have decades of pharmacologic evidence establishing that THC lowers IOP acutely, and we have strong professional consensus from the American Academy of Ophthalmology that marijuana is not recommended as glaucoma therapy. What has been missing is the bridge between those two bodies of knowledge: how often is recent cannabis use actually present in the exam room, and does it measurably alter diagnostic accuracy? This survey begins to answer the first question, but it cannot address the second without objective IOP and cannabinoid biomarker data collected in parallel.
For clinicians, the pharmacological consideration is straightforward. THC’s IOP-lowering effect peaks within 1 to 2 hours and dissipates within 3 to 4 hours, meaning the timing of use relative to tonometry is everything. CBD, by contrast, has not demonstrated reliable IOP-lowering effects and may even raise IOP in some studies. Given that 4.5% of patients in this survey reported daily use, the practical implication is that some patients may always present with confounded readings.
