Two months ago, I considered a potential role for a class of medications, statins, in glaucoma neuroprotection. Based on cross-sectional and longitudinal data, it would appear that the consumption of HMG-CoA reductase inhibitors are associated with a lower incidence of glaucoma. A prospective study has been designed and is currently awaiting funding.
But what about other medications that are commonly used for elevated blood pressure, diabetes, or high cholesterol? Could these medications be affecting intraocular pressure? Dr Ho and colleagues studied this topic and assessed the records of roughly 8000 individuals treated for a variety of systemic conditions and who had intraocular pressure measurements.
They found that some medications can raise or lower IOP. More accurately, we should say that some medications are associated with a higher or lower IOP. It would be difficult to show that the medicines have this effect without prospective, randomized trials. It is always possible that the underlying diseases themselves could be responsible for these findings, although the authors did make efforts to reveal if this was the case by controlling for important covariates.
Starting with perhaps the easiest topic, we have the use of systemic beta-blockers and intraocular pressure. Not only have systemic betablockers been reported to lower eye pressure, but they have been reported to be associated with a lower-magnitude pressure reduction when topical beta-blockers are added—implying that the systemic beta-blocker has already lowered the pressure somewhat before the topical agent was used. In this study, a slightly lower pressure was observed in patients who were using oral beta-blockers. The pressure in this group was about 0.45 mmHg lower, which was statistically significant. This is a neat result, but mostly just provided the proof of concept of this type of study design, which makes the next findings a little bit more interesting.
Several other medications found to be associated with a slightly higher intraocular pressure were statins, ACE inhibitors, angiotensin-receptor blockers, and the sulfonylurea class.
It should be noted that the magnitude of the pressure elevation was very modest, about 0.2 to 0.5 mmHg. Furthermore, it is always possible that the diseases for which the drugs were prescribed are responsible for the higher pressure measurements. Keep in mind that the authors controlled for many covariates including age, blood pressure, LDL cholesterol levels and HgA1C. Also, beta-blockers and ACE inhibitors are used to treat the same disease but had opposite effects, arguing against the disease as the root cause. While these controls do help to make sure that it is not the high cholesterol or high blood pressure causing the elevated IOP reading, the possibility still exists.
One factor that I discussed in a previous blog entry is corneal hysteresis. Corneal hysteresis describes the viscoelasticity of the cornea, and this variable has an impact on intraocular pressure measurements with Goldmann applanation tonometry (GAT). A higher corneal hysteresis will result in greater pressure readings, simply because of the cornea’s behavior while undergoing GAT. Hysteresis itself has its own associations, and one of them is that hysteresis is higher in patients with diabetes. So diabetics will have a higher hysteresis, and as a result, their IOP will read higher. We don’t quite know why diabetes is associated with a higher hysteresis level (crosslinking as a result of hyperglycemia?), but this association could be responsible for the measured higher IOP in those using medicines to treat diabetes. It is harder to explain why this effect would only be present for certain classes of medications, and of course this finding leads us back to the possibility that the medications themselves are likely responsible for the higher pressure readings.
In summary, some commonly used medications have a small but real effect on IOP. While the effect is real, it is likely not impacting clinical management. We can feel comfortable managing eye pressures knowing that for the most part, systemic medications are not having a profound influence on these values.