The concept of target IOP has long been debated, and new treatment options may allow us to be more comfortable going lower

Intraocular pressure is the only known modifiable risk factor in our quest to prevent glaucomatous optic nerve progression. Most practice guidelines recommend lowering IOP to a target commiserate with the level of disease. The concept of “target IOP” is now ingrained in our approach to treating glaucoma patients.

Although numerous studies have shown that reducing IOP can slow the rate of visual field progression, evidence for setting a target IOP is lacking. Years ago, it was ≤21mmHg, then ≤18mmHg, and now, a ≥25% reduction from “baseline” is the target for most patients. The EMGT¹, a well-designed, randomized controlled trial comparing a 25% IOP reduction versus no treatment in more than 250 patients with mild to moderate disease over 8 years, showed that a 25% IOP reduction from baseline slowed the rate of progression. However, 60% of treated patients still progressed at the target IOP reduction currently recommended.

Many will argue that one should follow treated patients and escalate therapy when progression occurs. This sounds reasonable, however, we don’t apply this approach to untreated patients with glaucoma because the risk of progression without treatment is considered to be too high. Yet, despite the high progression rate for modest IOP lowering (i.e., 25%) in treated patients, we apply a different logic and watch and wait. The other challenge is that our methods of progression detection are not precise, and it takes time to evaluate progression. Of course, determining “rate of progression” is helpful to differentiate “fast” from “slow” progressing disease, but most patients who have glaucoma will experience a progression in their disease over time.

So, do we need to reconsider target IOP, and do we need to go lower? In fact, IOP in and of itself is a random concept. The measurement of in-office IOP by Goldmann tonometry is just one point in a patient’s day, and doesn’t reflect a true baseline. Glaucoma patients are known to have wide diurnal IOP fluctuations, which may be a risk factor, and peak IOP may be more important to know.

Some evidence² has shown the achievement of IOP targets close to 12 mmHg, while keeping IOP below 18 mmHg, may halt disease progression. An re-analysis of CIGTS³ (most patients in this study had early disease) found that at a peak IOP of ≤13mmHg, there is not only stability of visual fields, but also net improvement.

Do we need to get closer to 12 mmHg for our glaucoma patients? This would require surgery for many patients. Traditional glaucoma surgery is typically a “last resort,” reserved for patients who have disease progression despite maximum medication therapy and who have very advanced disease. But newer surgical options, both blebless and bleb-forming, are making surgery more predictable, with a faster and smoother recovery, and, hopefully, a much better risk profile. I predict the shift to safer glaucoma surgery options will result in a shift to lower IOP targets.

Obviously, no one target IOP is appropriate for all patients, but it’s time to consider going lower, particularly in younger patients who have more than early disease. Although we need better evidence, I believe these patients are at the highest risk for blindness in their lifetime — and glaucoma remains one of the leading causes of blindness worldwide.

References

1. Heijl A, et al. Arch Ophthalmol. 2002;120(10):1268-1279.
2. The AGIS Investigators. Am J Ophthalmol. 2000;130(4):429-440.
3. Musch DC, et al. Am J Ophthalmol. 2014;158(1):96-104.