What is Target IOP?

There is enough evidence from well-designed population based clinical trials that elevated eye pressure is a risk factor for glaucoma development and progression. Therefore, the main strategy for preventing glaucoma in at-risk patients and for slowing progression in glaucoma patients is lowering IOP.

The graph below is from an article I coauthored with my colleagues which describes how the risk of glaucoma increases with increased eye pressures. (You can read the article here)

The Target IOP for you is basically a “guesstimate” by your eye doctor: he or she decides that this is the probable IOP level at which there will be no further damage to your optic nerve.

The World Glaucoma Association (WGA) defines Target IOP is “an estimate of the mean IOP at which the risk of decreased vision related quality of life due to glaucoma exceeds the risk of the treatment.”

How do we determine Target IOP?
The magic number actually is dependent on several factors. These include

1. Stage and severity of glaucoma
2. Eye pressure at the time of diagnosis
3. Age and life expectancy of the patient
4. Significant comorbidities and diseases
5. Risk factors for glaucoma progression
6. Quality of life impact of treatment for individual patient
7. Eye health perspective, fears and prejudices of the individual patient.

Other considerations would include the following:

1. Presence and severity of damage to involved eye, as well as the other eye
2. Rapid rate of progression of damage to involved or fellow eye
3. Family history of or genetic mutation predisposing to early onset disease or severe disease, or both, including any history of blindness in the family
4. African or Caribbean ancestry
5. Vascular risk factors: disc hemorrhage, high blood pressure (BP), nocturnal hypotension or dips in BP at night, migraine, Raynaud’s disease, diabetes mellitus, previous vein occlusion
6. Compliance and adherence to prescribed therapy

Which means, that ideally glaucoma treatment is tailored to the patient and his or her eyes only. The target eye pressure for both eyes may not necessarily be the same for both eyes. This also means, that the primary goal of your treatment is preserving your quality of life, and not just lowering your eye pressures.

So each time you visit your doctor, you will have a conversation about how the treatment is affecting you. If your eye drops are making you uncomfortable, your doctor may decide to offer you lubricating eye drops, a laser treatment or surgery. If your disease has not been progressive, your doctor may even consider decreasing your eye drops, and seeing you in a few weeks to reevaluate your eye pressure “target”.

Is Target IOP a fixed number?
Target IOPs change constantly, in fact your doctor will be reworking this number each time you get your tests done, depending on whether the glaucoma is stable or shows signs of progression. Most doctors will think of a target range (ie, upper teens, middle teens, lower teens), and may even decide to set a “goal” IOP to encourage you to participate more actively in your glaucoma therapy.

Once the goal is met, you can both rest easy, until the goal is revised, either upwards (if your glaucoma is stable) or in case of progression, your doctor will suggest a lower target eye pressure.

Broad thumb rules for setting the Target IOP
The more advanced the glaucoma is, the lower the IOP. The thinner the cornea, the lower the IOP. The younger the patient, the lower the IOP.

1. Ocular Hypertension
Most doctors will set a target pressure reduction of at least 20% to 25%, or look for a final target pressure of less than 21mm of Hg. In the Ocular Hypertension Treatment Study (OHTS), only 5% of the patients who had a 20% mean reduction in IOP, progressed to glaucoma, so this does seem like an effective target for most patients of ocular hypertension.
2. Early Glaucoma
For a patient with early disease, again, a reduction of at least 25-30% from baseline, or into the high teens is usually the target. In the Early Manifest Glaucoma Trial (EMGT), patients with newly diagnosed primary open-angle glaucoma and an average IOP reduction of 29% achieved a 50% reduction in the risk of glaucoma progression. A 30% reduction of pressure (sometimes, higher in case of advanced glaucomas) in Collaborative Initial Glaucoma Treatment Study (CIGTS) meant that there was no average visual field progression in 7 years because the glaucoma surgeons adhered to the target IOP.
3. Moderate Glaucoma
For patients with moderate disease, most doctors set an upper limit of less than 18 mm Hg with a reduction of at least 30% to 35% from the baseline IOP, aiming for around 15-16 mm of Hg. As is evident from the CIGTS and the Advanced Glaucoma Interventional Study (AGIS), this ensures that there is little or no glaucoma progression with this IOP.
4. Severe Glaucoma
In patients with severe glaucoma, your doctor will aim for low teens around 10-12 mm Hg. In fact, the AGIS showed that patients with a pressure consistently below 18 mm Hg combined with an average IOP of 12 mm Hg had almost no glaucomatous progression over a 14-year period follow up period. Very often, your doctor will consider a surgery in order to delay progression in case of advanced diseases.

Remember:

1. Target IOP is a range, and not just one fixed number.
2. Target IOP is modified over time, taking lots of factors into consideration.
3. Your eye doctor is responsible for taking care of your quality of life, and not just your eye pressures.
4. The “number” is only a broad goal towards which you must work. Your real goal is preserving your vision, and your vision related quality of life.
5. Talk to your doctor if you are not comfortable with your treatment plan, and he or she will be happy to tailor it to your eye health and vision needs.