26 Apr How Does Cataract Surgery affect Glaucoma and Intraocular Pressure?
A series of studies have now shown that cataract surgery tends to lower intraocular pressure (IOP). What does that mean for you? Let’s start with an explanation of what pressure does to your eye. The eye is a thin walled ball. If your eye did not have pressure higher than the air in the atmosphere it would collapse like a popped balloon. The air around us, by convention, has a pressure of 0. In a healthy eye, the IOP has from 10-21 mmHg of pressure. The eye needs to have some pressure, but if the pressure gets too high it can damage the fragile nerves responsible for vision. Glaucoma is an eye disease where the IOP is too high so patients take eye drops every day to lower the IOP.
The good news is that cataract surgery does tend to lower the IOP for many patients. In the OHTS study, 63 eyes of 42 patients had cataract surgery. Their IOP was compared to 743 other individuals of similar age that did not have cataract surgery. When they combined all of the data they found that the mean IOP decreased by 4 mmHg in those that had cataract surgery. The amount the IOP changed varied from one patient to another, but those with a higher IOP to start with, tended to have a larger drop in eye pressure. This is also great news because those with the higher eye pressures tend to be the ones that need the most help!
In the OHTS study this IOP lowering effect decreased very slowly over time but was still present at the end of the study three years later. In a study by Dr. Brooks Poley, et al. published in 2009, they also found that the IOP was lowered by cataract surgery and that those with higher starting IOP’s tended to have the greatest IOP reduction. They followed patients for an average of 4.5 years after their surgery and did not see the effect decrease significantly over time.
Patients with glaucoma need to be followed closely after cataract surgery as occasionally, the IOP rises for a few weeks before the longer term IOP lowering effects kick in. All put together, it is great news that on average, cataract surgery lower the IOP, the IOP lowering tends to be greater in those with the highest IOP, and that the effect tends to last a long time. Some glaucoma patients need even more IOP lowering than what cataract surgery alone can provide so other procedures can be done at the time of cataract surgery to reach their specific goals. I have attached an interview I gave on this subject at the national ASCRS meeting in San Francisco recently. http://ewreplay.org/ASCRS2013/sunday#