BLOG: A guide to postop ocular hypertension
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It’s not unusual for us to have more than three dozen patients on our schedules the morning after a typical cataract surgery day. Because the vast majority are doing well 1 day postop, these are usually brief examinations.
The most frequent patient concerns – a swollen eyelid, a dry or swollen cornea, a few flickering lights to the side – can be addressed quickly with a smile and reassurance; they will almost always resolve with time and on their own.
Probably the most common adverse event seen early in the postop period that requires some form of treatment is ocular hypertension. Having a strategy on when and how to treat it can help avoid the rare but real complication of optic nerve damage and vision loss.
On average, IOP is about 3 mm Hg higher the day after surgery. While the incidence of postop ocular hypertension varies depending on the experience of the surgeon as well as the definition of elevated pressure, studies have found around a 12% to 15 % incidence of IOP equal to or above 26 mm Hg 1 day after cataract surgery. The percentage of those with pressures higher than 40 mm Hg at 1 day has been reported at more than 2% (Kim et al.). If you see enough postops at 1 day, you will occasionally encounter a very high pressure.
Cause of increased pressure
So why is the pressure high? Several mechanisms have been proposed, some of which make more sense than others. The catchall term “inflammation” is given as a one explanation, yet high postop IOP frequently doesn’t correlate with the number of anterior chamber cells. Furthermore, IOP is usually lower in anterior uveitis, not higher. so the physical clogging of the trabecular meshwork by inflammatory cells or fibrin leading to a decrease in aqueous outflow isn’t by itself a convincing explanation.
An explanation that does make sense is that phacoemulsification causes trauma to the trabecular endothelium and a subsequent decrease of aqueous outflow. We see a similar dramatic rise in IOP with few anterior chamber cells in patients with trabeculitis from Posner-Schlossman syndrome. If the vibration from phacoemulsification can lead to a temporary shock and inflammation of the corneal endothelium and subsequent transient corneal stromal edema, it makes sense that it could also lead to the same temporary loss of function in the trabecular endothelium as well.
A second cause is the ophthalmic viscosurgical device (OVD) used to keep the eye’s shape during surgery. More commonly called viscoelastics, these clear viscous gels, such as Viscoat (chondroitin sulfate, sodium hyaluronate, Alcon) and Healon (sodium hyaluronate, Johnson & Johnson Vision), fill the intraocular spaces, including the angle. While one of the last steps in cataract surgery is to remove the OVD by aspiration, occasionally a small amount of so-called retained viscoelastic can coat and block enough of the trabecular meshwork to result in elevated IOP. That small amount of retained viscoelastic is eventually metabolized within a day or so.
When to treat
If the pressure is high on the day after surgery, is there a level of IOP at which it absolutely should be treated? And if so, how?
If you ask a group of experts, most would probably agree that an IOP higher than 30 mm Hg should be treated in a patient with an otherwise healthy eye. But there are reasons for treating an even lower pressure.
The first is a patient with preexisting glaucoma and pseudoexfoliative glaucoma in particular. These patients have an optic nerve that is more vulnerable to damage from moderate pressure spikes of even a short duration, so it is sensible to aggressively treat any ocular hypertension. At what level? Anything higher than 25 mm Hg is a good threshold, maybe even lower in someone with advanced glaucoma.
The second is a patient in pain, particularly aching pain. While a comfortable patient with a pressure of 27 mm Hg doesn’t in itself require treatment, we’d likely treat if the patient is complaining of pain. The reason? IOP peaks at 3 to 7 hours after surgery. Given that we rarely check IOP until hours later, we rarely know what the highest pressure actually was. Still, there can be clues. The first is the presence of aching eye pain, particularly one that began a few hours after surgery and was slowly improving. The second is corneal edema, but particularly epithelial edema.
How to treat
After it has been determined that treatment is in order, the treatment selection depends on the severity of the situation. Let’s start with the most extreme and go from there.
Very high pressure, higher than 45 mm Hg or 50 mm Hg or so, is frequently accompanied by pain and even nausea similar to acute angle closure. It these situations, a quick lowering of IOP with a paracentesis or wound burp can bring rapid relief of symptoms and pressure.
To burp a wound, it’s important to locate the port incision, the small 1 mm or so corneal stab wound that the surgeon uses for entry of various accessory instruments. This is one reason to observe and learn your surgeon’s technique. After placing several drops of topical anesthetic along with fluorescein, a sharp instrument such as jeweler’s forceps or a hypodermic needle is gently pressed against the posterior lip of the port incision until aqueous begins to drain. Do not attempt to burp the main clear corneal or scleral incision. Measure the IOP frequently and burp slowly to a pressure down in the mid-teens.
One clue that significant pressure has been relieved is the near immediate reduction or even complete clearing of corneal epithelial edema.
Using burping alone, the pressure will likely return to a high pressure without further treatment, which should entail a combination of aqueous suppressants, such as two tablets of acetazolamide 250 mg along with brimonidine 0.2% and timolol 0.5% topically. Any significantly high pressure should be rechecked every 30 minutes or so to ensure that the treatment is effective. What is a safe pressure at which to discharge a patient? There’s no exact guideline, but below 35 mm Hg is suggested because even those with otherwise healthy eyes are at risk for central retinal vein occlusion with pressures above 35 mm Hg for several hours.
For patients presenting with IOPs of 35 mm Hg without pain or glaucoma, instilling a topical aqueous suppressant, such as brimonidine and/or timolol, usually is effective. Rechecking the IOP again 30 minutes later to ensure that the treatment is working is a safe strategy, but not mandatory in an otherwise healthy and comfortable eye. We usually prescribe the medicine according to the open angle glaucoma dosage then recheck between 1 day to 1 week, depending on the level of concern, or most likely, when it’s convenient for the patient to return. The treatment can be stopped once normal baseline preoperative IOPs have been reached.
References:
Falck A, et al. Acta Ophthalmol. 2009;doi:10.1038/eye.2011.93.
Kim YK, et al. Eye. 2011;doi:10.1038/eye.2011.93.
McKellar MJ, et al. Ophthalmology. 2001;doi:10.1016/s0161-6420(00)00431-0.
O'Brien PD, et al. Can J Ophthalmology. 2007;doi:10.3129/can j ophthalmol.06-086.