Hypotony more than just a number; consider symptoms during therapy

August 7, 2019

While numerous techniques are available to surgeons, awareness is important

Managing hypotony is not based on the intraocular pressure alone. Symptoms are a big consideration and must be accounted for during treatment.

Reviewed by Eydie G. Miller-Ellis, MD

Hypotony, low IOP after surgery, can have an adverse impact on a patient’s vision. It is defined as an IOP of 5 mm Hg or less and generally occurs in the early postoperative timeframe, during periods of overfiltration. It can last for a few weeks. Chronic hypotony, while not uncommon, is another ball of wax because it can persist for longer than three months postoperatively.

The Tube versus Trabeculectomy Study found that about 13.5% of patients had chronic hypotony, but only about half experienced associated adverse effects, according to Eydie G. Miller-Ellis, MD, chief, Glaucoma Service, and professor of Clinical Ophthalmology, Scheie Eye Institute, University of Pennsylvania Perelman School of Medicine, Philadelphia. Numerous techniques are available to avoid chronic hypotony, but Dr. Miller-Ellis noted that awareness of the condition is important.

“We are concerned with choroidal expansion, which occurs when the IOP is lower than the intravascular pressure, and there is an elevated risk of choroidal detachment, hypotony maculopathy, and other associated complications,” she pointed out.

Not everyone has adverse effects as the result of an IOP below 5 mm Hg. Some patients can feel well in that scenario. On the flip side, clinical hypotony is the scenario in which a patient with low IOP experiences associated visual or ocular side effects, Dr. Miller-Ellis explained.

Monitoring IOP

When patients have progressive disease at IOPs of 12 or 15 mm Hg, clinicians want to establish an IOP at a level low enough to decrease the stress on the lamina and the retinal nerve fibers to preserve the vision and possibly improve the blood flow. However, while the not-too-low IOP value makes the clinician happy, he or she has to be concerned about how the patient is feeling and rule out any associated complications.

The signs associated with choroidal expansion- shallowing of the anterior chamber, choroidal detachment, choroidal hemorrhage, long-term hypotony maculopathy-are issues.

“The bigger concerns, even in patients who do not have visible choroidal detachments or hypotony maculopathy, are that they can have blurred fluctuating vision and some ocular discomfort,” Dr. Miller-Ellis said. “When the IOP is low, the globe can become deformed with every blink or eye rubbing and they develop visual symptoms based on that.”

Hypotony resulting from a big bleb can also cause bleb dysesthesia-dry eye or tear film disruption- which is even more problematic for many patients.

Risk factors

One complication, hypotony maculopathy, tends to develop more often in association with male gender, younger age, myopia, after a primary filtering surgery, in a phakic patient, and in Caucasians. Choroidal detachments tend to occur more often in older patients and shorter eyes, Dr. Miller-Ellis explained.Cases

Dr. Miller-Ellis described a representative case of a 54-year-old Caucasian man with pigmentary glaucoma, 4.0 diopters of myopia, and a corneal thickness of 520 μm.

The patient underwent bilateral trabeculectomies with mitomycin C in 2005 and 2006. The IOP remained under control until 2013, when it began to increase to the upper teens in one eye. The IOP increase was refractory to medical therapy. Bleb needling resulted in an IOP of 1 mm Hg. Months after the needling, the IOP remained low, between 2 and 3 mm Hg.

The patient’s vision was “quite good,” (20/25) without choroidal effusions or hypotony maculopathy despite the patient reporting some visual fluctuations and slightly less ocular comfort than the fellow eye that were not problematic for him. A second case was that of a 70-year-old Caucasian woman who had undergone trabeculectomy with mitomycin C in the right eye four years earlier.

The IOP in that eye was 8 mm Hg. The vision was 20/20 and the visual field was stable. There was no evidence of dellen. Despite the excellent clinical picture, the patient was extremely uncomfortable as a result of a persistent foreign body sensation. The patient had been referred for surgery in the other eye, but she refused because of the status of the right eye.

“Even if the corneal surface is good and there is no evident choroidal expansion, treating the surface disease is necessary to increase the patient’s comfort before another intervention is considered,” Dr. Miller-Ellis explained.

The third case was that of an 80-yearold African-American woman who underwent a phaco-trabeculectomy and had an initial IOP of 4 mm Hg with a shallow anterior chamber. By six weeks postoperatively, the IOP remained low but the anterior chamber had deepened and at six months postoperatively the IOP was 5 mm Hg.

The outcome was good, with 20/25 vision, no choroidal expansion, and a deep anterior chamber. The last case was that of a 69-year-old Caucasian woman who underwent a trabeculectomy with mitomycin C 13 years earlier. The bilateral IOPs were 4 mm Hg, but she complained of poor vision with acuities of 20/80 and 20/25 in the right and left eyes, respectively, with mild cataracts.

The refraction was moderate myopia with a corneal thickness of 510 μm. The patient had turned down bleb revision surgeries on multiple occasions. Dr. Miller-Ellis recounted that the patient had significant bilateral hypotony maculopathy with folds extending through the macula to the periphery. Over time, the vision has deteriorated further because of the cataracts.

However, there is little chance of the vision returning to normal with IOP normalization since the maculopathy is longstanding, but cataract surgery might provide some improvement.

When you consider how low the IOP can go, Dr. Miller-Ellis noted that the ideal goal might be between 8 to 12 mm Hg because you can maximize the protective effect of the IOP and maintain functional vision. “Even without choroidal detachments or hypotony maculopathy, we must focus on the patients’ symptoms,” she concluded.

“They need to feel well in order to accept that the surgery has been successful for them. While risk factors can be identified in our patients, they are individuals and can be unpredictable.”

Disclosures:

Eydie G. Miller-Ellis, MD
E: eydie.miller-ellis@uphs.upenn.edu
Dr. Miller-Ellis has no financial interest in any aspect of this report