This retrospective case series found that hyphema can occur months to years after ab interno trabeculectomy with the Trabectome, even in the absence of further ocular surgeries or trauma, and that the hyphema is likely caused by exertion or sleeping on the surgical side.
The Trabectome (Neomedix Corp) is a novel surgical device that reduces IOP by ablating a segment of trabecular meshwork and the inner wall of the Schlemm canal. Partial removal of these tissues results in a significant increase in outflow facility. However, removal of these tissues also is assumed to result in a permanent opening in the blood-aqueous barrier. Although intraoperative blood reflux is common, delayed-onset hyphema in the absence of further ocular surgeries or trauma has not been reported previously.
The authors reviewed the charts of all patients who underwent ab interno trabeculectomy using the Trabectome at the Mayo Clinic over a four-year period. Of 262 cases, there were 12 cases of delayed-onset symptomatic hyphema (4.6 percent).
The median time to onset of hyphema was 8.6 months after surgery (range, two to 31 months). Symptom onset commonly occurred on awakening. The most common characteristic was sleeping on the surgical side. Most hyphemas resolved within one to two weeks, except for one patient who required trabeculectomy for a refractory IOP spike.
They write that two likely mechanisms seem to explain most of these cases. First, physical exertion in some patients may result in an elevation of episcleral venous pressure to a level greater than IOP and may cause reflux of blood from the venous system into the anterior chamber. Second, ocular compression from sleeping on the surgical side may result in a temporary elevation of IOP with a slow decrease back to baseline as the compressive object (e.g., a pillow) is held in place. When the compressive force is removed, the IOP would decrease suddenly. In some patients, the magnitude of the decrease may result in an IOP less than episcleral venous pressure, and blood may reflux into the anterior chamber.
The authors note that if the blood-aqueous barrier is open after Trabectome, it is not clear why more patients do not experience late hyphemas. One possibility is that a healing response in most patients results in closure of the blood-aqueous barrier. It is also possible that the proportion of delayed-onset hyphemas is higher than the number reported in this case series because this series included only patients with symptomatic hyphemas confirmed with slit-lamp examination. Other patients may describe vague symptoms of intermittent foggy vision or a transient film over the vision on waking up, but do not obtain an eye examination at the time of symptoms. Also, asymptomatic microhyphemas may occur, but they were not identified in this series.
The authors conclude that symptomatic patients should identify and avoid these associated triggers because delayed-onset hyphema may be associated with intermittent IOP spikes that may require medical or surgical treatment.