In Hyphema, Suspect Red Cell Sickling
By Caroline Helwick
Elsevier Global Medical News
NEW ORLEANS - In patients with hyphema, sickling of red blood cells should be suspected, especially in African Americans and persons of Mediterranean descent, and prompt action taken to prevent vision loss.
Even a small percentage of sickled cells can produce ocular hypertension, leading to secondary optic nerve atrophy and retinal artery occlusion, said Dr. Morton F. Goldberg.
This condition is seen with "garden variety hyphema" caused by trauma or occurring postoperatively, Dr. Goldberg said in the inaugural Helen Keller Lecture, sponsored by the American Society of Ocular Trauma, at the annual meeting of the American Academy of Ophthalmology.
The normal anterior chamber environment has lower oxygen content than that in circulating blood or in viscera, and a higher concentration of ascorbic acid. Both conditions induce and maintain sickling of red blood cells.
"It is fair to conclude that aqueous humor is the most noxious fluid in the body, as far as sickling is concerned," he noted. "And there is something very deleterious about a hyphema associated with this," added Dr. Goldberg, former director of the Wilmer Eye Institute, Johns Hopkins University, Baltimore, where he is currently the Joseph E. Green Professor of Ophthalmology.
Sickled cells are dangerous in the anterior chamber because they obstruct outflow of aqueous humor and lead to ocular hypertension that is more prolonged and severe than with nonsickling cells. In the presence of sickled cells, even mild elevations of intraocular pressure (less than 30 mm Hg, for example) can lead to irreversible optic atrophy because vascular perfusion is already low and is easily made worse, he said.
This has been shown in vitro and in vivo and is an invariable phenomenon. In a rabbit model of hyphema, animals injected with sickled cells, compared with those who weren't injected, had a longer duration of hyphema (10 vs. 8.6 days) and intraocular pressure elevation (3.6 vs. 1.4 days), and a higher likelihood of spontaneous rupture (P less than .05 for all three).
The potential for this disaster is not limited to persons with actual sickle cell disease, but is also seen in individuals with sickle trait. "In this situation, sickle trait is just as dangerous as the systemically severe hemoglobinopathies," Dr. Goldberg said. The sickle gene is carried by up to 10% of blacks in the United States.
"In these patients, one does not usually suspect secondary optic atrophy because the optic nerve is not visible when there is a blood clot in the anterior chamber. But once the blood clot clears and one sees through the anterior chamber to the optic nerve, there comes the nasty surprise," he said.
Red blood cells preferentially sickle in the aqueous humor, while they may not be observed at all in the venous blood. This occurs because the rigid, elongated sickled cells cannot easily escape from the anterior chamber through the trabecular meshwork to enter the conventional up-flow channels, he explained.
Sickling is not identified via slit lamp examination, but by a routine sickle-cell solubility test, for which same-day results are available in most hospitals.
Once diagnosed, patients should be hyperoxygenated with a face mask as well as with a transcorneal delivery system. They should be promptly started on standard antiglaucoma medications, including β-blockers, α-agonists, prostaglandins, osmotics (once a day only), and carbonic anhydrase inhibitors such as methazolamide (Neptazane) rather than acetazolamide (Diamox).
The therapeutic goals are to avoid optic nerve ischemia, infarction, and atrophy; macular ischemia, infarction, and atrophy; and central or branch retinal artery occlusion.
If these antihypertensive measures are ineffective, clinicians should follow the "24 for 24 rule": If the average intraocular pressure is greater than 24 mm Hg for any consecutive 24 hours, intervene immediately and aggressively with paracentesis, which is usually curative, Dr. Goldberg said. "Although there are no controlled studies, validation of this therapeutic recommendation is derived from numerous reports in the literature and my personal observation. . . . The only caveat is to do it slowly so as not to decompress the eye," he added.