A complaint of double vision after cataract surgery can be disturbing not only for patients, but also for their physicians, who have to find the root cause of the symptom.
At Hawaii 2004: The Royal Hawaiian Eye Meeting, Mitchell B. Strominger, MD, noted that he typically sees about three or four cases of postcataract-extraction diplopia each week. Estimates in the literature place the rate of the complication at 10% of cataract surgeries, or what would work out to be about 100,000 cases each year, he said.
“The biggest thing is surprise after the cataract surgery,” he said. “If you don’t talk to your patients about it, it can really be distressing, and it can sometimes lead to litigious problems.”
Taking a careful history can help distinguish surgically induced diplopia from an existing condition that may have gone unrealized as the lens opacity progressed.
“I feel that double vision in adults is neuro-ophthalmic until proven otherwise because those are the really serious problems,” Dr. Strominger said at the meeting.
Neurologic or myogenic problems tend to be paretic in nature while, in more common problems (such as thyroid disease, trauma to the orbit, or surgery), eye movement is more restricted. Simple tests of forced duction and forced generation can help distinguish one type from the other, Dr. Strominger said.
He cited a study in the American Orthoptic Journal that found unrecognized systemic disorders, such as fourth nerve palsy, thyroid orbitopathy, Parkinson’s disease or stroke, accounted for about one-third of postcataract extraction diplopia cases in a population of 23 patients.
“The medical history is actually important,” Dr. Strominger said. “Rule out compressive optic neuropathy. Check their visual acuity, color, pupil examination, and look at their visual fields.”
Diplopia in strabismus
Another one-third of cases in the study resulted from a loss of fusion in strabismus patients. According to Dr. Strominger, these patients can develop reverse ocular dominance when their formerly strabismic eye becomes the dominant one.
“What happens is that your cataract is worse in your strabismic eye. So you take that cataract out and now all of a sudden that eye is your better seeing eye, and you’re starting to use that eye that was your nondominant eye now as your dominant eye, and you’re shifting your whole scotoma outside center,” he said.
He noted that one possible solution would be a bilateral cataract extraction, which would restore 20/20 and allow the patient to shift dominance back to the stronger eye.
The final one-third of patients in the study had acquired double vision during the cataract extraction procedure itself. Diplopia can result when the superior or inferior rectus muscles are injured either by the bridle suture or the anesthetic needle, Dr. Strominger said.
He noted these patients typically present with a vertical deviation of less than 4 DD, and that the injury is sometimes evident to the surgeon intraoperatively; the muscle might swell, for instance, if a ciliary vessel is lacerated.
He cited a study in which Capo and colleagues analyzed 28 patients with vertical diplopia that could not be explained by any existing systemic or functional conditions.
Their results showed that 89% of patients had either overactive or restrictive muscles due to an intraoperative injury. Patients were equally likely to have an inferior rectus as a superior rectus muscle injury, he said.
In 21 patients where investigators could determine the method of anesthesia administration, peribulbar and retrobulbar blocks were equally common, Dr. Strominger said. However, when patients received peribulbar anesthesia, they were 4.8 times as likely to have an inferior, rather than superior, muscle injury.
The investigators next performed retrobulbar injections on cadaver eyes to determine how the injuries were caused.
“They found that both the superior and inferior muscles could be injured with a 1.5-inch needle, and it was possible to reach the superior rectus muscle from the inferotemporal area without transecting or injuring the optic nerve,” he said. “So the side effects of retrobulbar anesthesia can be multiple.”
These side effects include direct injury to the vascular supply or to the nerve, restriction of the inferior rectus muscle, or paresis of the superior rectus muscle, he noted. The antibiotics themselves can also be myotoxic, causing temporary or permanent inflammatory responses, he added.
“So how do you prevent this? Well, you could use subtenon’s anesthesia with a blunt cannula. You could do topical anesthesia, or you could … avoid antibiotic injection when you do your subconjunctival injections over the inferior rectus muscle,” Dr. Strominger said.
For diplopia of less than 6 D, Dr. Strominger noted that he typically grinds or attaches a press-on prism into the patient’s glasses. If prisms fail to correct the problem, he then suggests surgery, or more rarely, an occlusion patch or contact lens, he said.
For Your Information:
- Mitchell B. Strominger, MD, can be reached at the Department of Ophthalmology, New England Medical Center, 750 Washington St. #450, Boston, MA 02111; 617-636-6769; fax: 617-636-3305; e-mail: email@example.com.
- Capo H, Roth E, et al. Vertical strabismus after cataract surgery. Ophthalmology. 1996;103:1521-2.