September 2009

 

CATARACT/ IOL

 

Ocular misalignment


by Matt Young EyeWorld Contributing Editor

   
While retrobulbar injections may have occasionally caused diplopia, the use of topical anesthesia may not eradicate this problem entirely Source: Gary L. Fanning, M.D.

While cataract surgery continues to undergo a refractive revolution to optimize visual outcomes, one uncommon problem—binocular diplopia (or misalignment)—threatens to cancel out visual improvements. A new study, published online in April 2009 in Graefe’s Archive for Clinical and Experimental Ophthalmology, reveals new details about this vision problem after cataract surgery and recommends solutions. “Ocular misalignment and diplopia following successful cataract extraction under topical anesthesia were uncommon [in our study], but disturbing to both the patient and the surgeon,” according to study co-author Jong Bok Lee, M.D., Department of Ophthalmology, Yonsei University College of Medicine, Seoul, South Korea.

Fortunately, there are solutions, including taking better patient history evaluations and avoiding certain types of anesthesia.

Solving the double vision problem

Dr. Lee analyzed 160 consecutive patients undergoing cataract surgery with topical anesthesia. Before surgery, 26 patients were found to have ocular misalignment. Five patients possessed exophoria while 21 had exotropia. Their mean angle of deviation overall was 7.2 +/–6.8 PD. Patients with diplopia pre-op benefitted from surgery. After the procedure, their angle of deviation improved statistically significantly to 5.4 +/–7.4 PD.

“This small change becomes meaningful when regarding patients themselves,” Dr. Lee reported. “We found three patients changed from exotropia to exophoria postoperatively, and one exophoric and three exotropic patients became orthophoric, even though 19 other patients had no change. The change of these seven patients who improved orthoptic status was 6.1 +/–1.4 PD.” Dr. Lee attributed these positive results to phacoemulsification improving the peripheral visual field.

Other patients in the overall study participant group, however, were not so fortunate. One day after surgery, 12 of 160 patients (8%) acquired ocular misalignment. Two months post-op, 7 of 131 patients (5%) still had it. However, none of these patients had symptomatic diplopia. Dr. Lee noted that ocular misalignment could occur in surgery through different means. They include muscle injury via needles, bridal sutures, or subconjunctival injections; muscle hemorrhage; and myotoxic effect from anesthesia. “Whatever the mechanism is, the muscle damage can produce ocular misalignment, and this is a prominent complication for a patient with good optical results after cataract surgery,” Dr. Lee reported. “In this study, cataract surgery was performed under conditions of minimum extraocular muscle damage; that is, with topical anesthesia and without any bridle sutures or subconjunctival injections. Thus, we can think that sensory deprivation by cataract or optical aberrations are the possible main causes in the development of the acquired ocular misalignment in our series.”

Retrobulbar anesthesia has been shown to be worse in terms of producing ocular misalignment, with as many as 22% of such patients experiencing ocular misalignment after cataract surgery, Dr. Lee noted. Dr. Lee therefore suggested that topical anesthesia is preferential to retrobulbar or even peribulbar anesthesia in terms of reducing the risk of ocular misalignment. To further reduce the risk of this complication, Dr. Lee recommended scrutinizing a patient’s medical history. It is especially important to evaluate diplopia, head tilting, amblyopia, strabismus, thyroid disease, diabetes mellitus, and extraocular muscle palsy, he noted. Two of the 7 patients in this series who developed ocular misalignment post-op had diabetes mellitus. “Furthermore, a pertinent preoperative orthoptic evaluation should be performed, and an adequate explanation regarding the incidence and the possibility of postoperative ocular misalignment and diplopia should be provided to the patients in the informed consent process,” Dr. Lee concluded. Ian Anderson, F.R.A.C.O., Subiaco Eye Clinic, Perth, Australia, has experienced the problems with ocular misalignment that cataract surgery can cause firsthand.

“You can create problems if you don’t properly assess patients beforehand,” Dr. Anderson said. “If, for instance, you have marked asymmetry in the biometry before the operation or a marked difference in refractive error, those are warning signs that a patient could have ocular problems after cataract surgery.” Patients who are found to have diplopia pre-op may also have it for different reasons. If patients have a muscular imbalance, for instance, then Dr. Lee recommended treating the cataract first and then treating the muscular imbalance. However, if a patient experiences diplopia for refractive reasons—high astigmatism and anisometropia, for example—then one must adjust the power of the IOL to minimize the imbalance. “If patients have diplopia before cataract surgery, usually you can make them happier,” Dr. Anderson said. “But if you cause them to develop diplopia, they can be the unhappiest patients you have dealt with.”

Editors’ note: Dr. Lee has no financial interests related to this study. Dr. Anderson has no financial interests related to his comments.

Contact information

Anderson: +61 8 6380 1855, ian@ianseyesite.net
Lee: 491209@yuhs.ac

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