Eyeworld

EW CATARACT 27 Diplopia was associated with congenital superior oblique palsy, confirmed via imaging M RI tests are commonly used to help diagnose and monitor organs of the chest and ab- domen, pelvic organs, blood vessels, and breasts, but new research has found a unique use in ophthalmology: determining the cause of diplopia. In a letter to the editor of Graefe's Archive for Clinical and Exper- imental Ophthalmology, published online in December 2010, Jeong- Min Hwang, M.D., Department of Ophthalmology, Seoul National Uni- versity College of Medicine, South Korea, reported an episode of binoc- ular diplopia after cataract surgery caused by congenital superior oblique palsy, as revealed by an MRI. "Congenital superior oblique palsy could be the cause of atypical very-late-onset diplopia that devel- ops in patients in their 70s after cataract surgery, and MR [magnetic resonance] imaging could be helpful in attaining the correct diagnosis," Dr. Hwang noted. Scanning for a diplopia cause Specifically, researchers discovered a 77-year-old man who developed diplopia after cataract surgery, which lasted for the 6-month follow-up pe- riod. This patient had no history of strabismus, head trauma, or diplopia. The patient had undergone pha- coemulsification with topical anes- thesia in the left eye. A posterior chamber IOL was implanted via clear corneal incision. Five weeks later, the same procedure was per- formed on the right eye. Visual acuity was 20/20 in both eyes when the patient was exam- ined. "He showed a head tilt to the left, and asymmetric face with the right fuller face," Dr. Hwang re- ported. "He had exotropia of 25 prism diopters (PD) and right hyper- tropia of 16 PD in the primary posi- tion, exotropia of 20 PD and right hypertropia of 16 PD in the right gaze, and exotropia of 25 PD and right hypertropia of 25 PD in the left gaze." Further, the patient had ex- otropia of 30 PD and right hyper- tropia of 18 PD with head tilt to the right. When the head was tilted to the left, he showed exotropia of 20 PD and right hypertropia of 16 PD. "He showed right superior oblique underaction and inferior oblique overaction," Dr. Hwang re- ported. MRI testing was performed using a 3-Tesla system. Researchers used the MRI to perform high-reso- lution imaging of cranial nerves in the brain stem. "Severe hypoplasia of the right superior oblique muscle was ob- served, and the right trochlear nerve was not identified in the perimesen- cephalic cistern," Dr. Hwang re- ported. Dr. Hwang found the results to be highly significant. "This case re- port is important for two reasons: Firstly, it indicates that diplopia as- sociated with congenital superior oblique palsy could develop during very late stages of life, i.e., when an individual is in their 70s," Dr. Hwang noted. "Secondly, it shows that the cause of diplopia associated with congenital superior oblique palsy can be verified by the absence of the trochlear nerve on high-reso- lution MR images of the cranial nerves. Even though consistent visu- alization of the trochlear nerve is the most challenging task owing to its small size, we could visualize the trochlear nerve in 100% of the con- trol individuals examined by using MR imaging with the highest possi- ble resolution." Researchers ruled out the possi- bility that the diplopia was anesthe- sia-related. "Extraocular muscle damage may be the most common cause of binocular diplopia after local anesthesia," Dr. Hwang noted. "In this patient, the cataract surgery was performed under topical anes- thesia. Therefore, the possibility of local anesthetic-induced myotoxic- ity was eliminated. Further, the re- sults of a three-step test were positive, and facial asymmetry sug- gesting a long-standing superior oblique palsy was noted." John D. Sheppard, M.D., pro- fessor of ophthalmology, microbiol- ogy, and immunology, Eastern Virginia Medical School, Norfolk, Va., interestingly added that supe- rior oblique palsy sometimes also can be caused by blunt head trauma or by vascular occlusive disease. "These etiologies can be ob- served for a period of time, monitor- ing for spontaneous resolution" Dr. Sheppard said. "This is all the more reason to be somewhat less paranoid [about the condition]." The use of an MRI to weed out the problem, while not highly eco- nomical, could help give patients a definitive diagnosis, thereby elimi- nating excessive subsequent inter- ventions, Dr. Sheppard said. Fortunately, post-op diplopia re- sulting from retrobulbar injections or intraoperative trauma has dimin- ished, Dr. Sheppard said. "Diplopia in those cases is more transient if related to retention time of the anesthetic agent," Dr. Sheppard said. "But physicians still need to be aware of the complica- tion that follows retrobulbar anes- thesia. There are modifications now in retrobulbar blocks that constitute a peribulbar approach, thus dimin- ishing the possibility of nerve injury, however rare. Modified injection techniques decrease complication rates." EW Editors' note: Dr. Hwang has no finan- cial interests related to this study. Dr. Sheppard has no financial interests related to his comments. Contact information Hwang: hjm@snu.ac.kr Sheppard: 757-622-2200, docshep@hotmail.com by Matt Young EyeWorld Contributing Editor New MRI use: Determining the cause of diplopia July 2011 Innovations continued from page 26 tage in that we can keep the cost of the device down and additionally allow steep subsidies for developing countries. Thus we can conduct our KPro development with substantial resources and a large number of re- search fellows. Dr. Henderson: Did you have many critics of the keratoprosthesis when you first introduced it? Dr. Dohlman: Perhaps some but more skeptics. This was for good rea- son considering the dismal history of keratoprosthesis in the past. At that time, infections, extrusions, and loss of eyes were extremely common and the whole scene was very dis- couraging, even as recently as 20-30 years ago. Fortunately, we are now in a much better position, even if smaller categories, like the autoim- mune diseases, are still problematic. Whatever success we have had should be credited to my staff col- laborators and my many research and clinical fellows over the years. It has been a group effort. It has been laborious but also challenging and fun. EW Contact information Dohlman: claes_dohlman@meei.harvard.edu

• Cover