High-Resolution Magnetic Resonance Imaging (MRI) QuantifiesOculomotor Nerve (CN3) Size in Congenital Neuropathic Stra-bismusKey Hwan Lim1, Elizabeth C. Engle3, Joseph L. Demer1,2; 1JulesStein Eye Institute, and 2Department of Neurology, David GeffenMedical School, University of California, Los Angeles, CA; 3Chil-dren’s Hospital Boston and Harvard Medical School, Boston, MAIntroduction: High-resolution MRI can now directly demonstrateinnervation to extraocular muscles and quantify optic nerve size. Wedeveloped a quantitative MRI technique to study CN3 and applied itto congenital fibrosis of extraocular muscles (CFEOM), congenitaloculomotor palsy, and Duanes retraction syndrome (DRS). Meth-ods: Oculomotor nerves were imaged at the brainstem using a 1.5-Tscanner and conventional head coils, acquiring heavily T2-weightedoblique axial MRI planes 1 mm thick parallel to the optic chiasm.We investigated 13 normal subjects, 10 subjects with DRS, 7 withCFEOM, and 3 with congenital CN3 palsy. Digital image analysiswas used to measure CN3 diameter, which was correlated withmotility findings. Results: CN3 was bilaterally hypoplastic in fivepatients with CFEOM. Mean (�SD) CN3 diameter in CFEOM was1.11 � 0.79 mm, significantly smaller than normal diameter of2.01 � 0.36 mm (P � 0.05). CN3 size variably correlated withclinical function. Mean CN3 diameter in congenital CN3 palsy wassubnormal at 1.28 � 0.46 mm. One patient with DRS showedunilateral CN3 hypoplasia. Mean CN3 diameter in DRS was 1.78 �0.52 mm, slightly but not significantly subnormal. Conclusion: CN3hypoplasia is quantitatively demonstrable using conventional MRIequipment in several forms of congenital neuropathic strabismus,including CFEOM and oculomotor palsy, and occasionally occurs inDRS. Quantitative, high-resolution MRI might be useful to clarifymechanisms of strabismus in clinically uncertain cases. Reference:Karim S, et al. Demonstration of systematic variation in humanintraorbital optic nerve size by quantitative magnetic resonanceimaging and histology. Invest Ophthalmol Vis Sci 2004;45;1047-51.

The Effect of Laryngeal Mask Airway Insertion on IntraocularPressure Measurement in Children Under General AnesthesiaMay K. Lim MRCOphth,1 Patrick O. Watts MBBS, MS, FRCS,FRCOphth,2 Achyut Mukherjee MRCOphth,1 Trevor Armstrong,2

Rhys Jones,2 Tazin Zatman2; 1Cardiff Eye Unit, University Hospitalof Wales, Cardiff, South Glamorgan, UK; 2Department of Anesthe-sia, University Hospital of Wales, Cardiff, South Glamorgan, UKPurpose: We aim to study the change in intraocular pressure (IOP)in children under general anesthesia, before and after laryngeal maskairway (LMA) insertion. From this we aim to recommend theoptimal timing of performing IOP measurements in these cases.Method: Intraocular pressure was measured in children after induc-tion and 1 minute after LMA insertion. Children (age �16) sched-uled to undergo elective ophthalmic surgery under a general anes-thetic were included. Children with a history of glaucoma or previ-ous intraocular surgery were excluded. Data were collected on theage of the child, the IOP, heart rate (HR), end-tidal CO2, and bloodpressure (BP), before and after LMA insertion. Results: Seventy-seven children with a mean age of 5 � 3.5 years (range: 4 monthsto 13 years) were included in the study. The mean IOP was 13.5 �4.0 and 13.8 � 4.6 mm Hg prior to LMA insertion and 15.5 � 4.0and 15.5 � 4.8 mm Hg after insertion of the mask in the right andleft eye, respectively (P � 0.000). A change in BP was significantlyassociated with an increase in IOP (P � 0.007) and the interactionbetween the change in the BP, HR, and CO2 affected the change inIOP measured after insertion of the LMA (P � 0.01). Conclusion:In our study, a small but significantly higher IOP was found afterLMA insertion than before. It is recommended that the measurementof IOP in children under general anesthesia be carried out before theinsertion of the LMA.

The Epidemiology of Pediatric Cataracts—The Toronto Expe-rienceZena Lim, Shehla Rubab, David S. Rootman, Alex V. Levin; TheHospital for Sick Children, Toronto, Ontario, CanadaIntroduction: To better characterize the epidemiology and outcomerelated to pediatric cataracts and to compare the success of cataractsurgery and visual prognosis between different subgroups. Meth-ods: Retrospective review of all charts of children who presented atthe Hospital for Sick Children, Toronto with cataracts from January1992 to December 2002. Results/Discussion: Identified were 1122eyes in 778 children; 44.5% of cases were bilateral. Posterior sub-capsular cataract was the most common morphological form(37.2%), followed by dense (21.0%) and nuclear cataract (15.6%).The etiology was idiopathic in 30.5%, and 26.2% were associatedwith systemic disease. Down syndrome was the most common ofcataract-associated syndromes. The median age at surgery was 36.0months. Follow-up from time of surgery ranged from 0.03 to 180.0months. In the group that underwent lens extraction and intraocularlens implantation, 54.0% achieved a final visual outcome of 6/9 orbetter. In the group that was left aphakic, 19.3% achieved a similaroutcome with visual rehabilitation. Glaucoma developed in 13.0%of eyes that underwent cataract surgery. IOL implantation wasassociated with a lower incidence of glaucoma. The incidence ofstrabismus was lowest in the group of children with intraocular lensimplantation and highest when contact lens was used for visualrehabilitation (P � 0.001). Eighty-seven cases (15.3%) requiredreoperation. There was no difference in the incidence of glaucomabetween cases that required reoperation and cases that underwentsurgery once. Conclusions: This study provides useful epidemio-logical data from a large, diverse population of children. It providesa better insight into the factors influencing treatment outcome.

Central Corneal Thickness in Children with Glaucoma or atRisk for GlaucomaJuan P. Lopez MD, Alex V. Levin MD, MHSc, FRCSC,Sharon F. Freedman MD, Kelly W. Muir MD, Lois Duncan; TheHospital for Sick Children, Toronto, Ontario, CanadaIntroduction: Tonometry readings may be artificially high whencentral corneal thickness (CCT) is elevated and low when CCT isdecreased.1 Little is known about CCT in pediatric glaucoma or eyesat risk for glaucoma (eg, aphakia, aniridia, uveitis).2 Methods:Children 18 years old were studied retrospectively and prospectivelyat The Hospital for Sick Children and Duke University from De-cember 2003 to March 2005. CCT was obtained by ultrasoundpachymetry awake or under general anesthesia/sedation. Results:Included were 332 eyes from 271 children [mean age 6.66 years (0.7months to 17.9 years)]: 141 eyes (42.46%) with glaucoma, 76(22.89%) at risk for glaucoma, 49 (14.75%) unaffected fellow eyes,and 66 (19.87%) control eyes. CCT was higher and Aphakic eyeshad thickest corneas [CCT � 0.635 mm (0.387 to 0.850 mm)].Using adult nomograms3 for adjusting IOP according to CCT,69.87% of eyes adjusted downwards and 23.79% adjusted upwards.Of glaucoma and at risk eyes, 13.82% were adjusted below IOP �21 and 1.38% were adjusted above, indicating a possible need forchanging clinical management. As pediatric CCT values extendbeyond the adult normogram, we present a new normogram forvalues in excess of 0.645. Discussion: This is the largest series ofCCT in children with glaucoma or at risk for glaucoma. Our datasuggest clinically significant adjustment of IOP may be needed inmany children. References: 1. Whitacre MM, et al. Am J Ophthal-mol 1993;115:592-6. 2. Hussein MA, et al. Am J Ophthalmol2004;138:744-8. 3. Doughty MJ, et al. Surv Ophthalmol 2000;44(5):367-408.

Journal of AAPOSVolume 10 Number 1 February 200688 Abstracts