3224 The law of the principal retinal planes: The function of the extraocular muscles is to maintain the principal retinal planes coplanar in all gaze directions

Oculomotor disturbances commonly occur as manifestations of Graves’ Oohthalmomthv. We investieated the outcome of this disorderfollowing e&ernal-beam orbital radiotherapy. We conducted a prospective study on 15 patients to assess the extent of ophthalmopathy by clinical evaluation, and measurement of the amplitude of gaze and the thickness of the extraocular muscles on computed axial tomography (CAT-scan) before and after orbital radiotherapy. This paper reports the results of this study and the effects of radiotherapy on the extraocular muscles are discussed.