Principles and general strabismus surgical rules in cyclovertical eye muscle palsies

Cyclovertical muscle palsies are very common. We propose rules that help clinicians and resident physicians diagnose easily the affected muscle. We simplified evaluation of the deviation by measuring it only in the cardinal directions of gaze and omit the oblique fields of gaze. Then the Beilschowsky forced head tilt test is done routinely along with measurement of the cyclotorsion by the double Maddox rod test. In oblique muscle palsy, when the vertical deviation is less than 15 prism diopters (PD), the procedure of choice is weakening of the direct oblique antagonist muscle. When the deviation is over 15 PD, the procedure of choice - unless there is spread of comitance - is to weaken, in addition to the antagonist oblique muscle, the contralateral inferior rectus (IR) muscle in superior oblique palsy (SOP) and the contralateral superior rectus (SR) muscle in inferior oblique palsy (IOP). In vertical rectus muscle palsy, the procedure of choice is to weaken the direct antagonist vertical rectus muscle alone when the vertical deviation does not exceed 15 PD. In case it exceeds 15 PD, a recess/resect procedure is done on the vertical rectus muscles. Horizontal rectus muscle transposition surgery is limited to total paralyses of the SR and IR muscles. Spread of comitance is more common in oblique muscle palsy than in vertical rectus muscle palsy. When it takes place, the incomitant vertical deviation in oblique muscle palsy becomes comitant and the rather comitant vertical deviation in vertical rectus muscle palsy becomes incomitant. When cyclotropia is associated with vertical deviation, proper surgery for the vertical deviation almost always corrects the clyclotropia. Isolated cyclotropia is extremely rare in cyclovertical muscle palsies. Despite careful observation to rule out bilaterality, and despite cautious surgery, an apparent palsy of the contralateral superior oblique (SO) may surprisingly and occasionally appear. Nevertheless, surgical overcorrection is not rare.