“Inverted Brown pattern”: A Tight inferior oblique muscle masquerading as a superior oblique muscle underaction – clinical characteristics and surgical management Guyton et al J AAPOS 2006; 10:565-572

Purpose To characterize and evaluate surgical management of patients with unilateral deficiency of depression in adduction i.e. SO underaction, without significant ipsilateral IO overaction

Methods Retrospective study Patients with diplopia in downgaze who had Ipsilat IO muscle weakening Contralat IR muscle recession Patients showed unilateral deficiency of depression in adduction, suggesting SO muscle underaction, with no or minimal IO muscle overaction 8PD hypertropia in involved quadrant of downgaze No more than 6-7PD of overelevation in adduction

Results 12 pts Exaggerated forced duction testing 3 had prev surgery for Brown syndr 4 had prev orbital floor trauma Exaggerated forced duction testing Recorded for 9 pts (other 3 not recorded) Tight IO muscle recorded for 7pts (78%), with no laxity of SO tendon

Results continued 12 pts 4 had contralateral IR muscle recession But in all 4, deficiency of depression in adduction recurred Ave FU 16mo (7wks to 5yrs) 8 had IO muscle weakening procedure IO recession (5) or IO denervation & extirpation (3) – for excessive tightness on exaggerated FDT Achieved overall improvement of ocular alignment 9 subsequent patients with similar pattern of misaligment treated with IO weakening Good results

Conclusions “Inverted Brown pattern” Caused by tight or inelastic IO muscle Treatment: IO muscle weakening procedure Even though no significant IO muscle overaction Better results than IR muscle recession

Discussion “Inverted Brown pattern” not the same as “Reverse Brown Pattern” “Reverse Brown Pattern” - Jampolsky coined the term to describe cases of Thyroid myopathy with asymmetric upgaze deficiencies due to asymmetric IR muscle tightening

Discussion “Inverted Brown pattern” inverted wrt Brown syndrome Difference: Y pattern sometimes seen in Brown synd No Y pattern in “inverted Brown pattern” Due to less side slip of IO muscle – firmly attached to IR muscle sleeve whilst more slip occurs with SO tendon causing Y pattern

Discussion Customary treatment for apparently underacting SO with no or minimal IO overaction Ipsilateral SO tuck or Contralateral IR recession Consider IO muscle weakening Good results (small numbers, no longterm follow-up) Analogous to Brown Syndrome Low complication rate (rare fat adherence syndrome)