Inverted Brown pattern A Tight inferior oblique muscle

“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 • 8 PD hypertropia in involved quadrant of downgaze • No more than 6 -7 PD of overelevation in adduction

Results • 12 pts – 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 7 pts (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 16 mo (7 wks to 5 yrs) – 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)