1. “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:

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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)