Decreased Bell's phenomenon after inferior and medial orbital wall decompression in thyroid-associated ophthalmopathy: a double-edged sword in management of the patients.

Purpose: To evaluate the changes in Bell's phenomenon after inferior and medial orbital wall decompression in patients with thyroid-associated ophthalmopathy (TAO).

Methods: This prospective interventional study included patients with moderate to severe non-active TAO, who underwent inferior and medial wall orbital decompression. Bell's phenomenon and adjusted Bell's phenomenon were evaluated at baseline and six months after surgery. Bell's phenomenon was assessed by holding the upper lid open during forced eyelid closure. Afterwards, the upward excursion, the distance between lower eyelid margin and lower corneal limbus, was measured. Adjusted Bell's phenomenon distance is defined as the difference between margin reflex distance two (MRD2) and Bell's phenomenon distance.

Results: Thirty TAO patients, including 15 males (50%), with a mean age of 43.6 ± 11.6 years, were enrolled. The distance of Bell's phenomenon significantly decreased after surgery by an average of 3.25 ± 1.57 mm (P < 0.001). In addition, the difference between pre- and post-operative distance of adjusted Bell's phenomenon was - 1.58 ± 2.13 (P < 0.001) corresponding to the worsening in the adjusted Bell's phenomenon.

Conclusion: The result of our study demonstrated that Bell's phenomenon decreases significantly after inferior and medial wall decompression, which could be considered a complication of this form of orbital wall decompression in TAO.