This is a review of five patients with upper lid ptosis or lid retraction secondary to large filtering blebs post-trabeculectomy. The authors review each case and apply a model to analyse the separate forces acting on the upper lid to explain, from a mechanical perspective, why the lid has retracted or become ptotic. They found that enlarged blebs can produce either lid retraction or ptosis depending on a number of factors, but the main determinant was the position of the bleb peak relative to the lid margin. A relatively high enlarged bleb exerts an additional net downward force on the lid and vice-versa. Other modifiable factors included the pull of the levator and Muller’s muscles, and the degree of canthal tendon laxity. Assessment of the relative contribution of these factors allows a targeted approach to correction of the lid position. Treatments include bleb revision, canthal tendon tightening, weakening or tightening of levator or Muller’s muscle either surgically or temporarily with botulinum toxin, and filler injection to add weight to the lid. Caution is required with ptosis surgery as a small elevation of a ptotic lid over an enlarged underlying bleb may shift the relative positions of bleb and lid margin resulting in lid retraction. In these circumstances, it may be impossible to achieve a normal lid position from lid surgery alone, and bleb revision may be appropriate. This is an interesting study of the forces acting on the upper lid, and demonstrates that a number of factors should be considered when assessing and treating lid malposition in these patients. Its main drawback is the small number of subjects.
Bleb-related changes in upper lid position
Reviewed by James Hsuan
A vector force model of upper eyelid position in the setting of a trabeculectomy bleb.
