Likelihood of Hering's Law After Ptsosis Surgery on One Eye

This question comes up frequently when patients present with with asymmetric or unilateral eyelid drooping. Naturally, it's a great question to sort out before surgery.

Putting a phenylephrine eyedrop in the droopier eye can simulate surgical elevation of the droopy eyelid. This usually gives a pretty accurate idea of what would happen with unilateral surgery.  Then your surgeon can discuss with you the merits of unilateral versus bilateral ptosis surgery. 

An experienced oculoplastic surgeon can surely help you weigh the options.

Hope this helps!

Mark Lucarelli, MD, FACS

Madison, WI

Answering this questions is a critical one for the oculoplastic surgeon.  Often someone will present with ptosis on one side and be advised to have ptosis surgery on both sides.  Herring's law says that both muscles that lift the eyelid get the same innervation.  So fixing the obviously ptotic side without addressing the other side can result in the "better" side looking heavy or ptotic after surgery.  Occasionally it is not clear if this will be the case.  Generally under these circumstances, it is appropriate to discuss this possibility so that one is prepared to have the second eyelid done if it should be necessary.

  This is truly an excellent question.  Unfortunately, there is no easy answer.  I try to carefully judge at the time of the consultation if a ptosis is truly unilateral or if there is bilateral but asymmetric ptosis.  I usually do a phenylephrine test to help me make this call but even after doing this for 26 years, I still get occasional (and unfortunate) surprises.  My simple answer is that if your ptosis was absolutely and completely unilateral to start with, I don't think the other eye will droop because of Hering's Law after unilateral surgery.