By Alon Kahana, MD, PhD (University of Michigan)

Ptosis (pronounced TOE-SIS, with a silent P) is caused by weakness of the muscles that open the upper eyelid. It can be referred to more colloquially as droopy eyelids, although droopy eyelids can also be caused by excess skin or brow drooping. In today’s blog, I will focus on the surgical approach to repairing ptosis by tightening of the eyelid muscle.

There are two muscles charged with elevation of the eyelid and one primary muscle charged with closing the eyelid. The two muscles elevating the eyelid are called the levator and Muller’s muscles. Levator muscle is a skeletal muscle that is embryologically related to the extraocular muscles that move the eye, and is similar to striated skeletal muscles that move our limbs. Muller’s muscle is a smooth muscle that is regulated by sympathetic innervation and responds to the level of adrenaline in the blood. It is Muller’s muscle that is responsible for the upper lids opening and retracting when we get very excited. The two muscles work in tandem and are intimately related to one another. Muller’s muscle appears to be primarily responsible for reflex lid elevation as well as triggering levator muscle, while levator muscle is responsible for the majority of the eyelid opening, particularly in primary gaze and in upgaze. Levator muscle also is responsible for maintaining the upper lid in a good position clearing the visual axis when a patient is looking down to read.

There are two general approaches to repairing an eyelid muscle that is weak or dysfunctional. One is to make an eyelid skin incision (usually at the lid crease), dissect down to the levator muscle, tighten it with sutures, and then close the incision. This technique, also called ‘external levator repair,’ requires that the patient be awake for the process of adjustment in order to achieve the optimal eyelid height, contour, and symmetry. Because the eyelid muscle is highly dynamic, such adjustments are absolutely essential to achieving optimal eyelid height, contour, and symmetry. The surgery is very effective and allows for repositioning of the eyelid crease, but can also lead to contour abnormalities and clearly requires participation by the patient.

Another approach to eyelid muscle repair is the internal ptosis repair. For historical reasons, this approach is commonly referred to as Mullerectomy. Indeed, the technique does end up removing a significant piece of Muller’s muscle (therefore, Muller-ectomy). However, it still appears to work primarily through tightening of the levator muscle. In that sense, it is not that different from the external levator approach. However, there are some specific advantages and disadvantages to the internal approach. On the disadvantage side, this approach will excise conjunctiva along with the muscles (basically collateral damage), and can only be used to elevate the lid by approximately 2 to 3 millimeters maximum. On the advantage side, the approach does not require patient cooperation because it follows a nomogram developed by Dr. Allen Putterman approximately 40 years ago. This nomogram correlates the amount of eyelid elevation with the response of the eyelid position to installation of eyedrops containing phenylephrine (a form of adrenaline).

Another advantage of the internal ptosis repair is that is it unlikely to change the position of the eyelid crease or contour of the eyelid. Therefore, it is particularly well-suited to correction of unilateral ptosis that is not particularly severe, as well as for patients with a limited lid crease, such as patients of Asian descent.

When being evaluated for eyelid drooping and told that the eyelid muscle is affected, an informed patient should ask the surgeon whether the approach would be an external approach requiring intraoperative adjustment, or an internal approach following a nomogram based on the response to phenylephrine installation. For most options, both options should be discussed openly.