By Alon Kahana, MD, PhD (University of Michigan)
For my first blog, I decided to talk about something that most oculoplastic surgeons consider fairly mundane; namely, droopy eyelids. Droopy eyelids are caused by the tissues of the eyelid interfering with the visual axis. This reduces the amount of light that enters the eye, causes a shadow over the light that does enter the eye, reduces peripheral vision, makes it harder to look up or maintain a clear visual axis in downgaze (reading position), and makes the eyelids feel heavy and tired.
From a surgical standpoint, droopy eyelids can be caused by one of three different mechanisms, or some combination of the three. These are: 1) dysfunction of the eyelid opening muscles, i.e. levator and Muller’s muscle; 2) excess skin hooding and draping over the lashes and eyelid margin to reduce peripheral vision and cause heaviness; and 3) brow and forehead drooping that causes the brows to droop and press down on the skin of the eyelids. It is quite common for two or even three of these mechanisms to coexist. The reason that understanding the mechanism of “eyelid droop” for each patient is so important from a surgical standpoint is that if surgery repairs just one of these causes, but the droopy eyelids were caused by two or even three of these mechanisms, then the result will be unsatisfying. It is, hence, critically important to achieve the correct diagnosis for the mechanism of droopy eyelids prior to engaging in surgery.
Here’s a fairly typical scenario to illustrate the issue. A middle aged patient presents with a complaint of droopy eyelids. Specifically, she complains that the skin of her upper eyelids drapes over her lashes and interferes with her peripheral vision. This is interfering with her ability to drive, reduces the amount of light that enters her eyes, and gives her a very tired feeling. Surgeons know that in order to blink properly and close one’s eyes, we all require approximately 20 millimeters of upper eyelid skin at a minimum. Let’s say that this patient’s upper eyelid skin measured 40 millimeters. That would make it double the norm. In that case, there would be a reasonable expectation that if 20 millimeters of skin were removed from the upper eyelid, the result will be improved peripheral vision and reduced weight on the upper eyelids. However, what if this patient’s upper eyelid skin only measured 28 millimeters, even when the lid is semi-stretched? In my experience, such a measurement suggests that there is more going on. The primary culprit might actually be the brows. You measure her brow position and it appears to be good. What is often missed is that the patient is actively trying to elevate the brows in order to reduce the eyelid skin hooding that is causing their symptoms. Therefore, the ideal way to measure the position of the brows is with the patient’s eyes lightly closed so they are not straining to see, which allows them to relax their forehead. With the forehead relaxed, the position of the brow and the contribution of brow descent to eyelid skin hooding (dermatochalasis), can be better appreciated and measured.
Another issue with measuring brow position is that most women shape their brows. The reason for this brow shaping will be a good topic for a completely separate blog. But it is a fact that many women will shape their brows to provide mild elevation and a mild arch. Therefore, if one measures brow position based on the position of the eyebrow hairs, one will likely underappreciate the brow descent. The skin of the brow is thicker and heavier than eyelid skin. Brow descent, even when the brow hairs appear to be in good position, can still cause eyelid skin to wrap, fold, and hood, causing symptomatic eyelid drooping. Therefore, it is critical to identify the eyelid/brow junction and ignore the position of the hairs. Identifying the eyelid/brow junction should focus on the subtle change from thin eyelid skin to thicker brow skin. A side-note: in the context of extensive brow shaping, a brow or forehead lift surgery may be contraindicated because elevating shaped brows may result in unwanted “surprised look.” There are ways to compensate for this, and it can be a topic for a future blog.
Finally, there are the upper eyelid retractor muscles, levator and Muller’s muscles. Both muscles are important for eyelid opening, although the primary eyelid opening muscle is the levator muscle. Repair of the muscles has absolutely nothing to do with excess skin or with brow position. The surgery requires dissecting into the deep muscle layer of the eyelid, and tightening or repairing the malfunctioning or weakened muscle. Sometimes this requires a patient to be awake for the procedure in order to achieve the optimal eyelid height, contour, and symmetry. I will address the different techniques for eyelid muscle opening procedures in a different blog. But for the purpose of this blog, I would like to mention something very important, which is that repair of upper eyelid ptosis by tightening the eyelid muscles can cause eyelid skin hooding. Now why might that be? It’s because a patient who has let’s say 30 millimeters of upper eyelid skin but at the same time has upper eyelid levator dysfunction and ptosis might have a low eyelid position that compensates for the excess eyelid skin. Specifically, the eyelid margin would be lower and hence the upper eyelid skin will be more stretched and less hooded. Furthermore, with the eyelid muscle not working well, patients tend to raise their brows. This further stretches the upper eyelid skin, and again masks the excess skin. The problem is that if a patient with eyelid ptosis and excess skin undergoes just eyelid ptosis repair with levator muscle tightening, at the end of that procedure the eyelid will open better but the eyelid skin will hood. Therefore, it is important to assess eyelid skin even in the context of true eyelid ptosis. This is so as to avoid a post-operative surprise that will make the patient rather unhappy; their eyes open better yet they have eyelid skin hooding that looks bad, causes excess weight, interferes with their peripheral vision, and will require a second surgery to address. A good preoperative evaluation should identify patients at risk for this so that the eyelid skin can be addressed at the same time as the levator muscle repair.
In summary, it is important to identify the correct mechanism for each patient who presents complaining of droopy eyelids. In a future blog, I will address the different techniques for correcting each one of these mechanisms and discuss the conundrum of brow ptosis and brow shaping,
Alon Kahana, MD, PhD
Kellogg Eye Center
University of Michigan