Mark A. W. Andrews, professor of physiology and director of the Independent Study Pathway at the Lake Erie College of Osteo­pathic Medicine, replies:

Generally speaking, heaviness of the muscles around the eyes, including the levator muscles that open the upper eyelids, is similar to fatigue of any muscle of the body. Ocular and brow muscles are especially prone to fatigue because they are active for most of our waking hours. Over the course of the day, they gradually grow leaden with extended use, as our arms and legs do.

Such a feeling may be compounded by general fatigue, including a lack of sleep, or by specific muscle overuse related to long hours of focusing on, say, a computer monitor. Excess skin of the eyelid, or prolapsed fat pads underneath the eyes, makes an individual more prone to this sensation. Chronic allergies and sinus infections may also exacerbate the heaviness, and sun exposure may cause eyelid swelling and thereby increase the probability that the drooping will interfere with vision.

Although heavy eyelids do not typically indicate underlying medical issues, some conditions do cause drooping eyelids, or ptosis. A stroke or a muscular disorder such as myasthenia gravis or myotonic dystrophy can damage facial muscles or their nerves and cause ptosis, as can elective facial surgery or interventions such as Botox injections to the brow.

Editor's Note: This story was originally printed in the November 2008 issue of Scientific American.

5 Comments

1. 1. signaleffect 08:45 PM 12/5/08

   Although an interesting idea, I completely disagree with the author. I think a neurologist specifically someone who specializes in sleep would agree with me and say that "heavy eyelids" are related to actions of the ventrolateral preoptic hypothalamus (VLPH) and less due to muscle fatigue. One can argue the idea about muscle fatigue because your eyelids get "heavy" directly after a large meal, specifically lunch for myself, which normally is about 5 hours after I wake up (not nearly enough time for my muscles to get fatigued). The siesta-syndromes are directly explained by the afferent inputs received by the VLPH after a meal. The VLPH is responsible for sleep activating functions via the Sleep Activating Center (SAC) which modulate the effects of the ascending arousal system (AAS) - basically decreasing them when the SAC is activated. The AAS is known to cause excitation to the autonomic nervous system which surprisingly enough innervates the levator muscles of the eye (specifically the levator palpebrae superioris). So if you block the AAS via the SAC of the VLPH you no doubt block the muscle of the eyelid that holds it open leading to "heavy eyelids."
   
   There are actually multiple examples the author uses that can be explained by the reasoning above. I will save them because it will take a lot more than a paragraph to go into but the above is one of the most direct explains proving the author wrong.
   
   Please correct me if I am wrong, since I am still just a 2nd year medical student but I think this is a pretty solid pathway and although the author's explanation is cute and seems logical, according to my training it is simply wrong.

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2. 2. NicholsEG 10:13 PM 12/5/08

   Heavy eyelids can also be an inherited condition. My brother and I have 15 first cousins on our mother's side. More than half of us have what we call the "Weant droop," after our family name. Our left upper eyelids, and only our left eyelids, droop down when we are seriously fatigued, or have been drinking. However, this is not a daily occurrence. We have always considered this to be a weak muscle.

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3. 3. vicher37 01:31 AM 12/6/08

   Awesome. MEdical schol 2nd grade student is really awesome. ANd has a critical thinking which I think I myself should adopt more!

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4. 4. grumble 05:03 PM 12/7/08

   Professor Andrews' hypothesis seems full of holes. Consider these simple points which disprove such a short-sighted idea: 1) Sleepiness can occur at any time during the day, such as after a meal or when taking certain medicines; 2) Sleeplessness disorders can keep someone awake for days, weeks or worse, with no apparent eyelid heaviness; 3) Some people can sleep with their eyes open.

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5. 5. Cerebral*Origami 11:16 AM 12/12/08

   I want to know why when I am trying to drive while extremely tired my eyes roll up when ever on coming head lights are too bright!
   
   (I have the same thing happen when I am experiencing an allergic reaction. I have to physically hold my left eye (my right hand is steering) when I drive to the hospital for a shot.)

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