Blink & Eyelid-Closure Problems

Blinking is not an all-or-nothing process. Several different aspects of blinking can become abnormal.

A person may blink less frequently, leaving the ocular surface exposed for longer periods between blinks. Blinks may be incomplete, meaning that the upper and lower eyelids do not fully meet. The pattern or quality of blinking may also change, making tear-film redistribution less effective.

These are different problems, but they can produce a similar result: the ocular surface is not being refreshed and protected by blinking as effectively as it should be.

Every time the eyes are open, the tear film is exposed to the environment. Between blinks, the tear film gradually changes. Water can evaporate, the surface cools, and eventually areas of the tear film may begin to break up.

A new blink normally interrupts this process. It redistributes the tears and restores a more uniform tear film over the ocular surface. If the interval between blinks becomes longer, the tear film has more time to become unstable before it is renewed.

This does not mean that there is one universally “correct” blink rate that everyone should maintain. Blink rate naturally changes depending on what we are doing, our attention, environment and many other factors. The important point is that the relationship between blink timing and tear-film stability matters. If the tear film tends to break up before the next blink occurs, parts of the ocular surface may repeatedly experience increased exposure and stress.

An incomplete blink occurs when the eyelids move toward each other but do not completely close across the ocular surface.

This can be surprisingly subtle. A person may appear to be blinking regularly while a small portion of the ocular surface — often inferiorly — remains uncovered during some blinks. That means blink frequency alone does not tell us whether blinking is effective. Blink completeness matters too.

When a blink is incomplete, the tear film may not be redistributed normally across the entire exposed surface. Some areas can therefore receive less effective tear-film renewal than others. Over time, repeated incomplete blinking can contribute to localized tear-film instability and ocular-surface stress.

Blinking is connected not only to the aqueous tear film but also to the meibomian gland system. The movement and pressure generated by the eyelids during blinking contribute to the delivery and distribution of meibum at the eyelid margin and across the tear film.

A complete blink brings the eyelids together and helps spread lipid material over the ocular surface. If blinking is repeatedly incomplete or altered, this process may also become less effective.

This creates an important connection between eyelid function and the lipid component of the tear film. It is another example of why dry-eye mechanisms are difficult to separate into completely independent categories. A blink problem can influence the tear film. A tear-film problem can influence the ocular surface. And ocular-surface discomfort can, in turn, influence blinking.

Blinking is what happens repeatedly while we are awake. But the eyelids also need to be able to close completely when the eyes are meant to remain closed, particularly during sleep.

When the eyelids cannot fully close, part of the ocular surface remains exposed. This is called lagophthalmos. If it occurs during sleep, it is often called nocturnal lagophthalmos. Even a relatively small opening can leave part of the cornea or conjunctiva exposed to the surrounding air for prolonged periods.

This is different from an incomplete blink. With incomplete blinking, the problem occurs during repeated blink movements. With lagophthalmos, the problem is that the eyelids cannot maintain complete closure when the eye should be closed. Both can increase ocular-surface exposure, but in different ways.

The tear film is designed to function on an ocular surface that is periodically refreshed by blinking and protected when the eyelids are closed.

If part of the eye remains exposed for too long, evaporation can continue without normal tear-film redistribution. The exposed area can become increasingly unstable and experience greater osmotic and mechanical stress. This can lead to exposure-related ocular-surface damage, particularly when the exposure is prolonged or repeated.

The location of the damage may also provide clues. For example, inadequate closure or incomplete blinking may disproportionately affect the lower or otherwise exposed parts of the ocular surface rather than producing identical changes everywhere.

So sometimes where the tear film breaks up or the ocular surface becomes damaged can be as informative as the fact that damage exists.

It is useful to distinguish these concepts:

• •reduced blinking means the eye remains open longer between blinks
• •incomplete blinking means the eyelids do not fully meet during some blinks
• •lagophthalmos means the eyelids cannot achieve or maintain complete closure when the eye should be closed

All three can increase ocular-surface exposure, but the underlying eyelid behavior is different. This distinction can matter when trying to understand what is happening in an individual person.

Yes. This is one of the reasons dry eye cannot be understood only by asking “Do I produce enough tears?”

A person may have reasonable aqueous tear production but still experience tear-film instability because the ocular surface remains exposed for too long between blinks or because an area of the eye is not adequately covered during blinking or sleep. Similarly, the meibomian glands may be producing meibum, but altered blinking may interfere with its normal delivery and distribution.

So the problem may not begin with the tear-producing structures themselves. It may begin with the mechanics of how the eyelids interact with the ocular surface.

As with other dry-eye mechanisms, eyelid and exposure problems can interact with the rest of the ocular-surface system.

Longer exposure can increase evaporation. Tear-film instability can increase ocular-surface stress. Surface stress can contribute to inflammation and discomfort. Changes in sensation and discomfort can influence blink behavior. And altered blinking can further affect tear-film stability and meibum distribution.

Over time, what began as a mechanical problem can therefore become connected with several other components of dry-eye disease.

There are many possible reasons. Blink behavior can change with visual tasks and sustained concentration. Eyelid closure can be affected by anatomical, muscular, neurological or other factors. Certain procedures or medical conditions can also alter normal eyelid mechanics.

But these are questions about why the problem developed. In this chapter, the important thing is simply to recognize that abnormal blinking and inadequate eyelid closure can themselves disrupt the tear-film and ocular-surface system.

Screens, Reduced Blinking & Dry Eye

Blink & Eyelid Assessment: what your doctor is looking for