Can CPAP Therapy Contribute to Dry Eye Disease?
Sometimes using a therapy to address one health concern can lead to unintended side effects.
In people who use positive airway pressure (PAP) therapy to treat their obstructive sleep apnea (OSA), around 5 to 10 percent may experience dry eye disease (DED).1 Older age and female gender increase this likelihood.2
DED related to PAP therapy usually relates to mask leak. But in rare cases, it can lead to something known as CRANS.
Mask leak and dry eye: a common occurrence
When a PAP mask cushion seals too loosely against the skin, or its headgear is overtightened, this can lead to pressurized air streaming from gaps in the seal. Commonly, air can leak along the bridge of the nose, shooting directly into the eyes.
Even when they’re closed, this constant stream of air can lead to DED.
Researcher and eye specialist Art Epstein told Sleep Review in 2016 that “even if the eye appears shut when sleeping, the eye may not fully close. Sometimes [patients will] wake up with abrasions, in pain, or not seeing well. And in the morning, it may take a while to get their tears going again.”3
Typically, dry eyes caused by PAP can be fixed by adjusting mask fit or switching to a different mask better suited to the user’s facial architecture and sleeping position.
However, there’s a different kind of DED that has no relation to mask fit.
Dry eye can happen without a mask leak
What is CRANS?
CPAP-associated retrograde air escape via the nasolacrimal system (CRANS) describes a kind of eye-related side effect linked to PAP therapy use not caused by mask leaks.
The nasolacrimal system is the draining mechanism in the eye that allows tears to flow through ducts into the nasal cavity.4
Pressurized air from PAP use can, in rare cases, escape the interior of the upper airway through these tiny ducts. Researchers still need to study CRANS more closely to better understand why it happens, but it could be related to air pressure levels or problems with the tear ducts themselves.
What we do know: CRANS was first identified in the literature in 2007.5 Research published in 2014 then sought to clarify it through an examination of 3 different case reports.
Each case involved complaints of dry eye from patients during overnight sleep lab tests, in which mask leaks were objectively ruled out as the source of discomfort.6 Instead, the seepage of pressurized air from their ducts seemed to cause their dry eyes.
What to do if you suspect CRANS
Do you have dry eye problems even though your CPAP machine data shows your mask isn’t leaking? You’re best advised to visit your sleep specialist to discuss the possibility that you may be experiencing CRANS.
They should be able to look at your PAP machine downloads to quickly determine any inherent mask leak issues. If they suspect CRANS, they can confirm it by:6
- Careful observation of mask usage during an overnight sleep study in the lab and/or
- Performance of a “saline bubble test”
What is a saline bubble test?
This simple, inexpensive, and straightforward approach quickly identifies and diagnoses CRANS. The medical specialist attending your sleep study applies a few drops of saline into your eyes while you’re awake and at rest on your back. Then you put on your PAP therapy mask and turn on your machine.
As the name of the test suggests, bubbles from the tear ducts in the bottom portion of the eye will confirm you have CRANS.7
The bubble test captures the escape of air from inside the upper airway through these tiny ducts in the eyes – precisely the opposite problem of those for whom dry eyes are caused by air blowing into them.
CRANS might lead to more than dry eye disease
CRANS might lead to more than just DED. Conjunctivitis and corneal ulceration are 2 conditions that medical specialists should be wary of when their PAP-using patients come in with dry eye complaints.6 In addition, eyelid flutter and watery eyes may be linked to it.7
CRANS treatment possibilities
Different kinds of approaches exist to deal with this rare condition, such as:8
- Replacing PAP therapy with an oral device
- Lowering PAP pressure, if possible
- Weight loss (to eliminate the need for PAP)
- Blockage of any lacrimal stents present for the treatment of problematic eye watering
Another way to correct CRANS may be to swap out your current mask (pillows, full face, or nasal) for something known as a total face mask. This mask completely covers the entire face like a shield. A few small trials of its use in patients with CRANS suggest it could help alleviate the problem.8
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