To Blink, or not to Blink?

It seems almost too obvious to mention, but just like you can’t see through a window when the window shade is pulled down, you cannot view or image the interior of the eye through closed eyelids.

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Obviously we need fully retracted upper and lower lids to get the best view of the fundus with our fundus camera, SLO, or OCT. Because these are noncontact imaging techniques, image quality is also dependent on a regular ocular surface and clear ocular media. An intact tear film is an important optical component of the ocular media. Simply put, to get the best images we need to strike a balance between fully retracted lids and frequent blinking to maintain the tear film.

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Top: Shadow from partially retracted upper lid appears at the bottom of the fundus image and degrades the OCT signal. Bottom: fully retracted lid improves the illumination of fundus image and improves signal strength in the OCT.
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Lashes partially obscure the retinal view in the top image. A fully retracted lid improves the view.

Many patients are nervous about their visual symptoms and what diagnosis the imaging procedure might detect. They often try hard not to blink during the session thinking it will help you get the best images. But their tear film will break up during this time and the view will become compromised until they blink again. And they often apologize for blinking!

To compound this dilemma, these imaging tests are often performed after a patient has undergone an extensive screening workup that includes IOP measurement, and application of topical anesthetic and dilating solutions. Patients may also undergo gonioscopy or macular contact lens examination prior to imaging. A disrupted tear film is an unintended side effect of these procedures and can adversely affect imaging quality.

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Top: irregular ocular surface causes degradation of both the fundus image and OCT as the tear film breaks up from lack of normal blinking. Bottom: after a few blinks, the view improves dramatically. Artificial tears would similarly improve the view.

It may seem counter-intuitive, but encouraging patients to blink frequently during imaging sessions can improve cooperation and image quality in fundus photography and OCT imaging. In our clinic, patients are often surprised that we encourage them to blink, having had procedures done in other clinics where they were sternly cautioned against blinking. In my experience as a consultant and workshop instructor, I have often heard OCT operators repeat the words “Don’t blink!” while performing a raster scan pattern that may take several seconds to capture.

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Artifact from blinking during a volume scan. Timing the patient’s blinking pattern can avoid this type of artifact.

They know that a blink will result in an artifact in the volume map, but fail to recognize the need for frequent blinking. I don’t really blame the operator. Often that’s how they were taught to perform the scan during a workshop or training session by the manufacturer’s trainer:

“Don’t blink! Don’t blink! Don’t blink! Don’t blink! Don’t blink! Don’t blink! Don’t blink!….”

No wonder the patients are afraid to blink! Frequent blinking not only refreshes the tear film, it makes the patient feel more comfortable and ultimately more cooperative. You’ll soon learn to recognize a patient’s blinking rhythm and you can time your image capture just as their upper lid is retracting after a blink. Gently encourage the patient by saying, “hold your gaze for just a moment” when you need just a second or two longer to capture a good image. When frequent blinking doesn’t work, application of artificial tears can also make a difference in patients with dry eyes or compromised tear film.

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Partial versus fully retracted upper eyelid. Image quality is compromised by the lid and lashes in the left images. Gently retracting the upper lid immediately after the patient blinked improves image quality.

During fundus photography, the flash of the camera will cause an involuntary blink that helps refresh the tear film. If the lid or eyelashes obscure the view, gentle retraction of lids with a finger or q-tip may help. You don’t need to forcefully tug on the lid, just retract it a couple of millimeters to get any lashes out of the way and reveal the entire pupil. Patients are often still able to blink with this mild retraction of the upper lid.

So encourage your patients to blink regularly and learn to capture the best images in between the blinks. If it weren’t for all the blinks, anyone could do this job!

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