Optometry in Focus: Dry Eye

Happy SaturdayMonday…Tuesday, y’all!
So, full disclaimer – I wrote this post on Saturday, only to be too tired to post it after a long day of traveling. When I finally looked at my blog on Sunday (since some of the content of my post felt familiar), I realized that I had already posted something dry eye related several months ago, in the form of a discussion on Computer Vision Syndrome.
But, who wants to let an hour or so of blogging go to waste?
Certainly not I!
Besides, considering the prevalence of dry eye in society, what harm will another post do?
Okay… now back to the post!
Today’s blogging challenge?
Coming up with a topic that I don’t need wifi to complete.  #inflightprobs
Thinking of flying though, I guess there’s no better time than now to discuss a common flight (and winter) problem:  dry eye.
So, before we can really jump into what dry eye is, let’s go over a quick ocular anatomy review!
First things first: the cornea.
    The cornea is the clear, front surface of the eye, that is responsible for a significant portion of your vision.  If this surface becomes hazy, clouded, swollen, or irregularly patterned, it causes significant distortions to vision.
    Around the cornea is the limbus – a special transition zone, where the cells responsible for corneal formation reside.
    After the limbus, we arrive at the conjunctiva.  The conjunctiva (or conj for short) is actually another thin, clear layer, that covers the rest of the front surface of the eye (the bulbar conj) and the inside of the eyelids (the palpebral conj).
    All of these anterior (or front) surfaces are bathed by tears to remain healthy and clear.
Great, we’re done now, right?
Not so fast.
Let’s take a little bit of a deeper look at the tears themselves.
Tears are, believe it or not, comprised of three layers – the mucin, or protein layer that allows the tears to remain on the front surface of the eye, the aqueous, or watery part of the tears that, well, helps them maintain the proper moisture content of the front surface of the eye, and finally, the outer lipid, or fatty layer.
These three layers work together to protect and nourish the front surface of the eye, by providing oxygen and nutrients, carrying vital immune cells, and washing away debris.
Okay, now onto dry eye!
Dry Eye

So, first things first, dry eye is an inflammatory condition affecting the anterior (front) surface of the eye. 

Dry eye, as everything else in life and optometry, comes in a couple of different forms:

  • Aqueous deficient – not enough (quality) tears are produced 
  • Evaporative – there’s not enough lipid, or fatty, component in the tears, causing them to evaporate more quickly, leaving the anterior segment dry and irritated.
These two types of dry eye, naturally, have different causes.
Aqueous deficient dry eye, as a problem with production, may be associated with age to corneal nerves, dysfunction of the lacrimal (or tear producing gland), or simply a natural age associated decrease.

Evaporative dry eye, on the other hand, is caused by improper lipid formation.  This is often due to a disease called Meibomian Gland Dysfunction, or MGD for short.

Who Has Dry Eye?
If I’m honest, literally anyone can suffer from dry eye.
Dry eye, as I’ve mentioned before, can be significantly exacerbated by external forces, such as a dry environment (ie an airplane or the desert), fans, heat, or air conditioning.
Additionally, dry eye may be worsened by excessive screen time, as screen time is proven to significantly decrease blink rate, and therefore tear distributions, as well as contact lens overwear.
Finally, dry eye has also been shown to worsen with age, disproportionately impacting post-menopausal women.

Signs and symptoms
While dry eye may affect anyone and everyone, the signs are typically similar in all age ranges of patients.
Generally, patients present with complaints of red, irritated, watery eyes, that often feel like something is in them.
They additionally also report variable vision, that seems to improve for a couple of seconds after blinking.
In addition to just physical signs and symptoms, your eye doctor may perform several tests to better understand your specific dry eye.
    Tear Break-Up Time (TBUT): In this, the doctor literally measures (in seconds) how long it takes for your tear layer to start dissipating or breaking up on the front surface of your time. This test is generally short – under 20 seconds total, 10 for each eye.  The lower your score is, the worse dry eye you generally have.
    Tear Meniscus Measurement: This test just involves looking at the amount of tears that lie on your lower eyelid while looking from behind the slit-lamp (big microscope). If it is too low, it is generally a sign that not enough tears are being produced.
    Schirmer’s Test:  Schirmer’s is another test of the amount of tears produced by the eye.  In this, a little piece of paper is put between the eye and the bottom eyelid for a (relatively) short amount of time, to quantitatively measure tear production.  This test has two varieties – one that involves numbing your eye first (decreasing reflex/automatic tearing), and one that… doesn’t.  **Not my favorite test**
    Phenol Red Thread Test: This test is very similar to Schirmer’s, however, instead of a smal piece of paper, a tiny red thread is place in between the eye and the bottom eyelid, to again quantitatively measure tear production.  This test is very quick (around 5 seconds/eye), and much less invasive than Schirmer’s – making it more enjoyable for patients and doctors alike!
    Corneal staining:  In this, a small amount of dye (generally fluorescein or lisasmine green) is placed in each eye, with the goal of highlighting inflammation on the front surface of the eye.  The staining pattern observed may help determine the cause of ocular dryness (exposure, etc).
    Meibomian gland expression: Meibomian gland expression is especially helpful when it comes to diagnosing MGD.  For this, the practitioner gently pushes on the meibomian glands (generally in the lower eyelid) to determine the expressivity and consistency of their lipid product (meibum).  Thicker meibum is generally indicative of MGD.
    Tearfilm osmolarity: Finally, or at least finally for now, some offices have the ability to test tearfilm osmolarity, typically using a device called Tearlab.  (How many of you remember back to Chemistry for what this means?  It’s something with number of particles/amount of water… right?). Higher values are more closely correlated with dry eye.
Phew. That was a lot.
Okay, so now that we know some of the ways dry eye can be diagnosed… what in the world do you do about it?
As a rule, there is a step-wise approach to dry eye treatment, that varies some depending on the original cause, however, I am out of time to write about them for today.  Catch y’all next time!
If you learned something from this post, please share it with a friend or family member!  If you liked it, please subscribe, or like my page on Facebook! And as always, if you have any questions or comments, please contact me – I’d love to hear from you!
If you’re interested in reading my first post, Computer Vision Syndrome: Addressing Dry Eye, click the link to check it out!
PS: My apologies for the formatting issues on this post.  I wrote it in Google docs (because, flying…) and then copied it over to blogger.  Lessons for next time…

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