What IS dry eye?

My take on dry eye.

I love to rotate things through the proverbial kaleidoscope, look at them from all different angles, and then try and come up with a sort of working composite. That's what I have attempted here for dry eye, from a layperson's perspective and on behalf of patients, because where my education-loving heart is planted is in helping patients and doctors understand each other better.

Patients, if you are new to dry eye — if the only thing you know is the term, without some of the basic physiology of it — I would encourage you to (a) Google it and look specifically for general information on the three layers or components of the tear film, and/or (b) glance through an article I wrote long ago called Dry Eye for Dummies.

A brief digression first...

There's dry eye... and there's DRY EYE. I mean, there are people whose eyes start bothering them a little bit late in the day or whose contacts don't stay comfortable for more than eight hours or whose eyes water in the wind... those are typical dryness symptoms which often seem like no big deal to them and thus they may go ignored (other than occasionally being doused with drops) for years at a time.

Then there are people whose eyes are uncomfortable morning to night, and quite possibly night to morning. That's a different ballgame altogether. I've spent many years working with this latter group, whose ranks are constantly being swelled by those who originally have very mild or infrequent symptoms for some time... but then something happens to push their quietly brewing dryness suddenly over the edge into a condition that starts actually impacting their life. 

In promoting dry eye awareness, one of my hopes is that more people at risk of a severer form of dry eye will get more educated about prevention early in the game.

Rebecca's definition of "Dry Eye" (as a disease)

Dry Eye is a failure of one or more parts of the tear systems encompassing production, distribution, and drainage (i.e. lacrimal glands, meibomian glands, goblet cells of the cornea & conjunctiva, eyelids, and puncta) to perform some or all of their fascinating, multi-faceted jobs to such a degree that the patient's eye comfort, eye health, and/or* vision are compromised enough to matter to the patient, doctor, or both.

Simply put: Anything that goes wrong enough with your tear film to matter to someone — which may or may not involve any actual lack of tears.

Examples?

• The common-or-garden-variety dry eye patient whose lacrimal glands are mostly fine but their meibomian (oil) glands are chronically clogged, resulting in rapid tear evaporation and constantly uncomfortable eyes.
• The cancer patient whose lacrimal and meibomian glands are irreparably damaged by disease, treatment, or both, leaving their corneas vulnerable to all the effects of excessive drying.
• The patient whose tears create a constant burning sensation because they don't have the right balance of components.
• The patient whose eyelids were left partially open by a lid surgery, with the result that their tears evaporate too quickly. 
• The patient with a leaky CPAP mask blowing onto their eyes all night in conjunction with their lids naturally not fully closing while they sleep, with the result that they dry out very quickly.
• The patient with Bell's palsy or damaged eyelid muscles, who can't blink and therefore isn't pumping out tears and whose corneas are constantly exposed.
• The patient with a little mild MGD but also huge puncta so their tears disappear down the drains much faster than normal.
• There are, I am sure, hundreds of variations on these themes!

*I understand that and/or is not a correct grammatical construct. In fact, I learned this anew in some extraordinarily interesting (but also confidential so I won't get into it) deliberations over a dry eye disease definition on an altogether different scale once upon a time. It may not be usable in scientific circles but for me, it's a lot handier than going into grammatical contortions to try and convey the same thing, ultimately less effectively. You just can't be too exclusive with dry eye because there really are so many variations on the theme.

Rebecca's definition of "dry eye" (as a phrase)

"Dry eye" is a thoroughly entrenched and therefore unavoidable yet inaccurate and trivializing misnomer whose ubiquitous use with reference to heterogeneous disease states of the tear system and/or the symptoms ostensibly related thereto frequently works to the detriment of patients.

Simply put: Welcome to my soapbox. 

For patients with moderate to severe symptoms, the term "dry eye" is a subtle but constant impediment to effective communication between dry eye patients and their healthcare professionals (both eye specialists and others) as well as their support systems. For patients who are 'merely' at risk of dry eye, this term can cause a great deal of harm by obscuring the understanding of risks and benefits. Try asking someone who got dry eye from an elective eyelid or laser eye surgery, or a short course of Accutaine, or a vasoconstrictor (redness reliever) or one of the older glaucoma eyedrops how well they think they understood what dry eye might be like. Hence the soapbox.

What does the medical-scientific world say that Dry Eye is?

Some conventional, user-friendly descriptions that don't strain the brain...

(American Academy of Ophthalmology)

If your eyes do not produce enough tears, it is called dry eye. Dry eye is also when your eyes do not make the right type of tears.

(Mayo Clinic)

Dry eyes is a common condition that occurs when your tears aren't able to provide adequate lubrication for your eyes. Tears can be inadequate for many reasons. For example, dry eyes may occur if you don't produce enough tears or if you produce poor-quality tears. 

Similar definitions are to be found everywhere. In various guises, you'll find the same concept, i.e. it's all about tear film quantity or quality (or both). It interests me that these almost always refer exclusively to tears, and almost always put aqueous deficient dry eye (i.e. inadequate tear production) first, even though for the majority of dry eye patients, that's not the issue!

Now for a polar opposite:

Or the elite international scientific community consensus definition....

According to TFOS Dry Eye Workshop II (DEWS II), and as presented in May as a teaser in advance of their full report being published July 15th, 2017 in Cornea:

(2017) Dry eye is a multifactorial disease of the ocular surface characterized by a loss of homeostasis of the tear film, and accompanied by ocular symptoms, in which tear film instability and hyperosmolarity, ocular surface inflammation and damage, and neurosensory abnormalities play etiological roles.

Bit of a mouthful, and obviously not intended for patients' use particularly, but it certainly conveys the complexity effectively. (By the way, keep an eye out for patient materials that TFOS will be producing subsequent to the publication of the report itself.

In the context surrounding this newly-minted definition, though — into which, incidentally, none of you will ever know how much time, labor, study and debate has gone — is something exciting and very relevant to all of us, and that is how very, very much the scientific community's understanding of dry eye disease has evolved and grown in just the last ten years! This means progress and good things for all of us.

As a marker, here is the definition in the original DEWS report, published in 2007:

(2007) Dry eye is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance, and tear film instability, with potential damage to the ocular surface. It is accompanied by increased osmolarity of the tear film and inflammation of the ocular surface. 

At first glance, the new definition looks suspiciously like a reshuffling of the same old words and phrases — osmolarity, inflammation, surface damage, and tear film instability. But it has a substantially different orientation and emphasis; it's less restrictive and substantially more flexible in what it encompasses; and it acknowledges the neurosensory aspect for the first time, which is a huge stride forward. Many dry eye pain patients of long standing will be keenly aware that terms like 'corneal neuralgia'  or 'corneal neuropathy' were virtually unknown if not as yet uncoined in ophthalmology practices at the time of the original DEWS report. (Incidentally, TFOS DEWS II has an entire section devoted to pain and sensation which is terribly exciting.) We've come a long way!

So it's evolving and will continue to. 

Progress is being made constantly, and we've seen a huge increase in resources being poured into dry eye research in recent years. Excellent trends and long may they continue!

What do YOU say that dry eye is?

There's the medical side, and there's the real life side. Most of us patients are less concerned with details of the medical side than with how we are affected — how it constrains our day to day lives. So tomorrow, we'll be exploring the surprising range of dry eye symptoms and hear from patients about what they mean to their lives.