When dryness of the surface of the eye persists well after environmental, chemical, or other irritants have gone, you may be diagnosed with some form of dry eye disease (DED).
We say “some form” because dry eye disease is an umbrella term encompassing several separate pathologies that can produce similar symptoms beyond the cardinal symptom of dryness.
Even when dryness, irritation, and other potential symptoms of dry eye disease subside after the irritant is removed, that doesn’t mean solutions aren’t available – especially if the irritant is attached to the person’s work and/or environment.
To better navigate the clinical (e.g., medicated eye drops and/or other conditions involved) as well as the sub-clinical sides of this oversimplified eye health issue, it’s best to start with a closer look at the science.
With that foundation in place – as well as some prevalence statistics to show just how common dry eye disease is – we can better appreciate the causes, symptoms, and treatments of dry eye disease.
The Pathophysiology of Dry Eye Disease
As detailed by this academic article published on StatPearls, dry eye disease is often classified as either “aqueous deficient” (insufficient tear production) or “evaporative” (tears evaporate too rapidly), though many cases blur the lines between these two classifications.
Before we explore those terms in-depth, it’s important to have a basic understanding of how the tear film of the eye works.
Like any other fluid matrix in the body, the thin film of fluid that covers the surface of the eye requires its “layers” (an oily lipid layer, the aqueous water layer, and mucin, a protein component of mucus) to stay in certain proportions with each other for proper lubrication of the eye to occur.
If, for reasons explored below, production of any of the layers falls outside of the norm required for a healthy balance – aka, homeostasis – then dry eye disease can occur.
This is a bit of an oversimplification, as outside elements introduced into an otherwise healthy tear film can also produce DED symptoms, but the point is to think of the tear film as a proprietary “formula” that needs to keep everything in proper ratios to function normally.
Mechanisms of Tear Film Damage
The StatPearls article referenced above describes a number of ways in which homeostasis of the tear film can be affected.
Keeping within the context of the well-established “aqueous deficient vs evaporative” paradigm, the former often involves a lack of tear production as a result of damage or dysfunction of the lacrimal gland.
The lacrimal gland is what produces the aqueous layer of tears, which is the most substantial layer in terms of volume.
Physical obstruction of the gland, disease and drugs/medications can all affect lacrimal gland function in this manner.
In the case of evaporative DED, tears are evaporating too quickly, which is most commonly associated with meibomian gland dysfunction.
The meibomian glands produce the oily lipid component of tears, which helps prevent their evaporation in normal circumstances.
Like the lacrimal gland, physical obstruction of the meibomian gland can impair its function, as well as atrophy (shrinking) and a few other causes to be discussed later.
Evaporative DED can also be caused by not blinking frequently enough and environmental irritants.
Finally, it’s important to note that both of these cases are associated with an excess of sodium and glucose in the tear film, which is often referred to as hyperosmolarity.
Hyperosmolarity leeches fluid from surrounding tissues while prompting the immune system to respond (the redness, irritation components), both of which do not bode well for eye lubrication and overall health when this occurs in the tear film.
DED Prevalence and Known Risk Factors
Factoring in the high potential for misdiagnosis as well as the proportion of DED sufferers who do not seek (official) treatment, most global estimates on DED incidence are extremely broad.
Global DED Prevalence
This finding in Ophthalmic and Physiological Optics, a journal of the British College of Ophthalmic Opticians, estimates the global prevalence of DED at 11.59% with a standard deviation of 0.04, bringing several illuminating trends out in the data.
For example, the prevalence was lowest in North America and highest in Africa, and DED symptoms are least reported during the fifth decade of life, “increasing linearly thereafter.”
Using DED diagnostic criteria from TFOS DEWS II, a very large database compiled over two years by more than 150 clinical research experts, the authors of this study produced an estimate as high as 29.5% of the world’s population.
Reiterating, when the same study produces estimates as drastically different as these, it’s hard to even hazard a guess, but even speculating into the 20-30% range suggests that billions of people are experiencing some form of DED.
This contemporary finding from Clinical Ophthalmology further confirms the unpredictability, estimating that “the prevalence of DED ranges from 5%-33%.”
Comorbidities and Demographics
Beyond reporting on the prevalence of DED throughout their population sample (9.1%), this cohort study of 79,866 participants in the Netherlands illuminated some clinically relevant connections to the disease, including the following:
- DED symptoms were highly prevalent in 20-30 year old participants.
- DED symptoms were “associated with comorbidities in almost all body systems, including musculoskeletal, gastrointestinal, ophthalmic, autoimmune…” and more.
- Female gender, contact lens use, irritable bowel syndrome, and some chronic pain syndromes (fibromyalgia, chronic fatigue) identified as strong risk factors.
- Depression and “burnout” also positively correlated
- Environmental irritants like air pollution were positively correlated.
Though these surface-level observations require more exploration in the vein of determining causality and mechanisms involved, they hint at a broader pathology than what many ophthalmologists tend to focus on.
On that note, it’s time to take a closer look at how DED is caused, presented, and treated in both formal and self-treatment scenarios.
The Clinical and Sub-Clinical DED Picture
Because there are several anatomical structures required to maintain the sensitive balance of the tear film layers, there are several potential causes of dry eye disease.
Even without any acquired or genetic defects impairing these glands, immune responses, lifestyle, and a broad range of diseases can directly or indirectly contribute to the onset of dry eye disease.
Generally, it can be safely assumed given the amount of demographic information we now have on DED prevalence that women are more commonly affected by dry eye, and that risk increases with age.
Because so many conditions and issues can feed into dry eye, and because of the myriad of similar symptoms these conditions can cause, dry eye is very frequently misdiagnosed – more on that in a moment.
Here are some of the most common causes of dry eye disease:
- Meibomian gland dysfunction
- Preservative toxicity (topical creams, eye drops, etc.)
- Chemical exposure
- Reaction to antihistamine, hormonal, and other kinds of drugs
- Skin disease affecting the eyelids
- Surgery, mechanical injury, chemical or thermal burns.
This isn’t an exhaustive list, but it covers many of the most common causes of dry eye disease.
There are several factors that can affect which symptoms a DED sufferer may experience and/or the severity of those symptoms, including environmental exposure, daily activity (staring at screens often?), age and health status, products and drugs used, and so on.
Conversely, some people who experience dry eye as a symptom of a larger and more complex condition may experience additional eye-related symptoms that other DED sufferers do not.
Adding another layer of complexity for diagnosing doctors, though some of the symptoms of DED are objectively measurable (redness, swelling, etc.), many are not, which is why patients need to be provided with the proper scales and questionnaires to express the full range of symptoms.
Speaking of, here’s another non-exhaustive list of several of the most common symptoms of DED:
- Dryness of the eye
- An itchy, stinging, irritated feeling
- Pain around the eye, possibly in nearby tissues
- Visual deficits (blurry vision especially)
- Difficulty fully opening eyes
Dry Eye Diagnosis and Treatment
The standard diagnostic practice of confirming one medical issue and ruling out all others – a process that doctors call differential diagnosis – is especially involved in the case of DED because this disease can be so closely related to other conditions and symptoms.
To prepare against a potential misdiagnosis, ophthalmologists have a ready-made list of closely related conditions that DED is often mistaken for, which includes conjunctivitis, blepharitis, bullous keratopathy, and a few others.
Key points in the evaluation process that helps doctors to whittle away these potential diagnoses include an examination and testing of the eyelid and tear film, evaluating the meibomian gland, screening for other diseases, and more.
When the patient is diagnosed with DED, doctors have various treatment paths they can choose to go down based on the severity of the disease and other mitigating factors.
Here are the most common treatment methods for DED in ascending order of severity:
- Lifestyle modification and education (less screen time, away from fans, use a humidifier, check your products etc.)
- Eye hygiene improvement, especially eyelid
- Medicated eye drops and/or ointments
- Moisture goggles
- Tear duct plugs
- Light therapy
- Anti-inflammatory medications
- Specialized contact lenses
- Surgical options
Options abound in the over-the-counter side for those treating DED without prescription products, with Rain leading the industry in safety and quality.
Rain’s 100% preservative-free eye drops are as gentle as they are effective, drastically reducing the chances of exacerbating your symptoms (like many preservatives are known to do) while addressing DED effectively.
If you find yourself in the pre-doctor-visit domain, and would still like to try a few options before seeking out an eye doctor, we highly recommend preservative-free drops like Rain.