Tear evaporation plays role in dry eye disease

Image Credit: AdobeStock/fizkes

Dry eye is a common disease. National statistics suggest that anywhere from 5% to 15% of the general population has some form of dry eye disease.¹ These are simply estimates; it is very likely that the incidence of dry eye is greatly underestimated.

Of those living with dry eye, approximately 9 in 10 are experiencing evaporative dry eye.² If not addressed, excessive tear evaporation may lead to worsening of the condition. It can trigger a cycle of inflammation and ocular surface damage that is not only painful but expensive; the annual cost of dry eye to the US economy was estimated at approximately $55 billion.³

Several factors contribute to the increasing prevalence of dry eye disease. As eye care providers, we are seeing the impact of increased screen time, as computers have become the default way of working and spending leisure time for millions of people. Use of desktops, laptops, iPads and tablets, smartphones, and nearly every other digital device has a potentially important effect.

Climate change, taking the form of extreme weather and other environmental factors, also likely plays a role in the recent pervasiveness of dry eye disease.⁴ Relative differences in humidity levels, some based on normal seasonal changes, can exacerbate the condition by increasing tear evaporation and decreasing the stability of the tear film. Even something as simple as a patient going from warm air to cold or cold to warm, quite common in the extremes of summer and winter temperatures, will affect the ocular surface. But these factors alone do not explain the prevalence of dry eye disease.

I have been practicing optometry for 22 years. When I graduated from optometry school, we thought that insufficient tear production caused most dry eye symptoms. That belief led to the widespread practice of lubricating the eye with artificial tears. If a patient did not improve with one type of artificial tear, we gave them another to try.

However, a concept started to gain currency over the next 2 decades, championed by Korb and Blackie, among others.⁵ They believed dry eye might not necessarily be caused by the eye’s failure to produce enough tears; instead, the condition may be due to an imbalance of the tears being produced. They theorized that the tears produced in patients suffering from dry eye might not be held on the eyes appropriately.

As a result, optometrists started examining how tears are maintained on the ocular surface via the eye’s lipid layer. This led to the realization that dry eye might be based on the health of the meibomian glands, which produce the outermost layer of the tear film: the lipid layer.

One of the most common etiologies of dry eye that we encounter in our practices is evaporative dry eye, which we know is caused by meibomian gland dysfunction. Although not all the cases we see in patients are evaporative dry eye, most dry eye cases have an evaporative component.

Around 1 billion people globally have meibomian gland dysfunction, which often impacts the composition and thickness of the lipid layer.⁶ When a patient’s lipid layer is compromised, increased dry eye symptoms can be heavily triggered by the environmental conditions a patient faces. Increased screen use and environmental factors, along with dry winters, the impact of air conditioning during the summer, and even exposure to UV rays, are examples of how the physical environment canexacerbate dry eye.

In a worst-case scenario, dry eye can cause chronic long-term anatomical changes. The mildest of these are visual disturbances/visual tasking and corneal staining, but over time we can see corneal scarring and a reduction in best corrected visual acuity. We can also see long-term eyelid margin changes, and corneal changes can occur that can become permanent.

These impacts are preventable if individuals are treated appropriately. We as clinicians need to provide therapies for patients to help their eyes function better, and we must also leverage the tools we have to reduce the influence of the environmental triggers previously mentioned. Based on my experience with affected patients, I am convinced that we can change the trajectory of the disease.

We have procedures that can leave the meibomian glands unobstructed and start the production of healthier meibum by creating warmth and pressure to yield results and help patients’ eyes to function better, ultimately providing the basis for more meibum to be produced. Although these procedures are very useful for patients who can afford them and for those who have full and otherwise healthy meibomian glands, those individuals who have begun to see a decrease in meibomian gland structure and functionality are more difficult to rehabilitate. This is where the creation of a pharmaceutical, which works to mimic the lipid layer and function as an antievaporative, can fill the void.

For patients who are not candidates for these procedures, those for whom an eye drop would be more convenient, or those who may benefit from additive therapy, we now have a pathway to provide them perfluorohexyloctane ophthalmic solution (Miebo; Bausch + Lomb).

A pharmaceutical that definitively treats signs and symptoms of evaporative dry eye is a welcome addition to our dry eye armamentarium; over the past 2 decades, the treatment of dry eye has focused on treating inflammation. We now have a drop that directly targets the evaporation causing the discomfort and visual problems associated with dry eye.

Perfluorohexyloctane ophthalmic solution is the first topical medication approved by the FDA to treat the signs and symptoms of dry eye by inhibiting tear evaporation. I believe most patients with dry eye are candidates for this pharmaceutical agent. We have prescribed it for people newly diagnosed with dry eye disease due to meibomian gland dysfunction and found it to be highly effective. We have used it on patients with dry eye who had used other prescription eye drops and discontinued treatment because of efficacy or tolerability concerns.

In addition, we have found that perfluorohexyloctane may complement current dry eye procedures, such as heating masks and in-office procedures. Our clinical experience almost identically mirrors what was seen in clinical trials, not only from a sign improvement perspective but symptom improvement as well.

What makes perfluorohexyloctane unique is that it is 100% active, which means it has 0% water. It does not abide by the same rules that we understand in other dry eye formulations or medications. It does not have a pH because it does not contain water; it does not have a preservative because it does not contain water. Perfluorohexyloctane works differently: it does not bind to a receptor on a cell to elicit its downstream effects but rather imbeds itself into the lipid layer of the tear film. Although the exact mechanism of action for perfluorohexyloctane in dry eye disease is not known, it is believed to replicate the functioning of healthy meibum, creating an antievaporative layer that enhances the lipid layer of the tear film. As a result, perfluorohexyloctane ophthalmic solution improves the ocular surface and reduces dry eye symptoms.⁷

We need 2 things to help patients: a clear diagnostic pathway that helps simplify dry eye for the eye care practitioner, and treatment options that not only address symptoms but also the signs that we are seeing at the slit lamp. Otherwise, patients may become complacent to the symptoms that they experience, and the pain and irritation may become normal for them, which can result in long-term eye damage, as we have seen.

More than ever, we as optometrists have options to offer our patients with dry eye, including those experiencing inflammation and tear evaporation. Now that perfluorohexyloctane has entered the scene, we have a treatment that can help individuals with excessive tear evaporation, regardless of the level of meibomian gland dysfunction or dry eye disease they may have. This molecule has unique properties, and we are learning about the impact of perfluorohexyloctane, not only from clinical trials but also through what we are seeing and hearing from patients.

I am thrilled by our growing ability to provide treatment that reliably improves the disease’s symptoms. We became health care providers to make patients’ lives better; when we can achieve that fundamental goal, it is deeply rewarding. For patients, access to a new treatment that effectively addresses the dryness and other symptoms of dry eye provides them with long-sought relief. With continued advances in dry eye therapeutics, the future for patients with dry eye is optimistic.

References:

1. Dana R, Meunier J, Markowitz JT, Joseph C, Siffel C. Patient-reported burden of dry eye disease in the United States: results of an online cross-sectional survey. Am J Ophthalmol. 2020;216:7-17. doi:10.1016/j.ajo.2020.03.044

2. Lemp MA, Crews LA, Bron AJ, Foulks GN, Sullivan BD. Distribution of aqueous-deficient and evaporative dry eye in a clinic-based patient cohort: a retrospective study. Cornea. 2012;31(5):472-478. doi:10.1097/ICO.0b013e318225415a

3. Yu J, Asche CV, Fairchild CJ. The economic burden of dry eye disease in the United States: a decision tree analysis. Cornea. 2011;30(4):379-387. doi:10.1097/ICO.0b013e3181f7f363

4. Alves M, Asbell P, Dogru M, et al. TFOS lifestyle report: impact of environmental conditions on the ocular surface. Ocul Surf. 2023;29:1-52. doi:10.1016/j.jtos.2023.04.007

5. Knop E, Korb DR, Blackie CA, Knop N. The lid margin is an underestimated structure for preservation of ocular surface health and development of dry eye disease. Dev Ophthalmol. 2010;45:108-122. doi:10.1159/000315024

6. Schaumberg DA, Nichols JJ, Papas EB, Tong L, Uchino M, Nichols KK. The international workshop on meibomian gland dysfunction: report of the subcommittee on the epidemiology of, and associated risk factors for, MGD. Invest Ophthalmol Vis Sci. 2011;52(4):1994-2005. doi:10.1167/iovs.10-6997e

7. Miebo. Prescribing information. Bausch & Lomb, Inc; 2023. Accessed March 29, 2024. https://www.bausch.com/globalassets/pdf/packageinserts/pharma/miebo-package-insert.pdf