The health of the ocular surface is essential for maintaining optimal vision and comfort. Many ocular conditions, including dry eye, glaucoma, and ocular hypertension, frequently necessitate long-term treatment with topical medications.
While these treatments are pivotal in managing the conditions, their repeated use, particularly when preserved with certain agents, can potentially compromise ocular surface health.
Ophthalmologists, as custodians of eye health, play an indispensable role in ensuring that treatments are not only efficacious but also safe for the ocular surface.
The importance of the ocular surface
The ocular surface system consists of the cornea, conjunctiva, eyelids, meibomian glands, and the tear film. It plays a crucial role in maintaining clear vision and protecting the eye from microbial infections and environmental stressors. Disruption of any component can result in discomfort, blurred vision, or more severe complications.1
How dry eye affects patients
Dry eye disease (DED), clinically known as keratoconjunctivitis sicca, is a multifaceted disorder of the tear film and ocular surface, resulting in ocular discomfort and an overall decrease in quality of life.
Individuals often describe a persistent or intermittent, gritty, or sandy sensation, which can intensify during prolonged screen usage, in dry environments, or under windy conditions. Patients also describe contact lens intolerance,2 or their eyes feeling tired even when they are not actually sleepy.3
Fluctuations in visual clarity, combined with heightened light sensitivity or photophobia, further underscore the distress associated with this condition. These symptoms may be especially pronounced during prolonged activities like reading or computer use and being in dry or low-humidity environments, including air travel, offices, or hotels.4
Common indications of dry eye
When the eyes are dry, they may produce reflex tears in response to irritation. However, these tears are not the same as the normal tears that lubricate the eyes. Reflex tears are produced by the lacrimal gland and contain less oil and mucus than normal tears.5 As a result, they do not provide adequate lubrication and can actually make dry eye worse over time.
Other common indications of dry eye include ocular redness, a burning sensation, and pronounced ocular fatigue, emphasizing the importance of a thorough patient history for accurate diagnostics.
Risk populations for DED
Dry eye disease should be considered in all patients. As one of the most densely innervated parts of the human body, the cornea receives its innervation from the ophthalmic division of the trigeminal nerve (V1).
Recent data suggest that patients with neuropathy have corneal nerve fiber damage and reduced corneal sensitivity, which can favor the occurrence of dry eye syndrome in three ways:6
- Reduced blink rate
- Increased evaporative tear loss
- Decreased reflex-induced lacrimal secretion
Aging remains a principal risk factor, with post-menopausal women showing a particularly increased susceptibility due to hormonal changes that affect tear production and composition.
Systemic conditions to consider with DED patients
Individuals with systemic autoimmune disorders, such as Sjögren’s syndrome, rheumatoid arthritis, and systemic lupus erythematosus, are at an elevated risk given the inflammatory nature of these diseases and their potential impact on lacrimal gland function.
Additionally, continuous positive airway pressure (CPAP) users, patients with Parkinson’s, thyroid instability, Bell’s palsy, and even those who have had blepharoplasty are at high risk for DED due to exposure and blinking issues.7
Medications, including antihistamines, beta-blockers, diuretics, and certain antidepressants, can alter tear secretion and subsequently predispose patients to ocular surface desiccation.8 Furthermore, prolonged digital screen usage, which often leads to decreased blink rate, along with environmental conditions such as low humidity and high wind, can amplify the risk in otherwise healthy individuals.9
Consequences of DED
Dry eye disease, while often regarded as merely uncomfortable, can lead to several significant ocular complications if not adequately addressed. Chronic inflammation of the ocular surface can precipitate epithelial defects, which, in turn, increase the risk for microbial keratitis, a potentially vision-threatening corneal infection. Persistent dryness can also result in the formation of filamentary keratitis, where strands of mucus and epithelial cells adhere to the cornea, causing marked discomfort.
Moreover, the lack of sufficient lubrication can lead to the development of punctate keratopathies, which are tiny erosions on the cornea that can coalesce, compromising the integrity of the corneal surface. Over time, if left untreated, these complications can culminate in visual impairment due to corneal scarring and irregular astigmatism.
Topical treatments: A double-edged sword
The intersection of DED and glaucoma treatment presents a significant clinical challenge in ophthalmology. Research suggests that the global prevalence of DED in people with glaucoma is substantially higher than in the general population.10
The conditions share some risk factors, such as age (being over 40) and having diabetes. Also, eye drops used to treat glaucoma and surgeries that alter the ocular surface, such as tube shunts and bleb formation, can also cause or exacerbate dry eye.11
Many glaucoma medications, particularly those preserved with benzalkonium chloride (BAK), have been implicated in exacerbating ocular surface disorders due to their cytotoxic effects on the corneal and conjunctival epithelium. Chronic exposure to these drops can disrupt the tear film, induce inflammation, and increase tear osmolarity, amplifying the symptoms of dry eye.
Additionally, glaucoma patients require multiple IOP-lowering medications several times a day. This causes a cumulative detrimental effect on the ocular surface. This confluence necessitates a careful balance in the management strategies, requiring the consideration of preservative-free (PF) glaucoma formulations to safeguard the ocular surface.
The perils of preservatives
One of the most commonly used preservatives in ophthalmic solutions is BAK. While effective as an antimicrobial agent, it can have adverse effects on the ocular surface epithelium, decrease tear film stability, and induce inflammatory responses.12 Over time, these can compound existing conditions, leading to symptoms such as redness, burning, stinging, and decreased vision.
Other preservatives like chlorhexidine, thimerosal, and polyquaternium-1, although less common than BAK, also have potential toxic effects on the ocular surface. Long-term preservative use can lead to epithelial cell loss, reduced tear break-up time, signs of ocular discomfort, and dry eye disease with all of its potential complications.13
Are preservative-free options the way forward?
Given the potential drawbacks of preservatives, there's a growing trend toward prescribing PF formulations. These products are free of harmful agents, reducing the risk of inducing or exacerbating DED. Several studies have highlighted the benefits of PF formulations, particularly in glaucoma patients.14
Switching to PF prostaglandin analogs, for instance, has been shown to improve tear film stability, decrease corneal staining, and reduce ocular discomfort. These findings emphasize that while the primary goal is to manage the intraocular pressure, the broader objective must encompass safeguarding the ocular surface health.15
Moreover, the advent of multi-dose containers with innovative designs, which prevent contamination without the need for preservatives, has made PF options more practical and accessible.
The ophthalmologist's role: Beyond disease management
As experts in eyecare, ophthalmologists bear the responsibility of ensuring a holistic approach to treatment. Studies have found that patients with glaucoma and dry eye disease are less compliant with their glaucoma drops.16 This is because the preservatives in glaucoma eye drops, such as BAK, can damage cells on the ocular surface, resulting in dry eye signs and symptoms.10
DED remains a prevalent and often underdiagnosed condition in ophthalmic care, with multifactorial implications ranging from mild discomfort to severe ocular morbidity.17 One of the pillars of effective DED management lies in early identification; ophthalmologists must be astute in detecting early signs, including ocular staining and decreased tear breakup time, particularly in high-risk populations on prolonged topical therapy.
Comprehensive ocular surface assessments can preempt severe manifestations, guiding timely interventions to prevent progression. A parallel strategy involves patient education. By elucidating potential side effects of their medications, notably the risk of DED, patients become empowered, often presenting to the clinician at the onset of symptoms rather than when complications have set in.
Moreover, therapeutic choices should be judicious; the decision between preserved and PF formulations is pivotal. Especially in individuals already demonstrating DED signs, ophthalmologists should lean toward PF formulations, which can be more benign to the ocular surface.
Conclusion
The ocular surface is a complex, delicate system integral to vision and comfort. In treating ocular diseases, it's essential to ensure that the cure isn't worse than the ailment. The adverse effects of preservatives in topical treatments underline the necessity for a holistic treatment approach.
Topical glaucoma therapies, while essential in managing intraocular pressure, possess an intricate relationship with DED. Many of the eye drops prescribed for glaucoma contain preservatives, most notably BAK, which have been recognized as potential culprits in destabilizing the ocular surface and exacerbating DED symptoms.
The chronic and frequent application of these medications can induce changes in the tear film, promote inflammatory responses, and lead to damage of the corneal and conjunctival epithelium. Further, glaucoma patients often necessitate polypharmacy, increasing the exposure to various preservatives and potentiating the adverse effects on the ocular surface.
Consequently, DED symptoms such as grittiness, burning, and visual fluctuations might be misattributed solely to the glaucoma regimen when, in fact, they signify a co-existing pathology. In managing glaucoma, especially in those with concurrent DED or at risk, ophthalmologists should consider preservative-free formulations. This will allow efficacious intraocular pressure control without compromising the integrity of the ocular surface.
This harmonized approach ensures that in our quest to preserve visual fields, we don't inadvertently diminish the patient's quality of vision or cause harm. As the guardians of ocular health, ophthalmologists must champion the shift towards safer treatment modalities, ensuring that interventions not only treat the primary ailment but also preserve the integrity of the eye in its entirety.
