CONTACT LENS DISCOMFORT
Discomfort and Dryness with Contact Lens Wear
What is the link between ocular surface health and success with contact lens wear?
By Desmond Fonn, Dip Optom, MOptom, FAAO
Discomfort and dryness are the most frequently reported symptoms of contact lens wear (Begley et al, 2000; Pritchard et al, 1999; Dumbleton, Woods et al, 2013), and it is common for these symptoms to increase toward the end of the day, frequently limiting patients’ wearing time. If the symptoms are severe and/or persistent, they may eventually lead to discontinuation of lens wear.
The magnitude of this complication and its negative impact on the growth of the contact lens industry prompted the Tear Film & Ocular Surface Society (TFOS) to review the literature associated with contact lens discomfort (CLD). The TFOS International Workshop on Contact Lens Discomfort resulted in a series of papers that were published in a special issue of Investigative Ophthalmology and Visual Science in October 2013. Unfortunately, the conclusion of this body of work was that relatively little is actually known about the etiology of CLD.
Ocular Surface—Healthy or Not?
The premise or belief is that any pre-existing condition of the ocular surface, including tear film abnormalities, can influence how well patients are able to wear contact lenses or may predispose lens wearers to some level of discomfort while wearing lenses.
Practitioners carry the responsibility of detecting any pre-existing issues by using various tests and instruments that are suitably sensitive to discern any abnormalities. Elaborate examination procedures using advanced technology may be employed to screen potential contact lens wearers and to ensure that the eye is in a healthy state to sustain all-day wear (or for sufficiently long periods).
In many cases, practitioners have to rely on their judgement to distinguish the “abnormal” from that which is “normal.” Many of the ocular variables observed in a clinical examination are not easily measurable. For example, tear stability, conjunctival hyperemia, or tarsal conjunctival smoothness are usually graded variables, which may lead to questionable repeatability and inter-observer differences.
Some patients who have marginally unhealthy eyes may slip “under the radar.” However, these occurrences are rare given that patients who typically present for contact lens wear are younger and, therefore, less likely to have any pre-existing systemic or ocular conditions that may impact successful lens wear.
In the event that mild, clinically insignificant conditions do exist that do not require treatment prior to lens wear, it would be reasonable to attempt lens wear and observe patients’ progress. Obviously, this does not include patients who require therapeutic contact lenses for conditions such as keratoconus that require careful consideration ahead of lens fitting.
Terminology Complicates the Matter
Once it has been determined that the ocular surface is sufficiently healthy to sustain lens wear, contact lens fitting may be undertaken. Once fitted, some symptoms accompanying lens wear are common. There are a number of terms that have been used (or misused) to describe the adverse ocular sensation that patients experience during contact lens wear.
Discomfort and dryness are the most commonly reported, but dry eye, contact lens dryness, contact lens-related dry eye, and contact lens-induced dry eye (CLIDE) are all terms that are used—sometimes interchangeably. Due to a lack of consensus and understanding of CLD as a condition, the TFOS Definition and Classification Subcommittee developed a definition and evidence-based classification scheme of CLD and clarified associated terminology (Nichols K et al, 2013). Their definition of CLD was:
“Contact lens discomfort is a condition characterized by episodic or persistent adverse ocular sensations related to lens wear, either with or without visual disturbance, resulting from reduced compatibility between the contact lens and the ocular environment, which can lead to decreased wearing time and discontinuation of contact lens wear.”
With the development of this definition, it was further suggested that the terms that incorporated “dry eye” should not be used in the context of CLD (or as alternatives to CLD). Instead, those terms “should be reserved for an individual who has a pre-existing dry eye condition, which may or may not be exaggerated when contact lenses are worn” (Nichols J et al, 2013). Furthermore, there does not appear to be evidence of supportive pathophysiology of these dry eye terms associated with CLD (Nichols K et al, 2013), so the terms should not be used as alternatives to CLD.
“Contact lens dryness” is sometimes used by patients as a symptom of contact lens wear, but that too is a misnomer, because it is unlikely that the contact lens actually becomes dry. Rather, it is the eye that feels dry.
Nichols K et al (2013) continue by suggesting that contact lens dryness can be used to describe a specific symptom of CLD. There is evidence that CLD and dryness are closely linked after seven hours of contact lens wear (regardless of material), but that this association does not exist soon after lens application (Fonn et al, 1999).
This is not a surprising result for a number of reasons. When the lens is applied, it is accompanied by a relatively large amount of fluid from the blister pack or solution; it is expected that patients will feel little or no dryness. There is a decrease in tear volume toward the end of the day, and this may contribute to the reported symptoms of dryness. This drying of the lens will increase the level of friction at the lens surface, which appears to correlate with CLD (Coles and Brennan, 2012).
Nichols K et al (2013) also describe the use and misuse of the term “intolerance” associated with contact lens wear. They suggest that this term refers to being unable to tolerate contact lenses, but that “intolerant” should not be used to describe a person who has discontinued lens wear.
Of final note is that it is well recognized by the TFOS working group that CLD is eliminated or alleviated by lens removal (Nichols J et al, 2013), confirming that the presence of the contact lens is ultimately responsible for the adverse sensation and any associated symptoms.
Prevalence of CLD
Prevalence is defined as the number of cases exhibiting a condition or being symptomatic of a condition in a given population. CLD is a subjective condition reported by symptomatic patients who may or may not have clinical signs induced by, or associated with, contact lens wear. The source of the most comprehensive literature search on CLD prevalence is the recent Epidemiology Subcommittee report from TFOS (Dumbleton, Caffery et al, 2013).
The prevalence outcome is, to some extent, dependent on the technique used to assess CLD, which is typically determined either by: 1) using a questionnaire, or 2) asking the patient to provide a “comfort” score, in which the patient is provided with a scale ranging from (as an example) very comfortable to very uncomfortable.
Determining CLD prevalence is also largely dependent on the type of study conducted. Prospective population-based or epidemiological studies of the natural occurrence of a disease or condition are the most highly regarded methodologies, but these have not been undertaken for CLD (Dumbleton, Caffery et al, 2013). Their research revealed that there are five population-based dry eye studies that included contact lens wearers: three in Japan, one in Canada and one in China. The studies ranged vastly in sample size (from 105 to 3,285 people), and the percentage of wearers who were symptomatic of ocular dryness and irritation ranged from 32% to 50%. The 14 clinical studies cited in the same paper that were conducted in institutions and private practices (not as highly regarded in terms of epidemiological research because of design limitations) reported a CLD range of approximately 30% to 80% of wearers.
Etiology of CLD
The most revealing—and disappointing—result of the TFOS workshop is that very little is known about the etiology of CLD. There is good agreement that lenses can provoke discomfort and dryness, and this is supported by the report of the TFOS Neurobiology Subcommittee (Stapleton et al, 2013), which suggests that the physical interaction of the contact lens with the ocular surface is the primary mechanism responsible for CLD. This is further supported by the fact that, in an otherwise healthy eye, symptoms dissipate almost immediately once the lens is removed. However, the exact element (or elements) of the lens that gives rise to CLD and end-of-day discomfort remains unknown.
Based on this lack of evidence of the cause for CLD, little can be said about the state of the ocular surface prior to contact lens wear that could result in CLD. Craig et al (2013) reviewed the literature on contact lens interactions with the tear film, and they concluded that tear film stability appears to have the strongest link to comfort during contact lens wear, rather than any single component of the tear film.
In Rohit et al’s (2013) recent review paper on the lipid layer of the tear film, the findings led them to conclude that the lipid layer alters in the presence of a contact lens. They also hypothesized that alteration of this layer contributes to contact lens discomfort.
And, to date, Best et al (2013) and Glasson et al (2003) appear to be the only ones who have shown an association between baseline tear film stability and discontinuation/intolerance of contact lens wear, but their work does not link this specifically to CLD.
Korb et al (2002) and Yeniad et al (2010) have reported that lid wiper epitheliopathy (LWE) occurs predominantly in contact lens wearers who have dry eye symptoms. However LWE as a cause of CLD has not been established. Friction from the lens surface is the suggested cause of this conjunctival condition, but this has to be proven experimentally.
Another conjunctival anomaly—lid parallel conjunctival folds (LIPCOF)—appears to be indicative of symptoms in contact lens wearers (Pult et al, 2009). However, the TFOS Clinical Trial Design and Outcomes Subcommittee concluded that, although LIPCOF may be predictive of CLD, there is no evidence of a direct correlation between severity of LIPCOF and CLD (Foulks et al, 2013). The TFOS Contact Lens Interactions with the Ocular Surface and Adnexa Subcommittee concluded that LWE and meibomian gland dysfunction had the strongest association with CLD and that there was only “some evidence” of a link between CLD and LIPCOF (Efron et al, 2013).
Consequences of CLD
The TFOS Definition and Classification Subcommittee included a useful figure on the progression of CLD in its paper (Nichols K et al, 2013). From the initial state of physical awareness and possibly visual disturbance (invariably after the adaptation period), the progression of CLD often leads to reduced comfortable wearing time, then reduced total wearing time, followed by temporary discontinuation and then permanent discontinuation.
The annual estimates of contact lens dropouts range from 10% to 30% (Dumbleton, Woods et al, 2013; Rumpakis, 2010), but it is almost impossible to estimate how many patients have discontinued permanently from lens wear in the last 10 years.
It would appear reasonable to estimate that the number of contact lens wearers could be 40% to 50% greater than it currently is—if the etiology of CLD could be uncovered and remedied. This would have a profound effect on the industry as a whole and, inevitably, improve the financial viability of contact lens practice globally.
Placing a contact lens on the ocular surface initiates multiple interactions with the eye that will ultimately determine the success or failure of lens wear. For patients to enjoy a lifetime of successful contact lens wear requires vigilant ongoing care by practitioners, ensuring patient compliance and that they always use the most suitable lenses and lens care products as recommended by their eyecare practitioner. CLS
This article was prepared with financial support from Alcon.
For references, please visit www.clspectrum.com/references and click on document #234.
Dr. Fonn is Distinguished Professor Emeritus and the founding director of the Centre for Contact Lens Research at the School of Optometry and Vision Science, University of Waterloo, Ontario, Canada. He is a past president of the International Society for Contact Lens Research and a founding member of the International Association of Contact Lens Educators, in which he served as vice president for 15 years. He served as editor-in-chief of Eye & Contact Lens from 2008 to 2013. He has received many awards and medals to honor his distinguished career. He has served as an advisor to Alcon and CooperVision.