Are you sitting and seeing comfortably? Then let’s begin.
But first, pause for a moment to think about the answer to that question. Are you sitting comfortably? How does your body feel right now? Where would you place yourself on a scale moving from absolute comfort to total discomfort or even pain? Comfort is complex and multifactorial. This is no less true when it comes to the eyes, specifically with regard to the comfort experience of contact lens (CL) wearers. This article explores the influences that affect CL comfort, examining how both physical and visual elements contribute to the overall comfort experience.
NO SIMPLE DEFINITION
Defining comfort and discomfort is not straightforward. Research in the field of ergonomics defines comfort as “a pleasant state or relaxed feeling of a human being in reaction to its environment” and discomfort as “an unpleasant state of the human body in reaction to its physical environment.”1 Interestingly, it is also not a binary concept, in which the presence of one indicates the absence of the other and vice versa; in fact, the absence of discomfort does not automatically result in comfort. Rather, without discomfort, nothing is experienced.2
To report comfort, more must be experienced, and for studies of ergonomics, that extra experience is related to luxury, relaxation, or feeling refreshed.1 In terms of CLs, overall comfort is influenced by both the physical and the visual experience (Figure 1).
PHYSICAL CONTACT LENS DISCOMFORT
With regard to the physical experience of CLs, discomfort is most often evident in the end-of-day sensations and reduced wear times that patients may describe. For some, it may simply be reported as an inability to wear lenses for as long as desired. For others, the sensations experienced may be described with words. For example, “dryness” and “discomfort” remain the most commonly cited reasons for dropout,3 especially for established wearers. Practitioners should be alert for these words or for alternatives such as “stinging,” “burning,” “gritty,” “scratchy,” or “irritated.” It is worth noting that new wearers experience issues with lens handling and vision, both of which can contribute to dropout among this group in addition to problems with comfort.
The Tear Film and Ocular Surface Society’s (TFOS) 2013 workshop reviewed the evidence available about contact lens discomfort (CLD) in relation to its etiology, investigation, and management. CLD is common, with around half of CL wearers affected on average. Unsurprisingly, the etiology of CLD is complex, with many possible causes contributing to the overall level of comfort experienced by wearers. The report described how contributors to CLD can be classified into CL and environmental factors. CL factors cover material properties, design, fit, and lens care. It remains challenging to study the contribution of these factors in isolation from each other; changing one material property to examine its effect on comfort invariably changes other elements within the CL. Table 1 contains a short summary of how these CL factors may contribute to CLD.4-9
|CL PROPERTY||CONTRIBUTION TO CONTACT LENS DISCOMFORT|
|Material||• No difference in comfort demonstrated between hydrogel and silicone hydrogel materials4|
|Surface Properties||• Low coefficient of friction is important in driving comfort4
• No peer-reviewed conclusive evidence between on-eye (in vivo) wettability and comfort5
|Bulk Properties/Design||• Lack of well-controlled studies linking comfort with modulus5
• Edge design does appear to modulate comfort, with a thin tapered edge significantly more comfortable compared to chisel and round edge designs6
• Steeper base curve associated with greater comfort in senofilcon A7
|Modality||• Daily disposables are more comfortable compared to the same lenses worn on a frequent replacement schedule8|
|Lens-Solution Combination||• Some evidence of lower comfort in patients who exhibit solution-induced corneal staining (SICs)9|
Addressing Physical CL Discomfort To effectively manage this multifactorial problem, there are two important considerations. The first step is to question patients thoroughly about their comfort experience. The amount of time for which CLs can comfortably be worn should always be established. If a gap of two hours or more exists between the total and the comfortable wearing time, it can be an indication of “less than successful wear,”10 which should prompt practitioners to investigate and manage the situation. Use of a validated questionnaire is recommend to quantify and track changes in symptoms over time. The CL Dry Eye Questionnaire (CLDEQ-8) asks specific questions about the frequency and intensity of dryness and discomfort symptoms.
The second important consideration in addressing CLD is to employ a methodical approach. The TFOS CLD report suggests a management strategy that involves addressing co-existing factors or other ocular or environmental factors prior to changing the CL. For instance, existing blepharitis should be managed first, followed by additional recommendations that may include increasing the CL replacement frequency by changing to a daily disposable and the use of lubricating drops. Table 2 summarizes the actions taken once any other co-existing factors have been addressed.
|Change care solution|
|Change to daily disposable (eliminate care system)|
|Shorten replacement frequency|
|Change lens design and/or material|
|Tear supplementation: lubricant/wetting drops, lacrimal inserts, punctal occlusion|
|Dietary supplements (evening primrose oil)|
|Topical medication (azithromycin)|
|Improve environment: humidity/airflow|
|*Papas EB, Ciolino JB, Jacobs D, et al. The TFOS International Workshop on Contact Lens Discomfort: report of the management and therapy subcommittee. Invest Ophthalmol Vis Sci. 2013 Oct 18;54:TFOS183-TFOS203.|
Finally, with regard to physical comfort, it must be acknowledged that studies suggest that a decline in comfort throughout the day may be more related to a fatigue-like response in the ocular tissues and to changes in the ocular environment rather than to the CL itself.11
The physical sensation of discomfort alone does not fully describe the CL wearing experience. To build a complete picture, the perceptual elements of visual comfort must also be considered. Visual comfort is, of course, relevant to all patients irrespective of CL wear. CL wearers, however, present a challenge to practitioners because both elements of physical and visual comfort must be considered to be able to fully understand and manage patients.
Although no single definition of visual comfort exists, there are similarities among descriptions. One author of this article, Dr. Buch, describes visual comfort as “the feeling of ease, well-being, or satisfaction with the visual environment.” Visual comfort has also been defined as “the subjective impression of comfort caused by visual stimuli.”12 A good example of the impact of visual discomfort is the fact that in the United States, it is listed as a condition with applicable signs and symptoms for diagnosis in the international classification of disease (ICD-10) codes used for medical insurance billing purposes.
The sensations experienced by patients when visual discomfort or eyestrain occurs range from pain to ache or tiredness around the eyes. Blurred or diplopic vision, headache, and ocular fatigue may also be experienced. Blurred vision has long been associated with visual discomfort, and uncorrected astigmatism can be a major cause of eyestrain, headache, and tired eyes.13 Accommodative and vergence anomalies are sources of eyestrain.14,15 Oculomotor imbalances resulting from poorly compensated phorias also contribute to eyestrain.
Squinting is a response to blurred vision or extraneous light sources, and it involves constriction of the orbicularis oculi muscle. Significant correlation between discomfort and blood flow to this muscle has been shown and suggests that pain around the eye may result from over activation of the orbicularis while squinting.16 Prolonged constriction of the corrugator supercilii muscle near the eyebrows has also been associated with migraine headaches, likely due to compression of the supraorbital and supratrochlear nerves that run through it.17
The contrast of the target, text size, and cognitive demand of the task also contribute to visual comfort.18 Blink rates decrease with near tasks,19 and incomplete blinks have been correlated with discomfort.18 The evidence that pupil constriction is a source of pain remains equivocal, with some studies reporting that pupil constriction does not directly cause discomfort20,21 and a recent study suggesting a more causal relationship.22 Irrespective of a direct link, pupil constriction is, of course, related to accommodation and convergence, and sustained near tasks place strain on this triad of close-focusing systems.
Digital Devices Many of the additional factors associated with visual discomfort arise from the type of near task performed. While reports of visual discomfort can be found dating back to ancient times, most relevant in today’s modern society are those tasks completed on digital devices. The magnitude of ocular symptoms is significantly higher when viewing digital displays compared to when viewing printed materials.23 Vision-related symptoms arising from the use of digital devices include eyestrain, blurred vision, dry eye, headache, and discomfort.
The use of digital devices is widespread: a 2017 survey of U.S. adults showed that just over three-quarters of Americans own a smartphone, with an even higher penetration of 92% among the 18- to 29-year-old age group.24 The term “computer vision syndrome” (CVS) characterizes a group of ocular and non-ocular symptoms, and when this complete range of symptoms is taken into account, a CVS prevalence of 90% has been reported.25 The use of the term CVS to describe symptoms seems to be gradually decreasing in favor of the newer descriptor “digital eyestrain.” In a survey of New York office workers, 40% reported “tired eyes” at least half of the time, with nearly one-third (31%) reporting “eye discomfort” at the same frequency.26
The type of device used varies, from desktop visual display unit (VDU) screens through to laptops and handheld devices. Each of these are used at different viewing distances and gaze angles, at different times of day, under different ambient illumination, and in varied environments. This presents a complex range of demands to the visual system.
Photophobia Visual discomfort can also be attributed to several ocular and systemic diseases as well as to medications. Photophobia is a cause of visual discomfort and is defined as “abnormal sensitivity to light, especially of the eyes.”27 Photophobia is associated with dry eye, migraine, depression, blepharospasm, progressive supranuclear palsy, and the use of medications such as barbiturates and benzodiazepines.27 It is linked to pain sensation, with functional magnetic resonance imaging (fMRI) recordings showing a pattern of activation suggesting that photophobia is perceived as a true pain stimulus.28 A more detailed discussion is beyond the scope of this article.
Glare We are all susceptible to being troubled by excessive light levels; just think of how we shield our eyes from the sun on a bright day or of how uncomfortable we can find oncoming headlights when driving at night. Viewing bright lights can cause the eye to respond with squinting and pupil constriction, which may lead to visual fatigue and discomfort. It is also common to respond to uncomfortable light levels by averting the eyes.
The American National Standards Institute/Illuminating Engineering Society (ANSI/IES) RP-1-12 standard states that “glare occurs when luminances, or luminance ratios are excessively high in relation to the state of adaptation.” A luminance ratio is the luminance of the glare source divided by the luminance of the target. The ANSI standard states that the luminance ratio should not exceed 10:1 for remote light or more than 3:1 between the target and immediate visual surroundings. Use of sunglasses does not change the luminance ratio; however, viewing through sunglasses feels more comfortable because overall retinal illumination has been reduced. This moves the exposure below the borderline luminance between visual comfort and discomfort (BCD value). The BCD value is commonly used by lighting engineers and architects when determining the optimum, comfortable levels of illumination of a room.
Glare reduces both contrast sensitivity29 and high- and low-contrast acuity.30 It is generally categorized into two types. Disability glare is “a temporary impairment of vision due to light” and is caused by loss of retinal image contrast resulting from intraocular light scatter.31 Discomfort glare is “a transitory irritation caused by light” and may be a response to the saturation of visual neurons.31 In addition to the luminance ratio and the size of and distance to the light source, a number of other factors contribute to discomfort glare. Awareness of these factors, summarized in Table 3, enables practitioners to offer better advice to patients who are troubled by glare-induced visual discomfort.
|FACTOR||CONTRIBUTION TO DISCOMFORT GLARE|
|Angle||• Glare worse with lower angle between glare source and line of sight|
|Contrast||• Glare worse with higher contrast between glare source and background luminance|
|Light adaptation||• Adaptive state of the individual, for example, the discomfort felt by a fully dark-adapted person when a room light is turned on|
|Wavelength of glare source||• Glare varies with spectral composition of light source; humans are most sensitive to the central range of the visible light spectrum, between 510nm and 550nm, and are typically more annoyed by shorter (e.g., 400nm) than longer (e.g., 700nm) wavelengths|
|Time of day||• Lower angle of the sun being more bothersome in the mid-morning and mid-afternoon|
|Natural mediators||• Lightly pigmented Caucasians more bothered by bright light compared to individuals who have increased pigmentation32
• Less visual discomfort has been correlated with higher macular pigment densities33
Compensating Behaviors A number of compensating behaviors are employed to help mediate visual discomfort. Squinting occurs in relation to uncorrected refractive error, binocular vision imbalances, and glare. Excess light is often blocked by a hand shielding the eyes or by the use of sunglasses. The compensating behavior particularly associated with glare is avoidance. Examples of this include looking away from car headlights at night or flipping down the visor when driving toward the setting sun.
OVERLAP BETWEEN PHYSICAL AND VISUAL DISCOMFORT
Figure 1 listed the physical and visual factors that contribute to overall comfort when wearing CLs. In reality, of course, these factors may overlap. In a survey of habitual reusable CL wearers, 59% reported a decline in comfort, overall lens satisfaction, and vision quality over the course of the day.34 Of this “declining” group, the most commonly described symptoms were “tired eyes” and “dry eyes.” The former refers to a visual factor, the latter to a physical sensation. Changes to the tear film could provide part of the explanation for these overlapping sensations of discomfort; CL wear promotes a more unstable tear film, which can lead to both discomfort/dryness and to fluctuations in vision.
Overlap between comfort and vision was investigated in a study that looked at the influence of vision on ocular comfort ratings.35 Under some circumstances, comfort was reduced with induced visual blur, and the authors suggested that complex psychological influences and higher-order sensory integration of vision and pain processes may be involved.
- Overall contact lens experience is influenced by both physical and visual comfort.
- Ask patients not only “How do your lenses feel?” but also “How comfortably can you see?”
- To improve physical comfort, apply a methodical approach to addressing issues.
- Visual comfort is often related to specific tasks or environmental conditions.
- To maximize visual comfort, advise on proper viewing techniques for near tasks and digital devices, correct any binocular imbalance, and pay attention to glare sources in the patients’ environment.
- In the future, it may be possible to deliver enhanced visual and physical comfort for CL wearers.
In terms of what is best for our patients, it is important to be aware that discomfort can manifest as both physical and visual sensations. Recognizing that the total comfort experience consists of both elements allows us to elicit better information from our patients and, from that, to make more useful recommendations to manage their discomfort. While we may regularly ask our CL wearers “How comfortable do your lenses feel?” we have an opportunity to also enquire “How comfortably can you see?”
Comfort and discomfort in CL wear is driven by multiple factors, which can overlap and influence each other. It is important to take a methodical approach to management. Follow best practice guidelines for addressing physical CL discomfort, and provide appropriate visual correction and advice on near focusing and light management to help optimize visual comfort. In doing so, practitioners will help improve their patients’ overall CL experience and satisfaction, potentially reduce their dropouts, and increase recommendations.
Future CL technology may be developed to aid some of the discomfort issues. For example, in addition to providing UV-blocking, it may be possible for a CL to selectively filter light to enhance visual performance. Remembering that in the field of ergonomics, comfort is achieved only when something additional is experienced, perhaps we can hope for future CL technology to not only help prevent feelings of discomfort, but actually to deliver enhanced visual and physical comfort for the wearers. CLS
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