Overview of Dry Eye
Dry eye (DE) is a heterogeneous, multifactorial disease characterized by a combination of ocular surface symptoms (dryness, pain, poor, or fluctuating vision) and signs (reduced tear break-up time, decreased tear production, corneal staining). The DE “umbrella” is often subdivided into categories based on underlying contributors which include aqueous tear deficiency, evaporative DE that is often seen with meibomian gland dysfunction (MGD), anatomical abnormalities (eg, lagophthalmos, conjunctivochalasis), and nerve dysfunction (peripheral or central). To complicate matters, contributors can co-exist in an individual patient1 and observed ocular surface and tear parameters are often disconnected from patient-reported symptoms.2 In addition, factors beyond the ocular surface have been associated with DE symptoms and/or signs including blink rate3 and systemic comorbidities (eg, immune disorders, diabetes, chronic pain conditions).4,5 Furthermore, factors outside the body can affect DE, including environmental factors both indoors and outdoors (eg, humidity, air pollution6,7), exposures (eg, light sources8), and activities (eg, prolonged reading9). In this review, we focus on the relationship between screen use (eg, smartphone, computer) and DE. We first present epidemiologic data regarding the connection between screen use and DE. We then focus on potential pathophysiologic mechanisms between the 2, and finally discuss potential therapeutic technologies and lifestyle modifications that may benefit individuals with symptoms and/or signs of disease.
Computer Vision Syndrome
The 21st century has given way to a global society increasingly dependent on a variety of technologies in personal, occupational, and institutional settings. Naturally, this has led to rising daily exposure to digital screens, with an accompanying rise in the prevalence of ocular complaints. Although many of these ocular symptoms fall under the purview of DE, significant discussion has been had in the realm of a related condition—computer vision syndrome (CVS).
CVS, or digital eye strain, refers to a spectrum of clinical vision-related and muscular symptoms perceivably resulting from prolonged and continuous use of visual display terminals (VDTs), such as computers, smartphones, televisions, and tablets.10 Different display device types are associated with unique profiles of visual effects, possibly due to differences in viewing positioning (distance and angle), patterns of use, screen resolution and contrast, image refresh rates, screen glare, color spectra, and other digital features.11 Common visual symptoms in CVS include dryness and irritation, sensations of burning, asthenopia, epiphora, hyperemia, blurred vision, diplopia, glare sensitivity, and transient deceptions in color perception. Other extraocular complaints associated with CVS frequently include musculoskeletal pain in the neck, back, and shoulders, carpal tunnel syndrome, and venous thromboembolism, and a higher prevalence for developing dermatologic conditions (ie, eczema, rosacea, seborrheic dermatitis).10 Given the global burden of screen-induced visual discomfort, identifying and managing its underlying causes can help improve physical wellbeing and workplace productivity.12,13
Articles for this narrative review were compiled from the National Library of Medicine MEDLINE database with a PubMed search for “dry eye,” “computer vision syndrome,” “visual display terminal,” and “screen use” with searches limited to the English language. All published scientific articles were considered including original research, meta-analyses, and systematic reviews. All searches were limited to the English language. Eligible articles were reviewed and summarized.
Epidemiology of Screen Exposure and DE
Modern lifestyles continue to become increasingly dependent on displays, with a rising global prevalence of ownership and daily use of handheld smartphone devices.8 The extensive use of computers in the workplace has led to a rise in visual health concerns and suboptimal visual function, causing significant physical and occupational burden; an estimated 50% to 90% of all computer users experience symptoms of CVS.14 Although there is a significant shared cohort of symptoms among CVS and DE, the visual manifestations of CVS may occur within and external to the context of DE.
Screen Use Is Associated With a DE Diagnosis
Prolonged use of VDTs is associated with a DE diagnosis, as shown in several large-scale studies.12,15–17 However, it is important to note that DE is variably defined by a constellation of symptoms and signs and as such, diagnostic parameters vary between clinicians and studies.
One large-scale population-based Japanese study sought to evaluate the association between daily hourly VDT use and DE diagnosis in 102,582 middle-aged participants (aged 40 through 74 years). DE diagnosis was defined either as a prior clinical diagnosis or the presence of “often” or “constant” symptoms of both eye dryness and irritation.18 Male and female participants were stratified into groups based on self-reported daily hourly VDT use. Among males, a higher prevalence of DE was found among individuals with ≥5 daily VDT hours (22.3%) as compared to individuals with <1 daily VDT hour (16.1%). A similarly higher prevalence of DE was found among female VDT users with ≥5 daily VDT hour (36.5%) as compared to users reporting <1 daily VDT hour (26.5%). This study demonstrated ≥5 daily VDT hours as a risk factor for DE diagnosis, with an overall greater female DE prevalence in regular VDT and non-VDT users. Unfortunately, DE has also been shown to associate with VDT use in younger individuals, as shown in a study of 3,549 young and middle-aged office workers (aged 22 through 60 years) in Japan with daily computer use.17 Together, these studies identify prolonged VDT use as a risk factor for DE (variably defined), with the frequency of disease ranging from 22% to 27% among males and 36% to 48% among females in Japan. Similar to other studies,19 females were more likely to have DE than men.
Screen Use Is Associated With DE Symptoms
A range of ocular symptoms have been anecdotally associated with computer use. Some of these symptoms are presumed to originate from tear and ocular surface dysfunction, including sensations of irritation, burning, and dryness. Other symptoms, such as asthenopia (ie, ocular fatigue or eye strain) and blurred and double vision, may originate from surface issues but also from dysfunction within the accommodative and vergence systems. Given the heterogeneous nature of ocular sensory processing and the subjectivity of symptom experience and reporting, it is important to note that, although helpful, these distinctions are not definitive indicators of disease origin. One of the most common computer-associated ocular complaints is asthenopia, experienced by an estimated 55% to 81% of VDT users.10,20,21 Sensations of eye dryness, redness, burning, and blurred vision have also been linked to screen use.8,10 In a study of 713 female undergraduates in Saudi Arabia, questionnaires were distributed regarding 6 CVS symptoms including headache, burning, redness, blurry vision, dryness or tearing, and neck or shoulder pain (rated on a scale of none, mild, moderate, and severe). The most frequent reported ocular symptom was burning (58.3%) followed by dryness (51.5%), blurred vision (44.6%), and redness (40.8%). The most frequent severe symptom was dryness (5.6%).22
Similar to the findings in Japanese office workers, time on electronic devices impacted DE symptoms, as ≥5 hours of screen time was found to be a risk factor for ≥3 CVS symptoms.22 In addition, DE symptoms have also been reported with short-term device use (ie, mobile device use for 1 continuous hour).8 Overall, these studies illustrate that continuous VDT use, both short- and long-term, is associated with a range of ocular symptoms, with asthenopia, dryness, and burning among the most frequently reported.
Screen Use Is Associated With DE Signs
Screen use has also been associated with DE signs. As above, the Osaka study recruited 561 young and middle-aged Japanese VDT users (aged 22–65 years, mean VDT use 7.9 hours per day) and assessed symptoms (12-item questionnaire, answered as "never,” “sometimes,” “often”, or “constantly”).12 Measured ocular surface signs included Schirmer test (considered abnormal if ≤5 mm in 5 minutes), Tear break-up time (TBUT) (considered abnormal if ≤5 seconds), fluorescein staining (considered abnormal if score of ≥3/9), and lissamine green staining (considered abnormal if score of ≥3/9). Individuals were then separated into groups based on the test results: “definite DE” was defined as 3 of 3 parameters—DE symptoms, tear film abnormality, and epithelial damage; “probable DE” was defined as 2 of 3 parameters and “non-DE” as 0 or 1 of 3 parameters.23 11.6% of subjects met criteria for “definite DE,” 54.0% for “probable DE,” and the remaining 34.4% for “non-DE.” Similar to previous studies,17,22 VDT time was a risk factor for DE, as >8 hours of use was associated with “definite” or “probable” DE (OR 1.94). Again, females had a higher frequency of DE than males (“definite DE,” 18.7% vs 8.0%; P < 0.05). Interestingly, contact lens use, certain co-morbid diseases (eg, hypertension, diabetes mellitus), and smoking were not risk factors for “definite” or “probable” DE.
A Turkish study further examined ocular surface parameters in 53 VDT users (>6 hours of daily use) and compared these findings to 49 controls (<1 hour of daily use).24 Fluorescein corneal staining was assessed in 5 areas of the cornea (range 0–3) for a total score range of 0 to 15. Tear meniscus height (TMH) and area (TMA) were evaluated by ocular coherence tomography twice, at 8 am (before work) and 5 pm (after a workday). VDT users had significantly higher DE symptoms [Ocular Surface Disease Index (OSDI), 12.8 ± 5.3 vs 8.7 ± 1.6] and corneal staining (2.04 ± 1.86 vs 0.65 ± 0.97) compared to controls. In addition, VDT users had decreased baseline (8 am) TMH and TMA compared to controls.
After working a full day, TMH and TMA were also decreased in VDT users (5 pm measurement) as compared to their 8 am measurements. However, TMH and TMA did not significantly change after a regular workday in the group of individuals who did not use VDT in their occupation (controls).24 This study highlights that regular VDT users have decreased baseline tear volume compared to non-VDT users, which further decreases after a work day. Unfortunately, DE signs have also been related to screen use in younger children.25 Taken together, these studies indicate that prolonged VDT use can negatively affect tear film stability, volume, and corneal epithelial integrity.
VDT Use Is Associated With Meibomian Gland Dysfunction
VDT use has also been associated with MGD.26,27 In Xiamen, China, one study examined the frequency of MGD in individuals with regular daily screen use (>4 daily hours of VDT use, n = 53) and controls (≤4 hours of daily VDT work time, n = 40).26 MGD was defined as the presence of lid margin abnormalities (range 0–4), meibum quality (range 0–3), or gland dropout on meibography (range 0–3 for each eyelid). Lid margin abnormalities that impacted the score included irregularity, vascular engorgement, gland orifice obstruction, and anterior/posterior displacement of the mucocutaneous junction. All MGD scores were higher in the regular-VDT group as compared to controls, including lid margin abnormalities, meibum quality, and gland dropout. Furthermore, all 3 MGD parameters also correlated positively with VDT working time (all P < 0.0001). Of note, the presence of MGD was associated with higher corneal staining and faster TBUT.26 This study illustrates that along with abnormal tear parameters, VDT users have a higher frequency of MGD compared to non-VDT users. Other studies have supported these findings.27 Overall, these studies point to relationships between VDT use, DE symptoms, and DE signs, including MGD.
VDT Use Is Associated With Goblet Cell Dysfunction
The Osaka Study also assessed the presence of mucin 5AC (MUC5AC), a mucin secreted by conjunctival goblet cells, in the 192 eyes of 96 young and middle-aged VDT workers (mean 8.2 daily hours of VDT use). Individuals were grouped by hours of VDT use into short (<5 hours, n = 38 eyes), intermediate (5–7 hours, n = 68 eyes), and long (>7 hours, n = 86 eyes) categories. Individuals in the long (5.9 ng/mg) and intermediate (6.5 ng/mg) groups had lower mean concentrations of tear MUC5AC expression compared to the short (9.6 ng/mg) groups, with significance between the long and short groups.28 This study shows that beyond tear and eyelid parameters, VDT use may also effect the health of goblet cells, with decreased mucin production on the ocular surface.
Pathophysiology and Mechanisms of Damage
Several common mechanisms have emerged as central causes of ocular surface damage and DE in VDT users, including decreased blink rate,3 MGD,27 and corneal phototoxicity.29 It is important to note, however, that the pathophysiology of screen-associated ocular damage is multifactorial and may vary among device type and patterns of use.22,30,31
VDT Users Have Abnormalities in Blink Rate
VDT use can affect blink rate. Specifically, a reduced mean blink rate and incomplete blink motions have been observed during computer use.3,32,33 In a study of 104 healthy office workers in Japan (age range 20–69 years), mean blink rate and palpebral fissure widths were measured in participants in 3 conditions: during VDT work, while reading a book at table level, and while relaxed. Blinking frequency was significantly decreased during VDT work (7 ± 7 blinks per minute) as compared to reading (10 ± 6; P = 0.001) and relaxed conditions (22 ± 9; P < 0.0001). Interestingly, ocular surface exposure, as determined by palpebral fissure width, was similar during VDT work (2.3 cm2) and in relaxed conditions (2.2 cm2), and decreased during reading (1.2 cm2).33 Given that ocular surface area exposure is directly proportional to increased tear evaporation,34 an increased area of exposure coupled with reduced blink frequency is proposed to contribute to reduced tear film viability in VDT users and may also explain why VDT use is more problematic than reading.
VDT users also more frequently exhibit incomplete blinks. In a study of 50 healthy individuals in Spain, participants were asked to read on a computer screen and book. Measurements of incomplete blinks (defined as any visibility of the cornea on blink completion) were recorded using video analysis. In contrast to the study above,33 spontaneous blink rates were similar between the 2 tasks. However, incomplete blink frequency was higher during VDT reading (median 13.5%) compared to book reading (median 5%).35 As some studies have found a correlation between incomplete blinks and inferior corneal staining,36,37 incomplete blinks are one possible explanation for the noted associations between VDT use and DE signs.
Reductions in blink frequency and blink amplitude have also been associated with DE symptoms in VDT users.3 In a study of 21 healthy subjects in New York (age range 21–29 years), blink frequency was measured during a 15-minute computer task, and each blink was evaluated for completeness (no part of the cornea being visible during the blink). A 10-item questionnaire (each symptom ranked from 0–10, total range 0–100) was administered at baseline and immediately after the computer session (reading complex stories taken from the internet) to evaluate DE symptoms. Overall, the mean DE symptom score after the computer task was 14.4. The mean blink rate during the task was 11.6 blinks per minute, which correlated negatively with the total symptom score. A mean of 16.1% blinks were incomplete, which correlated positively with total symptom score.3 Similar to DE signs, this study suggests that decreased blink rate and incomplete blinks are one possible explanation for the noted associations between VDT use and DE symptoms.
Increased task cognitive demand has also been linked to a decreased blink rate.38,39 In a US study of 16 individuals with DE (defined by diagnostic codes) and 16 controls, blink frequency was evaluated during a “high cognitive demand task” (reading a series of random letters and pressing the “space bar” when a particular letter appeared) and a “low cognitive demand task” (watching a movie). The blink rate was lower during the high versus low cognitive task in both the DE (9 ± 5 blinks per minute vs 21 ± 13) and control (9 ± 5 blinks per minute vs 14 ± 11) groups38; however, the difference was only significant in the DE group. This study identifies task difficulty in contributing to VDT-associated blink rate, particularly in individuals with DE.
The above studies suggest that inadequate blinking plays an important role in the loss of tear film homeostasis during VDT use, and that the effects are more exacerbated in individuals with preexisting abnormalities.
Blue Light and Corneal Toxicity
Toxicity from blue light may be another contributor to DE symptoms and signs in VDT users. Light emitting diode (LED) screens have become the predominant technology used in backlighted displays, including smartphones, tablets, computer monitors, and television sets. The peak emission wavelength of these “white-light LEDs” falls between 400 and 490 nm (Fig. 1), which manifests as blue light and includes the “high-energy visible” light range (400–450 nm).40 Although more studies have examined the pathogenic effects of blue light (410–480 nm) on retinal and circadian cycle dysregulation, some studies have examined this question with regards to the cornea.29
Blue light can cause reactive oxygen species (ROS) formation and oxidative damage in corneal cells. In an in vitro study of human corneal epithelial, light-emitting diodes of varying wavelengths (410, 480, 525, 580, 595, 630, and 850 nm) and doses (1, 2.5, 5, 10, 25, 50, and 100 J/cm2) were used to irradiate human corneal epithelial cells, and cell viability and ROS formation (ie, superoxide anion, hydrogen peroxide, and hydroxyl radicals) were evaluated. Cell viability was measured as a percentage using a colorimetric enzyme-linked immunosorbent assay. ROS production at each LED wavelength (dose of 5 J/cm2) was analyzed as fluorescence intensity on flow cytometry compared to baseline fluorescence. Among the LED wavelengths, only 480 nm and 410 nm wavelengths were associated with decreased cell viability. Specifically, viability decreased in a dose-dependent manner after 480 nm irradiation at ≥50 J/cm2 (∼60% viability at 100 J/cm2) and after 410 nm at ≥10 J/cm2 (∼10% viability at 100 J/cm2). In a similar manner, ROS production was higher at 410 nm (363.5 ± 3.8) and 480 nm (454.1 ± 10.3); no significant increases in fluorescence intensities were found after irradiation with all other LED wavelengths.
These data show that specific wavelengths of light in the blue spectrum (410 nm, 480 nm) are associated with corneal damage in vitro. Furthermore, given that reactive oxygen species disrupt DNA, protein, and lipid function at the cellular level, these data propose oxidative stress as a mechanism for blue light-associated ocular surface injury.29 In another study, blue wavelengths of light were shown to damage actively mitotic corneal epithelial cells in animal models41 in a dose-dependent manner.
A limitation of the above studies is that unlike blink dynamics, no studies have demonstrated a negative effect of blue light on corneal epithelial cells in vivo in humans. In fact, blue light-blocking tinted glasses and “night shift” modes on VDTs have been developed based on the available data, but there is limited evidence supporting their clinical use for VDT-associated DE.42,43 As such, more studies evaluating phenotypic corneal changes in humans exposed to blue light are warranted.
VDT Use Is Associated With Ocular Surface Inflammation and Mucin Changes
Various cytokines and chemokines, neuropeptides, and neurotrophins [ie, nerve growth factor (NGF)] play a role in the protection and viability of the ocular surface. In 1 study, cytokine levels between 7 individuals with clinically diagnosed DE and 7 healthy controls were compared, with significantly elevated levels of proinflammatory cytokines [eg, interleukin (IL)-1β, IL-6, IL-10, interferon-γ, and tumor necrosis factor-α, among others] in the DE versus control tear samples.44,45 DE symptoms specifically in VDT users have also been associated with ocular surface inflammation, including increased expression of inducible nitric oxide synthase (iNOS, a proinflammatory and neurotoxic cytokine).46–48 Given the function of iNOS in synthesizing toxic radical nitric oxide, this demonstrates the presence of oxidative and inflammatory ocular surface damage in VDT users.
Nerve growth factor can counteract some of these abnormalities given its pleotropic functions which include regenerating peripheral nerves and increasing corneal sensitivity, promoting conjunctival goblet cell density and mucin production, and augmenting tear production.49,50 Several studies have found increased ocular surface NGF levels in individuals with DE,51 likely due to a compensatory response to inflammation and corneal nerve damage.50 Novel studies have even explored a possible role for human recombinant NGF in the treatment of DE.52 In a study of 120 VDT users in Italy, individuals with severe symptoms expressed increased ocular NGF levels compared to those with moderate symptoms, although not compared to mild or no symptoms.47 Thus, DE symptom severity relates to local NGF changes in VDT users, although the relationship may be nonlinear and dependent on compensatory mechanisms as demonstrated in other disease states.53,54
Prevention and Treatment of Screen-Associated DE
DE symptoms are a significant component of CVS. As such, the identification and management of DE is a necessary measure in minimizing the negative consequences of CVS. Multiple treatments for VDT-associated DE have been advocated, particularly lifestyle adaptations (Fig. 2). Any approach plan must be individualized to the patient and practical for their work environment.
Treating the Underlying Components of DE to Prevent Compound Damage
The treatment of DE begins with artificial tears (AT) of various composition and viscosity.55 Individuals are advised to apply a lubricant eye drop periodically throughout the day if they experience ocular surface discomfort associated with VDT use. Although effective in combating signs and symptoms of DE, a study of 20 volunteers in Spain showed that topical lubricants may not prevent decreases in VDT-associated blink rate.56 This supports a central neural mechanism for VDT-associated reduction in blink rate, influenced by such factors as the difficulty required to complete the task,57 that may persist after treatment with AT.
Beyond AT, given associations between VDT use, inflammation, and MGD, anti-inflammatories (eg, topical cyclosporine) and lid therapies (eg, antibiotics and intense pulse light therapy) can also be considered in appropriate individuals.27 The purpose of these interventions is to decrease the severity of preexisting DE and minimize factors contributing to VDT-associated ocular discomfort. However, more work needs to be done to demonstrate that therapies often used to treat DE have an effect on VDT-associated DE.
Improving VDT Device Position
With a goal of reducing asthenopia and symptoms of ocular discomfort while optimizing comfort, studies have determined a preferred VDT viewing distance of 90 cm and slight downward gaze of 10 degree with some personal variations.58,59 In a study of 38 healthy VDT users in Germany, subjective ocular comfort and symptoms were evaluated at differing screen positions (varying distances and angles). An analysis of subjects’ preferred screen positioning, representing the most comfortable individual screen position, resulted in a mean distance of 90.1 ± 8.9 cm and gaze declination of 11.3 ± 3.4 degrees. Overall, this study identified that a VDT distance of ∼90 cm and downward gaze angle of ∼10° were associated with the lowest ocular discomfort scores and the highest favorability.59 Although other studies have corroborated these findings,58,60 it is important to note that interpersonal variability is expected. Users are encouraged to evaluate various working distances and inclinations to see whether this can reduce ocular discomfort symptoms.
Limiting Screen Time and Blink Modifications
With increasing evidence of the deleterious effect of continuous VDT usage, the obvious solution, although often impractical, would be to limit prolonged screen time. The American Academy of Ophthalmology and American Optometric Association thus make such recommendations as resting from computer work for 15 minutes for every 2 hours of use, and the “20–20-20 Rule” (after every 20 minutes of computer viewing, refocus on an object over 20 feet away for 20 seconds).61,62
Blinking exercises have shown modest efficacy in reducing DE symptoms and signs. In a study of 41 individuals with significant DE symptoms, as identified by questionnaires, participants were instructed to follow a blinking exercise protocol every 20 minutes during waking hours for a 4-week period. The exercise consisted of gently closing eyes for 2 seconds, opening eyes, again gently closing eyes for 2 seconds, followed by squeezing eyes closed for 2 seconds. The average number of daily blinking exercise cycles completed over the 4-week period was 25.6 ± 17.7. After the 4-week period, significant reductions were found compared to baseline in symptom questionnaires (Dry Eye Questionnaire-5: 11 ± 4 to 7 ± 3, and OSDI: 36 ± 18 to 22 ± 17) and TBUT (6.5 ± 2.4 to 8.1 ± 4.8 seconds). This study shows a mild alleviating effect of routine blinking exercises on DE symptoms and signs.63 Given the impact of blink changes on VDT-associated DE, blinking exercises may be incorporated into clinical care recommendations as a protective or therapeutic measure.
Optimizing Workplace Humidity
Given the long hours spent by VDT users in an occupational or home setting, the indoor environment may play a role in development of DE. Alterations in humidity have been associated with DE, particularly in the indoor setting.6,64 Both low and high humidity have been associated with DE, likely due to low humidity causing tear evaporation and thinning of the tear film,64,65 and high humidity environments favoring the survival, transmission, and growth of microorganisms.64,66 Optimal recommended humidity ranges from 40% to 55%, primarily due to effects on upper airway health and respiratory function.64,67
Using a humidifier has been found to modestly alleviate DE signs and symptoms in VDT users, and may be particularly useful in workplaces with low relative humidity.68,69 In a study of 44 young VDT users in New Zealand, individuals were asked to complete a 1-hour computer task without a humidifier and again with a USB-powered desktop humidifier.69 As compared to completing the computer task without humidifier, humidifier use resulted in greater ocular comfort scores and a higher TBUT, with no changes in tear-film lipid layer grading or TMH measurements. Thus, a desktop humidifier may be beneficial in the prevention of VDT-associated ocular damage.
VDT use has been associated with a number of DE symptoms and signs, most notably tear film instability. This instability may be driven by blink abnormalities, Meibomian gland and goblet cell dysfunction, corneal effects of the peak emission wavelength in modern LEDs, and ocular surface exposure. Individuals with preexisting ocular surface abnormalities seem to be more susceptible to VDT-associated DE. As such, we stress the management of underlying contributors to ocular surface dysfunction and modifiable DE parameters for preventing development and progression of VDT-associated DE. Optimizing VDT positioning, lifestyle modifications, blinking exercises, and workstation humidifiers serve as further ancillary treatments.
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