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HomemifeatureThe Great Unknown: Digital Devices’ Impact on Eyes

The Great Unknown: Digital Devices’ Impact on Eyes

Parents often ask optometrists about the appropriate length of time for a preschooler to play on an iPad, or whether a smartphone addicted teenager is harming their eyes. Adults commonly ask why does staring at a computer screen for eight to ten hours each day cause sore, red eyes and headaches. A clear understanding of how the use of smartphones, tablets, and computers impacts the visual system and ocular surface is needed to provide a truly useful response.

The integration of smartphones, tablets, and computers into our lives is widespread. In Australia, 89% of the population own smartphones,1 and it is predicted that by 2023, we will use our phones, on average, 65 times a day.2 Currently, almost half of smartphone users recognise their excessive use and try to limit it.2 In a survey of 18–24 year olds, two out of three smartphone users recognised they were using their devices too much, however, only half were trying to change their habits.2 Four times as many 19–25 year olds than those aged 76 years and older confessed to using smartphones for more than three hours a day.3 The widespread media coverage of recently released guidelines by the World Health Organization (WHO)4 on screen use by under five year olds is a testament to the general public’s desire to understand how much screen use is truly excessive and unsafe. Perhaps this is fuelled by growing self realisation of the widespread addiction to handheld devices.

It is widely understood that the use of handheld digital devices increases ocular and visual symptoms

The current Australian government recommendations for screen use for entertainment purpose is “maximum of two hours per day for children aged five to 17 years”.5 For children aged between two and five, a maximum of one hour per day is advised. Under two years olds should not have any screen time. WHO has similar recommendations of no screen time for one year olds and younger, and less than 60 minutes for two to four year olds.4 The WHO guidelines are designed to reduce inactive time in children, and to increase stimulating time with caregivers, and time spent in physical activity.

OCULAR AND VISUAL SYMPTOMS

It is widely understood that the use of handheld digital devices increases ocular and visual symptoms. Dry eye symptoms such as sore, watery, irritated, and burning eyes occur after as little as an hour of tablet use.6 Tired, uncomfortable eyes and blurred vision can be expected after 60 minutes of smartphone use.7 These symptoms worsen when the smartphone is viewed closer.7 Similar discomfort is likely with computer use, with longer hours exacerbating symptoms.8,9 Eyestrain is five times more likely when reading from an iPad compared to printed text.10 Using an iPad compared to a computer, or using a Kindle compared to printed text, is more likely to cause tired eyes, headaches, blurred vision at near, and difficulty refocussing.11,12

Ocular and visual discomfort associated with smartphones, tablets and computers: what we do and do not know,13 aims to understand whether changes to binocular vision, including accommodation and vergence and/or alterations in blinking, tear film, or ocular surface changes, account for the symptoms experienced with digital device use.

The review concluded that accommodation parameters such as amplitude, lag, and convergence ability are adversely affected by device use. Tear stability is also compromised with digital device use. However, there is insufficient evidence to conclude the impact on tear volume, ocular surface changes, and tear film composition. There is large diversity in how handheld devices are used, for example viewing distance, lighting, and screen size. Further research is needed to identify how such variations in use may impact the accommodation, vergence, blinking, and tear film of users.

BINOCULAR VISION: ACCOMMODATION AND VERGENCE

Figure 1. Summary of reported impact on binocular vision, blinking and ocular surface with smartphone and computer
use. The symbol  denotes computer and ) denotes smartphone and tablet studies.13

Lag of accommodation is indicative of the posture of accommodation and is a common diagnostic test in optometry exams. Smartphone and tablet use increases the lag after as little as 12 minutes and after as long as 30 minutes of use.14,15 No difference is noted between smartphone and tablet use.16 

Changes to accommodative facility with handheld digital device use is not well understood. Although 60 minutes of smartphone use and 30 minutes of reading from a tablet reduced binocular facility,17,18 30 minutes of watching a movie on a smartphone did not change facility findings post task.14

Amplitude of accommodation has been shown to reduce after handheld digital device use. Similar to computers, 20 minutes of iPad use reduced monocular accommodative amplitude by approximately three dioptres,11 and 30 minutes of smartphone viewing reduced binocular amplitude by 1.14 dioptres.14 There is a larger monocular reduction in amplitude after reading from a smartphone compared to a book.14 

The ramifications of such reduction in amplitude are yet to be fully understood in context of handheld digital device use. Furthermore, it is not known how amplitude will change with longer duration of device use.

VERGENCE

Vergence is one of the three components of the visual system’s response to a near target, with the other two being accommodation and pupil contraction. Convergence and divergence are indicative of adduction and abduction ability, respectively. Reduction in these can result in asthenopic symptoms when viewing near tasks.

Convergence ability is reduced after reading from an iPad for 20 minutes in non-presbyopic users.11 Similar findings have been found with LCD computer screens. Divergence measures are reduced similarly in non-presbyopic and presbyopic smartphone users.19

Near point of convergence (NPC) is indicative of maximum converging ability and it recedes further after smartphone use than computer use of just 20 minutes.20 After 10 minutes of recovery, the NPC finding returns to pre-usage level.

Limited evidence of phoria changes with smartphone use suggests a tendency for exophoria after 20 minutes of use in 20–30 year olds.20 This concurs with changes to phoria with computer use. Once again, 10 minutes of recovery brought phoria measurements back to levels in the first five minutes of smartphone use. Users who were 36–50 years old did not seem affected by phoria changes after 30 minutes of smartphone use.19

BLINKING

Adequate blink action is crucial for ‘spreading mixing, and distributing the tears and clearing… debris’21 and is responsible for spreading meibum to form the lipid layer of tear film, without which the aqueous component can evaporate. Ocular discomfort ensues with thinning of the pre-corneal tear film and accumulation of debris.

Reduced blink rate has been well established with computer use. In contrast, the findings with smartphones are conflicting. One study of 60 minutes of smartphone use found reduced blink rate during use,22 while another showed an increase after use.17 Comparing reading from print to reading from an LCD e-reader, the electronic device had a slower blink rate.23 Another study, however, found reading from a tablet resulted in a higher blink rate than from a book.24 

It is important to note that blink rate is significantly influenced by the task and its difficulty. A light conversation has a higher blink rate than a computer task.25 When an identical reading task is performed in print and on computers, blink rate is unchanged.26 This finding needs to be confirmed in smartphones and tablets. Digital devices are used widely, from light tasks such as scrolling through social media and messaging, to complex games and puzzles. It is likely then that blink rate, and consequently tear supply, will vary with type of use.

Another component of blinking that is important for uniform tear film spread is the amplitude of blinks. A partial or incomplete blink will prevent the whole cornea from being rewet. More incomplete blinks occur with tablets than with printed text.24

There is insufficient research into changes to blink rate with gaze angle. Higher gaze angle viewing, such as in upgaze, increases the exposed ocular surface area. It is not known how and if blink rate changes to cope with this, however a reduced blink rate does occur with lower gaze angle viewing.24 Since smartphones are most often used in downgaze, this is a key area requiring further study.

TEAR FILM AND OCULAR SURFACE CHANGES

Tear volume and stability are measures of efficacy of tear production and ocular surface. Adverse changes to either can lead to dry eye symptoms.

Tear volume levels seem unchanged with smartphone use of 60 minutes.15 This contrasts with computer use where Schirmer scores reduced after two or more hours of computer use in regular users.27 However, as little as 20 minutes of playing computer games can also reduce tear meniscus height.28 Pre-existing dry eye disease in computer users does not adversely affect tear volume.29 

Due to conflicting findings, it is unclear if tear stability, measured through tear break up time (TBUT) scores, reduces or remain unchanged with 60 minutes of smartphoneuse.6,17 Despite this, it is important to note that TBUT scores in nine and 10 year olds improved when smartphone use was stopped for one month.30 In this cohort of children, it was found that TBUT scores of less than 10 seconds and/or ocular surface staining was noted in children who used smartphones for three hours or greater per day, compared to those who used smartphones for less than one hour a day.30

Reduced TBUT is known to occur with as little as 20 minutes of computer use.28 Longer hours of computer use also adversely affects quality of meibum expression.31 There is no relationship between the number of hours and years of computer use and TBUT.27

Changes to tear film composition, such as reduced mucin production, increase of inflammatory markers, and increased tear osmolarity, have been reported in computer users.32-34 Such changes are yet to be investigated with smartphone use.

COMPUTERS VS SMARTPHONES VS TABLETS VS THE ‘NEXT’ DEVICE

The term Computer Vision Syndrome (CVS) has been used in literature for at least the last 20 years. Research to date has identified that increased asthenopic symptoms correlate with hours of computer use.8 Additionally, reduced amplitude of accommodation, reduced TBUT scores, and decreased tear volume occurs with computer use. Increased dry eye disease, based on symptoms and objective ocular surface changes, has also been reported during longer hours of computer use.

There is a dearth of literature that specifically examines the impact of smartphone and tablet use on binocular vision, tear film, and ocular surface. This can be attributed to the rapidly evolving technology sector and consequent diversity of handheld digital devices. This diversity includes viewing distance and time spent on devices, both of which may influence accommodation and vergence capability required for clear constant vision. Viewing distance in itself is dependent on screen size, which can vary from as small as digital watches and palm sized smartphones, through to large sized tablets. Furthermore, it is common for multiple devices, such as a phone, computer, and LCD television screen, to be used together at home and in business meetings. Changing focus to maintain clear vision between these devices will require robust accommodation flexibility.

The nature of tasks, from simple video chats to more complex tasks, such as playing puzzles or editing videos, will influence blink action. This will theoretically impact tear production and consequently the health of the ocular surface. As has been noted with computer users, alterations to tear film composition, such as mucin levels and osmolarity, may also occur with use of digital devices.

Every person, every day uses devices differently; sometimes phones are viewed for seconds and sometimes for hours. When it comes to the use of devices, the questions that remain are: how long do the changes in binocular vision and tear film remain after their use has stopped? Is the effect compounded by multiple device viewing or continued and repeated use during the day? Does pre-existing accommodative, vergence or ocular surface dysfunction worsen in these situations? And, are children affected differently to adults, since their habits of device use differ?

Every day, optometrists encounter patients with asthenopic symptoms who confess to hours of screen time, whether due to employment or leisure. Additionally, we see children as young as toddlers being preoccupied by such new ‘toys’. To effectively manage screen time, it is crucial that we gain evidence based knowledge of how these screens change our eyes and vision. Once we have a clearer understanding of this, it is hoped that appropriate evidence based guidelines can be made available to outline the appropriate use of smartphones, tablets and future devices.

This article summarises key points from Ocular and visual discomfort associated with smartphones, tablets and computers: what we do and do not know, published in Clinical Experimental Optometry, Wiley Publishing, 2019, Early Print.13 © 2019 Optometry Australia. 

Researchers at the School of Optometry and Vision Science at UNSW Sydney are working to expand our knowledge regarding the impact of digital devices on vision and the ocular surface. Dr Blanka Golebiowski and Associate Professor Isabelle Jalbert, along with PhD student Ngozi Chidi-Egboka, are currently enrolling participants in a study of the effects of smartphone use on the tear film of children and teenagers, to better understand if they are at risk of developing dry eyes. To find out more or enrol participants, email: n.chidi-egboka@unsw.edu.au. 

Sukanya Jaiswal graduated in 2013 from UNSW Sydney with an undergraduate optometry degree. She is now pursuing a Masters of Optometry from UNSW. Ms Jaiswal currently works as a full time optometrist in Western Sydney. 

Dr Blanka Golebiowski is an optometrist and Senior Research Fellow at the School of Optometry and Vision Science at UNSW Sydney. 

Dr Lisa Asper is an optometrist and Senior Researcher at the School of Optometry and Vision Science at UNSW Sydney. 

Dr Jennifer Long is an optometrist and Senior conjoint lecturer at School of Optometry and Vision Science at UNSW Sydney. 

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