The rapid expansion of digital technology has transformed how people work, study, read and access information. University students and working adults spend a substantial amount of time using computers, tablets and smartphones for reading and other visually demanding near tasks, with daily screen time often exceeding several hours and, in many cases, reaching levels considered excessive.¹ This shift has raised concerns about the impact of prolonged near work on visual function, especially on the accommodative system, which maintains clear retinal images during close viewing.² Prolonged digital near work has been associated with visual discomfort, headaches, difficulty refocusing and other symptoms of digital eye strain.^3,4 Understanding how different reading media influence accommodation is therefore essential for both visual comfort and long-term ocular health.

Accommodation does not always precisely match the dioptric demand of a near target, as young adults may exhibit either a lag (under-accommodation) or a lead (over-accommodation) depending on task characteristics, attentiveness and viewing conditions.^5,6,7 Previous studies comparing printed and digital reading have produced mixed findings.^5,8,9 Some reported comparable accommodative responses when viewing distance and stimulus parameters were matched and well controlled,^5,8 while others found that certain digital conditions, such as high-resolution smartphone screens, may alter accommodative behaviour.⁹ These inconsistent findings suggest that device type alone may not explain accommodative behaviour and that methodological differences across studies play a significant role.

Viewing distance is one of the main factors differentiating digital devices.^10,11 Young adults typically hold smartphones at shorter distances than printed materials or computer screens, often at 30 cm–35 cm or less, whereas computers are commonly viewed at 50 cm–70 cm.^10,12 Both accommodative and vergence demands are increased at closer viewing distance, which may contribute to eyestrain and visual fatigue more than extended, ergonomically suggested distances.^7,13,14 Research has also shown that sustained digital screen use may alter accommodative parameters such as facility, amplitude and microfluctuations.^15,16,17,18

The accommodative response can also be influenced by screen size and visual ergonomics in addition to distance.¹⁴ Compared to bigger displays like tablets and computers, smaller devices, like smartphones, frequently demand viewing smaller text on a compact, self-luminous display, potentially increasing accommodative and vergence effort.^9,14,15 Larger devices, on the other hand, are usually viewed from farther away with larger text and a more steady posture, which may lessen the overall accommodative load.⁵ Reviews on digital eye strain emphasise that accommodative and vergence problems are often driven by demanding near work and suboptimal ergonomics rather than screen exposure alone.^4,19

Despite growing interest in the visual effects of digital device use, several gaps remain in the existing literature. Many studies have focused on symptom-based assessment of digital eye strain and relied on self-reported discomfort, rather than direct physiological measurement.^20,21 Few studies have directly compared accommodative responses across multiple screen sizes within the same group of participants, but have been limited to one or two types of digital devices.^5,15,22,23 As a result, it remains unclear how commonly used reading media influence the accommodative system when key visual parameters are standardised. Accommodation response measurements, such as the monocular estimation method (MEM) dynamic retinoscopy, can offer a more accurate assessment of device-related visual demands by providing clinically relevant insight into accommodative behaviour during active near activities.²⁴ These measurements are essential for guiding ergonomic recommendations, providing clinical advice and interventions aimed at reducing accommodative stress caused by digital reading. Therefore, the present study aimed to compare accommodation responses during reading printed text and digital text presented on a smartphone, tablet and computer among young adults. The findings provide insight into how device type and screen size influence accommodative behaviour during everyday reading tasks.

A total of 32 university students (mean age 22.75 ± 1.30 years) completed the reading trials. The majority were women (87.5%), and all demonstrated normal or near-normal distance visual acuity (mean VA = –0.01 to –0.02 LogMAR). Most participants had low-to-moderate refractive correction, with spherical values averaging approximately –0.50 D in both eyes and small amounts of astigmatism (≤ –0.25 DC). Baseline accommodative and vergence measures were within age-expected clinical ranges. The mean amplitude of accommodation was 10.4 D – 10.5 D, and the mean near point of convergence (break) was 5.69 cm ± 1.28 cm. No manifest strabismus was detected on cover tests.

Figure 1 illustrates accommodative responses across all reading conditions. The median (Mdn) accommodative response was found at the same central tendency across printed (Mdn = −1.00 D, interquartile range [IQR] = 0.81), smartphone (Mdn = −1.00 D, IQR = 1.00), tablet (Mdn = −1.00 D, IQR = 1.00) and computer (Mdn = −1.00 D, IQR = 1.38) reading conditions. The boxplots represent the median, interquartile range and overall variability of accommodative response for each reading condition, with mean values indicated by (×).

This study examined how accommodation responses vary when young adults read printed text and digital text on a smartphone, tablet and computer screen. A lead in accommodation across was observed in all four reading trials, with the largest lead during smartphone reading and the smallest during computer use. This pattern suggests a device-dependent modulation of accommodative behaviour rather than a uniform response to near work alone. The presence of an accommodative lead aligns with what is typically expected in young, non-presbyopic individuals who frequently demonstrate strong tonic accommodation, proximal cues and highly responsive accommodative systems during sustained near task.^7,14,23,30 These individuals often demonstrate a tendency to over-accommodate during near tasks, especially when visual or cognitive demands increase.^6,31 Importantly, accommodative lead may occur even in the presence of visual discomfort and does not necessarily indicate visual dysfunction. This distinction is critical because some research on digital eye strain relies mostly on symptom-based evaluations that do not always correspond directly to objective accommodative measurements.^3,19 Thus, the accommodative lead observed in the present study reflects physiological accommodative behaviour under cognitively demanding reading conditions.

Computer reading produced the least accommodative response, which is probably due to larger screen size and longer viewing distances typically used with of computers. Ergonomics standards generally recommend a viewing distance of 50 cm–70 cm for computer tasks.¹¹ At these distances, both vergence and accommodative demands are reduced, resulting in less strain on the accommodation–vergence system.³² This pattern is in line with studies that indicate using a computer reduces accommodative stress as compared to tasks carried out at shorter viewing distances.^4,7,13 The relatively less accommodative response while reading with a computer in this study supports existing ergonomic guidelines and suggests that a larger screen display may offer a more visually sustainable option for prolonged near work.^13,19

Reading on a smartphone resulted in a significantly greater accommodation response than reading printed text, a computer or a tablet. This result emphasises the disproportionate visual demand imposed by handheld and smaller digital devices.^14,15 Young adults typically hold smartphones closer, often between 25 and 33 cm, which substantially increases the accommodative stimulus.¹⁵ Short viewing distances also raise vergence demand, and because accommodation and vergence are closely linked, the combined effort intensifies activation of the near triad.^16,17,33,34 Studies have also supported that larger accommodative lead during smartphone reading not only increased dioptric demand, but also heightened neural drive associated with sustained attention during near work.^35,36

Another key finding was that printed text, tablet and computer reading produced similar accommodative responses, with no statistically significant difference between them. This finding suggests that tablets may function similar to traditional printed materials than to smartphones with respect to accommodative demand, particularly when viewing distance and luminance are controlled.^5,14,22,37 A previous study has also reported comparable findings under controlled stimulus conditions.⁵ In typical use, tablets and printed text are about the same size and are usually held at distances around 30 cm–40 cm.¹⁰ Tablets may therefore offer an intermediate option between smartphone and computer, balancing between portability and less accommodative stress.

Several factors may contribute to the increased accommodative response observed with smartphones. Using a smaller screen often results in reduced character size and higher visual density, which potentially could lead to more frequent and prolonged fixation, and greater cognitive load during reading.³⁸ These visual behaviour changes may place additional strain on the visual system, thereby indirectly increasing accommodative effort.¹⁵ Digital eye strain literature consistently identifies accommodative and vergence stress as key contributors to symptoms such as eyestrain and headaches during screen use.^1,4,13 Taken together, our findings reinforce important implications. Young adults with borderline accommodative or binocular function may be particularly vulnerable to accommodative stress during prolonged smartphone reading. The results corroborate clinical recommendations that promote the use of larger screens, longer viewing distances and frequent breaks to mitigate accommodative overload associated with handheld digital devices.^4,19

The findings also have broader relevance to discussions about near work and myopia. Short viewing distances and intensive near tasks have been identified as environmental risk factors for myopia development and progression.^39,40 Although this study did not investigate a direct relationship between accommodative response and myopia, the higher accommodative demand associated with smartphone use corresponds with behavioural patterns implicated in increased near-work load.^14,35 The finding highlights the importance of device selection and viewing habits in discussions of visual health, especially among young adults who engage heavily with digital screens.

Accommodation response during reading varies according to device type and the size of the reading medium. Smartphones elicited the greatest accommodative response, indicating a higher accommodative demand compared with tablet, printed text and computer viewing, while computer use produced the lowest demand. These findings suggest that prolonged reading on handheld digital devices may place greater strain on the accommodative system.

From a clinical and ergonomic perspective, larger screens or printed materials should be preferred for extended reading tasks, particularly among young adults engaged in intensive near work. Collectively, the results underscore the importance of considering device type, ergonomic posture and viewing distance when advising students, educators and the public on safe and sustainable reading practices in increasingly digital learning environments.