Factors affecting outcome of acquired comitant esotropia with restricted use of digital devices: ACEDD Study 3

Introduction

Acute acquired comitant esotropia (AACE) is characterised by acute onset of esotropia without limitation of eye movement in children and adults.1 2 In recent years, an increase in the number of AACE cases, including ‘acute’ and ‘subacute’ cases, and cases reported several years after the onset of acquired comitant esotropia (ACE), has been reported, which is thought to be related to the widespread use of digital devices.3–8 Several studies have reported an association between the excessive use of digital devices and the development of acquired esotropia3 9 and that limiting their use improved esotropia.9 10 However, the definition of digital-device overuse remains ambiguous, and there is no standard for how long it should be reduced.

To confirm the relationship between hand-held digital device (DD) usage and ACE, we conducted a nationwide, multicentre, prospective study focusing on young patients.11 We observed changes in strabismus angle over a 3-month period following instructional DD usage. While some cases showed improvement in strabismus, the observed change was clinically modest, and the probability of cure was low, suggesting the presence of other parameters influencing the relationship between DD usage and ACE. To understand the characteristics of patients who are more likely to improve their ACE with instructions for DD usage and to clarify the relationship between DD-use time and outcomes, this study investigated the relationship between 3-month outcomes and various clinical parameters.

Materials and methods

Study participants

Participants comprised patients aged 5–35 years whose diplopia or esotropia was noticed by themselves or their guardians within 1 year of their initial visit and were subsequently confirmed as having esotropia. Details of inclusion and exclusion criteria are described in our first study.11 Between November 2019 and December 2021, 221 patients from 55 centres were enrolled (online supplemental material 1). Interviews with patients or their guardians covered the onset, ocular symptoms and DD usage. Patients underwent a detailed ophthalmologic examination at the initial visit, complemented by a neurological examination with head MRI/CT whenever feasible. Patients with neurological abnormalities were excluded from this study. Those with a history of amblyopia or strabismus were included. Spectacles were prescribed for patients without appropriate refractive glasses, and prismatic glasses were provided on request. A common study manual was used to standardise examination procedure at all the facilities.

We provided the following instructions regarding the use of DD: limit usage to less than 60 min/day for elementary school students and younger, less than 120 min/day for junior high school students and older, keep a minimum viewing distance of 30 cm and take a 5-min break after every 30 min of use. Participants were instructed to maintain a diary of how long they used DD per day (DD time) and visit the hospital in the first and third months for interviews and ophthalmological examinations. Patients were instructed to record the time of using DD with honesty and accuracy; in case the patient was of primary school age or younger, they were instructed to take help of their parent or guardian.

From the initial enrolment of 221 patients, 19 were excluded due to withdrawal of consent, lack of hospital visits before the study conclusion, or identification of abduction restrictions. Additionally, 25 patients who used DD for less than 60 min/day (for elementary school students and younger) and less than 120 min/day (for junior high school students and older) at the time of their initial examination were excluded from the study because they were considered unaffected by DD. Patients were also excluded if there were no data available on initial DD time (n=2) or outcomes (n=19), and finally 156 patients were included in the analysis (figure 1).

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Figure 1

Flow chart of study participants. In total, 156 patients with DD use at initial visits were originally analysed. For the analysis using multiple imputation for missing data, 177 patients were included. DD, hand-held digital devices.

Results

In total, 156 patients (mean age (SD): 16.4 (7.4) years old, 88 males) were classified into the cured (n=10, 6.4%), improved (n=58, 37.2%), unchanged (n=67, 42.9%) and worsened (n=21, 13.5%) groups. The baseline esotropia angle of all patients was 25 (0, 70) PD at distance and 20 (0, 70) at near, with a decrease to 20 (−10, 60) PD (p=0.002) and 18 (−6, 66) PD (p=0.04) at 3 months, respectively. Table 1 shows the background characteristics and comparisons across the four outcome groups.

In the univariate analysis, significant differences were observed in the number of patients who visited the hospital within 3 months of onset, angle of distance strabismus and stereoacuity. The median strabismus angle at distance in the cured group was 11 PD, which was significantly smaller than that in the other three groups (improved: 25 PD, p<0.01; unchanged: 25 PD, p<0.05; worsened: 30 PD, p<0.01). The median near stereoacuity of the cured group was 50 arcsec, significantly better than those of the unchanged and worsened groups (400 arcsec, p<0.05, and 1550 arcsec, p<0.01, respectively). Spectacles were prescribed for 42 (27%) patients for appropriate refractive correction, whereas prism glasses were already used by 10 (6.4%) patients at the initial visit and were newly prescribed to 22 (14%) patients. Prism glasses were prescribed with ground-in or Fresnel membrane prisms. No significant differences were observed in refractive values, undercorrection of hyperopia or myopia, anisometropia, or high myopia and the proportion of prism users in the four outcome groups.

Regarding the comparison of DD usage during the initial visit, no significant differences were observed among the four groups in terms of DD time, whether they were used at night, or whether the viewing distance was 30 cm away (table 1). Cluster analysis, categorising patients based on changes in DD time over three visits, showed that patients who reduced their DD time (clusters 1 and 2) typically achieved a reduction of more than half (online supplemental figure 1) Therefore, we defined successful DD time halving as cases in which the DD time after 1 or 3 months was less than half of the initial DD time, serving as a variable for change in DD time. Subsequently, we compared the DD usage conditions at the third-month visit and found no significant differences among the four groups in terms of whether they took breaks, maintained a distance of at least 30 cm, maintained the recommended time for use and achieved successful halving of DD time (Table 2).

However, in terms of DD time, at 1 and 3 months, the cured, improved, and unchanged groups showed a significant decrease in DD time (cured: p=0.023, improved: p<0.001, unchanged: p<0.001), whereas the worsened group showed no decrease in DD time (p=0.08) (figure 2). Table 3 shows the results of the ordinal logistic analysis, with the outcomes ordered as cured, improved, unchanged and improved (see online supplemental table S1 for the full table). The analysis revealed that the outcomes were influenced by small-angle strabismus at distance (p=0.023), good stereoacuity (p=0.003) and successful DD time halving (p=0.016). The results of the same regression analysis performed after imputing missing data were similar to those of the original analysis (online supplemental table S2).

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Discussion

In this study, we aimed to investigate factors associated with outcomes after 3 months of instructed usage of DD and appropriate spectacle wear. Of 156 patients, 10 (6%), 58 (37%), 67 (43%) and 21 (13.5%) were in the cured, improved, unchanged and worsened group, respectively. Factors associated with good outcomes were small angle esotropia, good stereoacuity and successful halving of the time spent using DD.

Regarding the change in DD time during the follow-up period, a decrease was observed in the cured, improved and unchanged groups, whereas no decrease was observed in the worsened group. Additionally, ordinal logistic regression showed that failure to reduce DD time by less than half of the original time was associated with worse outcomes. These results indicate that limiting the use of DD is expected to improve esotropia, whereas continued use may worsen the condition.

Some previous studies9 10 13–15 have shown an improvement in strabismus angle after restricting smartphone use. Lee et al9 reported that cessation of smartphone use improved esotropia in all 12 cases and reduced the strabismus angle by approximately 10 PD, from a mean of 27.75 to 17.50 PD at distance fixation. Other studies showed that reducing the use of DD improved esotropia and diplopia in 5 out of 1510 and 4 out of 10 cases,15 respectively. In contrast, one study16 found no improvement in esotropia with reduced smartphone use. Therefore, the effectiveness of this approach is controversial. Although the mechanism of esotropia development from smartphone use is not fully understood, it has been suggested that the viewing distance is shorter when using a smartphone than when viewing hardcopy text,15 17 and that excessive accommodation and convergence occur,2 5 10 15 as well as the absence of distance viewing (without divergence eye movement).18 We speculate that reducing the amount of time spent using smartphones will reduce this abnormal viewing condition and, in some cases where the esotropia is in a reversible stage, may influence improvement. In cases with a small strabismus angle, limiting the use of DD may be particularly beneficial, since a reduction of 10 PD may lead to a cure.

In this study, cluster analysis was useful in examining trends in the changes in DD time, which are expected to vary from case to case in terms of compliance. Notably, the factor of successful DD time halving, rather than the recommended time by age, was associated with the outcome (table 3, online supplemental tables S1 and S2). This may reflect individual differences in the sensitivity to the effects of DD usage on esotropia.7 19

Other factors associated with positive outcomes in this study were good stereoacuity and small-angle strabismus at distance. Stereo test results are influenced by the ocular position.20 Specifically, with a smaller strabismus angle, it is easier to maintain esophoria and better stereo test results can be expected. Regardless of the duration of DD usage, stereoacuity and strabismus angle were considered important prognostic factors for the outcomes in this study.

Regarding the relationship between the effectiveness of instructional DD usage and the duration from onset, while it has been reported that the strabismus angle is more likely to decrease in shorter periods since onset,13 non-reduction in the strabismus angle even within just 1 month after onset has been reported.16 In our study, a higher proportion of patients in the cured group presented within 3 months of symptom onset. However, this variable was not a significant factor in the multivariate analysis.

Concerning the classification criteria for the four outcomes, the inclusion of the change in subjective symptoms as a criterion may have introduced ambiguity in the classification decision. However, because some patients with a small strabismus angle from the initial examination were included, subjective symptoms were necessary to determine outcomes. Moreover, the change in strabismus angle was determined by 10 PD; however, the clinical significance of the change in strabismus angle differed depending on the original size of the angle. In cases with a large original esotropia angle, even a 10 PD reduction in the strabismus angle had less clinical significance; the improved group included such cases. Therefore, although a relationship between reduction in the use of DD by half and esotropia outcome was observed, we suggest that it is important to establish preventive strategies because it is difficult to cure esotropia with a large angle once it has developed.

Conclusions

In patients with ACE using DD at onset, providing instructions on DD usage resulted in cure in 6% patients and in improvement in 37% patients. Positive outcomes were associated with a small-angle esotropia, good stereoacuity and successful halving of DD time. Therefore, in patients using DD at onset, it may be worthwhile to attempt to halve the time of DD use first.