A total of 60 myopic children aged 6–16 years (26 males and 34 females) admitted to Beijing Tongren Hospital from August 2021 to August 2022 were enrolled in this study. The average age of the subjects was 10.63 ± 2.53 years. This study adhered to the principles outlined in the Declaration of Helsinki and received approval from the Ethics Committee of Beijing Tongren Hospital. Written informed consent was obtained from at least one of each child’s parents or other guardians, while verbal consent was provided by all the participants.

All patients fulfilled the following inclusion criteria: -6.00 D < spherical equivalent (SE) ≤ -0.50 D of both eyes; best-corrected visual acuity of 6/6; ≤ 0.75 D of astigmatism; ≤ 1.00 D of anisometropia; IOP less than 21 mm Hg; no accommodative anomalies; absence of severe ocular pathology or history; no topical or systemic medications; no severe systematic or mental diseases; full-time spectacle wearers to minimize the potential effects of changes in refractive correction methods on normal accommodation behavior; no history of wearing contact lenses within the four weeks preceding the testing period; None of the subjects used any methods of myopia controlling such as peripheral defocus spectacles, low-dose atropine, orthokeratology, etc. that might have affected their accommodation or IOP.

Each included subject underwent a complete ocular examination, such as noncycloplegic subjective refraction, IOP, binocular testing, slit-lamp biomicroscopy of the anterior eye, and a fundus examination was conducted to exclude patients with fundus disease. The best visual acuity was achieved using the principle of maximum plus during subjective refraction. Participants were instructed to wear spectacles with lenses prescribed during the subjective refraction for both the reading tasks and accommodation measurements.

The whole experiment lasted for approximately 2 h. After completing a comprehensive eye examination, each participant was asked to perform two reading tasks while seated: reading with the head bowed (neck flexed at a 45° angle) and reading with the head upright (neck in a neutral position). The sequence of these 2 reading tasks was randomized. IOP measurements were conducted using an Icare rebound tonometer (Icare TA01i, Revenio, Finland) for 6 consecutive times, and the average value was recorded. The measurements were taken only from the right eye of each participant.

The refractive state was measured before and after the 30-min reading period using an open-field autorefractor (WAM-5500; Grand Seiko Co., Ltd., Hiroshima, Japan), which has been shown to be reliable for NITM and its decay, as well as accommodative stimulus-response testing in its dynamic mode [31]. According to the manufacturer’s manual, the dynamic mode of the autorefractor had a precision of 0.01 D. The dynamic measurements were taken at a rate of approximately 5 Hz (five samples per second). The high-speed measurements were collected by connecting the Grand Seiko WAM-5500 autorefractor to a computer via an RS-232 C cable, and the resulting data output was automatically converted into an Excel spreadsheet [32].

Each participant was instructed to rest with their eyes closed in a completely dark room for 5 min to help alleviate any accommodative spasms. After the resting period, the participants were brought to the experimental room where they were seated in front of the open-field autorefractor, wearing their corrected spectacles, and under natural room light illumination. The autorefractor was used to measure monocular refractive errors of the right eye while the participants viewed the 20/30 Snellen letters at a distance of 6 m, with their corrective spectacles on. A total of 50 measurements were taken at intervals of 0.2 s [33]. The mean SE was computed from this data, which represents the average baseline distance refractive state. Baseline IOP measurements were obtained from the right eye prior to reading.

Next, the subjects began to read the text for 30 min at a distance of 33 cm, while adopting the corresponding body posture in sitting position. Both postures read the same material, consisting of paragraphs of words in 10.5-point Sim Sun Chinese font with darker letters on a lighter background, under an environmental luminance of 100 cd/m2. Subjects temporarily stopped reading for IOP measurements at 5, 10, 20, and 30 min. The IOP was measured in head upright position of both postures to eliminate the impact of changes in the angle of the tonometer on IOP.

Then, post-task distance refractive state measurements were immediately performed at the end of the half-hour reading session. After the 30-min reading period, the subjects were instructed to shift their focus to the distant Snellen target at 6 m. The autorefractor then continuously obtained distance refraction measurements for a period of 10 s, consisting of 50 measurements in total [33]. The post-task refraction was calculated by averaging the measurements obtained over a 10-s period. Finally, the subjects were asked to close their eyes for a 5-min recovery period, after which another IOP measurement was taken while they remained seated.

After completing one reading task, the participants were required to take a break of at least 30 min in a completely dark room before switching to the other reading task.

After the completion of data collection, the SE was calculated as the sum of the sphere power and half of the cylinder power. To determine the magnitude of NITM, the mean spherical equivalent of the distance refraction measurements taken pre-task was subtracted from the mean spherical equivalent of the post-task measurements.

All analyses were carried out using the SPSS software v25. The normal distribution of the variables was confirmed (P > 0.05) by the Kolmogorov-Smirnov test, and all data were presented as mean ± standard deviation (SD). To evaluate longitudinal changes in IOP, a repeated measures ANOVA was performed to compare the pre-work value with the value at each subsequent interval. To compare the significance of IOP changes within each posture at different time points, paired t-tests with Bonferroni correction were performed. The paired Student’s t-test was conducted to assess the significance of within-subject factors, specifically body postures (head bowed and head upright), on the changes in IOP and initial NITM. A significance level of P < 0.05 was used for all statistical analyses.