Jinhua Bao

Reading behavior of emmetropic schoolchildren in China

Knowing the actual behavior of readers will help us understand how near work influences a readers eyes, comfort, reading efficiency, pleasure, and the ability to learn to read. We designed a methodology for reading behavior research, and investigated the reading behavior of emmetropic schoolchildren in China and factors that influence their reading. Children from grades 2 through 5 read text in an armchair, at a desk, and when reading and writing at the desk with three different font sizes. Their preferred reading distance was very near to the eyes, averaging 28.5±6.4cm in the armchair, 25.4±6.6cm at the desk and 20.6±6.5cm in the reading/writing task, and was always slightly closer for the smallest font. Second grade children averaged just a 16.3±4.1cm reading distance in the reading/writing task. Head tilt and angle of gaze were altered by reading condition and font size. Reading speed was fastest at the desk and for those with longer reading distances and, surprisingly, for the smallest font size. Reading behavior is not a fixed entity but differs with grade level and reading condition. This suggests that reading behavior can be altered through better ergonomics and text design which may reduce myopia, aesthenopia, and binocular anomalies and help children read better.

Dynamic Changes in Ocular Zernike Aberrations and Tear Menisci Measured with a Wavefront Sensor and an Anterior Segment OCT

PURPOSE To measure dynamic change characteristics of spatial and temporal variations in the post-blink tear film of normal eyes. METHODS A wavefront sensor was used to measure dynamic changes in wavefront aberrations, up to the seventh order, for 10 seconds in a group of 33 normal young adults. Tear menisci were imaged with an anterior segment optical coherence tomography (AS-OCT) system and tear film break-up times (TFBUTs) were determined. RESULTS Systematic changes in main axis astigmatism (R(2) = 0.933, P < 0.0001), vertical coma (R(2) = 0.935, P < 0.0001) and spherical aberrations (R(2) = 0.879, P = 0.0002) occurred during the 10-second post-blink period. Both lower tear meniscus height and area increased by 10 seconds compared with the initial levels (P < 0.0001 for each). The change of vertical coma had significant correlation with the increase of lower tear meniscus areas during the 10-second post-blink period (R(2) = 0.181, P = 0.014). Subjects with TFBUTs < 15 seconds had significantly increased main axis astigmatism, vertical coma, and spherical aberrations by 10 seconds. Subjects with longer TFBUTs did not have any significant wavefront aberrations during that period. CONCLUSIONS Systematic changes in some Zernike aberrations after blinking are associated with the changes in tear menisci and TFBUT. There was a substantial individual variation in dynamic changes of Zernike aberrations, suggesting the necessity to explore individual differences in tear quality and tear performance. Dynamic wavefront measurement combined with anterior segment optical coherence tomography could provide a useful tool to understand spatial and temporal processes of the tear film in clinical practice.

An indirect method to compare the reference centres for corneal measurements.

Citation information: Xu J, Bao J, Lu F & He JC. An indirect method to compare the reference centres for corneal measurements. Ophthalmic Physiol Opt 2012, 32, 125–132. doi: 10.1111/j.1475‐1313.2011.00880.x

Comparison of Near Addition Value Prescription Methods for Myopic Children.

Purpose To compare personalized near addition values for myopic children that induce a reasonable phoria (Ph) (meeting Sheards criterion) and induce a null lag of accommodation at near and to evaluate changes in these metrics after lens adaptation. Methods Fifty-three myopic children participated in this study. Accommodative response, Ph, and fusional amplitudes (FAs) were measured at 33 cm through multiple addition lenses (0D, +1.00D, +1.50D, +2.00D, +2.50D, +3.00D). The adaptation effect on measured parameters was evaluated after 6 min of near work with each addition. The FA/Ph ratios were calculated for each addition and fitted using a rational function to obtain the optimal addition value satisfying Sheards criterion (FA/Ph ≥ 2). Lag of accommodation change in association with addition value was assessed using linear regressions to obtain the addition values inducing a null lag. Results Lag of accommodation (r = −0.987, p < 0.001) and Ph (r = −0.999, p < 0.001) decreased linearly with addition value. The 6-min adaptation induced a small but significant increase in accommodative lag and an exophoric shift (p < 0.05). Three FA/Ph patterns with respect to addition lenses were observed based on the near Ph: orthophoria/exophoria, low esophoria, and large esophoria. Addition values based on Sheards criterion (mean ± SD, +2.16 ± 0.79D) were significantly lower than those based on null lag (+2.83 ± 0.44D, t = 19.86, p < 0.001). The FA/Ph ratio was less than 2.0 in 75.5% of subjects with additions determined through null accommodative lag. Additions determined through FA/Ph ≥ 2 induced a lag of accommodation of 0.38 ± 0.42D. Conclusions Personalized near addition values using Sheards criterion were lower than those obtained through null lag of accommodation. These values should allow a better binocular balance especially for exophoric children.

Influence of Near Tasks on Posture in Myopic Chinese Schoolchildren.

PurposeTo investigate near-vision posture in Chinese myopic schoolchildren and compare near-vision posture during different near-vision tasks (i.e., playing video games, reading, and writing). MethodsThe study investigated 120 myopic children (grades 1 through 6 and aged 6 to 13 years). An electromagnetic motion-tracking system was used for continuous measurements of the working distance and head declination of the subjects while they were playing video games or reading or writing at a desk. The reading and writing documents were adjusted by grade level (i.e., grades 1 to 2, 3 to 4, and 5 to 6). For analysis, the subjects were grouped in two refractive groups according to their median spherical equivalent refractive error (−1.50D). ResultsThe myopic schoolchildren used close working distances for all tasks: 21.3 ± 5.2 cm (video games), 27.2 ± 6.4 cm (reading), and 24.9 ± 5.8 cm (writing). The mean head declinations were 63.5 ± 12.2 deg (video games), 37.1 ± 12.8 deg (reading), and 44.5 ± 14.1 deg (writing). Working distance decreased significantly across time for the reading and writing tasks (p < 0.001). Head declination increased significantly across time only for the reading task (p < 0.001). Grade level significantly influenced working distance, but the difference was not significant when working distance was adjusted by the subject’s size. No differences were observed within the refractive or the accommodative lag groups in terms of the posture data (p > 0.05). Working distance was negatively correlated with head declination (r = −0.53, p < 0.001). ConclusionsClose working distances were observed for Chinese myopic schoolchildren. The attention dedicated to each task, the task difficulty, and the page/screen size may affect near working distance and head declination. Handheld video games were associated with the closest working distance, which may be a risk factor for myopia progression, according to previous studies.

Design, methodology, and baseline data of the Personalized Addition Lenses Clinical Trial (pact)

Background: The aim of this study was to describe the design, methods, and baseline characteristics of children enrolled in the Personalized Addition lenses Clinical Trial (PACT). PACT aims to test the myopia control efficacy of progressive addition lenses (PALs) with personalized addition values compared with standard (+2.00 D) addition PALs and single vision lenses (SVLs). Methods: PACT is a randomized, controlled, double-masked clinical trial. Two hundred eleven myopic Chinese children (7–12 years) were enrolled and randomized into 1 of the 3 following groups: personalized addition PALs; +2.00 addition PALs; and SVLs. Personalized addition values were determined based on the highest addition that satisfied Sheard criterion. Axial length and other biometric data were also recorded. Results: At baseline, no differences were found between the right and left eyes for any of the main parameters. The enrolled children were 9.7 ± 1.1 years’ old with cycloplegic autorefraction (right eye [OD]: −2.36 ± 0.64 D), near phoria (1.0 ± 5.0 prism diopter esophoria), lag of accommodation (1.40 ± 0.50 D) and axial length (OD: 24.58 ± 0.74 mm). The personalized addition values ranged from +0.75 to +3.00 (average ± SD: 2.19 ± 0.73 D). Conclusion: PACT is a clinical trial evaluating whether myopia progression in children can be slowed by wearing personalized addition PALs compared with fixed addition PALs and SVLs as measured by cycloplegic autorefraction and axial length. Baseline data were comparable with those of previous myopia control studies in children. Subjects will be followed up every 6 months for 2 years.

ZERNIKE ASTIGMATISM AND VISUAL PERFORMANCE IN MYOPIC EYES BY RIGID GAS PERMEABLE CONTACT LENSES WEAR

Purpose: To investigate the effects of rigid-gas-permeable contact lens (RGP-CL) wear on Zernike astigmatism and visual performance in myopic eyes. Methods: A wavefront sensor was used to evaluate Zernike astigmatism for 21 eyes with minimum astigmatism and 18 eyes with moderate astigmatism under three different modes of refractive correction: the RGP-CL, spectacle lens correcting spherical equivalent (SL) and spectacle lens fully correcting spherical error and astigmatism (fSL). Contrast visual acuity was assessed with a VA tester at four contrast levels and two luminance backgrounds. Results: Compared to the SL wear, RGP-CL wear changed the main axis astigmatism from -0.09 ± 0.34 to 0.34 ± 0.22 for the minimum astigmatism group, while the contrast VA was improved about 0.05 LogMAR (F = 8.06, p < 0.01). For the group with moderate astigmatism, significant reduction in was found for both fSL wear (t = 4.78, p < 0.001) and RGP-CL wear (t = 6.29, p < 0.0001). The changes in astigmatism were significantly correlated between the fSL and RGP-CL wears (r = 0.897, p < 0.0001 for ; and r = 0.643, p = 0.004 for . Contrast VA was significantly improved for both fSL and RGP-CL wears and the improvements were significantly correlated between each other for all four contrast levels and two backgrounds. Conclusion: RGP-CL wear induces astigmatism for the eyes with minor astigmatism probably due to a correction of corneal astigmatism and thus a manifesting of the lens astigmatism. For the astigmatic eyes, RGP-CL wear has similar effect on correcting astigmatism as the spectacle lens wear with spherical-cylinder correction and also produces similar visual improvement.