Do school classrooms meet the visual requirements of children and recommended vision standards?

<div><p>Background</p><p>Visual demands of school children tend to vary with diverse classroom environments. The study aimed to evaluate the distance and near Visual Acuity (VA) demand in Indian school classrooms and their comparison with the recommended vision standards.</p><p>Materials and methods</p><p>The distance and near VA demands were assessed in 33 classrooms (grades 4 to 12) of eight schools. The VA threshold demand relied on the smallest size of distance and near visual task material and viewing distance. The logMAR equivalents of minimum VA demand at specific seating positions (desk) and among different grades were evaluated. The near threshold was converted into actual near VA demand by including the acuity reserve. The existing dimensions of chalkboard and classroom, gross area in a classroom per student and class size in all the measured classrooms were compared to the government recommended standards.</p><p>Results</p><p>In 33 classrooms assessed (35±10 students per room), the average distance and near logMAR VA threshold demand was 0.31±0.17 and 0.44±0.14 respectively. The mean distance VA demand (minimum) in front desk position was 0.56±0.18 logMAR. Increased distance threshold demand (logMAR range -0.06, 0.19) was noted in 7 classrooms (21%). The mean VA demand in grades 4 to 8 and grades 9 to 12 was 0.35±0.16 and 0.24±0.16 logMAR respectively and the difference was not statistically significant (p = 0.055). The distance from board to front desk was greater than the recommended standard of 2.2m in 27 classrooms (82%). The other measured parameters were noted to be different from the proposed standards in majority of the classrooms.</p><p>Conclusion</p><p>The study suggests the inclusion of task demand assessment in school vision screening protocol to provide relevant guidance to school authorities. These findings can serve as evidence to accommodate children with mild to moderate visual impairment in the regular classrooms.</p></div

Categorization of desk positions and the minimum and average distance visual acuity demand (Mean±SD (range)) at different desk positions in 33 classrooms.

<p>Categorization of desk positions and the minimum and average distance visual acuity demand (Mean±SD (range)) at different desk positions in 33 classrooms.</p

Comparison of variables in measured 33 classrooms to the Indian Government standard recommendations.

<p>Comparison of variables in measured 33 classrooms to the Indian Government standard recommendations.</p

Box plot representing the comparison of minimum distance visual acuity demand at different desk positions (front, middle and last row) between grades 4 to 8 and grades 9 to 12.

<p>Box plot representing the comparison of minimum distance visual acuity demand at different desk positions (front, middle and last row) between grades 4 to 8 and grades 9 to 12.</p

Average letter size, viewing distance and visual acuity demand, and comparison between different grades (grade 4 to 8 and grade 9 to 12 group) and schools (n = 8) in 33 classrooms.

<p>Average letter size, viewing distance and visual acuity demand, and comparison between different grades (grade 4 to 8 and grade 9 to 12 group) and schools (n = 8) in 33 classrooms.</p

Schematic of the multi-drop protocol for the measurement of epithelial permeability.

<p>At t = 0, a 0.35% fluorescein drop (0.35 gm of fluorescein/100 mL PBS buffer) is instilled on the bulbar conjunctiva and the tear fluorescence is measured (shown by red unfilled circles). After clearance of the dye (usually < 15 min), two drops of 2% fluorescein (2 gm of fluorescein/100 mL PBS buffer) are instilled 10 min apart (T₁ and T₂). About fifteen minutes after the second drop, the ocular surface is washed with CMC solution (carboxymethyl cellulose solution; Blue arrow). Next, stromal fluorescence is measured 3–4 times at time T_s (usually within 5–10 min after T₃). AUC_dL1 and AUC_dL2, which are assumed to be equal, are estimated based on the area under the curve calculated for the 0.35% drop (AUC*). The tear fluorescence in response to the probe drop is fitted to a single-exponential decay to determine F⁰_dp and k_d. F⁰_dp is then used to estimate F⁰_dL1 and F⁰_dL2. k_d for the 2% drops is assumed to be the same as that for the 0.35% drop. Hence, the first 0.35% drop is referred to as the probe drop. The 2% drops have been employed to load the stroma with measurable levels of fluorescein so that noise-free measurements of the stromal accumulation can be obtained. Therefore, the 2% drops are referred to as the loading drops.</p

Mathematical notations.

<p>Mathematical notations.</p

Inter-subject variability of fluorescein clearance after the probe drop in two subjects.

<p>The excitation slit was focused on the tear film and the fluorescence <i>vs</i>. time profile was obtained for 10 min. F⁰_dP and k_d are the intercept and slope, respectively, of the fluorescence decay in the tear film as per the exponential decay curve (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198831#pone.0198831.e004" target="_blank">Eq 4</a>) using non-linear least squares. Half-lives t^d_1/2 indicated in the inset were calculated from k_d. <b>Panels A and B</b>: Data from a subject showing rapid clearance of fluorescein with half-lives of only 88 and 96 seconds in the left and right eyes, respectively. <b>Panels C and D</b>: Data from a different subject showing a relatively slower clearance with half-lives of 208 and 210 seconds in the left and right eyes, respectively.</p

Estimated fluorescein elimination rate constant (k_d) following instillation of the probe drop.

<p>k_d was obtained as the slope of the fluorescence decay by fitting to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198831#pone.0198831.e004" target="_blank">Eq 4</a> according to ln F_dP (t) = ln F⁰dP—k_d t. The mean and SD values are 0.0142 and 0.0107 sec^-1, respectively (n = 49 eyes and 29 subjects).</p

Effect of the axial resolution on the measured fluorescence.

<p>The depth of the focal diamond is 2δ. From <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198831#pone.0198831.g002" target="_blank">Fig 2</a>, we note that δ is 140 μm. <b>Panel A</b>: Focal diamond (RED lines) across the tear film with fluorescein. Note that the tear film does not span the entire depth of the focal diamond. In the figure, F^A_d and C_F refer to the measured tear fluorescence and concentration of fluorescein in the tear film, respectively. <b>Panel B</b>: Tear film is thicker compared to that in Panel A so that F^B_d >F^A_d. <b>Panel C</b>: Focal diamond is positioned in the stroma. In this case, the measured fluorescence F^C_S would be proportional to C_F but independent of the stromal thickness, which is greater than 2δ. <b>Panel D</b>: Estimation of ICF. The intersection of the tear film with the focal diamond is a parallelepiped of volume given by t_d x 2W x H, where t_d is the thickness of the tear film, 2W is the maximum width of the focal diamond, and H is the thickness of the excitation slit beam. The volume of the focal diamond is given by 2δ x W x H, where 2δ is the axial resolution of the instrument (2δ ~ 280 μm). Hence, the ratio of the volume of the focal diamond to that of volume of intersection between tear film and focal diamond (defined as ICF, instrument correction factor) is given by (2δ x W x H) / (t_d x 2W x H). Hence, ICF would be δ/t_d, which is equal to 47 assuming a tear film thickness of ~ 3 μm [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198831#pone.0198831.ref038" target="_blank">38</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198831#pone.0198831.ref041" target="_blank">41</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198831#pone.0198831.ref043" target="_blank">43</a>]. This estimation assumes that the fluorescence in the stroma for a given concentration of fluorescein is not different from an equivalent amount of fluorescein in water. More specifically, fluorescein is assumed unbound in the stroma.</p