Journal of Pediatric Ophthalmology and Strabismus

Original Article 

Actual Visual Acuity Demands in the Classroom

Carolina Adams, MD; Shelby Leach, OD; Yocheved S. Kresch, OD; Steven E. Brooks, MD

Abstract

Purpose:

To address the knowledge gap regarding the actual acuity requirements needed in typical kindergarten through grade 12 classrooms by determining an actual logarithm of the minimum angle of resolution (logMAR) and contrast sensitivity requirements in a sample of classrooms for kindergarten through grade 12 in New York City.

Methods:

Measurements of classroom dimensions with specific attention to viewing distances were made in public and private school classrooms, at various grade levels from kindergarten through grade 12, in New York City. The dimensions of typical text shown to students on classroom smartboards and whiteboards was measured and the mean and range of logMAR values were calculated for various seating locations within the classrooms. Contrast between text and background was estimated by comparing digital images of actual classroom text to Pelli-Robson contrast sensitivity charts.

Results:

Fourteen classrooms in five schools were evaluated. Classroom dimensions varied from 8 × 10 feet to 23 × 23 feet. Mean logMAR values of lower case text on smartboards and whiteboards varied from 0.93 ± 0.29 (range: 0.83 to 1.32) in the center of the front row to 0.46 ± 0.21 (range: 0.10 to 0.79) in the center of the back row (P < .001). Contrast was also variable, being highest for black markers on whiteboards (0.00) and lowest on smartboards (0.15 to 0.60). Neither logMAR nor contrast sensitivity values varied significantly by grade level or school (P > .50 for both).

Conclusions:

The data reveal that logMAR demands and contrast vary substantially from classroom to classroom and within a classroom based on room dimensions and seating. Although generally supporting current acuity-based pediatric vision screening referral guidelines, the data also provide insight into the potential impact of reduced visual acuity and seating location on visual performance in the classroom. These findings suggest the need to develop logMAR and contrast standards that optimize visual content in classrooms while accommodating a wider range of visual capabilities.

[J Pediatr Ophthalmol Strabismus. 2021;58(1):48–54.]

Abstract

Purpose:

To address the knowledge gap regarding the actual acuity requirements needed in typical kindergarten through grade 12 classrooms by determining an actual logarithm of the minimum angle of resolution (logMAR) and contrast sensitivity requirements in a sample of classrooms for kindergarten through grade 12 in New York City.

Methods:

Measurements of classroom dimensions with specific attention to viewing distances were made in public and private school classrooms, at various grade levels from kindergarten through grade 12, in New York City. The dimensions of typical text shown to students on classroom smartboards and whiteboards was measured and the mean and range of logMAR values were calculated for various seating locations within the classrooms. Contrast between text and background was estimated by comparing digital images of actual classroom text to Pelli-Robson contrast sensitivity charts.

Results:

Fourteen classrooms in five schools were evaluated. Classroom dimensions varied from 8 × 10 feet to 23 × 23 feet. Mean logMAR values of lower case text on smartboards and whiteboards varied from 0.93 ± 0.29 (range: 0.83 to 1.32) in the center of the front row to 0.46 ± 0.21 (range: 0.10 to 0.79) in the center of the back row (P < .001). Contrast was also variable, being highest for black markers on whiteboards (0.00) and lowest on smartboards (0.15 to 0.60). Neither logMAR nor contrast sensitivity values varied significantly by grade level or school (P > .50 for both).

Conclusions:

The data reveal that logMAR demands and contrast vary substantially from classroom to classroom and within a classroom based on room dimensions and seating. Although generally supporting current acuity-based pediatric vision screening referral guidelines, the data also provide insight into the potential impact of reduced visual acuity and seating location on visual performance in the classroom. These findings suggest the need to develop logMAR and contrast standards that optimize visual content in classrooms while accommodating a wider range of visual capabilities.

[J Pediatr Ophthalmol Strabismus. 2021;58(1):48–54.]

Introduction

Pediatric vision screening has been extensively investigated in different community settings,1–5 and is a required element of pediatric well-care visits per the current joint guidelines of the American Academies of Pediatrics (AAP), Ophthalmology (AAO), and Certified Orthoptists (AACO), and the American Association for Pediatric Ophthalmology and Strabismus (AAPOS).6,7 In addition to detecting sight-threatening conditions and strabismus in young children, vision screening is also used in older children to detect potentially significant refractive errors that might adversely affect the ability of the child to succeed in school. The recommended acuity-based referral thresholds were intended to reflect age-appropriate acuity norms, based on the expert judgment of the AAP's Committee on Practice and Ambulatory Medicine, Section on Ophthalmology.7 However, given the perceived impact on classroom performance, it would be helpful to have corollary data regarding the actual visual demands encountered in classrooms. Referral thresholds for school-aged children could then be tailored to match actual visual requirements. Conversely, such data would also inform the development and implementation of rational age-appropriate opto-type standards in classrooms. Doing so could have the benefit of better accommodating children with visual deficits, including those who lack proper optical correction.

Current pediatric vision screening guidelines recommend screening examinations at least annually.6 For acuity-based screening, referral to a specialist is recommended if the acuity is 20/50 or worse in either eye in children younger than 4 years, 20/40 or worse in children 4 to 5 years of age, and 20/30 or worse in children older than 5 years.7–11 However, despite efforts at the primary care level to provide quality vision screening, only 30% to 60% of children ultimately receive a formal evaluation by a pediatric trained eye care provider,9 and compliance with glasses is highly variable.12 Multiple factors accounting for the low follow-up and compliance rates have been identified, including cost, lack of insurance, parental perceptions regarding necessity and urgency, and access to a pediatric eye care professional.12

These data suggest that limited resources, including the ability of parents to consistently provide glasses or contact lenses for their children, adversely affect the ultimate success of vision screening programs. These issues highlight the potential benefits of optimizing the specificity of acuity-based vision screening in school aged children in a way that reflects their actual visual needs, as well as developing appropriate guidelines and specifications for visual content in classrooms. Given the paucity of information in the literature,13-15 this study was designed to help close this gap in knowledge by investigating the actual logMAR and contrast sensitivity demands in a cross-sectional sample of kindergarten through grade 12 classrooms in New York City.

Patients and Methods

Classroom Dimensions

Classroom dimensions were measured to obtain actual viewing distances from various seating positions, including the sides and center of the front and back rows, to the smartboard or whiteboard. A typical classroom configuration is shown schematically in Figure 1. Permission was obtained from school officials at each of the schools visited.

Data collection sheet including ranges for Snellen and logarithm of the minimum angle of resolution (logMAR) equivalents at various seating locations. A and C = 20/102 to 20/229, B = 20/170 to 20/339, D and F = 20/54 to 20/109, and E = 20/57 to 20/123.

Figure 1.

Data collection sheet including ranges for Snellen and logarithm of the minimum angle of resolution (logMAR) equivalents at various seating locations. A and C = 20/102 to 20/229, B = 20/170 to 20/339, D and F = 20/54 to 20/109, and E = 20/57 to 20/123.

Text Dimensions and Contrast Quality

Horizontal and vertical dimensions of single letters from actual lecture content on smartboards and whiteboards in classrooms were measured in millimeters. Measurements of three separate, representatively sized, lower case and upper case letters were obtained for each classroom and mean values for each size were calculated. The teachers were not made directly aware of the study's purpose, and were simply asked by the school representative to leave the lesson plan text on display at the end of the school day.

The luminance contrast between text and background was estimated by taking digital photographs of the text on the smartboards or whiteboards and comparing the contrast to optotypes on a Pelli-Robson contrast sensitivity chart.16 Contrast sensitivity is defined as the log10 [background luminance/(background-optotype luminance)] of the lowest contrast optotype that an individual can accurately discern.17 The contrast between an optotype and a luminant background increases as the optotype's luminance approaches zero (ie, black optotype on white background). Conversely, the contrast between an optotype and the background decreases as the optotype's luminance increases and approaches background luminance. High contrast improves an optotype's visibility. An individual's contrast sensitivity refers to the minimum contrast required for the individual to correctly discern a standard optotype.

LogMAR and Snellen Equivalent Calculation

To calculate the angular size of the optotypes at different locations in the classroom, we assumed that (Letter Height)/(Viewing Distance) was approximately equal to the angular size of the optotype in radians, because tan = arctan for small angles. Radians could then be converted to minutes of angle by applying the following formula: (Minutes of Angle) = (Radians) × (360/2π) × (60).

To calculate a Snellen equivalent, we considered a 20/20 “E” optotype, by definition, to have an overall angular size of 5 minutes, with each light and dark bar of the “E” having an angular size of 1 minute. To calculate an approximate Snellen equivalent for a classroom optotype, we divided the total vertical angular size of the letter (in minutes of angle) by 5 and multiplied by 20. For example, a letter that had a total visual angle of 10 minutes was considered to be a 20/40 equivalent. The logMAR size of the optotype was calculated as the base 10 logarithm of the total angular size of the letter vertically (in minutes of angle) divided by 5, to reflect the angular size or minimum angle of resolution, of the component bars of the standard “E” (eg, logMAR = 0 for a 20/20 optotype, logMAR = 1 for a 20/200 optotype).

The following formulas were used to calculate the angular dimensions of optotypes:

  1. Angular size of optotype (minutes of angle) = (total optotype height/viewing distance) × (360/2π) × 60

  2. Snellen equivalent = (total optotype height/viewing distance) × (360/2π) × (60) × (20/5)

  3. logMAR = Log10 (total angular size of optotype in minutes/5)

Upper case letters were considered to represent the maximum angular sizes of optotypes in each classroom, and lower case letters were considered to represent the minimum angular sizes.

Statistical Analysis

Classroom dimensions, logMAR, Snellen equivalent, and contrast were grouped by grade levels (ie, elementary = kindergarten to 5th grades, middle school = 6th to 8th grades, and high school = 9th to 12th grades) and by seat location, (ie, front center, front side, back center, and back side). Measurements are presented as mean values with associated standard deviations. Differences in continuous variables between two groups were tested using an independent samples two-tailed t test. One-way analysis of variance was used to compare mean values among the different seat locations and grade levels. A P value of .05 or less was considered to be statistically significant.

Results

Classroom Dimensions

A total of 14 classrooms, in five different schools, were assessed. The classes included a range of grades from kindergarten to high school. Three of the schools were private and two were public. Two schools were located in Manhattan, one in the Bronx, and two in Brooklyn. The mean classroom dimensions were 16 × 18 feet (depth by width), with a range of 8 × 10 feet to 23 × 23 feet (Table 1). The seating configurations of the classrooms varied, with some classrooms having individual seating and some having shared tables for 3 to 4 students per table. The position of the smartboard or whiteboard also varied, with some classes having the board positioned off to one side, and others having it centrally located at the front of the classroom.

Mean Classroom Dimensions

Table 1:

Mean Classroom Dimensions

LogMAR Values

In most classrooms, text was projected onto smartboards. The use of whiteboards was infrequent. There were no chalkboards. The smallest, largest, range, and mean logMAR and Snellen equivalent of the letters are presented in Table 2, broken down by seat location in the classroom.

Average, Maximum, and Minimum Optotype Sizes in logMAR and Snellen Equivalent (N = 14)

Table 2:

Average, Maximum, and Minimum Optotype Sizes in logMAR and Snellen Equivalent (N = 14)

Overall, the mean logMAR equivalent of lower case letters from seats in the center of the front row was 0.93 (Snellen equivalent = 20/170), whereas the mean value from the center of the back row was 0.46 (Snellen equivalent = 20/58) (P < .001). Similarly, for seating on the sides of the classrooms, the mean logMAR equivalent of lower case letters from the side of the front row was 0.71 (Snellen equivalent = 20/103), whereas the mean value from the side of the back row was 0.43 (Snellen equivalent = 20/54) (P = .001). These values indicate that the visual acuity demand from the seating in the back row was, on average, almost triple that of the front row.

Table 3 shows the logMAR and Snellen equivalent values by grade levels and seat positions. The mean logMAR value of optotypes viewed from the center of the front row in kindergarten to 3rd grade was 0.79 (Snellen equivalent = 20/123). In contrast, the mean value was 0.91 (Snellen equivalent = 20/162) in 5th to 7th grade classes and 1.02 (Snellen equivalent = 20/209) in 9th to 12th grades. No data were collected from 4th and 8th grades. Although logMAR values varied from classroom to classroom, even within the same school, the mean values did not vary significantly by school (P > .05) or grade level (P > .05).

Visual Demands Based on Seating

Table 3:

Visual Demands Based on Seating

Contrast

Optotype contrast was high for black markers on whiteboards (Pelli-Robson chart optotype contrast sensitivity = 0.00), but varied from 0.15 to 0.60 on smartboards. The position of smartboards relative to the overhead room lighting and the level of room lighting appeared to affect contrast and created glare, although the effect of these factors could not be quantitatively measured.

Discussion

Narayanasamy et al14 determined that students spend approximately 80% of a typical school day in visual tasks, with 29% exclusively involving distance vision, suggesting that vision-related learning is an extremely important component of school-based education. Our data suggest that visual demands, as estimated from the logMAR values of optotypes shown to students, can vary greatly from classroom to classroom and within a given classroom based on seat position. Not surprisingly, the acuity demands of a back row seat were significantly higher than a front row seat, a disparity that predictably increased as room length increased. The logMAR difference between the front and back rows in our sample of classrooms was, on average, 0.47, corresponding to a roughly threefold difference in visual demand. In one 1st grade classroom, the difference was 0.81, representing a 6.4-fold difference.

Analysis of our data in the context of current vision screening guidelines6,7 suggests that children with visual acuity in the better eye of 20/30 or worse may have difficulty seeing letters from the back of some classrooms, whereas children in the front row may not have difficulty unless their visual acuity is worse than 20/80. Our findings are in general agreement with those of Langford and Hug,13 who also found that visual requirements increased significantly with back row seating. In contrast to their study, which found that visual demand increased with grade level from kindergarten to 5th grade, we did not find this trend. Their study did not assess demands in middle school or high school classrooms.

Contrast, which affects the visibility of text, was found to be highest with black markers on a whiteboard and lowest on smartboards in rooms with high levels of ambient illumination. This may be an important finding, because it has been reported that lecture content with low contrast can dramatically affect visual learning, especially in children with underlying visual abnormalities, including amblyopia.18–21

Although we did not attempt to measure the extent of letter crowding, we did notice that letters and words appeared at times to be closely spaced in some classrooms, particularly when whiteboards were used (data not shown). This is likely due to the fact that smartboards use computer-generated text, whereas the text on whiteboards is manually written by teachers, and therefore much more variable. Although crowding makes the visual resolution of individual optotypes more difficult in general, it has been identified as a particularly significant factor limiting reading speed in patients with amblyopia.22,23

According to New York State Department of Health guidelines, the square footage of classrooms should range between 17 and 22 square feet per student for rooms with less than 41 students and between 22 and 23 square feet per student for rooms with 41 to 60 students.24 The distance from the first row of seating to the screen is supposed to be no more than 1.5 to 2 times the width of the projected images (screen width). There are no stated differences in the mandated requirements with regard to grade level, nor are there requirements regarding classroom seating configuration or limits on distance to the back row. Perhaps more important, the guidelines contain no specific recommendations regarding optotype size or contrast,24 or appropriate alterations of these parameters in classes serving children with visual or cognitive impairment.

Our sample included schools from diverse neighborhoods and classrooms from public, private, and parochial schools. Although the sample size was relatively small, the wide range of logMAR and contrast values found among classrooms suggests that a larger sample size would have further defined the range and standard deviation of these values, but would not alter our fundamental conclusions. Because the actual classroom text was not uniformly formatted, and did not replicate the standardized form of optotypes used for visual acuity testing, our logMAR and Snellen equivalent calculations can only serve as approximations. Another limitation of the study is that the contrast between optotype and background was subjectively determined by comparing photographs of optotypes taken in the classroom to optotypes on a Pelli-Robson contrast sensitivity chart.17 However, because our methodology was internally consistent, our finding of marked inter-classroom variations is not likely due to methodological error. The impact of these variations on the visual performance of students, with and without visual impairment, requires further study.

Conclusions

Our data revealed that the mean logMAR demand to visualize lower case letters in the back row of a classroom was 0.46 (Snellen equivalent = 20/58), with a relatively wide range of values from classroom to classroom, even within the same school. By contrast, the mean logMAR demand in the front row was 0.93 (Snellen equivalent = 20/170). These data suggest that the currently recommended thresholds for referral in vision screening programs6,7 are sufficient to detect most children at risk for visual acuity related difficulty in the classroom.

The role of optotype contrast, and its variability among classrooms, is not addressed by current screening guidelines, but may also deserve consideration. To improve students' content visibility, higher contrast may be required, which can be achieved by selecting black letters against white backgrounds (contrast sensitivity = 0.00).

Finally, further studies correlating our data with uncorrected visual acuity data obtained from pediatric vision screening will help to clarify the proportion of children likely to encounter visual challenges in actual classrooms and to provide recommendations for policy development to better accommodate children with visual acuity impairments. This information can also help the Department of Education authorities establish lecture content guidelines among teachers and seating recommendations in the classrooms.

References

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Mean Classroom Dimensions

ParameterAll (N = 14)K to 3rd (n = 4)a5th to 7th (n = 4)a9 to 12th (n = 6)
Mean width (range, ft)16.7 (8 to 25.5)17.2 (8 to 25.5)12.8 (11 to 16)18.8 (13 to 23)
Mean depth (range, ft)18.5 (10 to 23)17.8 (10 to 24)16.8 (14 to 20)20.1 (14.5 to 23)

Average, Maximum, and Minimum Optotype Sizes in logMAR and Snellen Equivalent (N = 14)

ParameterlogMAR Maximum (Upper Case Letters)logMAR Minimum (Lower Case Letters)


Front CenterFront SideBack CenterBack SideFront CenterFront SideBack CenterBack Side
logMAR
  Mean ± SD1.23 ± 0.221.06 ± 0.190.76 ± 0.130.74 ± 0.120.93 ± 0.290.71 ± 0.160.46 ± 0.210.43 ± 0.17
  Range0.69 to 1.660.94 to 1.480.52 to 1.010.55 to 0.940.83 to 1.320.49 to 0.990.10 to 0.790.13 to 0.67
Snellen equivalent (20/x)
  Mean3402301231101701035854
  Range98 to 900174 to 60366 to 20470 to 174135 to 41761 to 19525 to 12327 to 93

Visual Demands Based on Seating

ParameterFront Center SeatingBack Center Seating


AllK to 3rda5th to 7tha9th to 12thAllK to 3rda5th to 7tha9th to 12th
logMAR
  Mean ± SD0.93 ± 0.290.79 ± 0.090.91 ± 0.251.02 ± 0.190.46 ± 0.220.25 ± 0.180.60 ± 0.220.50 ± 0.14
  Range0.59 to 1.320.71 to 0.910.59 to 1.180.80 to 1.320.10 to 0.800.10 to 0.520.38 to 0.800.29 to 0.69
Snellen equivalent
  Mean (20/x)17012316220957357963
  Range77 to 417102 to 16277 to 302126 to 41725 to 12625 to 6648 to 12639 to 98
ParameterFront Side SeatingBack Side Seating


AllK to 3rda5th to 7tha9th to 12thAllK to 3rda5th to 7tha9th to 12th
logMAR
  Mean ± SD0.95 ± 0.200.59 ± 0.060.66 ± 0.210.81 ± 0.210.42 ± 0.170.26 ± 0.120.50 ± 0.210.48 ± 0.12
  Range0.48 to 0.990.50 to 0.630.48 to 0.880.70 to 0.990.13 to 0.690.13 to 0.430.26 to 0.690.38 to 0.62
Snellen equivalent
  Mean (20/x)178779113052376361
  Range60 to 19563 to 8560 to 151100 to 19526 to 9726 to 5336 to 9747 to 83
Authors

From Edward S. Harkness Eye Institute, Columbia University Irving Medical Center, New York, New York (CA, YSK, SEB); and State University of New York College of Optometry, New York, New York (SL).

Supported by an unrestricted grant from Research to Prevent Blindness, Inc, and Jonas Philanthropies.

The authors have no financial or proprietary interest in the materials presented herein.

Correspondence: Steven E. Brooks, MD, Edward S. Harkness Eye Institute, 635 West 165th Street, New York, NY 10032. Email: Seb2204@cumc.columbia.edu

Received: April 25, 2020
Accepted: July 13, 2020

10.3928/01913913-20201019-01

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