The Efficacy of a Visual Screening Program to Reduce Later Amblyopia and Untreated Refractive Errors
Phase: NA
Conditions: Amblyopia
Sponsor: The Hospital for Sick Children

September 12, 2018 
 
PIs: Agnes Wong & Daphne Maurer 
The efficacy of a visual screening program to reduce later amblyopia and 
untreated refractive errors. 
 
Design. The proposed study is a single-masked cluster randomized clinical trial, with 
randomization and analyses occurring at the level of “schools” (i.e., we are not randomly 
assigning individuals to groups). In order to assess the efficacy of a visual screening program, 
we will compare outcomes in schools randomly chosen to receive the program and schools 
allocated to “care as usual”.  The screening tools match those to be rolled out by Ontario 
public health under a new standard in 2018-19 and ones recommended in the literature (see 
below). The outcome measures will assess later differences between schools receiving the 
visual screening program and control schools for prevalence of (1) visual and (2) reading 
problems. A lower prevalence of either or both problems in schools where the visual 
screening program was offered would provide evidence for the efficacy of vision screening. 
 
The trial is being conducted with students in senior kindergarten in the Toronto 
District School Board’s model schools for inner cities, where high needs can be predicted 
based on neighbourhood income and education [1]. We chose to conduct the trial with 
children in senior kindergarten, when children are typically 5 years old, because that is the 
grade during which vision screening is mandated by the new Ontario public health standard 
[2}, because our previous research indicates that the screening tools are more accurate in 
senior than in junior kindergarten [3], and because age 5 is sufficiently early to effectively 
treat or prevent amblyopia and appears to be early enough to offset the adverse effects of 
untreated refractive error on learning [see Background]. Phase 1—which includes sample 
size calculations, randomization of schools, and vision screening in the 25 selected schools 
—has already occurred with seed funding (details below). This was necessary in order to 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
Follow-up:  
 
 
Spring 2019 
Grade 1 
 
 
Fall 2019 
Grade 2 
 
 
 
Spring 2020 
Grade 2 
 
 
Intervention: 
(seed funding) 
 
 
March –  
July 2018 
Senior  
Kindergarten 
 
 
2018 – 2019 
Grade 1 
Excluded: 66 Schools with 
low enrollment and 9 
screened schools 
125 High Needs Schools 
Random Assignment 
• Follow up with parents and 
provide support 
• No intervention by research team 
• Care as usual 
Screened Schools (n = 25) 
• 1298 SK children screened 
• 552 (42%) children referred 
• 170 (13%) prescribed glasses 
Control schools (n = 25) 
• No intervention by research team 
• Care as usual: referrals by 
paediatricians/teachers 
Secondary outcome: % of 
below-average readers 
Follow-up outcome: % below-
average readers 
Primary outcome: prevalence 
of visual problems 
Secondary outcome: % of 
below-average readers 
Follow-up outcome: % below-
average readers 
Primary outcome: prevalence 
of visual problems 

2 
 
 conduct the first phase of the study before all Ontario children in senior kindergarten are 
mandated to receive visual screening in the 2018-19 school year.  
The visual outcomes will measure amblyopia, reduced stereopsis (an index of abnormal 
binocular vision that is linked to amblyopia), and untreated clinically significant refractive 
errors. They will be measured in Grade 2, after the children in the screened schools have 
had more than 1 year for treatment. This is sufficient time for treatment for amblyopia and 
its risk factors to be effective (see Background), so that, if the screening program is 
effective, there should be fewer cases of visual problems in the children attending schools 
that received the screening program than in the control schools. There should also be fewer 
cases of children with clinically significant refractive errors that are not being treated with 
glasses. Note that with this design the predictions are at the school level, not the level of 
individual children, and hence the analyses are not restricted to children who actually 
received screening in senior kindergarten or follow-up in Grade 2. Analyses at this level 
obviate against finding an apparent benefit of an intervention that is actually the result of 
which children (or parents) chose to participate in the intervention. That said, <1% of 
parents opted out of the screening offered in senior kindergarten. 
The learning outcomes will be the prevalence of reading one standard deviation below 
grade level in schools offered the visual screening program versus control schools. Reading 
performance is assessed routinely at the end of each year by the Toronto District School 
Board in the 50 schools that are part of this study. The TDSB research department has 
agreed to share the distribution of scores with us, as they did in the pilot study described in 
the Background. If the screening program is effective in identifying children with 
amblyopia, its risk factors, and significant refractive errors, and getting them needed follow-
up to receive treatment, then the distributions should differ between screened and control 
schools: there should be fewer children reading below grade level in the screened schools. 
We will compare the distributions at the ends of Grade 1 and Grade 2 in order to detect 
both immediate and any delayed effects. 
Intervention: Vision screening and facilitated follow-up 
Sample size.  Although we will be measuring a number of outcomes, we chose the sample 
size based on the prevalence of amblyopia, because of its well-documented lifetime health 
consequences. Specifically, we chose a sample size that would allow us to detect a 50% 
reduction in the prevalence of amblyopia. A pilot study involving 1200 children in junior and 
senior kindergarten in 6 of Toronto’s model schools for inner cities revealed a prevalence of 
amblyopia of 6%, a prevalence consistent with that reported for other multi-ethnic 
communities (see Background). Our experimental hypothesis is that a successful school-
based screening program will reduce the prevalence of amblyopia by half to 3%. For sample 
size, standard calculations for cluster random clinical trials were performed. Sample size 
calculations assumed an ICC of 0.01 and used a two-sided alpha of 0.05 with 80% power. 
Our final sample size is based on two estimates of cluster size: when senior kindergarten 
enrollment was set at 50 children per school, the estimated sample size was 46 schools (N = 
2,300 SK children), and when senior kindergarten enrollment was set at 41 children per 

3 
 
 school, the estimated sample size was 52 schools (n = 2,050 children). Because senior 
kindergarten enrollment is not uniform across schools, we chose a sample size that fell 
between these two estimates — 50 schools —with actual kindergarten enrollment ranging 
from 38-93 children in the 25 “screened” schools and 39-109 children in the control “care as 
usual” schools (Total N = approximately 3,000 senior kindergarten children).  
Selection of schools. The Learning Opportunities Index (LOI), a needs-based criterion of 
the TDSB [1], was utilized to select schools. LOI ranks schools based on external challenges 
affecting student success, such as median neighborhood income. The 125 schools with the 
most challenges are part of the Model Schools for Inner Cities program, and, as part of that 
program, receive annual reading assessments. We chose the 50 “model schools” with the 
highest senior kindergarten enrollment and randomly allocated 25 schools each to the 
“screened” versus control “care as usual” groups, excluding nine schools that had received 
vision screening (3 schools in our pilot study and 6 schools with ad hoc volunteer screening). 
Our biostastician, Prof. Kevin Thorpe, conducted this randomization utilizing a simple 
computer-generated allocation and was not involved in the actual screening. 
All 25 schools selected for the vision screening program participated. We expect similar 
cooperation from all 50 schools for the Grade 2 visual assessments because of the support of 
the TDSB (see letter from collaborator Maria Yau) and because all cooperate with the Gift 
of Sight and Sound, which provides a similar program for children in Grade 5. 
Vision screening.  We conducted vision screening in the 25 selected schools between 
March and May 2018.  There were three screening tools, the same tools to-be-used by 
Ontario Public Health in the newly mandated screening: 
(1) HOTV with crowding bars. This is one of the most sensitive tests of acuity for vision 
screening of young children [4]. The child is asked to recognize a letter (H, O, T, or V) 
that is surrounded by a bar on each side to induce the crowding effects typical of 
amblyopia. The child can name the letter or match it to the same letter on a card he/she 
is holding. Although the VIP studies recommend testing at 5 feet for children 3-5 years 
old, our previous studies indicated that the standard distance of 10 feet is not 
problematic for children 5-6 years old, i.e., senior kindergarten.  Testing occurs in a well-
lit room and begins with large letters and progresses to smaller letters until the child 
makes too many mistakes. The threshold is the smallest size for which the child 
correctly identified (or matched) 3 of the letters (in a maximum of 5 presentations). 
Testing is monocular with the other eye patched with a Fresnel eye patch that prevents 
peaking. In order to pass acuity screening, the child must achieve at least 20/32 in each 
eye [5]. Otherwise, he/she is referred for an eye exam. 
(2) Preschool randot stereoacuity.  The Randot Preschool Stereoacuity test is a reliable 
screening test for stereo depth perception that can be performed by children as young 
as 2.5 years old [6-7]. When tested against results from a gold standard eye exam, the 
Randot yielded better results than the Stereo Smile (originally used in the VIP study) 
for detecting strabismus, amblyopia, and anisometropia, although neither was very good 
at detecting anisometropia [7]. 

4 
 
 
We used this test in our previous study of the sensitivity and specificity of 5 tools against 
a full cycloplegic exam. For the 267 children in senior kindergarten, and a cutoff of 100 
arcsecs (consistent with the VIP study), almost all children passed, yielding a sensitivity 
for the Randot on its own of only .27 (95% CI .14, .4) but a specificity of .93 
(95%CI: .89, .97) [3]. However, 100 arcsecs may have been too lenient a criterion. The 
original normative data with 4355 children aged 3-18 years found that the mean 
stereoacuity for 3-year-olds (n=138) and 4-year-olds (n=217) was 100 arcsec while for 5-
year-olds it was 60 arcsec (n = 104) [6].  Later normative data [7] indicated that >80% of 
children between 60 and 72 months (5-6 years, i.e., the age of children in senior 
kindergarten) achieve a score of 60 arcsecs or better. Therefore, to avoid missing 
children with binocular eye problems, we used 60 arcsecs as the criterion for passing in 
Phase 1 of the current study. 
Testing occurs in a well-lit area, with a testing distance of 40 cm. The child is given a 
booklet in which the left page shows test shapes, such as a tree, and the right page shows 
random dot patterns in four quadrants. The child wears polarizing glasses that divide the 
random patterns into different images to the left and right eye, which, if fused, can be 
resolved into a three-dimensional stereoscopic image of the test shapes in 3 of the 4 
quadrants. Otherwise, the child sees only random dot patterns. The child’s task is to 
indicate which shape, if any, is present in each quadrant of the dot patterns by naming it 
or matching it to a shape on the left page. Children are tested beginning with easily 
resolved patterns (disparity level of 800 arcsec) and then the task is gradually made more 
difficult with successive disparity levels of 400, 200, 100, and 60 arcsec levels. Children 
unable to get 2/3 shapes correct at the 60 arcsec level are referred for an eye exam. 
(3) Plusoptix autorefractor. Our earlier studies used both the Spot (WelshAllyn) and the 
Plusoptis. Both measure refractive errors by focusing a light onto the child’s eye and 
recording how its reflection from the retina returns to the camera—as an appropriately 
focused spot, a blurred spot indicating myopia or hyperopia, or as a slit indicating 
astigmatism. It can also detect whether there is anisometropia (unequal refractive errors 
in the two eyes), a condition that can quickly leads amblyopia. The results, like previous 
studies [8-10}, indicated that they have reasonable sensitivity and specificity and that the 
results are very highly correlated, with the PlusoptiX having slightly higher sensitivity 
(.72 vs. .67) and the Spot having slightly higher specificity (.94 vs. .90).   Therefore, we 
decided to use only one autorefractor for this study, namely the PluxoptiX, the one with 
higher sensitivity to detect eye problems. 
The child is tested in a dimly lit space, either a separate room or a large pop-up tent 
within a larger room. The child sits 100 cm away from the handheld device and is asked 
to look at the lighted smiley face in the middle. The device automatically takes 
measurements when the child is at the right distance and fixating. Testing in a dim space 
facilitates capturing the child’s attention on the lighted smiley face and obtaining good 
measurements because of the increased pupil size. 

5 
 
 
In our original study of 712 kindergarten children, all of whom received full eye exams, 
we used the autorefractor screening cutoffs recommended by the American Association 
of Pediatric Ophthalmology and Strabismus [5]:   hyperopia >+3.5D; astigmatism >1.5D; 
myopia >-1.5 D; anisometropia 1.5D SE. ROC analysis of the results suggested that a 
cutoff of +2 for hyperopia would improve sensitivity without lowering specificity 
significantly. Therefore, we used the following referral criteria in Phase 1: hyperopia 
>+2.0D; astigmatism >1.5D; myopia >-1.5 D; anisometropia 1.5D SE [3]. 
Children who did not pass all three screening tests were referred for full cycloplegic 
optometry exams, scheduled at school for the convenience of the parents. Children already 
wearing glasses were tested on acuity and stereoacuity while wearing their glasses and 
referred if they did not pass, because they might need a prescription change. Vision 
screening was completed by internationally trained medical graduates working with the 
Toronto Gift of Sight and Sound. They were trained and monitored by our research team. 
Screening time averaged 15 minutes/child (range 11-23 minutes). Overall, 552 (42%) of the 
screened children were referred for an optometry exam, although the referral rate ranged 
from 25 to 63% across the 25 schools.  
The follow-up optometry exams were standardized and occurred in the school, unless it 
was more convenient for the parent to go to the optometrist’s office. They were full exams, 
with cycloplegia, with the parent present, and followed a standard protocol specified by the 
research team and recorded on a standardized assessment sheet for each child (Appendix 1). 
Specifically, they were asked to assess visual history, monocular visual acuity at near and far, 
strabismus, binocular function, abnormalities of the anterior segment, and cycloplegic 
refraction. A member of the research team was present at each in-school exam and assured 
that each child’s optometry assessment sheet was completed fully. If the child needed 
glasses, the frames were picked out at the time of the exam and dispensed either at the 
school or the optometrist’s office. Overall, 364 (66%) of the parents of referred children 
arranged for an in-school optometry exam, a percentage similar to that we found when we 
offered a similar program in 42 schools in 15 communities across Ontario [3]. Glasses were 
dispensed to 170 (13%) of the screened children. 
To facilitate follow-up, optometrists were chosen with offices near the schools. For 3 of 
the 25 schools where this was not possible, an out-of-town optometrist conducted the in-
school exams, but a community optometrist with an office near the school accepted the 
patients for any needed follow-up. All parents agreed to be contacted by the community 
optometrist and our program when it is time for follow-up. With the parent’s continuing 
consent, we will monitor children in “screened” schools who have a visual problem for two 
years, by reminding parents about follow-up appointments and replacing broken and lost 
glasses. The frequency of monitoring will vary depending on the child’s condition and 
decisions by the treating optometrist. Because the goal of our research is to evaluate the 
efficacy of a screening program, our primary concern is that screening correctly identifies 
children with visual problems and facilitates their care for amblyopia and/or refractive 
errors. Whether the recommended treatments are optimal or whether children comply with 
the prescribed treatments will not be addressed in this study.  Rather, the study will assess 

6 
 
 whether a program of vision screening and facilitated follow-up is effective, when it is 
implemented in the real world, complete with real-world limitations like student absences 
on the day of screening, lost glasses that are not replaced, parents who do not show up for 
optometry exams, etc. The control “care as usual” schools will not receive any intervention 
by our research team, but children may receive care through regular referral channels (e.g., a 
teacher may recommend that a child see an optometrist; a parent may take the child for a 
routine exam). 
Follow-up: Visual outcomes in Grade 2  
We will employ different testers for visual assessments in Grade 2 than those involved 
in Senior Kindergarten, in order to prevent experimenter bias; specifically, Grade 2 testers 
will not know whether a particular school was part of the “screened” or control “care as 
usual” group. Each screener will also be blind to the results of the other tests.  
All assessment will occur during a 2-month period in the late fall of 2019, after the 
school routine has settled, and be randomly scheduled among the “screened” and control 
“care as usual” schools. We anticipate that principals of all 50 schools will agree to 
participate because no Toronto principal has declined our vision screening program in the 
past and because principals of these high-needs schools welcome extra services for their 
children. 
Parents will be sent a letter describing the vision checking and will be given the option 
to opt out. We anticipate that few parents will opt out, because less than 1% did so when 
the children were in senior kindergarten. Parents will receive a letter indicating whether or 
not the child passed the vision checks.  When the child did not, the letter will indicate the 
need for a follow-up optometry exam and provide advice on how to book an OHIP-covered 
eye exam.  
Primary Clinical Outcomes: Amblyopia and Untreated Refractive Error 
Amblyopia. One primary outcome measure is the prevalence of amblyopia in “screened” 
vs. control “care as usual” schools in Grade 2 (i.e. after allowing at least one year for 
treatment). We will use the HOTV Paediatric wall chart with proportional spacing to 
measure the acuity of each eye, while the untested eye is patched. By Grade 2, children can 
be tested with linear letter charts, which are more sensitive to the crowding effects of 
amblyopia than charts with crowding bars or other arrangements [11]. If any child is unsure 
of the names of the letters (e.g., because they are in the process of learning English), the test 
can be based on matching to a card held by the child with the same letters. Amblyopia will 
be defined as a 2-line or greater difference in acuity between eyes [12], or, in the rarer cases 
of bilateral amblyopia, acuity worse than 20/40 in the eye with better acuity [13]. Children 
wearing glasses will be tested while wearing the glasses and, should they fail with glasses, the 
parents will be informed that the child may have outgrown the glasses and to check with the 
optometrist to see if a follow-up appointment is warranted. 

7 
 
 
A secondary measure will be stereoacuity, which is reduced in patients with some types 
of amblyopia [14], often secondary to strabismus. We will use the Randot test of stereopsis 
because it includes values down to 20 arcsecs (unlike the preschool version that stops at 40 
arcsecs) and because by Grade 2, virtually all children can understand the instructions. The 
cut-off for normal stereoacuity will be 30 arcsecs, the mean value found in normative data 
for children 7-8 years old [6]. Although monocular cues can lead to spurious results at the 
larger disparities of the Randot, they are not an issue for disparities less than 140 arcsecs 
[15]. As with acuity, the measure of interest is best corrected vision and hence children with 
glasses will be tested while wearing them. Should the child fail with glasses, the parent will 
receive a note that the child’s glasses may have been outgrown and to check with the 
optometrist about follow-up. 
Untreated refractive errors. The second primary outcome measure is the prevalence of 
clinically significant refractive errors that are not being treated by prescription glasses. We 
will measure refractive error using the PlusoptiX autorefractor, as we did for the senior 
kindergarten children, but with the cut-offs adjusted to be appropriate for Grade 2. There 
are variable opinions about what level of refractive error is clinically significant at this age, 
but a reviews of the evidence and of current practice [16-17] suggest: hyperopia ≥+1.5D, 
myopia ≥ -1.oD, astigmatism ≥0.75D, and anisometropia ≥1.0D.  
As a clinical service, parents of children who do not pass all three tests will receive a 
letter recommending that they book a full eye exam. Children already wearing glasses will 
not be tested with the autorefractor because any refractive error is already under treatment 
and because autorefractors do not work accurately through glasses. However, if they do not 
pass the visual acuity and/or stereoacuity tests, their parents will receive a letter indicating 
that the child may have outgrown the glasses and that they should check with their 
optometrists to determine if it is time for follow-up. 
Secondary outcomes: Reading scores 
Educational assessments are collected annually by TDSB at all high needs schools. using 
the Canadian Test Centre’s CAT4 [18].  These are standardized achievement tests, with 
normative data based on the testing of over 60000 students in kindergarten through Grade 
12 from over 300 schools across Canada, stratified to capture a representative sample. TDSB 
has agreed to share with us the distribution of scores from each of the 50 schools for the 
Reading subtest. We will analyze the distribution of scores in “screened” versus control 
“care as usual” schools in Grade 1 (shortly after the intervention) and Grade 2 (after over 1 
year for treatment). 
Analyses of data. The statistical analyses have been planned with our co-investigator, Dr. 
Thorpe. Demographic data describing the students at each school will be summarized with 
descriptive measures (age, sex). The primary outcome (prevalence of amblyopia) will be 
analyzed using the method of Generalized Estimating Equations [19] for binary outcomes 
with a logit link and school as the unit of clustering. The detection effect will be expressed 
as an odds ratio with 95% confidence interval. Similar analyses will be performed separately 
for the proportion of children with reduced stereoacuity and untreated refractive errors. 

8 
 
 Children already wearing glasses will be included in the analyses of amblyopia and 
stereoacuity but not in the analysis of untreated refractive errrors. 
For the reading assessments. the data will consist of the distribution of scores across 9 
standardized categories, centred on the normative value of 5. Because ~75% of children will 
not have a visual problem, we do not expect vision screening to increase the mean reading 
level; instead, we hypothesize that screening will lead to fewer children with untreated eye 
problems and thereby reduce the proportion of children experiencing reading difficulties 
(i.e., 1 standard deviation below the norm; children farther below the norm are likely to have 
additional problems).  Therefore, as with amblyopia and other visual disorders, we will 
compare the proportion of children in screened versus control schools with a score below 
the norm. Data for Grade 1 will reveal if the vision screening program results in fewer initial 
reading problems. Data for Grade 2 will reveal if any difference emerges after more than 1 
year of treatment for children in the “screened” schools. We will use percentage turn-over 
(i.e., number of children leaving and joining a school between SK and Grade 2) for each 
school as a factor in the regression analyses because such turnover will work against finding 
an effect of screening at the school level.  
A positive effect of the visual screening program will manifest as significantly fewer 
children in Grade 2 with amblyopia, reduced stereopsis, untreated refractive errors, and/or 
below average reading scores in screened schools compared to control “care as usual” 
schools. If so, subsequent studies can assess which parts of the visual screening program are 
essential in the Ontario health care context in order to identify children with eye problems 
(e.g., is screening alone effective without in-school follow-up exams?) and assure they receive 
treatment, thereby preventing or ameliorating amblyopia and eye-related learning 
difficulties.  
 
 
 

9 
 
 
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