This document summarizes a study that evaluated the effectiveness of a placebo therapy program designed for a clinical trial on convergence insufficiency. The study developed a placebo therapy program intended to simulate real vision therapy/orthoptics without actually stimulating accommodation or vergence. At the end of the 12-week treatment period, subjects were asked which treatment they thought they received and how sure they were of their answer. Ninety-five percent of subjects receiving real therapy and 83% receiving placebo therapy thought they received real therapy. The majority of subjects in both groups were somewhat, pretty, or very sure of their answer. The study concluded that the placebo therapy program was effective in maintaining subject masking in this clinical trial.

1. CLINICAL REPORT
Feasibility of Using Placebo Vision Therapy in a
Multicenter Clinical Trial
MARJEAN TAYLOR KULP, OD, MS, FAAO, ERIC BORSTING, OD, MS, FAAO,
G. LYNN MITCHELL, MAS, FAAO, MITCHELL SCHEIMAN, OD, FAAO,
SUSAN COTTER, OD, MS, FAAO, JEFFREY COOPER, OD, MS, FAAO,
MICHAEL ROUSE, OD, MS, FAAO, RICHARD LONDON, MA, OD, FAAO,
JANICE WENSVEEN, OD, PHD, FAAO, and THE CONVERGENCE INSUFFICIENCY
TREATMENT TRIAL (CITT) INVESTIGATOR GROUP
College of Optometry (MTK), and Optometry Coordinating Center (GLM), College of Optometry, The Ohio State University, Columbus,
Ohio, Southern California College of Optometry, Fullerton, California (EB, SC, MR), Eye Institute, Pennsylvania College of Optometry,
Philadelphia, Pennsylvania (MS), College of Optometry, State University of New York, New York, New York (JC), College of Optometry,
Pacific University, Portland, Oregon (RL), and College of Optometry, University of Houston, Houston, Texas (JW)
ABSTRACT
Purpose. The Convergence Insufficiency Treatment Trial (CITT) Investigator Group conducted a preliminary study
assessing the effectiveness of home-based push-up therapy and office-based vision therapy/orthoptics for the treatment of
convergence insufficiency (CI). The CITT group developed a placebo therapy program that was designed to simulate real
vision therapy/orthoptics. The purpose of this paper is to evaluate the effectiveness of this placebo therapy program in
maintaining masking of subjects randomized to the office-based treatment arms (real or placebo).
Methods. Subjects (ages 9 to 30 years) were enrolled, stratified into two groups by age, and then randomly assigned to
one of three treatment groups: pencil push-up therapy, office-based vision therapy/orthoptics, or office-based placebo
vision therapy/orthoptics. At the end of treatment, subjects in the two office-based therapy groups (placebo and real) were
asked: (1) which treatment do you think you received? and (2) how sure are you about your answer?
Results. Ninety-five percent of subjects assigned to real therapy and 83% assigned to placebo therapy thought they were
in the real therapy group. Of the subjects who thought they received real therapy, 90% assigned to real therapy and 89%
assigned to placebo therapy were “somewhat sure,” “pretty sure,” or “very sure” of their answer. Those assigned to real
therapy had more responses in the “very sure” category.
Conclusion. The CITT placebo therapy program was effective in maintaining subject masking in this multicenter clinical
trial.
(Optom Vis Sci 2008;85:255–261)
Key Words: convergence insufficiency, placebo, vision therapy, orthoptics, vergence
V
ision therapy is a common treatment for convergence in-
sufficiency (CI), a vergence disorder that affects approxi-
mately 5% of school-aged children and is often associated
with symptoms when performing near work such as double vision,
sore eyes, blurred vision, headaches, and/or the need to re-read the
same line.1–3
However, studies investigating the effectiveness of
vision therapy have been criticized because of inadequate controls
for subject masking.4,5
That is, the subject may improve because of
the expectation that the treatment will be effective. To address this
potential bias, the Convergence Insufficiency Treatment Trial
(CITT) Investigator group developed a placebo-based treatment
arm for use in a multicenter randomized clinical trial pilot com-
paring the effectiveness of office-based vision therapy/orthoptics
and home-based pencil push-ups as treatments for subjects 9 to 30
years of age with symptomatic CI.6,7
Patients may show clinical improvements that are not due to the
intervention itself, but instead are attributable to natural history,
regression to the mean, and/or “non-specific” treatment effects.8
The natural history of some diseases is to improve even without
treatment. Improvement from regression to the mean occurs when
1040-5488/08/8504-0255/0 VOL. 85, NO. 4, PP. 255–261
OPTOMETRY AND VISION SCIENCE
Copyright © 2008 American Academy of Optometry
Optometry and Vision Science, Vol. 85, No. 4, April 2008

2. a patient presents for treatment when symptoms are at their peak
and then feels better as the symptoms return to their usual lower
(mean) level. Non-specific effects of treatment, such as the patient-
provider interaction and patient’s belief in the effectiveness of the
treatment, also have been reported to have a significant effect on
treatment outcome.8–11
For example, a placebo effect has been
reported to be manifest in neuroimaging studies,12–16
mediated by
the dopaminergic system and associated with the anticipation of
clinical improvement.13
However, controversy remains regarding
the existence of a placebo effect.9–11,13,17–22
Whereas a non-significant
placebo effect has been reported for binary or objective outcomes,
a small significant placebo effect has been reported for continuous
subjective variables (i.e., patient-reported outcomes).21
Irrespec-
tive of this controversy, placebo-controlled clinical trials, in which
a placebo arm is included to control for bias as well as potential
placebo effects,21
have become standard for investigating the clin-
ical effectiveness of a treatment.17
Although there is no single def-
inition of a placebo,22
the placebo treatment is generally thought to
be an inert or innocuous therapeutic procedure that is designed to
simulate the real therapy that is being studied.8,12,17
In vision therapy/orthoptics, the stimulation and manipulation
of accommodation and vergence is the active therapy. However, it
is possible that the associated aspects of administering therapy,
such as the therapist-patient interactions and patient’s belief in the
effectiveness of the treatment, may also influence the treatment
outcome. Thus, for a placebo therapy program to be effective,
treatment would need to be very similar to real therapy in admin-
istration, yet not produce stimulation of accommodation or
vergence.
Few previous studies of vision therapy/orthoptics have included
a placebo therapy control. Those that have used a placebo control
investigated specific aspects of a therapy program (e.g., computer
vergence therapy, accommodation, timing of vergence therapy),
included only a small number of subjects, and did not evaluate the
effectiveness of placebo therapy as a control (e.g., the effectiveness
of the subjects’ masking was not assessed).23–27
The CITT Group designed a 12-wk placebo therapy program
consisting of activities that presumably did not stimulate accom-
modation or vergence (beyond levels of typical near or distance
viewing conditions) or small sequential saccadic eye movements.
The placebo program was designed to simulate real vision therapy
so that subjects randomized into the placebo group would perceive
that they were receiving real therapy and thus would be more likely
to adhere to the assigned treatment program. The purpose of this
paper is to evaluate the effectiveness of this placebo therapy pro-
gram in maintaining subject masking in a randomized clinical trial.
METHODS
Subjects
Subjects between the ages of 9 and 30 years were recruited via
internal referrals, external referrals, and advertising by six clinical
centers (Pennsylvania College of Optometry, Southern California
College of Optometry, State University of New York College of
Optometry, The Ohio State University College of Optometry,
Pacific University College of Optometry, and University of Hous-
ton College of Optometry). Subjects were stratified into two
groups based on age [children (ages 9 to 18 years) and young adults
(ages 19 to 30 years)] because of the possibility that children and
adults may respond differently to treatment. Children Ͻ9 years of
age were excluded because of their limited ability to respond reli-
ably to the Convergence Insufficiency Symptom Survey (CISS).
The institutional review boards of each participating academic
institution approved this research. Each adult subject or a parent or
guardian of each child provided written informed consent and
authorization to use personal health information in research. Par-
ticipating children provided assent.
Major eligibility criteria for the trial included ages 9 to 30 years
inclusive, exophoria at near at least 4⌬
greater than at far, a receded
near point of convergence break of 6 cm or greater,28
insufficient
positive fusional convergence at near [i.e., failing Sheard’s criteri-
on28,29
or minimum positive fusional vergence of Յ15⌬
base-out
(blur if present, otherwise break)], and a score of Ն9 on the CISS
V-13. A complete listing of the eligibility and exclusion criteria
have been reported previously.6,7
The CISS score (a subject-
reported symptoms questionnaire) was the primary outcome mea-
sure in the CITT.1,2,6,7
Eligible subjects were randomly assigned with equal probability
to one of three treatment groups: pencil push-up therapy, office-
based vision therapy/orthoptics, or office-based placebo vision
therapy/orthoptics. Randomization was achieved on the study’s
website using randomly selected blocks of six so the sequence of
treatment assignments could not be predicted. Randomization was
performed separately for each site to ensure approximately equal
numbers of subjects in each treatment group.
Each subject knew whether he or she had been assigned to
office-based treatment or home-based pencil push-up therapy.
However, the subjects assigned to the two office-based treatment
groups did not know whether they were assigned to real or placebo
therapy. Because the focus of this paper was to report whether or
not placebo therapy was effective in maintaining subject masking,
the third treatment group (pencil push-up therapy) will not be
discussed further in this paper.
Each treatment program was 12 wk in duration with a masked
primary outcome examination occurring after 12 wk of treatment.
Both the real and placebo office-based therapy groups received
weekly (60-min) in-office therapy visits administered by a trained
therapist. Procedures to be practiced at home were prescribed for
15 min, five times per week. Because the therapists were trained in
vision therapy/orthoptics, they were able to distinguish between
true and placebo therapy and were not masked to treatment assign-
ment. However, the therapists were instructed to encourage and
give positive reinforcement to all subjects in the same manner
regardless of treatment assignment.
The real therapy program consisted of standard vision therapy/
orthoptics techniques for subjects with CI. The program included
techniques such as Brock String, Free-Space Fusion Cards, Vecto-
grams, Computer Orthoptics™ for vergence, the Aperture Rule
and plus minus lens flippers. A complete description has been
published previously.6,7
The placebo therapy program included 18 therapy procedures
that were designed to give the impression of real vision therapy/
orthoptics procedures yet not stimulate vergence, accommodation,
or small saccadic eye movement skills beyond normal near and
distance viewing conditions. Four procedures were performed dur-
ing each office therapy visit (8 to 10 min each) and two procedures
256 Placebo Vision Therapy in a Multicenter Clinical Trial—Kulp et al.
Optometry and Vision Science, Vol. 85, No. 4, April 2008

3. TABLE 1. Placebo therapy procedures.
Technique Goal
Visit 1
Computer placebo accommodation Improve focusing and speed of response
Ductions Equalize monocular inputs
Monocular brock string-level one Equalize monocular inputs
Visual closure with filter glasses Eye teaming
Visit 2
Computer placebo accommodation Improve focusing and speed of response
Ductions Equalize monocular inputs
Monocular brock string-level two Equalize monocular inputs
Visual closure with filter glasses Eye teaming
Visit 3
Computer placebo accommodation Improve focusing and speed of response
Bailey-Lovie acuity Equalize monocular inputs
Monocular brock string-level two Equalize monocular inputs
Visual closure with filter glasses Eye teaming
Visit 4
Computer placebo accommodation Improve focusing and speed of response
Bailey-Lovie acuity Equalize monocular inputs
Monocular brock string-level three Equalize monocular inputs
Visual closure with filter glasses Eye teaming
Visit 5
Computer placebo accommodation Improve focusing and speed of response
After image Equalize monocular inputs
Red/red therapy Eye teaming
Visual figure ground with filter glasses Eye teaming
Visit 6
Computer placebo accommodation Improve focusing and speed of response
After image Equalize monocular inputs
Red/red therapy Eye teaming
Visual figure ground with filter glasses Eye teaming
Visit 7
Computer placebo vergence Improve eye teaming and speed of response
Hess Lancaster Eye teaming
Yoked prism flippers Eye teaming
Visual figure ground with filter glasses Eye teaming
Visit 8
Computer placebo vergence Improve eye teaming and speed of response
Hess Lancaster Eye teaming
Yoked prism flippers Eye teaming
Visual figure ground with filter glasses Eye teaming
Visit 9
Computer placebo vergence Improve eye teaming and speed of response
Modified Thorington Eye teaming
Bernelloscope level 1 Eye teaming
Visual spatial attention with filter glasses Eye teaming
Visit 10
Computer placebo vergence Improve eye teaming and speed of response
Modified Thorington Eye teaming
Bernelloscope level 1 Eye teaming
Visual spatial attention with filter glasses Eye teaming
Visit 11
Computer placebo vergence Improve eye teaming and speed of response
Double maddox rod Eye teaming
Bernell-o-scope level 2 Eye teaming
Visual spatial attention with filter glasses Eye teaming
Visit 12
Computer placebo vergence Improve eye teaming and speed of response
Double maddox rod Eye teaming
Bernell-o-scope level 2 Eye teaming
Visual spatial attention with filter glasses Eye teaming
Placebo Vision Therapy in a Multicenter Clinical Trial—Kulp et al. 257
Optometry and Vision Science, Vol. 85, No. 4, April 2008

4. were assigned for home therapy each week. Each procedure was
prescribed to be performed for two to six weeks. Some procedures
were designed to appear to have increasing levels of “difficulty.”
This therapy program was comprised of traditional vision therapy/
orthoptics procedures that were modified to be monocular rather
than binocular as well as testing procedures that did not require
significant demand on the vergence, accommodative, or fine
saccadic eye movement systems. Similar to real therapy, subjects
frequently wore filter glasses and were told that the glasses were
important to ensure that both eyes were being used together. As in
the real therapy procedures, objectives and goals were established
for each placebo procedure to motivate subjects to engage in the
therapy activities. Therapists reviewed the objective of each proce-
dure with the subject before starting each technique. For example,
one modified placebo procedure was performed on the Computer
Orthopter, in which the subject wore the appropriate filter glasses
and performed vergence therapy at zero vergence demand only.
The “stated” goal of this procedure was “to improve eye teaming
and speed of response.” Table 1 lists the placebo therapy proce-
dures along with their stated goals.
Treatment adherence was monitored for both placebo and real
therapy groups by using a home log. Subjects were instructed to
record the time spent and objectives achieved. At each office treat-
ment session or follow-up visit, the therapists reviewed these logs
and encouraged adherence. In addition, after 4, 8, and 12 wk of
treatment, the therapist was asked to estimate the subject’s adher-
ence to the treatment protocol using the scale “0%,” “1 to 24%,”
“25 to 49%,” “50 to 74%,” “75 to 99%,” or “100%.” Adherence
estimates were obtained for procedures practiced both at home and
in-office.
At the end of treatment, subjects in the two office-based therapy
groups (placebo and real) were asked: (1) “which treatment (pla-
cebo or real) do you think you received?” and, (2) “how sure are
you about your answer?” Subjects responded to question 2 with
“very sure,” “pretty sure,” “somewhat sure,” “a little sure,” and
“not at all sure.”
Statistical Analysis
All statistical analyses were performed using SAS version 9.1
(Cary, NC). Comparison of adherence information was performed
using the Wilcoxon Rank sum test. A ␹2
or Fisher exact test was
used to compare the two treatment groups with respect to dichot-
omous outcomes such as completed study or not.
RESULTS
Thirty-two subjects (9 to 18 years old: n ϭ 17; 19 to 30 years
old: n ϭ 15) were randomized to real therapy, whereas 29 subjects
(9 to 18 years old: n ϭ 15; 19 to 30 years old: n ϭ 14) were
randomized to placebo therapy. As previously reported, demo-
graphic and clinical data from the eligibility examination were
neither statistically nor clinically different between subjects as-
signed to the two treatment groups in the study population overall
(p Ͼ 0.35 for all comparisons) or within the two age strata (ages 9
to 18 and 19 to 30 years; p Ͼ 0.30 for all comparisons).6,7
The primary outcome examination was completed within the
12 Ϯ 2 wk window by 27 of 32 (84%) of subjects assigned to real
therapy and 25 of 29 (86%) of subjects assigned to placebo ther-
apy. The completion rate was not related to treatment assignment
(␹2
p-value ϭ 0.99).
The therapists rated the adherence to office therapy to be very
high in both groups at 4, 8, and 12 wk (Table 2). Estimates of
adherence to home therapy, however, were somewhat less, ranging
from 63% to 82% with a marginal decline in adherence by the real
therapy group towards the end of the program. There were no
significant differences between the two treatment groups in the
therapists’ assessment of subject’s adherence to office or home
protocols after 4, 8, or 12 wk of therapy although the difference
between groups in adherence to the home protocol at the 12-wk
visit approached significance (Table 2).
Of the subjects who completed the primary outcome visit, 81%
(22 of 27) of those assigned to real therapy and 92% (23 of 25) of
those assigned to placebo therapy responded to the two questions
concerning group assignment. Of these patients, 95% (21 of 22) of
the subjects assigned to real therapy and 83% (19 of 23) assigned to
placebo therapy thought they had been assigned to real therapy
(Fig. 1). Subjects in the placebo group were as likely as those
assigned to real therapy to think they had been assigned real ther-
apy (Fisher exact test p ϭ 0.35). For subjects age 9 to 18 years,
100% (12 of 12) assigned to real therapy and 91% (10 of 11)
assigned to placebo therapy thought they received real therapy
(p ϭ 0.48). Similarly, in 19- to 30-year-olds, 90% (9 of 10) as-
signed to real therapy and 75% (9 of 12) assigned to placebo
TABLE 2. Percentage of subjects estimated to adhere to therapy protocols at least 75% of the time, by group assignment
and time in therapy.
Time
Vision
Therapy/Orthoptics
Placebo Vision
Therapy/Orthoptics
p-valuen % n %
Office protocol adherence
4 week 28 100.0 26 96.2 0.84
8 week 27 100.0 24 95.8 0.69
12 week 26 100.0 25 92.0 0.59
Home protocol adherence
4 week 28 82.1 26 76.9 0.77
8 week 27 81.5 24 75.0 0.84
12 week 26 63.0 25 80.0 0.05
258 Placebo Vision Therapy in a Multicenter Clinical Trial—Kulp et al.
Optometry and Vision Science, Vol. 85, No. 4, April 2008

5. therapy thought they had received real therapy (p ϭ 0.59). There
was no statistically significant difference between age groups in the
percentage of patients who thought they had received real therapy
(p ϭ 0.59).
Of the subjects assigned to placebo therapy who thought they
received real therapy, 89% (17/19) said they were “somewhat
sure,” “pretty sure,” or “very sure” of their answer (Fig. 2). In
contrast, only 25% (1 of 4) of those assigned to placebo therapy
who correctly identified their treatment assignment were “some-
what sure,” “pretty sure,” or “very sure” they had been assigned to
placebo therapy. Nine of the 10 subjects aged 9 to 18 years and 8 of
the 9 subjects aged 19 to 30 years, assigned to placebo therapy who
incorrectly guessed their treatment group assignment, were at least
“somewhat” sure of their response. Confidence in response was not
related to age (p ϭ 0.55) in subjects assigned to placebo therapy
who thought they had received real therapy.
An analysis of confidence level overall (irrespective of group
assignment and whether the subject was correct or incorrect in
his/her perception of group assignment) showed that there was no
significant difference in the confidence level of children between
groups [percent “very sure” or “pretty sure” of response: 75% in
real therapy and 54.6% in placebo therapy (p ϭ 0.30)]. On the
other hand, the adults in the placebo group were significantly less
sure than the adults in the real therapy group [percent “very sure”
or “pretty sure” of response: 90% in real therapy and 41.7% in
placebo therapy (p ϭ 0.019)]. Also, only subjects assigned to real
therapy reported being “very sure.”
DISCUSSION
This investigation found no significant difference between sub-
jects assigned to real or placebo therapy in completion rate for the
primary outcome exam or in the therapist’s assessment of subject’s
adherence to office or home therapy protocols after 4, 8, or 12 wk
9-18 yo (n=11) 19-30 yo (n=12) Overall (n=23)
0
10
20
30
40
50
60
70
80
90
100
Percentage
Real Vision Therapy
Placebo Vision Therapy
FIGURE 1.
Perceived treatment for subjects assigned to placebo vision therapy.
Very sure Pretty sure Somewhat sure A little sure Not at all sure
0
10
20
30
40
50
60
Percentage
Received Real Vision Therapy
Received Placebo Vision Therapy
FIGURE 2.
Confidence level for all subjects who felt they were assigned to real vision therapy.
Placebo Vision Therapy in a Multicenter Clinical Trial—Kulp et al. 259
Optometry and Vision Science, Vol. 85, No. 4, April 2008

6. of therapy. The difference between groups in adherence to the
home protocol at the 12 wk visit approached significance due to a
slight decline in adherence in the real therapy group. It is possible
that the significant improvement in symptoms which occurred in
the real therapy group6,7
led to a decrease in motivation to com-
plete the home therapy protocol.
Subjects in the placebo group were just as likely as those assigned
to real therapy to think they had been assigned real therapy. There-
fore, subjects were effectively masked. There was no difference
found between groups in how sure subjects were of their answer in
the 9 to 18 year old subjects. Among the 19 to 30 year old subjects,
those in the real therapy group felt more sure of their answers than
those in the placebo therapy group. The greater degree of certainty
in adults in the real therapy group and the fact that only patients in
the real therapy group reported being “very sure” may be attribut-
able to the significant improvement in symptoms which occurred
in this group.6,7
The results of the subjects’ perception of group assignment can-
not be compared to previous studies of vision therapy/orthoptics
that used a placebo control23–27
because none of the studies eval-
uated this parameter.23–27
Furthermore, it is not possible to di-
rectly compare the changes in symptoms or objective signs found
in the current study to those found in the two previous studies that
included placebo vision therapy/orthoptics due to methodological
differences (e.g., clinical techniques used to measure fusional ver-
gences, inclusion of normal subjects, and small sample size in pre-
vious studies).23,24
Although direct comparison is not possible, the
current study showed that the placebo group demonstrated small
changes in the clinical signs of CI6,7
similar to previous studies of
vergence vision therapy/orthoptics that included a placebo therapy
arm.23–25
Because this study did not include a ‘no treatment’
group, it is unknown whether the observed changes in the placebo
group are due to the subject-provider interaction, a placebo effect,
and/or natural fluctuations in the disease process. Regardless, the
placebo serves as a control against which active treatments can be
evaluated.
These findings demonstrate the effectiveness of subject masking
in the placebo treatment arm and the feasibility of including a
placebo therapy control group in future clinical trials evaluating
the effectiveness of vision therapy/orthoptics.
ACKNOWLEDGMENTS
Supported by the National Eye Institute of the National Institutes of Health,
Department of Health and Human Services. We would like to thank Karla
Zadnik, OD, PhD, and Israel A. Goldberg, PhD, for their advice and help in
the development of the research design for this study. Presented as a paper at the
American Academy of Optometry meeting in December, 2002.
Received July 6, 2007; accepted December 3, 2007.
The Convergence Insufficiency Treatment Trial (CITT) Investigator
Group
Clinical Sites
Listed in order of number of subjects enrolled into the study, with city, state,
site name and number of subjects in parentheses. Personnel are listed as (PI) for
Principal Investigator, (I) for Investigator, (C) for Coordinator, and (T) for
Therapist.
Philadelphia, PA - Pennsylvania College of Optometry (31)
Mitchell Scheiman (PI) Michael Gallaway (I), Jo Ann Bailey (I), Karen Pollack (T).
Fullerton, CA - Southern California College of Optometry (21)
Susan A. Cotter (PI), Michael W. Rouse (I), Eric Borsting (I), Susan M. Shin
(I), Raymond H. Chu (I), Carmen N. Barnhardt (T), Soonsi Kwon (T), John
H. Lee (T), Yvonne Flores (C).
New York, NY - State University Of New York, College of Optometry (19)
Jeffrey Cooper (PI), Jerry Feldman (I), Audra Steiner (I), Rose Hughes (T),
Jennifer Colavito (T), Esperaza Samonte (C).
Columbus, OH - The Ohio State University College of Optometry (18)
Marjean Taylor Kulp (PI), Michael J. Earley (I), Andrew J. Toole (I), Heather
R. Gebhart (T), Ann M. Hickson (T).
Forest Grove, OR - Pacific University College of Optometry (2)
Richard London (PI), Jayne L. Silver (T).
Houston, TX - College of Optometry, University of Houston (2)
Janice Wensveen, OD, PhD (PI).
Columbus, OH, The Ohio State University College of Optometry, Optom-
etry Coordinating Center: G. Lynn Mitchell (PI), Linda Barrett (I).
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Marjean Taylor Kulp
The Ohio State University College of Optometry
338 West 10th Ave.
Columbus, Ohio 43210
e-mail: kulp.6@osu.edu
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Optometry and Vision Science, Vol. 85, No. 4, April 2008