University of Southern California Dissertations and Theses

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Health-related quality of life in preschool children with strabismus or amblyopia

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HEALTH-RELATED QUALITY OF LIFE IN PRESCHOOL CHILDREN WITH
STRABISMUS OR AMBLYOPIA

by

Ge Wen
________________________________________________________________

A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(BIOSTATISTICS)

August 2009

Copyright 2009 Ge Wen

ii
DEDICATION

The author dedicates this work to her family and her friends who have supported her
unconditionally. Without their encouragement and love, it is impossible for the author to
overcome the difficulties and complete this work.

iii
ACKNOWLEDGMENTS

The author wishes to acknowledge the chair of her thesis committee, Dr. Stanley Azen,
who served as mentor, father and friend. The author wishes to acknowledge the
invaluable assistance and instructions from all the members in her thesis committee,
including Dr. Roberta McKean-Codwin, Dr. Wendy Mack and Dr. Kristina
Tarczy-Hornoch. The author wishes to acknowledge the contributions made by all the
members from Multi-ethnic Pediatric Eye Disease Study group, including Dr. Rohit
Varma, Dr. Sue Cotter and Dr. Mark Borchert. The author wishes to acknowledge the
Department of Ophthalmology and Preventive Medicine, and Doheny Eye Institute at
University of Southern California that supported this research and was funded by the
National Eye Institute and the National Center on Minority Health and Health Disparities
and National Institutes of Health.

iv
TABLE OF CONTENTS

Dedication ii
Acknowledgments iii
List of Tables v
Abstract vi
Introduction 1
Methods 3
Results 7
Discussions 16
Conclusions 19
Bibliography 21

v
LIST OF TABLES

Table 1: Characteristics of the Analysis Cohort, the Multiethnic 9
Pediatric Eye Disease Study.
Table 2: Parent-Reported PedsQL Total Scale and Sub-scale 11
Scores by Strabismus or Amblyopia.
Table 3: Adjusted Mean PedsQL Composite and Sub-scale 12
Scores Stratified by Strabismus or Amblyopia Status.
Table 4: Estimated Mean PedsQL Scores by Strabismus Status, 14
Adjusted for Age, Gender, Race, and Family Income and
Excluding Children with Systemic Health Conditions or
Prior Diagnosis of Strabismus.

vi
ABSTRACT

The Multi-Ethnic Pediatric Eye Disease Study (MEPEDS) was designed, in part, to
explore the relationship between eye diseases and health-related quality of life (HRQOL)
in young children.

The Pediatric Quality of Life Inventory (PedsQL), a measure of general HRQOL, was
administered to the parents of a population-based sample of children aged 25 to 72 months
in MEPEDS. It consists of 4 sub-scales (physical, emotional, social, and school
functioning) and 3 composite scores (physical summary, psychosocial summary, and total
scale). Children with strabismus or amblyopia were identified following a comprehensive
eye examination. Regression models were used to evaluate the associations of HRQOL
with strabismus or amblyopia in children ≧ 25 months and ≧ 30 months, respectively.
The results showed that strabismus was associated with statistically significantly lower
HRQOL scores and amblyopia was not associated with any detectable decrease in general
HRQOL in this young age group.

1
INTRODUCTION

Vision and ocular health are important contributors to children’s ability to process
information from their environment and to participate in many everyday activities such as
reading, playing and socializing. Despite improved clinical screening methods and
treatment options in infants and children over the past few decades, there is a lack of data
on epidemiological aspects of ocular problems in children and how these conditions affect
their daily lives. With this in mind, the Multi-Ethnic Pediatric Eye Disease Study
(MEPEDS) was designed, in part, to explore the relationship between eye diseases and
health-related quality of life (HRQOL) in young children. The emphasis of this report is
pediatric HRQOL with respect to strabismus or amblyopia.

Strabismus is a condition in which the eyes are not properly aligned with each other. The
most common forms are esotropia (inward turning) and exotropia (outward turning).
Strabismus is one cause of amblyopia and can interfere with normal binocular depth
perception. Because strabismus is cosmetically noticeable to other children and adults, it
also has negative effects on a child’s self-image and perception by others, with potential
significant psychosocial consequences(Nelson and Wagner 1997; Johns, Manny et al. 2005;
Goff, Suhr et al. 2006; Jackson, Harrad et al. 2006; Mojon-Azzi and Mojon 2008;
Mojon-Azzi, Potnik et al. 2008; Nelson, Gunton et al. 2008).

2
Amblyopia is characterized by reduced vision in an eye or both eyes that appear to be
physically normal. Unilateral amblyopia results from conditions that affect the normal
development of binocular vision, such as strabismus or anisometropia. Bilateral
amblyopia results from conditions that cause abnormal visual input to both eyes, such as
bilateral refractive error. The onset of amblyopia begins in early childhood and the loss of
vision can be permanent and persist into adulthood unless successful treatment is received
at an early age. Persons with unilateral amblyopia often have decreased depth perception,
as well as reduced sensitivity to motion, poor contrast sensitivity, and poor visual acuity in
the affected eye(Webber and Wood 2005). Children with bilateral amblyopia, additionally,
have bilateral acuity deficits.

In the current study, we used the Pediatric Quality of Life Inventory 4.0 Generic Core
Scales (PedsQL)(Varni, Seid et al. 1999). The PedsQL was selected because it is a brief
and developmentally appropriate instrument designed to measure core dimensions of
pediatric HRQOL, including physical, emotional, social, and school functioning, as
outlined by the World Health Organization. The feasibility, reliability and validity for
detecting clinical changes using this instrument have been demonstrated by a number of
studies evaluating children with and without a variety of health conditions(Varni, Seid et al.
2001; Varni, Burwinkle et al. 2002; Varni, Seid et al. 2002; Varni, Burwinkle et al. 2003;
Varni, Burwinkle et al. 2003; Varni, Burwinkle et al. 2004; Varni, Burwinkle et al. 2004;
Varni and Burwinkle 2006; Varni, Burwinkle et al. 2006; Varni, Burwinkle et al. 2006;
Varni, Burwinkle et al. 2007; Varni, Limbers et al. 2007). At the time MEPEDS was

3
designed, there was no vision-specific instrument for assessing HRQOL in a
population-based sample of children. This is one of the first studies to explore issues of
HRQOL in association with strabismus or amblyopia in a pediatric population.

METHODS

Study Design

The MEPEDS is a multi-ethnic, population-based study with a sample of children in Los
Angeles County, California who were under 6 years of age at the time of clinical
examination and questionnaire interview. The study design and sampling plan of
MEPEDS has been described previously(Varma, Deneen et al. 2006). In brief, it is
designed to establish the prevalence of common eye conditions in African-American,
Hispanic, Asian and Non-Hispanic White children, identify risk factors that may predict
these conditions, and explore the relationship between physical and psychosocial
functioning and the prevalence and severity of various ocular disorders.

Eligible MEPEDS participants included children who were 6 months to 72 months of age,
living in one of 44 census tracts in and around the city of Inglewood and 8 census tracts
Study Population

4
from the city of Riverside in Los Angeles County, California at the time of the clinical
examination and questionnaire interview.

Eligible children were identified through a door-to-door census of the homes in the 52
census tracks. Eligibility criteria included: (1) age 5 to 70 months on the day of the
household screening and (2) parent or legal guardian confirmed that the child was a
resident of one of the selected MEPEDS census tracts. Informed consent form was
obtained from the parent or legal guardian of eligible children followed by a brief in-home
interview that included basic demographics and history of known eye conditions. Eligible
children were then scheduled for a comprehensive eye examination at the local MEPEDS
clinic. A more detailed in-person interview with the child’s parent or guardian including
the PedsQL was also conducted at the clinic (see details below).

In-Clinic Eye Examination and Questionnaire Interview

All children underwent a comprehensive eye examination, which has been previously
described in detail(2008). Briefly, the protocol included: assessment of ocular alignment,
measurement of HOTV visual acuity using the ATS protocol on the Electronic Visual
Acuity tester(Moke, Turpin et al. 2001) and cycloplegic refraction. Strabismus was
assessed by cover-uncover testing (for which Krimsky testing was substituted only if the
child would not permit cover testing) and alternate cover testing, and defined as any

5
strabismus, at distance or near fixation, with or without glasses. Strabismus was evaluated
for children ages 6 months to 72 months. Amblyopia was defined as a 2-line difference in
visual acuity between eyes (20/32 or worse in the worse eye) with a corresponding
unilateral amblyopia risk factor (strabismus, anisometropia, or visual axis occlusion), or
bilaterally decreased visual acuity (worse than 20/50, or worse than 20/40 if >=48 months
of age) with a bilateral amblyopia risk factor (bilateral visual axis occlusion or bilateral
high ametropia). Visual acuity was measured in children 30 to 72 months of age who were
able to complete testing using ‘HOTV’ optotypes(Moke, Turpin et al. 2001; Cotter,
Tarczy-Hornoch et al. 2007); optotype visual acuity testing was not performed in children
younger than 30 months.

The questionnaire was administered by a study interviewer to the parent of each child at the
time of the clinical examination, or subsequently by telephone if the child was
accompanied to the exam by a person other than a parent or legal guardian. Details of the
interview have been described elsewhere(Varma, Deneen et al. 2006). The questionnaire
consisted of demographics, medical history, and the PedsQL. The latter was administered
to parents of children aged 25 months and older. The medical history included questions
about whether a doctor had ever told the parent that the child had health conditions such as
mental retardation, cerebral palsy, Down syndrome, convulsions or seizures, and
retinopathy of prematurity, and also whether or not a doctor had ever diagnosed the child
with strabismus or amblyopia,.

6
The 23-item instrument was designed to measure core dimensions of pediatric HRQOL
using a modular approach. Each question is scored on a 0-4 scale (0=never, 1=almost
never, 2=sometimes, 3=often, 4=almost always) which can be reversely transformed to a
0-100 linear scale, where higher scores indicate better HRQOL. Sub-scale scores are
computed as the sum of the scores for individual items divided by the number of items
answered. A psychosocial health summary score is computed as the mean of the 15 items
answered in the emotional, social and school functioning sub-scales. A physical health
summary score is the same as the physical functioning sub-scale (8 items). The total scale
score is computed as the mean of all 23 items. In MEPEDS, the parent-proxy report of the
instrument was used.

Statistical Analysis

T-tests were performed to compare the mean scores (sub-scale and total scale) between
groups with and without strabismus or amblyopia; two-sided p-values were reported.
Analysis of covariance was used to compare the mean scores by disease status after
controlling for potential confounders such as age, gender, race, and family income. For
strabismus, all sub-scale and total scale scores were additionally adjusted for parental
knowledge of co-morbid conditions and history of strabismus. Co-morbid conditions
included mental retardation, cerebral palsy, Down syndrome, convulsions or seizures and
retinopathy of prematurity.

7
Generalized linear models were used to further evaluate associations of HRQOL with eye
disease characteristics and severity. For strabismus, the disease types of interest were
esotropia or exotropia, intermittent or constant, and severity: mild (0-9 prism diopters),
moderate (10-30 prism diopters) and severe (>30 prism diopters). Sub-scale and total scale
scores were also compared for strabismic children with good depth perception and
strabismic children with poor depth perception. For amblyopia, the disease types of
interest were unilateral or bilateral, and severity, which included severe (visual acuity in
either eye <=20/80) or not severe. Analyses were conducted using SAS software 9.1
(SAS Institute, Inc., Cary, NC) at the 0.05 significance level.

RESULTS

Study Populations

A total of 6,492 eligible children in the census tracts surveyed by MEPEDS completed the
clinical examination. Of the 6,492 children, 4,463 (68.8%) were 25 months or older and
had been evaluated for HRQOL as well as strabismus; these children were eligible for our
strabismus-related analyses. Of the 6,492 children, 3,529 (54.4%) were 30 months or older
and were evaluated for amblyopia based on optotype visual acuity measurements; these
children were eligible for our amblyopia-related analyses.

8
The characteristics of the children eligible for each analysis are shown in Table 1. Briefly,
in the strabismus cohort (n=4,463), 124 (2.8%) children were diagnosed with strabismus.
Of these, approximately 50% of the children were female and 58% had a family income
lower than $20,000. The majority of children recruited at the time of the analyses were
Hispanic (48%) or African American (47%), with a small number of Non-Hispanic Whites
(3.7%) and Asian (1.1%). Out of the 3,529 children who were eligible for amblyopia
related analyses, 74 (2.1%) had amblyopia. 51% were female, 57% of families had an
income lower than $20,000 and the majority of the children were Hispanic (48%) or
African American (46%) .

9
Table 1: Characteristics of the Analysis Cohort, the Multiethnic Pediatric Eye Disease Study.

a

Amblyopia Cohort Strabismus Cohort
Total
(N=3,529)
Non-Amblyopia
(N=3,455)
Amblyopia
(N=74)
Total
(N=4,463)
Non-Strabismus
(N=4,336)
Strabismus
(N=127)
Gender
Male 1726 (48.9) 1688 (97.8) 38 (2.2) 2251 (50.4) 2193 (97.4) 58 (2.6)
Female 1803 (51.1) 1767 (98.0) 36 (2.0) 2212 (49.6) 2143 (96.9) 69 (3.1)
Age (months)
25-36 374 (10.6)
b
372 (99.5) 2 (0.5) 1180 (26.4) 1160 (98.3) 20 (1.7)
37-48 1003 (28.4) 980 (97.7) 23 (2.3) 1111 (24.9) 1085 (97.7) 26 (2.3)
49-60 1115 (31.6) 1089 (97.7) 26 (2.3) 1129 (25.3) 1083 (95.9) 46 (4.1)
61-72 1037 (29.4) 1014 (97.8) 23 (2.2) 1043 (23.4) 1008 (96.6) 35 (3.4)
Race
Non-Hispanic White 144 (4.1) 142 (98.6) 2 (1.4) 163 (3.7) 159 (97.6) 4 (2.4)
Hispanic 1689 (47.9) 1644 (97.3) 45 (2.7) 2132 (47.8) 2076 (97.4) 56 (2.6)
Black/African-American 1629 (46.2) 1603 (98.4) 26 (1.6) 2086 (46.7) 2021 (96.9) 65 (3.1)
Asian 38 (1.1) 38 (100.0) --- 47 (1.1) 47 (100.0) ---
Other 29 (0.8) 28 (96.6) 1 (3.4) 35 (0.8) 33 (94.3) 2 (5.7)
Family Income Level
≥ $20,000
c

1186 (33.6) 1163 (98.1) 23 (1.9) 1451 (32.5) 1414 (97.5) 37 (2.5)
< $20,000 1992 (56.5) 1948 (97.8) 44 (2.2) 2571 (57.7) 2490 (96.9) 81 (3.1)
a
In each cell, the numbers are counts and percents are in parenthesis. In the total columns, the percents are out of the entire cohort of each disease;
while in other columns, the percents are out of the total number of each stratum.
b
For amblyopia, the first age group is 30-36 months.
c
For amblyopia, 351 refused to answer this question or answered ‘do not know’ ;
for strabismus, 441 refused to answer or answered 'don't know'.

10
The associations of strabismus or amblyopia with HRQOL were also evaluated after
adjusting for potential confounders such as gender, age, race, and family income. In the
strabismus models, all the adjusted scores were statistically significantly different between
children with strabismus and children without, including the total scale score, 2 summary
scores, and all the sub-scale scores (Table 3). For amblyopia, there were no significant
differences between the amblyopia and non-amblyopia groups for any of the PedsQL
scores after adjusting for these potential confounders (p>0.05) (Table 3).
The Associations of Strabismus or Amblyopia with HRQOL

The means and standard deviations of the PedsQL sub-scale and total scale scores for the
whole sample and for children stratified by presence or absence of ocular diseases
(strabismus or amblyopia) are shown in Table 2.

Statistically significant differences were found between children with and without
strabismus for the total scale score, 2 summary scores (physical and psychosocial health),
and for 2 of the 3 psychosocial sub-scales (emotional and school functioning). (p<0.05)
Children with strabismus had lower HRQOL scores and the score differences ranged
from approximately 3 to 5 points. The difference in the social functioning score by
strabismus status did not reach statistical significance (p=0.07). In contrast, none of the
mean scores were significantly different between the children with amblyopia and the
non-amblyopia group. (p>0.05 for all)

11
Table 2: Parent-Reported PedsQL Total Scale and Sub-scale Scores by Strabismus or Amblyopia

Strabismus Whole Sample
(N=4463)
Non-Strabismus
(N=4336)
Strabismus
(N=127)

Mean SD Mean SD Mean SD p-value
Total Scale Score

a

92.0 9.6 92.1 9.4 87.9 15.1 <0.01
Physical Health Summary Score 94.2 9.7 94.3 9.4 89.9 17.0 <0.01
Psychosocial Health Summary Score 90.6 11.2 90.8 11.0 86.7 15.8 <0.01
Emotional Functioning 87.5 14.8 87.7 14.6 82.4 18.9 <0.01
Social Functioning 93.2 12.4 93.3 12.2 90.4 17.7 0.07
School Functioning 90.7 13.2 90.9 13.1 86.8 15.6 0.04
Amblyopia
Whole Sample
(N=3529)
Non-Amblyopia
(N=3455)
Amblyopia
(N=74)

Mean SD Mean SD Mean SD p value
Total Scale Score
a

92.0 9.3 92.0 9.3 91.5 9.0 0.63
Physical Health Summary Score 94.3 9.3 94.3 9.3 94.6 8.9 0.75
Psychosocial Health Summary Score 90.6 11.0 90.6 11.0 89.5 11.1 0.41
Emotional Functioning 87.3 15.0 87.3 15.0 85.0 15.3 0.19
Social Functioning 93.3 12.0 93.2 12.0 93.9 11.8 0.66
School Functioning 91.0 12.6 91.0 12.6 91.0 12.0 0.98

a
The scores are compared using 2-sample t-tests and p-values are reported. Significant p-values are bolded.

12
Table 3: Adjusted
a

Mean PedsQL Composite and Sub-scale Scores Stratified by Strabismus or Amblyopia Status

Non-Strabismus
(N=4,336)
Strabismus
(N=127)
Non-Amblyopia
(N=3,455)
Amblyopia
(N=74)

LS Mean LS Mean
b
p value LS Mean LS Mean p value
Total Scale Score 93.8 89.7 <0.01 93.7 93.6 0.96
Physical Health Summary Score 96.0 91.7 <0.01 95.8 96.6 0.46
Psychosocial Health Summary Score 92.4 88.4 <0.01 92.3 91.7 0.65
Emotional Functioning 89.3 84.2 <0.01 89.3 87.5 0.32
Social Functioning 95.1 92.3 0.01 94.9 96.1 0.40
School Functioning 93.4 89.2 0.01 93.2 93.3 0.99

a
Adjusted for Age, Gender, Race and Family Income; significant p-values are bolded.
b
LS means (least square means) are within-group means appropriately adjusted for the other effects in the model.

13
We further evaluated the impact of parent’s knowledge of the child’s history of
co-morbid conditions or strabismus on the strabismus and PedsQL association. Children
with a known history of co-morbid health conditions or strabismus had significantly
lower HRQOL scores than children without a known history. However, among children
who did not have a history of co-morbid conditions, strabismus was still significantly
associated with lower HRQOL scores including the total scale score, the 2 summary
scores, and emotional and school functioning sub-scale scores (p<0.05, see Table 4).
Among those children who weren’t diagnosed with strabismus before participating in the
MEPEDS, strabismus status was significantly associated with lower HRQOL scores
including the total scale score, 2 summary scores, and emotional and social sub-scale
score. (p<0.05) (Table 4)

The association between strabismus and HRQOL scores did not differ significantly for
children with esotropia versus exotropia, or between children with intermittent or
constant strabismus. (p>0.05) All 3 composite scores were significantly lower for
children with esotropia or exotropia and normal eye alignment (p<0.05). Children with
intermittent strabismus had worse composite scores (all 3) than normal children, while
children with constant strabismus had worse composite scores for 2 scales (total and
physical only). (p<0.05)
The Associations of Type and Severity of Strabismus or Amblyopia with HRQOL

14
Table 4: Estimated Mean PedsQL Scores by Strabismus Status, Adjusted for Age, Gender, Race, and Family
Income and Excluding Children with Systemic Health Conditions or Prior Diagnosis of Strabismus

Excluding children with systemic
health conditions (N=4,392)
Excluding children with prior
diagnosis of strabismus (N=4,372)

Non-Strabismus
(N=4,272)
Strabismus
(N=120)
Non-Strabismus
(N=4,299)
Strabismus
(N=73)

LS Mean LS Mean
a

p
value LS Mean LS Mean
p
value
Total Scale Score 93.8 91.3 <0.01 92.2 87.7 <0.01
Physical Health Summary Score 96.0 93.9 0.01 94.4 90.0 <0.01
Psychosocial Health Summary Score 92.4 89.7 <0.01 90.8 86.2 <0.01
Emotional Functioning 89.2 85.1 <0.01 87.7 82.3 <0.01
Social Functioning 88.6 86.4 0.32 93.4 89.5 <0.01
School Functioning 87.8 84.2 0.03 91.0 88.8 0.32

a

LS means (least square means) are within-group means appropriately adjusted for the other effects in the model.

15
Among the 127 children with strabismus, 11 had a magnitude of 1-9 prism diopters, 85
had a magnitude of 10-30 prism diopters, and 21 had a magnitude greater than 30 prism
diopters (10 children lacked this data and could not be classified). The strabismus group
with a magnitude of 10-30 prism diopters had the worst HRQOL scores and differed
significantly from the non-strabismus group for all the 3 composite scores (p<0.05). No
significant differences in composite scores were found for children by angles of
strabismus, although the numbers of children in these groups were small.

Because strabismus may be associated with deficient stereopsis, we also tested whether
the association of strabismus with HRQOL scores was dependent on the presence or
absence of stereopsis. Paracoxically, the strabismic children without stereopsis had a
higher total HRQOL index than the strabismic children with stereopsis (p=0.04); the
physical or psychosocial summary scores did not differ significantly according to
stereopsis, suggesting that impaired depth perception is not the basis for the impact of
strabismus on HRQOL.

There were no significant differences in any of the 6 scores between children with
unilateral or bilateral amblyopia, and normal children (p>0.05). Pair-wise comparisons
indicated that all 3 composite scores showed no significant differences for children with
non-severe amblyopia, or severe amblyopia compared to children without amblyopia, or
between groups of amblyopic children with or without stereopsis. (p>0.05)

16
DISCUSSION

Using PedsQL, we found that strabismus was associated with significantly lower scores for
physical and psychosocial health, including emotional, social, and school functioning.
The associations exist even after controlling for gender, age, ethnicity, and family income
level. We also assessed whether the apparent association could be explained, at least in part,
by parent’s knowledge of their child’s other systemic diseases that could influence quality
of life or strabismus diagnosis prior to the MEPEDS evaluation. After controlling for both
of these factors in the multivariable analyses or restricting to children without a history of
co-morbidities or strabismus prior to the MEPEDS clinical exam, we still found a
significant relationship of strabismus with physical and psychosocial health.

The negative association with HRQOL was not specific to any particular type of
strabismus, as it was seen both for esotropia and exotropia, and for both intermittent and
constant strabismus. Strabismus could affect HRQOL through its impact on depth
perception, or because of the anatomical abnormality visible to others, or both. The fact
that an impact was seen for intermittent strabismus as well as constant strabismus, and the
fact that PedsQL scores were no higher in strabismic children with stereopsis than in
strabismic children without stereopsis, both suggest that the most important factor is the
visible misalignment of the eyes.

17
Studies on the impact of strabismus have been conducted previously in both adults and
children. By means of simulation photographs, the influence of strabismus was found to
play a very significant role in selecting a partner in adults(Mojon-Azzi, Potnik et al. 2008)
or in selecting a playmate in kids(Johns, Manny et al. 2005). It has been shown that
strabismus causes embarrassment to the patient, and corrective surgery for strabismus
significantly improves patients’ psychological and physical functioning in both adults and
teenagers using standard measures or questionnaires such as the Hospital Anxiety and
Depression Scale and the WHO Quality of Life measure(Jackson, Harrad et al. 2006;
Nelson, Gunton et al. 2008). These photograph-based studies assess the responses of
others to an individual's cosmetic appearance. Our results are consistent with the general
conclusions of studies in other age groups, in terms of the overall negative impact of
strabismus on an individual’s HRQOL.

MEPEDS is one of the first studies to provide a direct measure of the likelihood of
psychosocial consequences in a population-based, pediatric population. The differences of
mean PedsQL scores between non-strabismic children and strabismic children in this study
ranged from approximately 2 to 5 points in all domains. Compared to some other studies
of clinic based samples which also used PedsQL, the mean difference found in the present
study was much smaller. Because the children in our cohort were relatively young, the
impact of strabismus may increase as they grow older and enter more complicated social
environments, therefore our findings may represent the minimal impact of strabismus on
HRQOL.

18
In MEPEDS, we did not detect a measurable impact of amblyopia on HRQOL. There are
several possible reasons for this. First, the PedsQL instrument may be insensitive to the
effects of amblyopia on specific vision-related aspects of HRQOL. Studies in adults have
concluded that vision-specific instruments are more sensitive than general instruments to
quantifying the impact of vision disorders(Rosen, Kaplan et al. 2005; Tripop,
Pratheepawanit et al. 2005; Birch, Cheng et al. 2007). Pediatric vision-specific instruments
are required to fully evaluate the potential impact of amblyopia on vision-related HRQOL.
Second, it may be that the influence of amblyopia only becomes apparent at older ages,
when more visually demanding school activities such as reading come into play. Third,
most amblyopia in this population was anisometropic rather than strabismic(2008), and
therefore the disorder, unlike strabismus, was not apparent to casual observers; this would
reduce the likelihood of the child being teased or self-conscious about the eye condition,
and thus make it less likely to have an impact on social and emotional functioning. Finally,
it may be that unilaterally decreased vision (constituting the majority of the amblyopia in
this population(2008)) impacts HRQOL minimally in childhood, because the child can see
well with the better-seeing eye; it should be noted that this assessment does not take into
account the child's future, lifetime risk of developing bilateral visual impairment as a result
of later disease or damage to the good eye(Rahi, Logan et al. 2002).

A significant strength of our study is the large sample of children and high response rate.
The MEPEDS is a population-based study with a large number of children with strabismus.
Our high response rate to the PedsQL among parents of eligible children (96% of parents of

19
eligible children completed the PedsQL) makes it likely that our findings are representative
of all eligible study children and our findings may be generalizable to other strabismic
children in the 2 to 5 year-old age range .

A limitation of our analysis is the reliance on a general HRQOL instrument. At the time the
study began, there were no tools specifically designed to evaluate the HRQOL due to eye
diseases in children, so we selected the PedsQL. In addition, our focus on
African-American and Hispanic children in the analysis cohort means that the study
findings are not necessarily applicable to children of other ethnicities, although our
findings were robust to adjustment with regard to ethnicity.

CONCLUSION

This study shows that strabismus was associated with statistically significantly lower
health-related quality of life scores based on the parents’ self-report, including physical
and psychosocial scores. These associations still exist after controlling for gender, age,
race, family income, other systemic health conditions, and prior knowledge of the
diagnosis. The results suggest that early detection and treatment of strabismus may have
far-reaching benefits for children, although further studies are required to assess whether
HRQOL scores improve following strabismus treatment. On the other hand, amblyopia
was not associated with worse general pediatric HRQOL. Given that amblyopia is a

20
common and treatable condition, its association with targeted vision-related tasks requires
further exploration.

21
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Abstract (if available)

Abstract The Multi-Ethnic Pediatric Eye Disease Study (MEPEDS) was designed, in part, to explore the relationship between eye diseases and health-related quality of life (HRQOL) in young children.

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Asset Metadata

Creator Wen, Ge (author)

Core Title Health-related quality of life in preschool children with strabismus or amblyopia

School Keck School of Medicine

Degree Master of Science

Degree Program Biostatistics

Degree Conferral Date 2009-08

Publication Date 08/04/2010

Defense Date 05/01/2009

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag amblyopia,health-related quality of life,OAI-PMH Harvest,PedsQL,strabismus

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Azen, Stanley Paul (committee chair), Mack, Wendy J. (committee member), McKean-Cowdin, Roberta (committee member)

Creator Email dove1000@gmail.com,gwen@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-m2472

Unique identifier UC1107799

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Legacy Identifier etd-Wen-3146.pdf

Dmrecord 171887

Document Type Thesis

Rights Wen, Ge

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Repository Name Libraries, University of Southern California

Repository Location Los Angeles, California

Repository Email cisadmin@lib.usc.edu