Does amblyopia affect educational, health, and social outcomes? Findings from 1958 British birth cohort
BMJ 2006; 332 doi: https://doi.org/10.1136/bmj.38751.597963.AE (Published 06 April 2006) Cite this as: BMJ 2006;332:820
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We thank Dr Simons for concurring that our study makes a new,
fundamental contribution to the debate on amblyopia screening and note
that he also agrees that there is a need to further elucidate the
disability associated with amblyopia [1,2]. Extensive psychophysical and
neurophysiological work has elegantly delineated measurable, statistically
significant deficits in specific components of vision, such as contrast
sensitivity, which occur in amblyopia. The question we would ask is if
these deficits translate into functionally significant differences that
mean that on average those with amblyopia are disadvantaged in their
everyday lives. We would reassure him that the population we studied was
sufficiently large and representative for such major outcomes to be
elicited.
The response from Dr Alevizos highlighted a key issue in the
management of amblyopia which is that good outcomes are not universal
[3,4]. This emphasises the need to ensure that screening is carefully
targeted at those who are most likely to benefit from such treatment, as
we discussed in our paper.
We recognise that some individuals with amblyopia, especially where
it has failed to respond to treatment, experience significant problems as
a result of the absence of stereo vision. However, there are many
individuals who do not have such experiences. Thus, on average, as shown
in our study, it is difficult to identify any significant impact of
amblyopia on education, health and social outcomes or occupation.
Importantly, to justify screening for amblyopia as a means of obviating
potential occupational preclusion, it is necessary to be certain that good
improvements in acuity (and for some occupations normal vision) can be
achieved with treatment in childhood and that these are sustained
throughout adult life in all cases. Current data suggest that such
improvement is neither universal nor accurately predictable [4].
On the issue of occupational preclusion, in private correspondence
about our paper, Dr Saundby of the Organisation of Europe Air Sports
highlighted that occupation preclusion without justifying evidence is
discriminatory in the current legal framework [5], the onus being on the
discriminator to justify the discrimination. In Europe the argument for
monocular pilots was won on evidence from the USA that there were 3,200
amblyopic pilots over a thousand of whom were airline pilots whose
accident rate was no greater.
In conclusion, we reiterate that ophthalmic professionals should
engage in work delineating the safety risks associated with amblyopia, so
that affected individuals are advised more informatively and occupational
preclusions are more firmly evidence-based.
1. Rahi J S, Cumberland P M and Peckham C S. Does amblyopia affect
educational, health, and social outcomes? Findings from 1958 British birth
cohort. BMJ 2006; 332: 820-825
2. Simons K. Does amblyopia affect educational, health, and social
outcomes? Findings from 1958 British birth cohort. BMJ Rapid response (7
April 2006)
3. Alevizos A G. Does amblyopia matter? A patient-physician
perspective. BMJ Rapid response (13 April 2006)
4. Clarke MP, Wright CM, Hrisos S, Anderson JD, Henderson J,
Richardson SR. Randomised controlled trial of unilateral visual impairment
detected at preschool vision screening. BMJ 2003;327:1251-4
5. Council Directive 2000/78/EC of 27 Nov 2000 establishing a
general framework for legal treatment in employment and occupation.
Competing interests:
None declared
Competing interests: No competing interests
While childhood visual screening still remains both a critical and
controversial matter, a core issue, in my opinion, arises post-diagnosis.
Even following the discovery of the problem and the eventual correction of
strabismus and/or refractive error, physicians/ophthalmologists need to
address a greater concern: that of ensuring young patients’ compliance to
treatment of a “lazy eye”. Central to this is the matter of raising the
awareness of the familial environment, which needs to comprehend the
severity of the risk of visual acuity reduction, as well as its serious
consequences. In many cases, the focus is placed on the aesthetic results,
rather than on the extent of the residual visual deficit: the patient and
their family are often pleased with the visibly “successful outcome” (i.e.
correction of strabismus), and unilaterally deficient vision can all too
easily go unnoticed owing to the counterbalancing effect of the visually
unimpaired “good” eye.
Below I offer a testimony of my own case, in the hope that something useful
may be drawn from my personal experience. Having been a preterm infant
nursed in an incubator for 40 days, I was subsequently diagnosed, aged 3
years old, with amblyopia due to strabismus and underwent corrective
surgery at the age of 5 years old. My parents actively sought the best
medical advice, which included surgery at one of Athens’s top private
clinics in the 1970s, but never insisted on my covering the unaffected
eye, unaware as they were of the severity of my condition and of the
importance of post-operative therapy for a successful clinical outcome. In
my case, then, the physician did not succeed in communicating this crucial
information to the familial environment, which unfortunately resulted in
the affected (amblyopic) eye losing almost entirely its visual acuity
(macular vision 0/40), maintaining only peripheral vision. To compound the
problem, the unaffected eye suffers from astigmatism with an overall
visual acuity of 8/10 with a -3.50 myopic astigmatic refractive
correction.
Although the residual visual deficit did not appreciably hamper my
educational progress, it certainly restricted my life choices. As a
physician, I was forced to rule out all surgical specialties (these were
simply not an option), and elected to follow a career as a general
practitioner, which, in all likelihood, would not have been my first
choice otherwise.
Moreover, this deficit could not have had a positive
impact on my psychological development during childhood, adolescence and
early adult life, for all the remarkable practical limitations it posed
with regard to several activities. These ranged from incompetence at
school sporting activities (football, basketball, etc), to the inability
to obtain a driving licence, or the exemption from the (compulsory in
Greece) military service, having been judged inadequate. And what is
surely more irksome than life-altering, as far as everyday activities are
concerned, bi-dimensional vision has meant that I am more accident-prone
than most, both at home and in the workplace. Going downhill or down a
staircase, for example, can prove to be tricky undertakings, while
spilling drinks and bumping into objects seem to be the order of the day.
In my opinion (both professional and personal), amblyopia, even when
confined to one eye, can be a burdensome impairment/disability, one that
can cause the patient to experience a severe sense of physical handicap,
as well as pose an array of practical, physical limitations. T
he most
important factors in dealing with it successfully are, undoubtedly, early
and effective screening, combined with consolidated and holistic
treatment. The importance of the latter should also not be underestimated.
Competing interests:
None declared
Competing interests: No competing interests
This is a landmark study and the authors are to be congratulated on
what was obviously a major undertaking. However, in view of the
fundamental questions this study may be seen to raise about the utility of
amblyopia screening and treatment, it appears worth noting some mitigating
factors:
1. Approximately half (53%) of the study amblyopic sample had
straight eyes,(1) meaning that they were anisometropic amblyopes.
Anisometropic amblyopes appear likely to exhibit better binocularity than
strabismic amblyopia,(2, 3) as illustrated by the improvement in
stereoacuity that can be achieved in some such patients simply from
refractive correction.(2, 4) A recent study found, in anisometropic
amblyopes, a correlation between stereoacuity and various eye-hand
coordination tasks,(5) and this connection’s strength may have been
underestimated due to the methodology used.(6) The implication here may
be that a population with a higher proportion of strabismic amblyopes
might show worse results than the present study on some of the
characteristics measured. (Other population studies have ranged from a
larger proportion of strabismic amblyopes(7-10) to approximately equal
proportions like the present study,(11) to a larger proportion of
anisometropic amblyopes(12).)
2. 37.7% of the strabismic children in the study were classified as
normal due to normal visual acuity in both eyes, since the authors state
that the strabismics could not be differentiated from true normals on the
study’s measures.(1) However, this finding would appear to raise question
about those measures, particularly those used to test eye-hand
coordination, notably ball catching at age 16. The reduced or absent
stereopsis that even the acuity-normal strabismic patients presumably
exhibited would have reduced their performance on measures related to such
coordination, if the study’s findings just noted(5) are correct. Seven-
year-olds strabismic children were found to have lower such performance
with a similar task (ball-throwing) in another study (although amblyopia
was not found to be so correlated).(13) Furthermore, a variety of
sophisticated eye-hand measures have been found to show deficits in
monocular, relative to binocular, testing conditions, with loss of
binocular disparity apparently the variable responsible for the
difference.(2)
If, then, the acuity-normal strabismic patients in fact had an eye-
hand coordination deficit, grouping them with the normals would
artifactually reduce the difference between the patient and nominally
normal groups on the pertinent study measures.
3. The study was based on a 1958 cohort and the oldest patient
tested was only 41 years of age. The significance of this age limit is
suggested by a previous study whose patient sample had a mean age of 67
years. It found a relative risk of 2.7 (95% CI 1.6-4.6) of visual
impairment occurring in the better eye of amblyopes, compared to
normals.(14) Another survey, by the authors of the present study, had a
sample median age of 72 years and concluded that amblyopes face a lifetime
risk of serious vision loss in their better eye of at least 1.2-3.3%.(15)
These findings suggest that, if the cohort of the current study(1) is re-
examined in another 26 to 31 years, there will be found a longer list of
vision-impairment-based harms with a significant prevalence than there is
in the present study.
4. The present study’s cohort was the product of a health care
setting in which amblyopia was screened for and treated. The point is an
important one because one health care policy conclusion that might be
drawn from this study’s findings is that detection and treatment of
amblyopia be halted as not worthwhile. If that were done, and the
present study then repeated 41 years later, the resulting prevalence and
severity of amblyopia in the sample, and the consequent functional harms,
would presumably be much greater than in the present study. For instance
the amblyopes equivalent to those classed as resolved in the present study
would, in that future study, still be amblyopic. If the future study were
then repeated with that new cohort at age 67, the differences with the
present study would presumably be larger still. Thus, if the present
study’s data were used to justify cessation of amblyopia detection and
treatment, the end result might end up a self-denying prophecy. That is,
the next, untreated, generation’s such study would seem likely to
contradict the null findings of the present study on at least some of the
measures used.
In conclusion, I would concur with the authors’ recommendation that
further and more sophisticated study of this matter, particularly of
safety-related areas, is needed.
Kurt Simons, research associate, Krieger Children’s Eye Center,
Wilmer Institute, Johns Hopkins Hospital. Baltimore, MD 21287
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cohort. BMJ, 2006.
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13. Howard M, Williams, C, Bell, JC et al. Is the presence of
strabismus and/or amblyopia associated with poorer motor skills in seven
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15. Rahi J, Logan, S, Borja, MC, et al. Prediction of improved vision
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Competing interests:
None declared
Competing interests: No competing interests
Re:Does amblyopia matter? A patient-physician perspective.
THANK YOU for this extremly valuable patient perspective on
amblyopia. I am an optometrist with an emphasis on pediatrics with one
mission in mind: STOP perfoming school screenings and REPLACE them with
universal eye exams! I am speaking to all the pediatricians in my area on
precisely this topic--screenings at schools or at a well care exam will
miss every single hyperope at risk of amblyopia. The strabismics (folks
with an eye turn) are actually at an advantage in that they are caught in
a general doctors office. It makes no sense to maintain a vision
screening that misses up to 65% of the kids in need. A QALY value allows
us to focus on interventions that give the greatest return at the lowest
cost. If interventions cost less than $50,000, it is generally cost
effective; if it costs less than $20,000, it is highly cost effective. It
has been shown that universal eye exams are very cost effect, with a QALY
of $18,390. I thought your perspective on the social implications of
amblyopia were very helpful!
Competing interests: No competing interests