Original Paper - Fundació Catalana Síndrome de Down

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SD-DS
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INTERNATIONAL MEDICAL JOURNAL ON DOWN SYNDROME
2002: vol. 6, number 3, pp. 34-39
Original Paper
Ametropia and strabismus
in Down syndrome
J. Puig, E. Estrella, A. Galán
Hospital Universitario Vall d’Hebron. Barcelona
Correspondence
Dr. J. Puig
Diagnóstico y Terapéutica Ocular
Tuset, 23-25, 3º 3ª
08006 Barcelona
Spain
Article received on: 19-Feb-02
Translator: Mary Fons
Abstract
Purpose: To analyze the characteristics of ametropia
and strabismus in children with Down syndrome.
Patients and methods: A complete eye examination
was carried out in 546 children with Down syndrome.
Results:Visual acuity was 100/200 or greater in only
21% of eyes examined. Amblyopia was present in 9.7%
of children. Mean spherical equivalent was +1.02
diopters; 72% of the eyes were emetropic or hyperopic
and 28% were myopic; 17% of the eyes had a negative
astigmatism of 2 diopters or greater. Strabismus was
found in 240 cases. Only 1.2% had an isolated vertical
deviation. Incomitant esotropia was the most frequent
finding in this study. Conclusions: Ametropia and
strabismus in Down syndrome are different from the
general population in frequency, type, low incidence of
amblyopia and causes of torticollis.
Keywords: Ametropia, Strabismus, Down syndrome,
Pediatric ophthalmology
Introduction
The large number of people with Down syndrome
and the diversity of medical conditions associated with
it require integrated care to be multidisciplinary and
coordinated among different specialists.
A higher-than-normal prevalence of eye problems in
this patient group has been reported for years;
particular issues are extrinsic eye motility (strabismus)
and refractive error (myopia, hyperopia and
astigmatism) [1, 2, 3].
Thus, a complete eye examination at an early age is
required, to detect these conditions and take effective
action before the consequences become irreversible.
The aim of this paper is to quantify and describe
strabismus in a large population of patients with Down
syndrome, as well as conditions that may cause it or
result from it, such as refractive errors, low visual
acuity and amblyopia.
Patients and methods
A complete eye examination was carried out for 546
patients with Down syndrome, 295 boys and 259 girls,
referred to our clinic by Fundació Catalana Síndrome
de Down. Their ages ranged from 1 month to 18 years;
mean age was 6 years and 5 months, with a standard
deviation of 4.65 years.
In every case, the examination included extrinsic
eye motility, refraction under cycloplegia and
ophthalmoscopy. For patients who were old enough
and sufficiently cooperative, visual acuity was
determined with and without optical correction, along
with manifest refraction, binocular vision and
biomicroscopy of the anterior pole.
Visual acuity was tested with the Teller visual
preference test, Pigassou’s optotypes and Snellen’s Eoptotypes, using normal parameters. The protocol for
inducing cycloplegia consisted of instilling 0.5%
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2002: vol. 6, number 3, pp. 34-39
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atropine drops (t.i.d. the day before the visit and b.i.d. the
day of the visit), or 1% cyclopentolate drops (every half
hour, starting two hours before examination). Manifest
refraction and refraction values obtained by skiascopy
without cycloplegia were never considered adequate.
Eye motility was assessed by determining deviation
in the primary position, using the Hirschberg corneal
light reflex test for near vision, cover test for far and
near vision, and prism testing whenever the patient was
sufficiently cooperative. The Lang, Titmus and TNO
tests were employed for binocular vision. Funduscopy
was performed using an indirect ophthalmoscope and
20 D lens.
After the first eye examination, follow-up was
always recommended at 6-month intervals, or more
often when warranted.
Results
Each of the patients included in this study was seen
1 to 9 times, with a mean follow-up of 54.31 months.
Results therefore comprise 2,486 examinations
performed on 546 children.
We have grouped results under three headings:
visual acuity, refraction, and strabismus.
a) Visual acuity
Reliable visual acuity data were obtained for 401 of
546 patients, that is 73.44%. Only 21% tested above
0.5; 71% tested above 0.2.
The difference in visual acuity between the eyes was
0.3 or more in 39 of the 401 children for whom acuity
was established. Of these 39 cases, 23 had considerable
anisometropia; 11 were attributed to strabismus; the
(a)
35
remaining 5 were caused by a unilateral eye condition
(cataract, retinopathy, or optic nerve malformation).
b) Refraction
Refraction values are missing only for 32 cases out
of 546, who failed to show up at the scheduled
appointment for refractive testing under cycloplegia.
Mean refraction for the eyes that were examined
was +1.026 4.18 D. In 72% of cases, refraction values
were positive or neutral; in other words, the children
were either emetropic (no refraction error) or
hyperopic; the remaining eyes were myopic, with
negative refraction values (28 %).
Negative astigmatism at or above 2 diopters was
found in 17% of children.
A comparison of spherical equivalents in both eyes
(adding half the cylinder power to the sphere power,
keeping the positive or negative sign) showed a
difference of more than 2 diopters (anisometropia) in
24% of patients.
Errors of refraction were treated conventionally by
prescribing spectacles when refractive error was
significant enough to compromise development of
eyesight or influence the course of strabismus. Lasik
surgery was elected for one of these patients, who had
high myopia (-20.75 D spherical equivalent) and deep
hearing loss, which were alienating him from his
environment, and who was not amenable to optical
correction using spectacles or contact lenses.
c) Strabismus
Extrinsic ocular motility values were obtained for
all 546 children. Strabismus was diagnosed in 240
(44%), as follows:
(b)
Figure. 1. Incomitant strabismus. Note the convergent misalignment of the right eye, each picture at a different angle (A and B).
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(a)
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(b)
Figure. 2. Intermittent strabismus. Sometimes misalignment is present (A), other times it is absent (B).
• Esotropia (convergence of visual axes): 194
(35.5%).
• Esotropia with vertical deviation: 23 (4.2%).
• Exotropia (divergence of visual axes): 16 (2.9%).
• Vertical deviation alone: 7 (1.3%).
Esotropia in these children was classified as
follows:
• Sporadic (highly infrequent, detected only on
occasion): 16 (16/217).
• Microesotropia (misalignment of less than 5º): 31
(31/217).
• Incomitant (angle of deviation varying more than
10º, excluding accommodative esotropia): 44
(44/217) (Fig. 1).
• Intermittent (variable angle of misalignment, with
a 0º minimum; i.e. deviation was very apparent at
some times and non-existent at others, during a
single examination or on different days): 69
(69/217).
• Comitant (deviation angle did not vary at all, or
no more than 10º): 52 (52/217) (Fig. 2).
• Accommodative (misalignment was corrected
with appropriate hypermetropic spectacles, as
long as patient was not made to accommodate): 5
(5/217).
Vertical deviations found alongside horizontal
deviation were due to:
•
•
•
•
Superior oblique palsy: 3 (3/23).
Superior oblique overaction: 2 (2/23).
Inferior oblique overaction: 11 (11/23).
Deficient elevation in adduction compatible with
Brown syndrome: 7 (7/23).
Cases of isolated vertical deviation were due to (Fig.
3):
•
•
•
•
Elevation palsy: 2 (2/7).
Inferior rectus palsy: 1 (1/7).
Inferior oblique overaction: 2 (2/7).
Superior oblique palsy: 2 (2/7).
Out of 240 children with strabismus of any kind, 17
(7.08%) were found to have torticollis secondary to
their eye condition (Fig. 4):
• Chin-up: 8 (8/17). Head tilt in these cases was
either due to A syndrome accompanying esotropia
or to nystagmus with null point in downgaze.
• Head over one shoulder: 9 (9/17). These were
secondary to superior oblique deficiency and, in
isolated cases, due to complex nystagmus null
points.
After careful assessment of each specific case,
surgical treatment was proposed for 72 of the 240
patients with strabismus (30%).
Non-surgical treatment (monitoring, refractive
correction, occlusion, penalization, etc.) was elected
for the remainder, owing to a number of circumstances:
• Strabismus was sporadic or deviation angle was
decreasing.
• No misalignment in primary position.
• Inadequate data because parents or guardians
failed to keep the follow-up schedule.
• Very small deviation angle.
• Poor prognosis due to other, more problematic
eye conditions.
• Accommodative strabismus.
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Figure 3. Deficient elevation of the left eye in adduction.
However, only 35 of these patients (48.6%) actually
underwent surgery. The reasons varied widely (Fig. 5):
• Preference for surgical facilities closer to the
child’s home town.
• Risk to life due to a concomitant systemic
condition.
• Economic issues.
• Parents opting not to have surgery, having
interpreted that the only indication was esthetic,
as there could be no guarantee of improved visual
acuity or binocular vision.
Strabismus surgery for children with Down
syndrome was planned according to the same
parameters applied for any other child.
Outcome was considered satisfactory after a single
surgical procedure for 27 of the 35 patients operated. Of
the 8 remaining cases, 6 had undercorrected esotropia
after surgery; the other 2 had overcorrected esotropia.
Four of the patients whose initial outcome was rated as
poor underwent further surgery with good results.
Down syndrome due to their higher systemic
susceptibility. However, topical atropine drops placed
on the conjunctiva appear merely to cause the pupils to
dilate faster and longer [9, 10]. No significant adverse
effect has been recorded, except for occasional flushed
faces, just as frequent in other children.
Visual acuity was poor in a large number of cases.
Although some authors feel that children with Down
syndrome have less keen vision as a result of
morphological changes in the central nervous system
[11], we feel that this is merely attributable to
cooperation issues, since acuity testing is subjective
and largely depends on children’s responses, and these
particular children easily lose interest. However, the
fact that a difference in visual acuity of 0.3 or greater
was only found in 39 of the children was judged
significant. This is a very low rate of medium to severe
amblyopia. In 23 cases, the cause was high
anisometropia; strabismus was found in only 11 such
patients. Considering the fact that children with
strabismus who do not have Down syndrome have a
50% rate of amblyopia, and children with microtropia a
90% rate, we wonder why strabismus is less likely to
cause amblyopia in children with Down syndrome –
might they have a lower capacity for cortical
suppression?
When we analyze strabismus in these patients, the
first striking finding is its high prevalence. The
prevalence of strabismus in the general population is 45%, but in this study of children with Down syndrome
we found a rate of 44%. Previous studies found similar
rates, ranging from 30% to 44% [8, 12].
We note that there is a strong tendency to esotropia,
and few cases of vertical deviation associated with
horizontal deviation, whereas the latter are very
frequent in non-Down-syndrome strabismus patients,
who have this association in 90% of congenital cases
Discussion
This is the long-term ophthalmologic study with the
largest population of pediatric Down syndrome patients
so far, with a mean follow-up of 5 years. Other
published studies used a smaller sample and gave the
outcome of a single examination, with no follow-up, or
else involved an older population.[4, 5, 6, 7].
Only Haugen and Hovding reported a mean followup of 55 months, on a group of 60 children. [8]
Concerning examination methods, many believe
that atropine should not be used for children with
37
Figure. 4. Head tilt over the right shoulder.
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2002: vol. 6, number 3, pp. 34-39
(b)
Figure 5. Surgically corrected esotropia: pre-surgery (A) and post-surgery (B).
and 25% of acquired cases. Perhaps the reason is,
among others, that strabismus tends to be acquired
rather than congenital in children with Down
syndrome. According to Haugen and Hovding, mean
age of onset of strabismus in the group of children with
Down syndrome which they studied was 54 6 35
months [8].
The low rate of inferior oblique overaction in
association with esotropia, as well as cases of deficient
elevation in adduction, cause us to wonder whether it is
the shape of the orbit in Down syndrome that is causing
this altered oblique muscle function.
Only 5 of the children had accommodative
strabismus, a very low rate compared to the non-Down
population. It is also low compared to a study by Hiles
[13], where half of all esotropia cases were
accommodative, and all but one were solved with
glasses or myotic drops. There are published reports
showing diminished accommodative facility in children
with Down syndrome [8, 14]
The number of intermittent strabismus cases is
strikingly high. The potential role of accommodation in
these cases was explored, but no correlation with
refractive error emerged; neither was misalignment
found to be concurrent with accommodative strain. If
intermittent noncomitant non-accommodative esotropia
is termed “innervational” in children without Down
syndrome, we must assume that most cases of esotropia
in children with Down syndrome are innervational.
Another salient finding is the number of microtropic
misalignments (31 microesotropia cases); as
mentioned, these misalignments have not caused
amblyopia, unlike microtropia in children without
Down syndrome. Does this represent a primary
incapacity for foveal fusion, causing alternating
strabismus? Might such an incapacity be the cause of
strabismus in most Down syndrome patients, with or
without an innervational component unchecked by
fusion amplitude, which in turn would be lacking
because of failure to develop proper binocular vision?
Children with Down syndrome often have
torticollis, or head tilt, all the more frequently the
younger they are. It is fostered by generalized
hypotonicity and the hyperlaxity of the atlantoaxial
joint, but in 17 cases we found the cause of torticollis to
be eye-related, caused by either nystagmus null points
or oculomotor imbalance.
Outcomes of surgery are no different from
outcomes in children without Down syndrome, who are
more often undercorrected initially. Longer-term
follow-up may show late overcorrection, as in the case
of non-Down patients with esotropia.
References
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