Download Astigmatism in children: changes in axis and amount from birth to six

Astigmatism in Children: Changes in Axis
and Amount from Birth to Six Years
Jane Gwiazda, Mitchell Scheiman,* Indra Mohindra, and Richard Held
Noncycloplegic refractions of 1,000 children aged 0-6 years revealed a high incidence of astigmatism,
especially in the first 2 years of life. Before age 4Vi years, most of the astigmatism was against-therule and after that age most was with-the-rule. Of 19 children who did not show astigmatism in the
first year, only one acquired it by 4 years. Of 29 children who had large amounts of astigmatism in
the first year, all showed elimination or a large reduction in the amount of the cylindrical error by 4
years. These results are relevant to the etiology of astigmatism. Invest Ophthalmol Vis Sci 25:88-92,
1984
It is now well documented that infants have a high
incidence of clinically significant astigmatism. 1 " 5
Mohindra and colleagues,3 using noncycloplegic retinoscopy, found that 45% of a sample of 276 infants
showed significant astigmatism [> 1.0 diopters (D)] in
the first year of life. Similar findings have been reported
using cycloplegic retinoscopy1'4'5 and photorefraction.2
Most of the astigmatism in the first year is againstthe-rule, ie, minus cylinder axis 90°.1>5
Refraction data from school-aged children, on the
other hand, show a much lower incidence of astigmatism, and most of it is with-the-rule, ie, minus cylinder axis 180°.6 For example, Hirsch6 reported that
between the ages of 6 and 12 years, 4% to 7% of the
children showed more than 0.75 D of astigmatism,
almost exclusively with-the-rule. Based on his longitudinal data, Hirsch concluded that there is not much
change in astigmatism during the school years. If a
child is going to have a large amount of astigmatism,
he or she will have it by 6 years of age.
The high incidence of astigmatism in infancy and
the much lower incidence in school-aged children imply that much of the early astigmatism must be eliminated between 1 and 6 years. And, since infants tend
to have against-the-rule astigmatism and older children
have with-the-rule, changes in axis must also be occurring during this time. However, the few refraction
studies that cover this age range present conflicting
findings. Atkinson et al7 reported that the incidence
of astigmatism (^0.75 D) declined to adult levels, 810%, by 18 months of age. Mohindra and Held,8 on
the other hand, found that the incidence of astigmatism
(>\.O D) was still high, almost 40%, as-late-as 5 years
of age. Neither study reported data on the axis of astigmatism. Woodruff"9 reported both the axis and
amount of astigmatism compiled from the refractions
of 631 children between the ages of 1 and 6 years. His
results showed a trend to more astigmatism with increasing age. Three percent of 2-year-old children
showed 0.75 D or more of astigmatism, while by 6
years of age, 10% showed this amount. Most of the
astigmatism was with-the-rule. Larger amounts (S*2.25
D) of against-the-rule astigmatism were never seen.
Studies of early astigmatism are important in order
to understand the development of the human visual
system. Some adult astigmats show optically uncorrectable losses of acuity (meridional amblyopia) for
edges in the orientations that are presumed to have
i
'- 1 - T e ( i by their astigmatism since early childnooa. ine amblyopia is assumed to be produced by
the habitual blurring.10 Tracking the refractions of
young children during development will provide more
information about the timing of a sensitive period,
during which astigmatism may have deleterious effects
on the development of the visual nervous system. The
refraction data are also relevant to the etiology of astigmatism and its prognosis.
In this study we report cross-sectional refraction data
obtained from a group of 1,000 children aged 0-6
years. In addition, we report longitudinal changes in
refractions in a group of 48 children who were followed
for a period of at least 4 years beginning shortly after
birth. This is the first time that refractions have been
tracked in very young children.
From the Department of Psychology and Brain Science, Massachusetts Institute of Technology, Cambridge, Massachusetts.
Supported by grants from the National Institutes of Health
(EY01191, EY02621, EY02649).
Submitted for publication January 18, 1983.
•Present address: The Eye Institute, 1201 W. Spencer St., Philadelphia, PA 19101.
Reprint requests: Dr. Richard Held, E10-145, Department of Psychology and Brain Science, Massachusetts Institute of Technology,
Cambridge, MA 02139.
88
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No. 1
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ASTIGMATISM IN CHILDREN / Gwiozdo er ol.
Materials and Methods
One thousand children aged 0-6 years comprised
the cross-sectional sample. Ninety-seven percent were
white, 2% were black, and 1% Oriental. Informed consent of the parents was obtained prior to undertaking
the study. Upon initial refraction, 609 children had
less than 1 D of astigmatism, and 391 had 1 or more
D. In the first year, 63% of the children had mean
spherical refractions between - 1 . 0 and +1.0 D, with
a mean o f - 0 . 2 D. Over years 1-6, 90% of the children
had mean spherical refractions between —1.0 and
+1.0 D, with a mean of +0.5 D. Children with phoria,
tropia, or ocular disease were excluded from the sample. Infants were recruited by a letter describing the
MIT research program in infant vision sent to parents
in the Cambridge, Massachusetts area. Names and addresses were obtained from the birth records on file
in the Cambridge City Hall. Responses to the letters
that resulted in participation in the study averaged
10%. Older children were recruited from day care centers, nursery schools, and camps in the Cambridge
area. Forty-eight of the children were refracted from
4-20 times in the first year, and periodically thereafter,
until they reached at least 4 years of age. These children
comprised the longitudinal sample.
Refractions were obtained by the near-retinoscopy
procedure," performed by two experienced refractionists (MS and IM) without pre-knowledge of any
earlier findings obtained from children in the longitudinal sample. It has been shown that near-retinoscopic refractions of children are highly correlated with
their cycloplegic refractions1 l l 2 and that repeated nearretinoscopic measurements of the same children made
within a short period of time rarely deviated by more
than ±0.5 D. 3
In the near-retinoscopy procedure, the child fixated
the light of the retinoscope in an otherwise dark room.
Retinoscopy was performed at a fixed distance of 50
cm without cycloplegia. The streak was moved quickly
between the two principal meridians to determine the
cylindrical power and axis. The vergence of the retinal
reflection was neutralized through the use of a graded
set of lenses mounted in a bar for easy manipulation.
An adjustment factor of -1.25 D was added to the
spherical component at neutrality to obtain the static
distance refraction of the eye. This factor was used
rather than the —2.0 D, which would be correct for
the working distance of 50 cm, because it has been
determined that an average tonus adjustment of+0.75
D must be added to the static refraction obtained by
near-retinoscopy.13 In experiments with both infants
and adults, Owens and colleagues showed that the beam
of a retinoscope, when viewed in a dark room, does
not stimulate accommodation. 14 They further showed
440 81 29
34 34 52
68 69
80 60 37 16
Amount of astigmatism
0 > 30 D
D 2.0- 2.99 D
• 1.0-1.99 D
0-5
12-17
6-11
24-29
36-41
48-53
18-23
30-35
42-47
AGE (months)
60-65,
5459
66-71
Fig. 1. Incidence of clinically significant astigmatism on initial
refraction of 1,000 children aged 0-6 years. The total number of
children refracted within an age group is given above each bar.
that, in this situation, the eye focuses for an intermediate distance, referred to as the dark focus or resting
state of accommodation. On average, this effect can
be compensated for by applying a standard tonus adjustment of+0.75 D. Thus, —2.0 D (working distance)
+0.75 D (average tonus adjustment for dark focus)
= — 1.25 D, the adjustment factor applied to the spherical component of the refraction.
All refractions were written using the minus cylinder
convention. The axis of the cylindrical component was
classified as with-the-rule if the minus cylinder axis
was at 180° ± 15°, against-the-rule for minus cylinder
at 90° ± 15°, or oblique (other than with-the-rule or
against-the-rule; usually either 45° in one eye and 135°
in the other, or 30° in one eye and 120° in the other).
Results
Figure 1 shows the proportion of 1,000 children
aged 0-6 years who had 1 D or more of astigmatism.
These data are based on the initial refraction of the
right eye of each child. Results of a chi square test
showed that the distribution of amounts of astigmatism, including <1 D of astigmatism, varied as a function of age (x 2 = 123, df = 15, P < 0.001). It can be
seen in Figure 1 that both the incidence and amounts
of astigmatism are highest in the first two years and
decline thereafter:
Data from the children with clinically significant
astigmatism shown in Figure 1 are divided by axis in
Figure 2. In the first three years of life (0-35 months),
the proportion of children who have against-the-rule
astigmatism is not significantly different from the proportion who have with-the-rule (x 2 = 1.4, df = 1, n.s.).
However, for older children (3-6 years), there is a
higher prevalence of against-the-rule astigmatism be-
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90
INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE / January 1984
n
235 34
12
0-5
16
12-17
6 11
10
16
24 29.
18-23
16
14
13 12
9
4
3641
30-35
42 47
54-59
6671
AGE (months)
Fig. 2. Refraction data from children with clinically significant
astigmatism broken down by axis. The total number of children
with astigmatism (> 1.0 D) within an age group is given above each
bar.
fore 4'/2 years (54 months), and a higher prevalence
of with-the-rule after that age (x2 = 4.45, df = 12, P
< 0.05). Over all ages, only a small proportion of children ever show oblique axis astigmatism.
Table 1 shows the change in amount and axis as a
function of age for the children in the longitudinal
sample who had significant astigmatism at 6 months
of age. Of these, 16 children had against-the-rule astigmatism at 6 months of age, 8 children had withthe-rule astigmatism at 6 months, and 5 children had
Vol. 25
oblique axis astigmatism at 6 months. All 29 children
showed a significant reduction in the amount of astigmatism between 6 months and 4-6 years of age (t
= 13.4, df = 28, P < 0.001). Of the children who had
large amounts of against-the-rule astigmatism at 6
months (Table la), by 6 years of age, one third of the
children had small amounts of against-the-rule astigmatism, one third had shifted axis to small amounts
of with-the-rule astigmatism, and one third had no
astigmatism. It should be noted that only one of the
6-year-olds had greater than 1 D of astigmatism, and
the axis remained against-the-rule.
For the children who had large amounts of withthe-rule astigmatism at 6 months (Table lb), there was
a shift to smaller amounts of with-the-irule astigmatism
or to no astigmatism at all with increasing age. None
of the children acquired against-the-rule astigmatism.
Three of the 5 children who had large amounts of
oblique axis astigmatism at 6 months (Table lc) shifted
to small amounts of with-the-rule at 5 years. Overall,
then, much of the early astigmatism was either eliminated or reduced in amount, with an indication of a
shift in axis to with-the-rule.
Nineteen children in the longitudinal sample never
showed significant astigmatism in the first year. They
were periodically refracted until at least 4 years of age,
and in that time, only one acquired significant astigmatism. This child acquired 1.5 D of with-the-rule
Table 1. Longitudinal refraction data*
X90
Age (yrs)
Total n
refracted
No
astigmatism
0.5-0.99
1-1.99
2D
0.5-0.99
1-1.99
2D
0.5-0.99
1-1.99
2D
6
10
4
3
1
1
0
0
0
2
0
2
2
0
0
1
0
1
0
1
0
0
0
0
0
0
0
0
0
2
1
1
1
0
1
0
0
0
2
0
0
0
1
0
2
3
0
0
0
0
0
3
0
0
0
0
0
0
0
0
3
8
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
0
0
0
0
0
0
0
0
0
0
4
1
1
2
0
2
2
0
1
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
2
2
1
0
5
0
1
1
0
0
0
0
1
1/2
1
2
(a) 3
4
5
6
16
16
13
12
10
8
9
0
0
2
2
2
2
2
3
2
1
2
1
1/2
1
2
(b) 3
4
5
6
8
8
5
6
5
2
2
0
0
0
0
0
1
0
1/2
1
2
(c) 3
4
5
5
4
3
3
0
2
0
5
6
5
1
Oblique
XI80
0
0
0
0
0
0
0
1
0
0
0
0
0
0
1
1
1
1
0
1
• (a)—from 16 children with against-the-rule astigmatism at 6 months; (b)
from 8 children who had with-the-rule astigmatism at 6 months; and (c) from
5 children with oblique astigmatism at 6 months.
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2
0
0
0
0
0
4
4
3
2
1
1
1
3
1
91
ASTIGMATISM IN CHILDREN / Gwiazda er ol.
No. 1
astigmatism in his right eye at age 2 years and has
kept it until age 6 years.
Discussion
Results of the present study indicate that the large
amounts of astigmatism shown before 2 years of age
are greatly reduced or eliminated by 4 years of age.
With respect to the axis of astigmatism, 4-5 years is
a time of transition. Before age 4'/2 years, most children
have against-the-rule astigmatism and after that age,
with-the-rule. These findings have been confirmed using cycloplegic retinoscopy15 and photorefraction.16
Longitudinal data from Dobson and colleagues15 agree
with our findings in showing that the large amounts
of astigmatism seen in infancy are eliminated or greatly
reduced by school age. In addition, the axes of astigmatism of individual children may shift from large
amounts of against-the-rule or oblique in the first year
to small amounts («SO.5 D) of with-the-rule by school
age. There is no indication of a shift in axis in those
children who initially have with-the-rule astigmatism.
With-the-rule astigmatism predominates until at
least 9 years of age. Inspection of patients' records at
the New England College of Optometry (Boston, Massachusetts) revealed that of 47 patients aged 5-9 years
with significant astigmatism, 80% showed with-therule.
The changes in astigmatism with age documented
in the present study are relevant to the etiology of
astigmatism. The fact that much of the early astigmatism is against-the-rule and then is either gradually
eliminated or becomes with-the-rule may reflect increased eyelid pressure with age. 1718 It has been shown
that changes in lid pressure can produce changes in
the amount of astigmatism. Robb19 found that patients
who had hemangiomas of the eyelid as infants showed
astigmatism in the involved eye at a later age. Since
the axis of the astigmatism varied systematically with
the location of the hemangioma, the pressure of the
lesion is inferred to have changed the corneal curvature.
Wilson and colleagues20 showed that retracting the
eyelids of young adults with a lid speculum for at least
10 sec produced less with-the-rule astigmatism in corneas that had more than 1.0 D of with-the-rule astigmatism. The same mechanism could account for the
increase in against-the-rule astigmatism shown by older
(more than 40 years old) patients.21'22 Results of a
study by Baldwin and Mills,22 examining both keratometry readings and refraction data, indicate that most
of this increase could be accounted for by steepening
of the cornea in the horizontal meridian, most likely
due to decreased eyelid pressure in later years.
An analogous explanation can be offered for the
increase in with-the-rule astigmatism seen after 4'/2
years. This explanation presumes that most of the early
astigmatism is corneal and is supported by Howland,
who recently found in young infants a high correlation
between total astigmatism measured by photorefraction
and corneal astigmatism measured by photokeratome17
the natural form
t r y 23,24 According to Gullstrand,
of the cornea is against-the-rule. This is the most prevalent type of astigmatism found in young children.
After 4V2 years, the increase in with-the-rule astigmatism could reflect increased eyelid pressure, which
would produce greater flattening of the cornea in the
horizontal meridian, since maintained pressure must
be greater along the horizontal.
Since most of the early astigmatism is either eliminated or greatly reduced in amount, one wonders
whether there are any lasting effects. Gwiazda and colleagues25 found that children who had a large amount
of myopic astigmatism as infants and later lost it,
showed reductions in acuity for the edges oriented
along the formerly myopic focus when tested at 4 to
7 years of age. No such reductions were found in formerly hyperopic children. This finding may account,
in part, for the unusual patterns of orientational anisotropy shown by some 5-10-year-old nonastigmatic
children.2526 However, given that most infant astigmats
have relatively small amounts of hyperopic astigmatism, there should not be a large number of older children and adults with meridional amblyopia resulting
from early uncorrected astigmatism.
One final conclusion emerges from the longitudinal
results. If a child does not have astigmatism in infancy,
he or she is unlikely to acquire it at a later age, at least
up to 4-6 years of age.
Key words: astigmatism, axis of astigmatism, refractions, nearretinoscopy, visual development
Acknowledgments
The authors thank Joseph A. Bauer, Jr., Shinsuke Shimojo,
and Dr. Jeremy Wolfe for their helpful suggestions.
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