of Astigmatism in Infants.
The following information is derived from
the conclusions I have drawn from my study of
available research and from personal clinical
Most infants are born with a small amount of
astigmatism of the eyes. Probably a little over
half of the Caucasian (European type)
infants are born with ATR astigmatism. The
great majority of Chinese infants are
usually born with astigmatism that is WTR.
A greater proportion of pre-term infants
compared to term infants is born with ATR
astigmatism. In the embryonic stage, the cornea
is normally formed with ATR astigmatism (horizontal
meridian is steepest). The structure of the
cornea is such that its growth involves a greater
rate of flattening of the cornea in the
horizontal meridian. The cornea thus
progressively decreases in its degree of ATR
astigmatism and then begins to increase in WTR
astigmatism when the horizontal meridian becomes
flatter than the vertical.
In some infants, such as the Chinese, the time
at which the cornea begins to develop WTR
astigmatism is most often prior to birth. However,
in Caucasian infants, the time of this transition
is usually around the time of birth or shortly
afterwards. The rate at which the cornea develops
WTR astigmatism is mainly genetically determined.
A very small proportion of infants fails to ever
completely lose the ATR astigmatism of the cornea,
which then persists throughout life. By one year
of age, most infants develop a small degree of
WTR astigmatism of the cornea that is opposed by astigmatic
focusing (see meridional accommodation (MA)
below) involving the lens in the eye and to some
extent, the cornea.
In some cases, the WTR astigmatism of the
cornea cannot be prevented from increasing beyond
the level of the opposing ATR astigmatism of the
lens in the eye. This can occur if the drive
towards WTR corneal astigmatism is abnormally
high, or the neuro-muscular mechanism that limits
the corneal WTR astigmatism (MA) is weak due to lack
of iron etc. This results in the most common
type of astigmatism of the eyes in children i.e.
MA involves a feedback mechanism to detect the
presence of astigmatism before astigmatic
focusing is stimulated. Thus adequate visual
experience is also needed to provide feedback
on the state of the vision. Some infants develop
a high degree of WTR astigmatism before the
retina matures to a level that enables clear
vision and the operation of the visual feedback
mechanism of MA (i.e. about six months of age).
The high amount of MA that is then required to
reduce the WTR astigmatism of the cornea may not
be achievable, resulting in WTR astigmatism of
To detect any significant deviations from the normal at an early
stage, all infants should be examined preferably around six months
of age but no later than one year of age. Special emphasis should
be paid to diet and visual experience (see Section
A) if such deviations are noted. If there are no signs of improvement
by eighteen months of age, corrective lenses may be necessary to
prevent amblyopia (lazy eye) due to the astigmatism.
Even after two years' of age (up until about twenty years), the
horizontal meridian of the cornea in most normal-sighted people
continues to flatten slightly and at a decreasing rate. If it were
not for MA, the eye would develop WTR astigmatism. The shape of
the cornea remains fairly stable in young adulthood. From middle
age and onwards, the horizontal meridian of the cornea usually becomes
steeper for reasons explained below.