Primary intraocular lens (IOL) implantation has become increasingly acceptable in children because of advances in surgical
techniques, improved lens technology and a better understanding of refractive outcomes in paediatric eyes.
The advantages of primary IOL implantation in paediatric cataract surgery include dispensation with contact lenses or high
power glasses and reduced anisometropia in children with unilateral cataracts. However, it is imperative that the appropriate
lens power is used in order to achieve the desired long-term refractive outcomes.
Dealing with myopic shift
Achieving a satisfactory long-term refractive result following IOL implantation in infancy requires that allowance is made
for the rapid axial growth and myopic shift which occurs during childhood.1-4 The mean quantity of myopic shift owing to axial growth of the eye from age three months to 20 years has been shown to be
9.7 D in aphakic eyes.5 Meanwhile, the rate of axial growth has been found to be slower in pseudophakic eyes (Figure 1) in comparison to aphakic eyes, yet the mean absolute quantity of myopic shift is greater in pseudophakic eyes because of
the optical effect of the change in relative position of the IOL within the eye.6
Figure 1: Pseudophakic eye.
We have found a mean myopic shift of 5.43±3.7 D in patients during the first 12 months following infantile cataract surgery
with IOL implantation but this was significantly greater (mean 6.26±2.91 D) when surgery was carried out at less than 10 weeks
of age and in patients with Trisomy 21 (a chromosomal abnormality).7 This value is similar to that found in the first year in infants following IOL implantation for unilateral congenital cataracts.8
The initial desired refractive outcome following paediatric cataract surgery is hypermetropia, the amount of which depends
upon the age of the child.5,9
When congenital cataract surgery is carried out at four to eight weeks of age, the initial desired refractive outcome following
lens implantation is approximately 9 D of hypermetropia.
We reduce the level of target hypermetropia according to the age of the infant, aiming for approximately 6 D at age six months
and 4 D at age 12 months (although these amounts are determined on an individual basis, depending on factors such as co-pathology,
refraction in the fellow eye, etc.). However, the amount of myopic shift is, in our experience, extremely variable and so
there is wide final variation in refractive outcomes. Some studies have demonstrated a greater myopic shift in unilateral
pseudophakia in infants compared with bilateral cases,10 but we have found no significant difference between unilateral and bilateral cases.7
The desired refractive outcome is approximately 2 D by age two and 1 to 2 D by age three, reflecting the fact that the majority
of growth of the eye has occurred by this age. This is stable until approximately age 11 to 13 when there is a further small
amount of growth of the eye. The desired refractive outcome is emmetropia or low myopia thereafter (depending on the refractive
error in the fellow eye).
Biometry for paediatric cataract surgery
Appropriate refractive outcomes following paediatric cataract surgery with IOL implantation requires accurate biometry, which
should be carried out by personnel experienced in biometry in infants and children. In younger children, biometry is conducted
under the same anaesthetic as the surgery itself, whereas in older, more co-operative children, biometry can be carried out
prior to surgery while the child is still awake.