IOL implantation in children

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

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

Target refraction

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.