Discussion
In this observational study, we found a satisfactory visual outcome after primary IOL implantation in infants with congenital bilateral cataract who were operated on before 12 weeks of age. With such a young age at surgery (median 35 days, and the oldest one 10 weeks of age) as well as the long follow-up time of median 6.1 years, we believe that this study provides important new knowledge about primary IOL implantation in this young patient group.
In the last decade, improvements in surgical technique, technology and better understanding of the growth of the eye have led to a more positive attitude among paediatric cataract surgeons to implant an IOL even in the youngest infants. Still, there exist controversies and challenging aspects, especially in those below 6 months of age, and there is to date no consensus regarding the minimum age for primary IOL implantation. The controversies are due both to the higher risk of VAO requiring additional surgery, to the risk of developing secondary glaucoma and to the unpredictable myopic shift that leads to variability in refractive outcomes.5 6 8 On the other hand, primary IOL implantation has the advantage of providing a partial optical correction at all times and may allow for a more optimal visual development and thereby preventing amblyopia. Vasavada et al7 found that visual rehabilitation was faster in pseudophakic compared with aphakic eyes. This is assumed to have a positive impact on the activity of the child and likely also the overall functional development. Primary IOL implantation in children also has the advantage of better visual stimulation than aphakia in patients who refuse to use glasses or contact lenses even if prescribed.
In the present study, the median CDVA at the follow-up examination was 0.5 logMAR without age correction. Since visual acuity improves as a result of visual stimulation during the first few years,12 we also accounted for different ages at follow-up using a regression model with an age trend (figure 1). This gave a predicted age-corrected mean CDVA of 0.45 logMAR at 5 years of age. This was somewhat inferior to the visual outcome of the Toddler Aphakia and Pseudophakia study (TAPS).9 However, they excluded most children with chromosomal and neurodevelopmental anomalies from the visual acuity summaries, and the age at surgery was 1 to 7 months. After removing the children with Down syndrome and the one with Lowe syndrome from our study, the median CDVA of the better-seeing eye was comparable to the TAPS study. Our results are also in accordance with previous reports of primary IOL implantation in an older age group.5 7 However, in these studies, the infants who were operated as early as in our study were left aphakic, and these aphakic children did not achieve a similarly good visual outcome.5 7 Furthermore, age at onset of cataract is an important factor of the visual outcome in these patients, and contrary to other studies on paediatric cataracts, we only included infants with visually significant cataract at birth. The visual outcome in the present study was in accordance to the other studies,5 7 9 that also included patients who were more likely not having visually significant cataract at birth with, therefore, a potentially more favourable visual prognosis.
Studies have shown that younger age at surgery increases the risk of VAO.5 14 In the present study, all patients were operated within 12 weeks of age, and all eyes required treatment for VAO. Vasavada et al, Bothun et al and Solebo et al reported lower incidences of VAO (10% to 39%) in studies with a higher age at surgery.5 7 9 The different incidences of VAO in the literature may also be explained to an extent by different surgical techniques and also classification; for example, in our study, we had a rather inclusive definition of VAO as all surgeries necessary to obtain a clear visual axis. Our high incidence of VAO may be explained by the close follow-up, and an aggressive approach to treat VAO in order to reduce the risk of amblyopia, but probably first of all the low age at cataract surgery. As primary IOL implantation causes more reoperations due to VAO,5 9 it has been questioned whether such repeated exposure to general anaesthetics during this key period of neurodevelopment may be dangerous for these small children. However, a recently published randomised trial did not find an increased risk of neurocognitive or behavioural deficits after multiple general anaesthesia in infancy.15 Nevertheless, newer approaches as the bag-in-the-lens can be considered in some selected cases to reduce VAO,16 however, this technique can be challenging in this young patient group.
Secondary glaucoma remains the most serious sight-threatening complication after cataract surgery in infants.17 Previous studies have discussed various potential risk factors, such as early surgery, especially in the first month of life.18 We found a cumulative glaucoma risk of 10%, which is in accordance with previously reported 5-year incidences of 5%–13.8% for bilateral paediatric cataract.5 7 Furthermore, the role of primary IOL implantation following congenital cataract surgery has been reviewed in previous reports. Several studies have not found any significant difference in the incidence of secondary glaucoma between aphakic eyes and eyes with primary IOL implantation.7 19 Others have found that the risk is higher in aphakic eyes,20 and that the presence of an IOL is protective for the development of secondary glaucoma.18 However, these reports may suffer from selection bias, as the surgeons may choose IOL implantation in eyes that are less likely to have complications.19 Still, a recently published systematic review and meta-analysis by Zhang et al17 concluded that there is a significantly lower risk of secondary glaucoma after primary IOL implantation in patients under 2 years of age with bilateral congenital cataract in comparison with aphakia.
In the present study, we found a high variation in refraction at the follow-up examination and mostly with a large myopic shift. Selection of an IOL with appropriate power for implantation in paediatric eyes is complex, as IOL power calculation formulas give a large prediction error in these young children.21–23 The high myopic shift and unpredictable refraction are disadvantages of primary IOL implantation in infants.6
Implanting the IOL in the capsular bag is preferable, as sulcus fixation increases the risk of IOL malposition, postoperative inflammation and secondary glaucoma.24 The alternative to primary IOL implantation is aphakia, with or without secondary IOL implantation later in childhood, when IOL power predictions may be more reliable.25 With secondary implantation, however, it may be difficult to dissect the anterior and posterior capsule apart; one study found that the IOL had to be implanted in the ciliary sulcus in as many as 72% of the cases.26 In our study, all eyes had the IOL placed in the capsular bag.
The clinical implication of the present study is that cataract surgery in infants younger than 12 weeks of age is safe in terms of visual outcome. The incidence of secondary glaucoma is similar to that reported after primary IOL implantation in older infants. However, the risk of VAO is high, and the parents must be informed that frequent follow-up examinations and additional surgery for VAO in general anaesthesia are necessary. Another disadvantage is that the high myopic shift in young children gives a rather unpredictable final refraction. The advantage of an implanted IOL, however, is that it provides a permanent continuous correction of aphakia, which may be favourable especially during early childhood to prevent amblyopia and to enhance visual development.
The strength of the present study is that it includes an unselected and nationally representative group of the youngest infants with bilateral cataract in Norway. Other advantages are few surgeons, a long and close follow-up, and that all infants had a comprehensive prospective study examination. Limitations of the study are the non-comparative design and that some data were obtained by retrospective review of medical records. Another limitation is the small sample size. However, the study participants included most of the patients with visually significant bilateral cataract at birth operated on in a 10-year period in a university hospital clinic. In conclusion, our study shows that primary IOL implantation before 12 weeks of age gives a favourable visual outcome and that it can be considered as a primary modality of treatment, with the appropriate surgical and anaesthesia experience, and close follow-up.