Visual axial opacity clearing
VAO clearing was reported in 5 studies11,22,34,37, and
the I2 was 23%.
As shown in Figure 9, the primary
IOL had a significantly higher incidence of VAO clearing compared with
primary
aphakia,
[OR=9.33, 95%CI: (5.21, 16.73), p=0.27].
Discussion
The present meta-analysis demonstrated that the postoperative VA in
primary IOL group was better than that in primary aphakia group. These
results were consistent with previous studies. Birch et al showed that
IOL may support better VA development when a cataract was extracted
after age 1, while the difference would taper off with the age reaching
4 years39,40. Vasavada et al22.
reported that more infants in primary IOL group had documentable VA than
aphakia group during early postoperative follow-up, and this trend
continued until age 5. This result indicated that the visual
rehabilitation was faster in pseudophakia group, especially in early
postoperative follow-up. However, in the IATS study, the VA was similar
in IOL group and contact lens group both in the first (1 year old)6 and last follow-up (4.5 years old)11. This could be explained by better compliance of
contact lenses or spectacles in the aphakia group. The IATS study
offered free contact lenses and spectacles for the enrolled subjects.
Moreover, trained personnel assessed the vision and monitored the
compliance through regular home visits. 41 This may
not be carried out in the real world, particularly in developing
countries. Actually, constant optical correction during this crucial
period is very important for children. A faster visual rehabilitation
will impact the activity and overall functional development of the
children. Therefore, primary IOL implantation may provide better VA for
pediatric patients, especially those under age 5.
Our
meta-analysis did not see any difference in glaucoma incidence. Many
hypotheses proposed the mechanisms of glaucoma after infantile cataract
surgery. However, there is no unanimous conclusion. The mechanisms of
secondary glaucoma
of
pseudophakia eyes and aphakic eyes might be different. The filtration
angle of infants is susceptible to postoperative inflammation. Thus, IOL
implantation in infants will cause chronic inflammations that induce
changes of iris root or trabecular meshwork (TM)42-44. This might
explain the glaucoma in pseudophakia eyes. As for aphakic glaucoma,
since the mechanical absence of lens in the eye, TM cells would be
exposed to the lens epithelial cells (LEC). Michael et al. specified
that LEC induced changes in TM cells that resembled changes in primary
open-angle glaucoma45,46.
It is worth noting that the
mechanism of glaucoma is still unclear. But we could not make any
attempt to investigate the mechanisms of secondary glaucoma after
infantile cataract surgery in this meta-analysis.
Analysis of unilateral subgroup
indicated there were much fewer
infants with strabismus in primary IOL group compared with primary
aphakia group. This was consistent with the studies by Autrata et al31. and Lambert et al. Previous studies also suggested
that the incidence of strabismus in IOL group was relatively
low47-49.
The absence of natural lens in unilateral eye will lead to anisometropia
and aniseikonia, which are related to secondary strabismus following
congenital cataract surgery. Primary IOL implantation offers a stable
retinal image with minimal aniseikonia as well as full-time optical
correction for surgery eye. Moreover, children have to wear contact
lenses or spectacles to get optical correction in case of absent lenses.
The compliance of wearing contact lenses will be affected by the
complications associated with contact lenses like corneal infection.
Hence, this might explain the higher incidence of strabismus in primary
aphakia group.
Postoperative VAO is very common in infants after congenital cataract
surgery. According to the previously published literatures, IOL
implantation is associated with higher VAO incidence in congenital
cataract children, especially those younger than 6
months50-52. The average incidence of VAO after IOL
implantation is 44.0%, while the incidence is up to 80% when the
patient is younger than 6 mouths53. The IOL in
capsular bag acts as an obstacle and prevents the anterior and posterior
capsule leaflets from fusing, while the capsule edges will seal more
effectively in aphakic eye. In our meta-analysis, primary IOL group had
a noticeably higher incidence of VAO clearing than primary aphakic
group, which was consistent with the RCT study conducted by IATS and
other previous studies.11,34,54,55.
Our meta-analysis has some limitations. First, even though this
meta-analysis is the first systematic review on this topic, it included
retrospective studies rather than just RCTs. Thus, the level of evidence
will be weakened by the inclusion of retrospective studies. However,
there is no denying that it is very difficult to conduct RCT among
paediatric cataract children. Second, the pooled effect of complication,
especially the glaucoma incidence, might be affected by the inconsistent
diagnostic criteria adopted in these studies. Third, the control group
of these included studies was either primary aphakia followed by contact
lens or primary aphakia followed secondary IOL implantation. Third,
given the number of patients in each study is relatively small, we could
not draw explicit conclusion on the difference in postoperative visual
performance.