In our study, we evaluated the risk of the postoperative visual axis obscuration, comparing two possible approaches of the primary aphakia correction. We concentrated on the specific group of patients in terms of the timing of primary surgical intervention in the age of 4–16 weeks.

The main aim of the congenital cataract surgery is to secure the clear visual axis. Furthermore, the proper timing of the surgery and the adequate aphakia correction are some of the crucial demands to provide the best possible conditions for the proper development of visual functions [2, 4,5,6,7,8]. Delayed surgery in case of the optically significant lens opacification can lead to the irreversible deprivation amblyopia and poor development of the central fixation with its consequences as nystagmus or strabismus. On the other hand, early cataract surgery can lead to a higher risk of postoperative complications [9,10,11].

Despite improvements in microsurgical techniques for cataract surgery, the development of secondary membranes and proliferation of lens material remains a major complication that often requires additional surgical procedures and hinders good visual outcomes in infants [2, 11, 12]. The risk of residual lens epithelial cell proliferation and PVAO development is reduced by performing a PCCC with an AV [9]; however, regrowth of the lens material is still possible. Development of PVAO after congenital cataract extraction with a PCCC (5 mm in diameter) and AV has been reported and showed that lens epithelial cells can proliferate even without the posterior lens capsule and anterior hyaloid support [13]. It was suggested that a larger posterior capsulectomy and a more extensive vitrectomy might prevent the formation of a secondary cataract [14]. Nonetheless, the PVAO is still the most common complication of paediatric cataract surgery and a reason for an additional surgery indication [12].

Many of the published results of the incidence PM and PVAO are consistent with our findings [8, 10, 15, 16].

Kuhli-Hattenbach et al. reported in 2008 the incidence of PVAO in aphakic eyes with primary surgery before 18 months of age was 9.2% [10]. Plager et al. also described very similar results. The primary surgery age in the latter study was comparable to our study groups and ranged from 3 weeks to 5 months (mean 2.5 months). The authors observed that 12.1% in the aphakic group required a second procedure for PVAO compared to 80.0% in the pseudophakic group [16].

On the other hand, Vasavada et al. reported PVAO in only four eyes (10.8%) in children with primary hydrophobic IOL implantation combined with PCCC and AV. Trivedi et al. reported visual axis opacification in infants with the same primary procedure in 23.6% of cases and Sukhija et al. in 13% of cases [17,18,19]. However, the mean age of the primary surgery in these reports was higher than in our study group (Vasavada 4.8 ± 2.4 months, Trivedi 6.0 ± 3.2 months and Sukhija 7.13 ± 2.32 months).

Lundvall and Zetterström observed ‘after-cataracts’ in 38.6% of infants without IOL implantation, with PCCC and AV; the mean age of surgery was 3.25 months [7]. The term ‘after-cataract’ was defined by the authors to include both PM and PVAO. The incidence of these complications was higher compared to our study. This could be partly explained by much lower doses of postoperative local steroids in the Swedish study (i.e. dexamethasone t.i.d. for the 1st week, b.i.d. for the 2nd and 3rd weeks and q.d. during the 4th week).

Solebo et al. published results of congenital cataract surgery in children during the first 2 years of life [3]. In groups with a primary IOL implantation, visual axis opacification (lens proliferation into the axis or inflammatory/pupillary membrane across the axis or capsular phimosis) was observed in 37% of bilateral cataracts and 42% of unilateral cataracts. In groups with primary aphakia, the same complication was reported in 13% of bilateral cataracts and 26% of unilateral cataracts. Data from that study were collected for 12 months postoperatively. This shorter follow-up period could have led to different complication frequencies compared to our pseudophakic group. However, the median interval between the primary and secondary surgery (3.9 months) was similar to our data but the 1-year follow-up period was much shorter than the follow-up in our study. Also, the mean age of primary surgery in groups with a primary IOL implantation was greater than in our study (13 weeks in bilateral and 35 weeks in unilateral cataracts). Interestingly, it was also much higher than the mean age of primary surgery in aphakic groups of the same study (7 weeks in both bilateral and unilateral cataracts). This fact could potentially lead to a reduction in complication rate in the pseudophakic group. The complication rate in our pseudophakic subgroup with surgeries performed at higher ages (i.e. 9–16 weeks) was similar.

Trivedi et al. described opacification of the visual axis requiring a secondary surgical procedure in 37.9% of eyes (11 of 29 pseudophakic eyes, mean age of primary surgery 4.8 ± 3.7 months). However, the rate was statistically significantly higher in infants when the primary surgery age was under 6 months of age (50% vs. 18.2% in infants undergoing surgery at ages greater than 6 months) [20]. Thus, the data may correspond with our observation of a higher incidence of PVAO in children undergoing primary IOL implantation at younger ages.

In the Infant Aphakia Treatment Study (IATS), more complications were observed in pseudophakic eyes compared to aphakic eyes during the first 5 years after surgery, and most complications occurred during the first year. PVAO (40%) and PM formation (28%) were the most common complications in the pseudophakic group, while the rates were low in the aphakic group (both 4%). We observed a higher incidence of PVAO in the pseudophakic and aphakic groups (72% and 16%, respectively) in our study. The incidence of PM was higher in the pseudophakic group (40%) in our study, while the incidence of PM in the aphakic group was similar (7%) [11].

In the Toddler Aphakia and Pseudophakia Study (TAPS), 178 eyes (96 children) were evaluated. TAPS is a registry of children treated by surgeons at the 10 centres who participated in the IATS. As in our study, the median surgery age was 2.5 months (range 1–7 months), and visual axis opacification including pupillary membranes was more common in pseudophakic (32%) than aphakic (8%) eyes, and adverse events, in general, were associated with younger age and smaller corneas. Visual outcomes were not affected by aphakia management [21].

At a time when the safety of cataract surgery with IOL implantation in adults was regarded as safe (15 years ago), one of several controversies was whether primary IOL implantation in infants with congenital cataracts was acceptable. Despite multiple problems with the fitting of aphakic contact lenses, many surgeons were enthusiastic about primary IOL implantation and believed that it could improve visual outcomes [8, 15]. It was generally accepted that congenital cataract surgery should be performed in the first 4–6 weeks of life in cases of unilateral cataracts, and during the first 6–8 weeks of life in cases of bilateral cataracts, to prevent the development of stimulus deprivation amblyopia, strabismus and nystagmus [2, 5, 6]. However, most publications report outcomes of cataract surgery at much higher ages, usually in children between 6 and 12 months. Our study concentrated on younger infants and found that even very small differences in the age of surgery (range 0–8 weeks vs. 9–16 weeks) increased the risks of complications in the pseudophakic group and increased the risks of PVAO in the aphakic group. This may also explain why we observed more complications in infants with IOL implantations compared to some other reports.

There was higher proportion of monocular cataracts in the group with primary IOL implantation in our cohort. This fact could theoretically be related to a higher number of eyes with persistent foetal vasculature (PFV). As this condition could predispose to PVAO, we subsequently inspected both groups for PFV. There were 9 eyes (13%) with PFV in pseudophakic group and 16 eyes (21%) with PFV in aphakic group. Therefore, higher number of PVAO in pseudophakic group in our cohort should not be related to the presence of PFV. We did not evaluate the visual outcomes in our study. However, according to published data, visual outcomes of infants with primary IOL implantation remain at least comparable with the aphakic groups in the majority of reports [8, 15, 22].