Discussion
One of the most marked differences between adult and paediatric cataract surgery is the behaviour of the lens capsule during the procedure. Paediatric patients have a highly elastic lens capsule and surgeons often find it challenging to perform the capsulorhexis.7 Femtosecond laser can contribute to the achievement of predictable, reproducible, centred and perfectly round-shaped capsulotomy while decreasing the manual surgical steps and manipulations and consequently potentially decrease the risk of surgical complications.6 8 11 The objective of the present study was to analyse safety and efficacy of FLA anterior capsulotomy in a large patient cohort. Visual outcomes following paediatric cataract surgery are strongly correlated with the period of visual deprivation. The decision regarding timing of the surgery is based on the patient’s clinical condition and the presence of visually pronounced cataract. The use of IOLs for the management of infantile cataract remains questionable. This is due to the limited accuracy of IOL power calculation, along with the higher rate of visual axis opacification and increased risks of postoperative complications.13–16 Multiple studies report benefits for visual acuity, if the surgery with IOL implantation is performed at very early age.16–20 In our practice, the surgery is preferably performed in young infants with a significant visual depravation, starting from 8 weeks of age, as in subjects younger than 4 weeks higher risk of postoperative complications have been reported.21–24
The use of low-energy FEMTO LDV Z8 femtosecond laser for the purpose of laser-assisted anterior capsulotomy was investigated in 51 eyes of 33 paediatric patients aged from 2 months to 13 years. Currently, there are only few studies focusing on the use of the femtosecond lasers in children with a limited number of cases performed as off-label procedure and without reports on visual outcomes.8 9 11 25
Intraoperative outcomes
In our study, the incidence rate of capsular tear was 5.88%. Similar incidence rates in paediatric population were reported with common manual anterior capsulotomy techniques. Wilson et al reported an incidence rate of 6.2% with the manual continuous circular curvilinear anterior capsulorhexis and a 5.3% incidence rate with the vitrectorhexis technique.26 In all our cases, the capsule tears occurred during manual completion of the FLA capsulotomy. A large case series study with 1500 FLACS procedures in adult patients reported the intracapsular manipulation in cases with tissue bridges or microtags as the primary cause for anterior capsular tears.27 The laser power parameters have an important role in obtaining a free-floating capsulotomy.8 In this case series, laser power between 75% and 90% was optimal in obtaining an anterior capsulotomy with no residual tissue bridges and very limited amount of cavitation bubbles. Despite the high likelihood of a continuous capsulotomy with a free capsule cap, it is still advisable to make sure that no residual tags exist using adequate detection method, for example, using high magnification when inspecting capsule edge with the microscope, and if necessary, taking proper manual surgical adjustments to ensure completion.
The anterior capsulotomy diameter programmed at the laser platform was calculated using the Bochum formula, which adjusts for age-dependent enlargements of the laser-assisted capsulotomy.10 Recently, a new formula was validated in 2–6-year-old patients with congenital cataract.28 In contrast to Bochum formula, the new one does not take into account patient’s age at time of surgery. Although physical measurements on the achieved capsulotomy diameters were not performed, in all cases, satisfiable results were achieved. Since, for paediatric cataract surgeons, it is vital to be able to use a formula that applies to children of all ages, we are currently performing a study, where laser-assisted anterior and posterior capsulotomies are being assessed in a large cohort of paediatric patients.
It is important to note that in all our cases, no lateral canthotomy was necessary to instal the laser patient interface onto patient’s eye. This avoided all potential long-term sequelae associated with such a procedure in infants.29 In only a limited number of cases (approximately 1 case out of 10 patients based on our routine medical practice), difficulties in the vacuum application of the sterile patient interface due to a very narrow palpebral fissure or a small orbit were observed, and such patients were not included in this study. In such instances, we immediately opted for the manual cataract procedure and, thus, avoided any eyelid lacerations or eyelid bruising. At the time of writing of the manuscript, the manufacturer announced release of a new liquid patient interface specially designed to comply with small orbit and small interpalpebral apertures, which should comply even better with the eyes of infants.
FEMTO LDV Z8 is a compact and mobile femtosecond laser platform. It does not require any major adaption of the surgical room environment, or surgical flow, as there is no need to move the patient to another operating room to perform the laser-assisted step. Despite the fact that we did not measure the overall surgical time of laser-assisted surgeries, we did not perceive any significant difference in total surgery time or general anaesthesia duration if compared with the manual procedure. A prior report on the comparison between FLACS performed with FEMTO LDV Z8 and conventional phacoemulsification cataract surgery (CPCS) in adult patients showed that the mean overall surgical time of FLACS was 5.2 min longer than CPCS.30
In adult patients, low-energy femtosecond lasers have shown better FLACS outcomes (better capsulotomy quality, lower incidence of miosis, lower rate of subconjunctival haemorrhage) than high pulse energy femtosecond lasers did.31 To support this, no cases of intraoperative pupil miosis or subconjunctival haemorrhage were observed in all our paediatric patients.
Postoperative outcomes
In accordance with our outcomes, very similar unilateral and bilateral percentages of postoperative PCO development were reported in studies with similar follow-up periods.32 33
PCO was most frequent in infants younger than 12 months of age, where 65.00% of all cases developed PCO. Multiple studies report same or higher rates of PCO development in very young children after cataract surgery in which the posterior capsules are left intact.34–36 Intraoperative posterior capsulorhexis and anterior vitrectomy are considered standard surgical steps in young children, because they reduce the rate of PCO.37 However, a partial or complete closure of the posterior capsule still occurs in up to 40%–80% of paediatric cases, thereby leading to a decrease in visual axis clarity as well as to decreased visual functions.14 23 38
PCO occurrence may be mitigated by performing of posterior capsulotomies, but due to current lack of clinical evidence on the associated risks of paediatric FLACS with laser-assisted posterior capsulotomy, in this large cohort study, a conservative approach was followed. In fact, FLACS with posterior capsulotomy is a more demanding procedure involving supplementary surgical steps and an additional vacuum-docking of the laser patient interface on the patient’s eye.8 Nevertheless, we believe that in children, FLA posterior capsulotomy may facilitate the surgical step of obtaining a perfectly sized and circular posterior capsulotomy, centric to the anterior capsulotomy. In fact, performing paediatric posterior capsulorhexis manually is challenging as the posterior capsule is very thin, fragile and often hardly visible.39–42 Based on the long-term safety observed in this study, currently we are performing a new study where we perform laser-assisted anterior and posterior capsulotomies during cataract surgery in a large cohort of paediatric patients. This will allow investigating the potential impact of posterior laser-assisted capsulotomy on the development of PCO and the need for subsequent Nd:YAG laser treatment.
Visual outcomes
The present study is the first one to report long-term visual outcomes after paediatric cataract with FLA anterior capsulotomy. So far, all the existing studies pertained to the assessment of feasibility of the surgical procedure.
Overall, our results correlate with the previously reported data on unilateral and bilateral paediatric manual cataract surgery. Nyström et al published their results on phacoemulsification and primary implantation of ‘bag-in-the-lens’ IOL in a series of 109 eyes of 84 children with a median age of 2.5 years (range: 2 weeks to 14.1 years) and reported that 37.5% of unilateral cases and 55.6% of bilateral cases attained a postoperative long-term CDVA of 20/40 or better.43 To better understand the correlation between the preoperative age-specific condition of the eye and postoperative visual outcomes, the results in our study were stratified into two groups, that is, corresponding to patients from 0 to 12 months of age, and those older than 12 months. In general, the visual outcomes of the present study for both age groups are in line with previous findings. In a study by Lesueur et al in 165 eyes of 107 children, a mean CDVA of 0.925 LogMAR (20/168) for unilateral cases in patients younger than 7 months of age and 0.322 LogMAR (20/42) for unilateral cases in patients older than 7 months of age were reported. For bilateral cases in patients younger than 7 months, the mean CDVA was 0.425 LogMAR (20/53) and it was 0.206 LogMAR (20/32) for bilateral cases in patients older than 7 months.17 Lu et al presented the visual results of primary IOL implantation in 16 infants (26 consecutive eyes) aged 6–12 months. At last follow-up the mean CDVA for the unilateral cases was 0.98±0.18 LogMAR (20/191) and 0.50±0.14 LogMAR (20/63) for the bilateral ones.44
In a study by Ram et al, mean CDVA in 10 unilateral cases (range: 8–14 years) was 0.49 LogMAR (20/62) 1 year after non-toric IOL implantation.45
In our study, the mean CDVA in unilateral cases younger than 12 months of age was 20/40. This visual acuity result is generally better than previous literature reports on final unilateral cataract visual outcomes in infants. It is to be noted that we only report on four cases and all the four infants were actually younger than 6 months of age at time of surgery. Looveren et al reported in five children (eight eyes, two unilateral cases, three bilateral cases) younger than 6 months of age a mean CDVA at the end of follow-up of 0.32 decimal (20/63).46
One of the study limitations was that no comparison group (standard manual surgery) was included in the analysis. For this reason, the rates of intraoperative and postoperative complications could not be compared between the two methods performed by the same surgeon. In addition, because of the very young age of the majority of our patients, we encountered difficulty in testing and interpreting children’s visual function. The visual acuity results may be affected, among others, by patients’ attention and time of examination. An additional challenge was the examination of the child’s eye, especially during the assessment of a postoperative complication. In young children and in uncooperative children, all ophthalmologic examinations including anterior segment and Fundus examination were performed under inhalation anaesthesia.
In conclusion, the paediatric cataract surgery with laser-assisted anterior capsulotomy using a mobile and compact low-pulse energy femtosecond laser is safe and reliable. In this paediatric case series, the low-energy femtosecond laser offered the benefits of achieving a safe anterior capsulotomy, low number of intraoperative complications as well as significant improvement in CDVA. Although the data presented in this study were collected prior to the European CE approval, the FEMTO LDV Z8 is today the only femtosecond laser on the market indicated for use in paediatric cataract surgery.