This prospective case series study showed the efficacy (efficacy index value of 1.18 ± 0.3), safety (safety index value of 1.09 ± 0.24), and long term stability of Visian ICLs for correcting pediatric myopic anisometropic amblyopia in cases of unilateral high myopia and non-compliance with the conventional treatment modalities. To date, the present study comprised the largest number of pediatric patients who implanted an ICL for correcting anisometropic amblyopia, and it is also the first study to document this long follow up interval that reached up to 54 months. Thus, the present report validates the use of Visian ICLs in young children and teenagers without concerns about their long-term refractive stability or about the development of long-term complications.
Our studied population included cases of unilateral high myopia. This population was shown to be more prone to develop anisometropic amblyopia, even with trials of conventional treatments with spectacles, contact lenses, and occlusion therapy.17
For all candidates included in the present study, the cylindrical component did not exceed 3 D in the operated eye and the difference in the cylindrical component between both eyes was no more than 2 D. We excluded patients having higher cylindrical errors that would require toric ICLs for correcting this high astigmatism, assuming that the corneal toricity will change along the time and thus implanting a toric ICL at this young age would possibly require a secondary exchange within few years. Even though our enrolled patients had relatively low cylindrical values, the patients who were left postoperatively with a visually-significant cylinder were corrected by spectacles, especially that this study aimed at correcting the anisometropic amblyopia rather than attaining glass independence for the candidates.
Implantation of PC-pIOLs in children for preventing and treating anisometropic amblyopia can be considered as a preferable technique by many surgeons, and also, after proper counselling, by many parents. This can be attributed to the efficacy and safety of the procedure in restoring the visual performance, the lack of post-operative noxious precautions which are encountered with the corneal refractive surgeries (especially with the younger ages), the significantly lower risk of endothelial cell loss than the AC-IOLs (especially with the inevitable eye rubbing in children), the unbreaching of the corneal architecture (allowing for future successful corneal refractive surgeries if needed), and the reversible nature of the technique (if needed).18
The enrolled pediatric cohort in the present study did not experience post-operative complications. Lack of surgical experience and an improper vault size are the two main reported risk factors for a higher incidence of developing pediatric secondary cataract (in cases with low vaults) or pupillary block glaucoma (with high vault values) following the surgical intervention.18 Yet, it is noteworthy that the complications related to the improper ICL vault were more frequently encountered with the older ICL models. The newer model ICLs (V4c used in this study as well as the newer model V5) include a central port which greatly minimizes the risk of either cataract development or pupillary block.19 The absence of the two aforementioned risk factors in our study may clearly explain the absence of post-operative complications in our recruited patients.
In our studied pediatric population, the mean vault value was within the normal ranges and towards the higher normal values. A relatively higher value for the pediatric ICL vault has been advocated, considering the expected progressive reduction of the central vault over time with the slow (yet steady) axial growth of the crystalline lens over the years. That is why higher vault values (within the normal ranges) can be more preferable for younger age groups.20
Worthy of mention is that the compliance with the occlusion therapy was poor for most of the pediatric cohort, which has also been reported in previous studies.21,22 This can be attributed to many factors, including mainly skin irritation, poor cosmetic appearance, lengthy treatment periods, and the stress suffered by the child and his parents. These factors make the occlusion therapy difficult to achieve and more likely to be abandoned or applied considerably less than required. This validates the use of the ICLs at an early phase if the conventional therapy is ineffective, so as to avoid the occurrence of anisometropic amblyopia.
The parents of the pediatric cohort reported improved physical and social activities within a short period of the ICL implantation. These short-term enhancements cannot be attributed to simple maturation of the children that requires longer time intervals, so we can attribute these improvements to the better visual performance following the ICL implantation.
Previous studies reported the outcomes of implanting iris-fixated ICLs for correcting pediatric anisometropic amblyopia. Though the visual outcomes were satisfactory, some complications were documented, including progressive endothelial cell loss with eye rubbing (that is mostly uncontrollable with younger ages) and iris chaffing. Furthermore, the relatively short follow up intervals render the results of these studies unreliable for the true evaluation of the possible consequent complications.20,23−28
To the authors’ knowledge, few case series studies were conducted on implanting PC-pICLs for myopic anisometropic children. All these studies recruited a fewer number of children than the present study, and the follow up ranges were shorter. Table 2 displays the clinically relevant results of these studies, which are collectively in accordance with our study results in validating the stability and the absence of significant complications after implanting PC-pICLs.29–33
Table 2
Summary of the clinically-relevant data of the previous studies performed on the implantation of Posterior Chamber Visian Intraocular Collamer Lenses (ICL) for pediatric cohorts.
Authors | Year | Number of eyes | Range (mean) of age (years) | Mean Preoperative Unaided Distance Visual Acuity | Mean Preoperative Corrected Distance Visual Acuity | Mean Preoperative Spherical Equivalent | Mean ICL power | Mean Post-operative Unaided Distance Visual Acuity | Mean Post-operative Corrected Distance Visual Acuity | Mean Post-operative Spherical Equivalent | Follow Up Period (months) |
Elmassry et al. | 2017 | 12 | 2–15 (8) | 0.9 | 0.4 | -11.28 | - | 0.0.3 | 0.1 | -1.82 | 12 |
Zhang et al. | 2016 | 11 | 5–17 (11) | 2.15 | 1.5 | -15.34 | - | 0.95 | 0.75 | -0.92 | 8 |
Lesueur and Arne | 1999 | 5 | 3–16 (9) | - | - | –12.8 | -15.5 | All gained lines | All gained lines | + 0.5 | 11.8 |
Alio et al. | 2011 | 11 | 2–15 (8) | 1.1 | 0.84 | -10.14 | - | 0.65 | 0.36 | -1.16 | 60 |
TYCHSEN et al. | 2016 | 40 | 2–17 (10) | 1.72 | - | -9.2 | - | 0.48 | - | + 0.56 | 15.1 |
BenEzra et al. | 2000 | 3 | Reported as individual cases (9,14, and 18 years old), and all showed improvements in the visual performance. |
We also performed a subgrouping for the enrolled cohort that was based on the refractive condition of the fellow eye. This aimed to declare whether the eyes with low myopia in the fellow eye had a more favorable visual prognosis along the follow up visits than those with emmetropia in the fellow eye, assuming that the amblyopic eye will be favored from the refractive aspect after the ICL implantation. Although our study did not show significant differences between the two groups, we believe that these results should be negated or reinforced by future studies performed on larger cohorts and having a more equivocal number of patients in both groups (as the eyes in group 1 with low myopia in the fellow eye represented 39.5% only of the enrolled patients).
In our studied cohort, specular microscopy was not performed for the patients. Previous reports have documented that PC-pICLs are much safer on the corneal endothelium than AC-IOLs.18 Even though we do not expect a significant compromise for the corneal endothelium by the implanted ICLs, further studies may reassure this by performing specular microscopy along the follow up periods. Moreover, future longitudinal studies for even longer follow up intervals are advocated to more robustly declare the refractive stability and the safety of the Visian ICLs. Besides, highlighting the impact of improving the visual performance on the binocular vision is recommended in the upcoming studies.