Intraocular lens (IOL) implantation has become the standard of care for the optical rehabilitation of children with cataract from the toddler age group and up. The use of IOLs in the infant age group, however, remains controversial. Factors that make the use of IOLs less optimal in infants than in older children include surgical challenges, higher complication rates, future ocular growth with less predictability of ultimate refractive error, and affect on amblyopia treatment. To their advantage, IOLs represent a low-maintenance, optically superior option for any age group. This article outlines the broad challenges and factors the physician should consider before implanting IOLs in infants with cataract.
Compared to the eyes of older patients, infant eyes are smaller with more compact anterior segments. The sclera is much softer, the anterior capsules are much more elastic, and the posterior capsules are frequently incompetent such as in persistent fetal vasculature (PFV) and posterior lenticonus.
Newborn corneal diameters can be in the range of 9-11 mm and even smaller with significantly microphthalmic eyes. Eyes harboring nuclear cataracts and PFV, the 2 most common types of congenital cataracts, are always smaller than the normal eye. Axial lengths are frequently in the 16-17 mm range.
The infant sclera has yet to take on the rigid characteristic of that found in adults and older children. The eyes are easily collapsible, and the intraoperative fluid dynamics are critical to avoiding intraoperative complication.
Anterior capsule characteristics
The anterior capsules of infants are much thicker and more elastic than those of older patients. The forces required for tearing a capsulorrhexis must, therefore, be stronger and directed more radially to achieve the intended circumferential tear. Infant cataracts are also often quite opaque, making visualization of the capsule more difficult. A mechanized capsulotomy (vitrectorrhexis) can be employed in such cases.
Posterior capsule characteristics
Posterior capsules in infants frequently opacify quite rapidly over the course of weeks or months if left intact. Therefore, all infant cataract surgeries must be accompanied by a primary capsulectomy with anterior vitrectomy. Many experienced pediatric cataract surgeons prefer to approach the posterior capsulectomy/vitrectomy through the pars plana after the cataract has been removed, and the IOL is placed in the capsular bag. Persistent fetal vasculature cataracts are typically associated with a thick, vascularized posterior capsular membrane that must be excised. This may require intraocular scissors. Posterior lenticonus-type defects are always associated with a weakness of the posterior capsule, making handling of the lens more challenging. Manipulation of the posterior capsulectomy and vitrectomy introduces an additional source of potential complication when compared to cataract surgery in older patients.
Higher Complication Rates
Studies have shown that the complication rates in infants undergoing cataract surgery with IOL implants are higher than surgeries on infants without IOL implantation. The most common complication is a re-opacification of the visual axis with proliferated cortical lens fibers. When no IOL is placed in the capsular bag, this proliferation of lens epithelial cells typically results in the formation of a Sommerring ring where the proliferated cells are sequestered out of the visual axis. Placement of an IOL in the capsular bag prevents the leaflets from fusing, and the reproliferated lens cells are free to migrate across the surface of the IOL. Although surgical aspiration of these cells is not difficult, 40%-80% of infants must return to the operating room in the first few months following cataract surgery.
Other potential complications include pupillary membrane formation from excessive inflammation and complications related to handling of the vitreous and glaucoma. The rate of glaucoma in infants undergoing IOL implantation has not been shown to be significantly different from infants undergoing cataract surgery without IOL implantation.
Unpredictable Refractive Growth
Several studies have shown the inevitable myopic shift throughout the first and second decades in children undergoing IOL implantation. This shift becomes more predictable and lesser in magnitude with advancing age at the time of surgery. In a few studies to date, the only consistent finding of refractive change after IOL implantation in infants is that it is unpredictable. The myopic change in the first decade can be anywhere from a few diopters (D) to 12-15 D or more. This unpredictability leads some authorities to question whether it would ultimately be better to wait until the child is at least several years old prior to implanting the IOL.
Amblyopia remains the largest obstacle to surmount in the battle to obtain an optimal visual result, especially when the cataract is unilateral. Controversy exists in regard to what the preferred, immediate, postoperative goal should be. Most authorities subscribe to the theory that the implant power should be that which would be best for the patient when fully grown. In order to achieve this, the infant must initially be made significantly hyperopic with the hopeful expectation that the hyperopia will become negligible by the end of the second decade. This scenario requires that the child wear spectacles from a very early age, and that changes in refraction are corrected by updating the spectacle power when needed.
Another school of thought suggests that the amblyopic child should be left with little or no residual refractive error at the time of initial surgery on the theory that this will promote more effective amblyopia management. The shortcoming of this strategy is that the infants will soon change from their initial refractive error, meaning that glasses will be inevitable in a short amount of time. In addition, pseudophakic children need a bifocal lens to promote near tasks such as reading. Multifocal lenses should play no role in young children whose refractive errors are still changing.
The Infant Aphakia Treatment Study
The Infant Aphakia Treatment Study (IATS) was designed to provide a scientifically valid answer to the question of whether implantation of IOLs in infants is desirable. This multicenter national study funded by the National Institutes of Health (NIH) began enrolling patients in January 2005. As of this writing in March 2007, the study is ahead of pace and on track to complete enrollment by mid-2008. The infants enrolled all have unilateral, congenital cataracts that were operated on when they were less than 6 months old. They have been randomized to receive either an IOL at the time of implant surgery or more conventional cataract surgery without an IOL. The latter group will be fitted with an aphakic contact lens.
The infants in this study will be operated on under a strict study protocol that involves careful video assessment of all surgeries by the IATS’s steering committee, and they will be followed closely for up to 5 years. Assessment of treatment outcomes will include optotype visual acuity, complications, myopic shift, and measurement of the level of parenting stress associated with each study arm.
Summary and Conclusion
Ultimately, the decision whether or not to implant an IOL in an infant comes down to weighing the factors in favor of implantation against the factors in favor of aphakia. Some of the advantages of an implanted IOL are that it can most reliably be placed in the capsular bag at the time of the original surgery, where it will remain in place unlike contact lenses which are more prone to loss. The IOL can also provide superb optics, and it requires no handling by the patient or the patient’s parents. On the other hand, infant pseudophakia with residual hyperopia requires nearly constant spectacle correction, and the predicted refractive outcomes may not be realized when the child is fully grown. IOL implantation may also be associated with a higher complication rate. Until the results of the IATS are made available, it seems reasonable to conclude that the optimal method of optical rehabilitation for an infant undergoing cataract surgery remains unknown. Surgeons contemplating cataract surgery in infants should, therefore, consider all the above factors before recommending IOL placement in infants.
The author states that he has no financial relationship with the manufacturer of any product discussed in this article or with the manufacturer of any competing product.