Indications for IOL implantation in children have changed dramatically during the past two decades, and I now believe that IOLs should be considered to be the primary means of both monocular and binocular aphakic correction in all children older than 1 to 2 years of age. Some contraindications to IOL implantation in children do exist, and these are discussed here subsequently. The advantages of IOLs over contact lenses and aphakic glasses are significant and as the experience with IOL implantation in children continues to demonstrate its safety, the benefits of the procedure now appear to outweigh whatever concerns still exist over unanswered long-term safety questions. IOLs have essentially become the standard of care in treating aphakia in older children, and their use is becoming more common in infants and young children also.^2,3 The advantages of IOLs include the following:

These advantages are not, however, absolute and are diminished by the need to provide for accommodation with bifocal or reading glasses and to correct residual refractive errors, either at the time of implantation or later, secondary to ocular growth, with glasses alone or combined with the use of contact lenses. Other disadvantages include the nature of IOL implantation as a surgical procedure with the potential for complications and questions regarding long-term safety.

For the optical correction of monocular or binocular aphakia in infants younger than 12 months of age, the contact lens remains the current modality of choice for the pediatric patient because of its safety, optical quality, and, perhaps most important, its ability to be changed in power with growth of the eye. In a study of patients undergoing unilateral IOL implantation before 6 months of age, 8 of 11 eyes had postoperative complications requiring reoperation and significant myopic shifts occurred by 1 year after surgery, which would make overcorrections with glasses or contact lenses necessary.⁴ It is to be hoped that the complication rate seen in this early study of patients undergoing IOL implantation during infancy will decrease with increased surgical experience with the procedure in young infants. A multicenter, randomized, controlled clinical trial comparing the use of IOLs and contact lenses for the treatment of aphakia in infants, the Infant Aphakia Treatment Study, is currently being conducted under the direction of Scott Lambert, MD.

In patients unsuited for contact lens use, an IOL must be used to avoid amblyopia. Few infants are, however, truly intolerant of contact lenses if the resources are available to provide the lenses and if the parents are adequately trained and motivated for contact lens use. Use of monocular aphakic spectacles is not acceptable because of the aniseikonia produced and the physical problem of keeping eyeglasses on an infant’s face. At present, IOL implantation in patients younger than 1 year of age should be approached with great caution.

Children with traumatic cataracts, who are seldom younger than 1 year of age, are frequently found to be poor candidates for contact lens wear because of sensitivity of their eyes after injury, high or irregular astigmatism (although rigid contact lenses are often required in such cases to achieve best optical correction), or psychological resistance after their experiences with the trauma, followed by one or more surgical procedures. IOL rehabilitation should be strongly considered either primarily or secondarily in children with traumatic cataracts in whom the nature of the injury does not produce a contraindication to lens implantation. In cases in which the risk of marked postoperative inflammation, hemorrhage, retinal detachment, or endophthalmitis is high (e.g., lens trauma with release of cortical material and nuclear fragments throughout the AC and vitreous), or in cases with extensive iris trauma or loss of tissue, a prudent surgical decision might be to perform a primary surgical repair and leave IOL implantation to be performed as a secondary procedure if necessary.

An IOL is also the only alternative for the patient with a monocular radiation-induced cataract.⁵ Keratitis sicca associated with a history of radiation therapy is an obstacle to successful contact lens wear. Radiation-induced keratitis sicca may be present at the time of cataract surgery or may develop unpredictably months to years later.

Patients with bilateral cataracts and large-amplitude nystagmus are especially good candidates for IOL implantation. Aphakic glasses are less than optimal in this situation because of the ring scotoma produced by the high hyperopic lenses, and the movement of the eyes may make contact lens wear difficult in some cases. IOLs are also particularly valuable in patients whose behavior makes them poor candidates for glasses or contact lens use. An example is the resistant, combative, or self-abusive, mentally retarded child.

There is a relative contraindication to the use of IOLs in children with chronic inflammatory disease. Although a small series of children with chronic uveitis and IOLs has been reported without any IOL complications,⁶ the investigational nature of pediatric lens implantation suggests the need for a cautious approach. The same logic encourages a cautious approach in aphakic children with glaucoma. Use of an IOL may, however, be advantageous, compared with use of a contact lens, in a patient with a filtration bleb. Use of AC lenses in children with glaucoma is contraindicated, just as it is in adult patients.

Lens implantation is also contraindicated in cases of microcornea, nanophthalmos, or microphthalmia with corneal diameters of less than 9 mm, because of difficulties with lens size. Eyes with corneal endothelial disease must be approached cautiously when considering secondary lens implantation, and AC lenses are contraindicated in these cases.

AC lenses are contraindicated in cases of aniridia, either congenital or traumatic, and in cases in which trauma has left the angle and iris unable to provide support to the lens. AC lenses are also contraindicated in eyes with shallow ACs (e.g., in retinopathy of prematurity). Proximity of an AC IOL to the cornea also makes use of this type of lens unadvisable for patients who are prone to, or cannot be made to understand not to, rub their eyes. This exception applies to many of the very young, uncooperative, or mentally retarded children in whom the use of a contact lens is impossible. PC IOLs are advisable in these situations because of their greater margin of safety for the cornea and AC angle.

The normal newborn eye has a mean axial length of 16.8 mm and a mean keratometric power of 51.2 diopters (D); in adults, the mean axial length is 23.6 mm and the mean keratometric power is 43.5 D. More than half of this growth in axial length occurs before 1 year of age, with slower rates of increase in axial length until 15 years of age.^7,8 The change in mean keratometric power occurs almost completely within the first 6 months of life, with only minor changes after that.⁸ Growth of the eye raises two issues in regard to pediatric IOL implantation: the problem of implanting a lens of fixed haptic size in a growing eye, and the problem of implanting a lens of fixed optic power in a growing eye.

The haptics of modern PC IOLs are flexible, and this allows for some latitude in ocular diameter without problems of tissue erosion and distortion being caused by placing an IOL designed for an adult’s eye in a child’s. This is not true for Kelman-style, four-point [S2]multiflex AC lenses, which must be sized appropriately to avoid chronic pain or tissue erosion from a lens that is too large, or to avoid the later development of lens movement and damage to the iris or angle (or both) caused by a lens that is too small. These lenses are best reserved for patients older than 2 years of age in whom the anterior segment has essentially reached its adult size.

The second problem of implanting a lens of fixed power in a growing eye is more complex. Some authors recommend implantation of IOLs with powers calculated to produce emmetropia at the time of implantation.^9,10,11,12 This strategy results in a myopic shift with ocular growth.¹³ Every 1 mm of increase in ocular length results in approximately 2.50 D of myopic shift. An implant of 28 D producing emmetropia in an 8-month-old infant may very well induce 6 to 7 D of myopia and anisometropia when the child is 3 years of age, necessitating the use of a contact lens to correct the residual refractive error and minimize the resultant aniseikonia. For older children with ocular growth essentially completed at the time of surgery, this plan produces the desired result.

Other authors have advocated implantation of adult-power IOLs (20-D PC IOL or 19-D AC IOL) in young children, presumably allowing the child to grow toward emmetropia.^14,15,16 In a child younger than 2 years of age, and certainly in an infant younger than 1 year of age, this results in significant residual hyperopia in the years following implantation, a condition that must be corrected. In the very young child, this often requires use of a contact lens if a minimization of aniseikonia is to be achieved, defeating the purpose of implantation rather than aphakic contact lens use. Presuming that the eye eventually attains an axial length and corneal keratometric power close to 23 mm and 44 D, the eye ultimately becomes close to emmetropic; in addition, the fellow eye must also be close to emmetropic for anisometropia not to occur. These two presumptions are not true in all cases and may not be true in even most cases.

Ocular growth has many influencing factors, and no study to date provides the information necessary to predict with any certainty how an aphakic or pseudophakic eye will grow. The effect that cataract surgery and aphakia have on the growth of the eye, as well as the effect of the patient’s age at the time of surgery, remains unclear. Wilson et al. in a study examining lensectomized monkeys, reported a shortening of aphakic eyes compared with fellow eyes.¹⁷ In contrast, Rasooly and BenEzra have reported axial elongation with unilateral aphakia in children with congenital cataracts, concluding that this was related to amblyopia rather than aphakia.¹⁸ Axial elongation can be induced in animal models by visual deprivation; however, this association may be less significant in humans than in animals.^19,20 Sinskey et al have presented a case report of a 7-year-old bilaterally aphakic patient who had intermittent contact lens correction in one eye and a PC IOL in the fellow eye.²¹ Both eyes were correctable to 20/20. The axial length of the eye with the contact lens increased compared with that of the pseudophakic eye; the authors proposed that the difference resulted from different visual input quality in the two eyes.

A study reporting the change in aphakic refraction of children with unilateral congenital cataracts showed a decrease in mean spheric equivalent during the first year of life from +30.75 D to +26.36 D, with a less rapid decrease after that; the mean at 2 years was +23.06 D, at 3 years +21.29 D, and at 4 years +20.86 D.²² McClatchey et al have developed a logarithmic model of refractive growth of the aphakic eye showing that the mean refraction follows a logarithmic decline from birth through 20 years of age.^23,24,25 These studies do not address the effect of amblyopia or the role that initial diagnosis (e.g., persistent hyperplastic primary vitreous, microcornea, microphthalmia, among others) may have on the rate of growth.

The refractive status of the fellow eye and familial patterns of myopia or hyperopia are also likely to be factors in growth of the pseudophakic eye. Additionally, virtually no information is available to determine the effect of how cataract surgery is performed (posterior capsule intact, partially removed, completely removed; vitrectomy performed, extensive or limited), or whether the presence of an IOL (in the capsular bag, in the ciliary sulcus, or in the AC) has a role in growth of the eye. Kora et al have studied the effect of IOL implantation on ocular growth in children.²⁶ They found a tendency for the operated eyes to become myopic, without a significant difference in the postoperative increase in axial length in the operated and unoperated eyes. ACs of the operated eyes tended to be deeper. In a multicenter study, McClatchey et al demonstrated that pseudophakic eyes showed a lesser rate of refractive growth than aphakic eyes (-4.6 D vs. -5.7 D). The mean quantity of myopic shift was greater in pseudophakic eyes than in aphakic eyes (-5.26 D vs. -4.54 D) as a result of the optic effects of the change in distance of the IOL from the nodal point of the eye with growth of the eye.²⁵

At present, questions remain unanswered concerning how to best determine what power IOL should be implanted in a young child. This is one of the major obstacles in pediatric lens implantation and will remain so until methods are available for easy and safe modification of the refractive status of the pseudophakic eye, or until implants are available that “grow” as the natural crystalline lens does. For now, the goal in determining IOL power must be to achieve a compromise between providing emmetropia at the time of implantation and providing emmetropia after ocular growth has been completed. Fortunately, most of the ocular growth and resulting “compromise” in IOL power necessary occurs during the first year of life. Beyond the age of 2 years, the clinical significance of potential IOL power problems is reduced.

Although it may be argued that few patients with monocular congenital cataracts develop any great degree of binocular function, promoting the development of at least gross fusion and stereopsis by minimizing aniseikonia is recommended. Minimizing aniseikonia is even more important in patients with developmental or traumatic cataracts so that binocularity can be preserved.²⁸ With these compromise goals in mind, my recommendation for determination of IOL power takes into consideration the age of the patient at the time of surgery, presumed patterns of ocular growth, and the refractive status of the fellow eye.

As already discussed, lens implantation in patients much younger than 1 year of age, who are in a rapid phase of ocular growth, is seldom required and is best avoided if at all possible. For patients younger than 1 year of age, the IOL power is calculated using axial length and keratometric measurements to produce a postoperative refraction of +6.00 D. Many of these patients have hyperopia in their pseudophakic eyes more than 5 D greater than their fellow eyes, and these patients will be required to wear a contact lens or temporary unilateral aphakic spectacles in addition to the IOL for some months until some ocular growth has occurred. For patients between 1 and 2 years of age, postoperative refraction of +4.00 is chosen as the target. Patients between 2 and 4 years of age have lens calculations performed to obtain a spherical equivalent refraction equal to that of the fellow eye, and this resulting lens power is reduced by 1 D to allow for ocular growth. Patients older than 4 years of age receive IOLs with powers calculated to match the spherical equivalent refraction of the fellow eye. In patients older than 10 years of age, lens power is calculated for emmetropia, and adjustments are made to avoid >3.00 D of postoperative anisometropia. Additional adjustments from the calculated lens power are made in all cases if it appears as though the patient has a strong likelihood, based on current refraction and heredity, of developing high myopia or hyperopia. Correction of residual postoperative refractive errors is made with single-vision glasses to produce a net refraction of -2.50 D (for clear vision at near) until 2 years of age and after that with the true refraction for distance and a +2.50 bifocal for both eyes. Hyperopia in the normal phakic eye is undercorrected by 1.00 to 2.00 D. Use of this rough algorithm for IOL power selection is unlikely to lead to a need for IOL exchange or long-term contact lens overcorrection based on unacceptable anisometropia in this author’s experience.

An additional source of error in IOL power selection that is more likely to occur in pediatric patients than in adult patients is inaccuracy in measurement of axial length or keratometric power. Special attention must be made to obtain visual axis measurements of axial length and keratometry in poorly cooperative children or in children who are being examined under anesthesia. A 1-mm error in measurement of axial length results in a 2.50-D refractive error, and a 1.00-D error in keratometry changes the calculated implant power by 0.9 D. In an eye with an axial length of <20 mm, a 1-mm error produces a change of 3.75 D. Errors of this magnitude may easily be made if measurements are off axis. Although the third-generation theoretical formulas are felt to be more accurate in adult patients with shorter eyes, a study comparing the predictive accuracy of four common IOL power formulas (SRK-II, SRK-T, Holladay, and Hoffer Q) in children did not reveal any significant predictive differences between the formulas.²⁹ IOL power prediction may be more prone to error in small eyes (those with axial length <20 mm), and the older SRK formula should not be used in these short eyes as it predicts significant undercorrection.30

All of the typically used IOL power formulas predict IOL powers for lenses placed into the capsular bag. If the IOL is placed in the ciliary sulcus rather than the capsular bag, the power of the lens should be reduced by 1.0 D and for lenses calculated to 28.0D or more by 1.5 D. 31.

With the IOL now being the preferred means of aphakic correction for most patients with cataracts, most patients will now have cataract surgery with primary PC lens implantation within the capsular bag. The exceptions to this are infants younger than than 1 year of age, many patients with lens sublation, and some patients with traumatic cataracts. The major advantages of capsular fixation compared with sulcus fixation of the haptics include placement of the IOL the maximum distance from the cornea, posterior iris pigment epithelium, iris root, and ciliary processes; reduction of iris chafing and pigment dispersion; no contact with the ciliary body, or erosion of lens haptics into the ciliary body; avoidance of chronic uveal tissue chafing with breakdown of the blood-aqueous barrier; and easier explantation if necessary.^32,33 Because of these advantages, every effort possible should be made to place the IOL haptics within the capsular bag rather than in the ciliary sulcus. In cases where the capsular integrity for IOL placement within the capsular bag has been lost during lens aspiration, where zonulysis has occurred secondary to trauma, or in lens subluxation cases alternative placement of the IOL may be necessary.

Procedure decisions in secondary IOL implantation for aphakic patients previously rehabilitated with contact lenses depend on whether capsular support for a PC lens is present. If the cataract surgery has been performed leaving a rim of capsule, secondary implantation of a PC IOL into the ciliary sulcus can be performed without difficulty. In cases in which such support is absent, for example following trauma, a choice must be made between iris suture fixation of a PC IOL³⁴, scleral fixation of a PC IOL, or use of an AC IOL. Although many complications have been described with the use of older AC IOL designs (many of which are the result of poor quality of manufacture), the safety record of the modern flexible, one-piece, all-polymethyl methacrylate (PMMA), open-haptic AC IOL suggests that these lenses are safe and that they may be preferable to sulcus fixation of PC IOLs with iris or ciliary body sutures.^37,35 Both types of lenses have definite advantages and disadvantages, and the answer as to which is best will not be the same for all patients.

AC IOL implantation has the advantage of being technically much easier and faster than suture fixation of a PC IOL. In many cases, secondary implantation of an AC IOL can be performed without any vitrectomy. Suture fixation of a PC IOL requires additional vitrectomy in all patients except those who have undergone extensive vitrectomy already. The presence of iridocapsular synechiae complicates placement of a PC IOL and in many cases greatly adds to the intraoperative manipulation necessary for lens implantation. Implantation of an AC IOL may be performed much more easily in such cases. Removal of an AC IOL is also much simpler than removal of a PC IOL. This advantage may be of particular importance when considering the potential need for lens exchange owing to power inaccuracy.

AC IOLs are contraindicated in cases of corneal endothelial disease, microcornea, distortion of the iris or angle architecture (e.g., trauma, glaucoma), and, perhaps of greatest concern in the pediatric age range, in patients in whom eye rubbing may be a chronic problem. Many of these patients may also be poor candidates for contact lens wear, and suture fixation of a PC IOL may be their only option for aphakic correction.

Suture fixation of a PC IOL to the iris, with the haptics in the ciliary sulcus, has the potential for complications including iris chafing, pigment dispersion glaucoma, and chronic uveitis, but these complications appear to be rare with the use of modern PC IOLs. Suture fixation to the sclera is a technically more difficult procedure entailing much more intraoperative manipulation and potential trauma than implantation of an AC IOL. Passage of fixation sutures carries with it the potential for hemorrhage from the major arterial circle of the iris and the ciliary body. Additionally, the haptics not uncommonly may be located not in the ciliary sulcus but on the face of the ciliary body, with the potential for chronic irritation, erosion, and possible hemorrhage. Knowledge of the anatomy of the ciliary sulcus can increase the likelihood of accurate haptic placement and decrease the potential for problems.^27,36 However, variations in the anatomy of the area occur, with placement of surgical landmarks less than absolute, especially in pediatric patients. Sulcus fixation of a PC IOL does not have any advantage over the use of a modern open-haptic AC IOL in terms of disruption of the blood-aqueous barrier.³³ It is doubtful whether a lens with scleral fixation placed into the sulcus would affect the blood-aqueous barrier any less, and whether it remains equivalent to the AC IOL remains to be determined.

A disadvantage to scleral fixation or iris suture fixation of a PC IOL is the possibility of lens decentration or dislocation. In addition to problems with placement of the sutures causing lens decentration, tilting, or iris chafing complications, potential late loosening or breakage of the suture itself may lead to cases of lens dislocation, because stability of the lens results primarily from the presence of the suture and not necessarily from fibrous encapsulation or ciliary sulcus placement of the haptics.⁸³[KPC3] Evidence also exists for some long-term biodegradation and alteration of polypropylene.³⁷ These are particular concerns in pediatric patients.