Introduction

The child’s eye is unique. Not only does the surgeon dealing with a pediatric cataract need to understand its neurophysiology and anatomy in the here and now, but he or she needs to be able to predict the effect of his/her surgical actions on the phenomenon that is emmetropization and the consequences thereof decades into the future. The surgery itself while extremely important is merely the first step in a long journey; the younger the child the harder that journey is likely to be.

Epidemiologic consideration and terminology

The incidence of pediatric cataract varies from 1 to 6/10 000 live births in Europe. Infant refers to children less than 1 year of age, and pediatric refers to children under the age of 16 years.

Clinical features, diagnosis, and differential diagnosis

Five components are needed to define a cataract: when they appear, the degree to which the opacity occupies the capsular bag, anatomically where in the lens the opacity lies, its etiology, and morphology. Cataracts may present at birth (congenital) or develop through the first few years of life (developmental); they may be total or partial; they may be nuclear (fetal or embryonal), sutural, lamellar, capsular (usually anterior) or subcapsular (usually posterior), or polar (posterior or anterior); they may be inherited or sporadic with the latter including the acquired variety such as infectious (in utero TORCH infections), metabolic (e.g. galactosemia, Lowe syndrome, galactokinase deficiency) or secondary to other ocular conditions (e.g. persistent fetal vasculature, PFV). Morphology of cataracts includes descriptions such as anterior pyramidal, membranous, pulverulent, blue dot, and other specific entities such as anterior or posterior lenticonus. Such specifications sometimes help with systemic diagnoses (e.g. anterior lenticonus should alert the surgeon to the possibility of Alport syndrome) while pyramidal cataracts are often associated with corneal astigmatism1.

It is very important that the parents of all children with cataracts are also examined with dilation of the eyes to exclude an inherited opacity. It is worth noting that an autosomal dominant cataract may express itself phenotypically differently in the same family pedigree.

The differential diagnosis of a pediatric cataract is that of leukocoria. In infants and toddlers this differential includes retinoblastoma, total retinal detachment (stage V retinopathy of prematurity, Norrie disease, and incontinentia pigmentii), large retinochoroidal colobomas, Coats disease and rarely Toxocara granulomas.

Anatomical considerations

The average axial length of an infant is 16.5 mm at birth. There is a rapid growth of the eye in the first 18 months of life with an average growth of 3.75 mm. By 13 years of age the average axial length is 23 mm². Parents often ask if an intraocular implant would have to be removed as the child’s eye grows; this is not so if the implant is placed in the bag. This is because once the lens fibres are removed the bag stops growing. It is therefore important to know that the capsular bag diameter also changes with age. (The capsular bag diameter for the purposes of understanding the dimension available for an implant to be placed is the diameter of the crystalline lens + 1 mm). On average, the capsular bag diameter is 7 mm at birth, 9 mm at 2 years, 9–10 mm at 5 years, 10–10.5 mm at 16 years, and 10.5 mm > 21 years of age2.

Fundamental principles and goals of surgery

There are three important fundamental principles for successful pediatric cataract surgery:

Indications for surgery

Dense bilateral total cataracts are the clearest indication for intervention. Partial cataracts can be more difficult to assess as can lamellar cataracts. In older children (usually over 4 years of age) a glare test should be adopted to see if the child’s visual acuity reduces. For unilateral cataracts controversy exists as to the usefulness of intervention especially when the better eye is unaffected and normal. Nevertheless, this author believes that as long as surgery is performed early (before 8 weeks) for unilateral cases, aggressive amblyopia therapy can lead to some useful vision4. If a child presents late with either unilateral or bilateral cataracts, old photos form younger ages of the child should be examined for ‘red eye’, indicating absence of significant opacity.

If possible a pattern VEP can be very useful to assess deterioration in vision in a preverbal child but access to such tests is usually limited.

Preoperative assessment

The preoperative assessment in children is crucial. A systemic evaluation is necessary to ensure fitness for anesthetic and exclude any health threatening condition, e.g. metabolic disorder. In all cases where the retina cannot be visualized an ocular ultrasound should be performed. Preoperative assessment will also allow surgical planning. If a child has a microphthalmic eye or a capsular bag diameter of less than 8 mm then implantation with a common adult lens (total diameters range from 12 to 13.5 mm) may not be safe. Lensectomy can be considered under such circumstances and capsule sparing techniques can be used for possible secondary implantation when the child is older. Spontaneously dislocated lenses such as those seen in Marfan syndrome may have an implant sutured into the sclera5, but this is not a preferred technique for this author due to the high rates of lens dislocation and displacement.

If an implant is being considered there are several issues to consider. The first is biometry. This can be done awake in older children (usually over the age of 5 years) or under anesthetic immediately prior to surgery. This necessitates a large stock of lens powers. The two most commonly used equations in the United Kingdom for children are Hoffer Q and SRK-T. This author uses the former for axial lengths 20 mm or less and the latter for all other cases. It is worth noting that the Hoffer Q equation relies not on an A constant but on a value called the ACD. This is the predicted anterior chamber depth and the value given by manufacturers is for ADULT EYES and not children. Therefore the surgeon needs to be aware of this before using this equation.

Anesthesia

General anesthesia delivered by a trained pediatric anesthetist is optimal.

Operation techniques

These need to be considered in terms of location of wound, suturing of wound, capsulotomy technique for the anterior and posterior capsules, cataract removal, implant placement, and vitrectomy.

Since there is little evidence at present to suggest that in high risk groups, i.e. children under the age of 1 years, implantation of an IOL has a protective effect against developing glaucoma, this author prefers a corneal approach close to where the limbal vessels reach clear cornea. In this way the conjunctiva is spared in case filtration surgery may be needed for any secondary glaucoma in the future. In children all wounds should be sutured and using 10-0 vicryl the induced astigmatism has been shown to resolve after 6 weeks6.

Capsulorrhexis in children is more difficult than in adults because of the increased elasticity of the capsule and the importance of being able to size the rhexis accurately so that the rhexis opening is smaller than the optic. This is important to prevent lens decentration and forward displacement of the IOL, which may lead to iris/optic capture (Figs 17.1 and 17.2). Therefore many techniques have been developed including diathermy, vitrectorrhexis, and TIPP rhexis (two incision push pull)7 (Fig. 17.3). The former two are unfortunately associated with an increased risk of tears within the rhexis during manipulation8,9. Accumulating evidence suggests that if the posterior capsule is left intact in children under the age of 610, visual axis opacification occurs very soon after surgery especially in children less than 2 years of age. Most authors also perform anterior vitrectomy. This author performs posterior capsulotomy with anterior vitrectomy in all children under 4 years of age; between 4 and 8 years only a posterior capsulotomy is performed and thereafter the posterior capsule is left intact. The rationale is that after 8 years of age most children are cooperative enough to allow YAG capsulotomy awake.

Fig. 17.1 The IOL is securely stable between the anterior and posterior rhexis. This is 5 years post-surgery.

Fig. 17.2 In this case the anterior capsule opening was larger than the optic of the IOL and 3 years after surgery the child was found to have iris/optic capture.

Fig. 17.3 Anterior capsulorrhexis using the TIPPrhexis technique is shown using a micro-capsulorrhexis forceps. Note the use of micro-instruments allows smaller wounds to be made.

The technique of posterior capsulotomy also varies. The approach can be anterior or pars plicata/plana. In infants with axial lengths of less than 20 mm, it is usually easier to place the implant in the intact bag and then close the wound and fashion a pars plicata entry into the vitreous to perform posterior mechanical capsulotomy and anterior vitrectomy. It is worth noting that with an anterior approach it is important to keep the anterior hyaloids face intact until vitrectomy is done if planned; this avoids traction on the vitreous face, which may transmit to the vitreous base and can predispose to retinal detachment7. To this end it is worth remembering that Berger’s space is a potential space about 3.5–4.5 mm in diameter. This space can be expanded with viscoelastic to push the anterior hyaloids to face posteriorly.

The pediatric lens is very soft and can almost always be aspirated. Sometimes calcific components can be difficult to aspirate. During lens aspiration it is important in opaque lenses to aspirate the peripheral lens matter first before taking the central nucleus in case there is a posterior defect. If this is present and the central nucleus is taken first, there is a risk of vitreous traction when the peripheral lens matter is aspirated (Fig. 17.4).

Fig. 17.4 Bimanual technique is used to aspirate the lens.

Placing the implant is an important part of the technique. If there is a posterior capsulotomy already present, it is important to place the trailing haptic into the bag and not rotate the IOL to avoid posterior migration into the vitreous of the implant, especially in children less than 4 years of age. Viscoelastic can be left in the eye if necessary to stabilize the implant; if this is done Acetazolamide (4–7 mg/kg q.i.d) is needed for 2 days. Wherever possible it is important to place the IOL in bag and not the sulcus (Fig. 17.5), but of course there are exceptions such as secondary IOLS. In this latter case one piece rigid PMMA implants are more stable than three piece hydrophobic acrylic implants. Posterior capsule optic capture is favored by some authors; this technique is very useful if for some reason the anterior rhexis has a tear or if the child has aniridia and there is a worry about the size or stability of the anterior rhexis.

Fig. 17.5 This is an infant sent for a second opinion after developing glaucoma. The implant was placed in the sulcus. Note the haptic in the sulcus (white arrow) and the iris root pushed forward and in apposition to the trabecular meshwork (blue arrow).

Removing viscoelastic when a posterior capsule opening is present should also be done very carefully. Reduce the bottle height and, if using a bimanual technique, enter the anterior chamber with the aspirating port first to avoid increasing the anterior chamber pressure so much that the IOL is displaced through the posterior opening. This author avoids removing viscoelastic from under the IOL, especially in children under 4 years of age, because the IOL can flip into the posterior segment by the sudden movement of viscoelastic from beneath the IOL into the aspiration port. Acetazolamide should be used as described above but usually only for 1 day if the anterior chamber, anterior to the IOL is evacuated.

Subconjunctival steroid and antibiotic should be used. Intracameral antibiotic may be used instead of the subconjunctival route. Orbital floor triamcinolone should be used in all cases considered to be at high risk for inflammation.

Intraoperative complications

Careful manipulation of tissues avoids most complications. However, in children the iris can prolapse; this is usually because the child is not anesthetized deeply enough. Make sure the pCO₂ is 4 or below – talk to the anesthetist. Anterior capsulorrhexis can be complicated by tears out to the equator; a macroscopically circular opening may tear during manipulation. Anterior chamber trampolining, i.e. sudden fluctuation in anterior chamber pressure, has been reduced with bimanual techniques but the anterior chamber may still flatten while operating. This is injurious to the endothelium; check that the irrigation is not blocked or that the fluid has not finished. Also try not to lift the anterior lips of your wounds – press down on the posterior lips of the wounds to deepen the anterior chamber. Lens aspiration or lensectomy with the vitrector done carefully should not result in inadvertent pupil sphincter damage. Small pupils can be opened with iris retractors. If inadvertent pupil damage and bleeding occur then intraocular diathermy should be used to stop bleeding if it persists. Leaving too much blood in a young eye invariably leads to fibrin formation and synechiae.

Posterior capsulotomy may result in an opening too large for safe in the bag implantation of an IOL. IT IS REALLY IMPORTANT THAT AN IMPLANT IS NOT PLACED IN THE SUCLUS OF VERY YOUNG CHILDREN (see Fig. 17.5). It is safer to leave the eye aphakic and place a secondary implant 6 months later. Counseling parents preoperatively of this eventuality will save a protracted and anxious discussion after the event.

Postoperative care

Topical steroid/antibiotic drops are given hourly for 24 hours during waking hours with ointment at night. A dilating drop is also given three times daily initially. All drops are tailed off over 4–5 weeks. Rarely fibrin clots may form and if very dense these can be cleared with TPA (recombinant tissue plasminogen activator).

Refraction should be performed within the first week and the younger the child the greater the impetus to give refractive correction even if it is spherical equivalence. REMEMBER a child under the age of 4 years is rarely interested in the world beyond the reach of its arms; therefore these children should be given an over-correction to leave their focal length at about to a metre. Older children need bifocal prescription with a +3. Add to the distance prescription.

In cases of unilateral cataracts, or bilateral cases where vision is better in one eye, appropriate amblyopia therapy is ESSENTIAL. Without this the operation may as well not have been done in children under the age of 10 years.

Postoperative complications

These include inflammation, posterior capsular or visual axis opacification, and deposition of pigment on lens, lens/iris capture, lens decentration, retinal detachment, vitreous wicks, and glaucoma.

The advent of microsurgical techniques and better implants has led to a decrease in inflammation, and pigment deposition. Despite posterior capsulotomies with or without anterior vitrectomy, visual axis opacification may still occur. Retinal detachment can be avoided if the techniques discussed above are adhered to. The major complications in terms of lifelong risk are aphakic and pseudophakic glaucoma. Rates of this vary depending on which study is alluded to. While there is some evidence of a protective effect with primary implantation, it is by no means unequivocal. This means that all children who have undergone cataract surgery especially under the age of 4 years should be monitored for the development of glaucoma.

Assessment of surgery: self-evaluation; result of surgery

This is perhaps the most important part of the whole process. Visual outcome, presence of complications, and successful visual rehabilitation are, by the time the child is 8 years and above, the only valid assessments of outcome.