Despite the continuing threat of amblyopia, in children, the prognosis for a good visual outcome after cataract surgery has improved dramatically over the past two decades. Not only has there been an increased understanding of the sensitive periods for the development and reversal of amblyopia, but also, surgical techniques used during cataract removal have improved and there are advances in optical correction of the remaining aphakia.1 However, cataract surgery in children remains complex and challenging. Achieving a consistently good visual outcome from the treatment of childhood cataracts is difficult even for the most talented and diligent ophthalmologist. A primary reason for inconsistent visual outcomes that result from cataract removal in children is that, unlike the treatment of adult cataracts, the timing of cataract surgery in children is paramount. In fact, the timing of surgical intervention affects visual results in children to a much greater extent than the surgical technique or method of optical correction utilized by the surgeon. 2
In a young child, a cataract does not merely blur the image received by the retina, it also disrupts the development of the visual pathways in the central nervous system.3 Therefore, cataract surgery in young children cannot be viewed purely as a technical problem and an end unto itself. Rather, it is an integrated component of the treatment of amblyopia.
Childhood cataracts represent the major preventable cause of lifelong visual impairment.4 The incidence of cataracts during infancy have been estimated as high as 6 per 10,000 births.3 Approximately 45% of these cataracts are unilateral; the remainder are bilateral. However, the total incidence of cataracts in childhood is several times greater than this estimated figure due to the effects of trauma, metabolic disorders, radiation treatment, and the need for corticosteroid medications in some children. Also, a seemingly expanding number of families manifest autosomal dominant transmission of acquired lamellar cataracts, which most frequently occur in the toddler and preschool years.
Work by Birch and Stager5 has shown that the critical period for surgical treatment of dense unilateral congenital cataracts is from birth to 6 weeks of age. While they found no prognostic advantage when surgery was performed before 6 weeks of age, the chances for good visual acuity (better than 20/80) began to lessen after this age. When bilateral dense congenital cataracts are present, permanent sensory nystagmus occurs if surgery is delayed beyond 3 to 4 months of age. Partial cataracts and cataracts acquired after infancy present a greater difficulty regarding determining the proper timing for surgery.
When a child beyond infancy presents with dense, central opacity of uncertain duration and Snellen visual acuity cannot be accurately measured, surgery is indicated within a few weeks of detection. Partial cataracts are sometimes managed initially with nonsurgical methods. A trial of patching may be indicated if the level of visual loss seems disproportionate to the density and size of the cataract. Pharmacologic dilation of the pupil may be helpful as an adjunctive or temporizing treatment.
Surgical removal of a partial or moderately dense cataract in a literate child is usually indicated when the cataract reduces the Snellen visual acuity to 20/50 or 20/60. However, individual judgments must be made based on documented progression of the cataract and the child's visual functioning, visual needs, and expected best visual outcome. In addition, evidence of abnormal axial elongation associated with a moderate or severe cataract should prompt surgical intervention. This disruption of emmetropization results from "deprivation of form vision." Abnormal eye growth often accompanies amblyopia but has also been demonstrated in its absence.6,7
Surgical Intervention: Historical Perspective
In 1957, Costenbader and Albert8 stated that they had not seen a single child who benefited by the removal of a congenital cataract. The risk of thick secondary membranes, glaucoma, and corneal decompensation after multiple surgeries was so high that surgical aggressiveness seemed ineffective. Even if the visual axis could be maintained, dense deprivation amblyopia, secondary to late initial intervention, usually robbed the infants born with unilateral fetal nuclear cataracts of any useful vision. Children affected bilaterally inevitably developed sensory nystagmus and legal blindness. Some surgeons resorted to optical iridectomies for these fetal nuclear congenital cataracts to avoid the inflammatory response and membranes that developed when the lens was entered.
The advent of vitreous suction cutting devices in the mid-1970s revolutionized pediatric cataract surgery. In 1976, Parks and colleagues began cautiously removing the center of the posterior capsule and a portion of the anterior vitreous during the initial cataract surgery in young children with the help of the new automated devices.9,10 The investigators used the new lensectomy to operate on the posterior capsulectomy and anterior vitrectomy of 23 infantile eyes; none of these eyes required reoperation. In contrast, 32 reoperations were needed in 28 eyes following lens aspiration alone.
By the mid-1980s, the transition to mechanized lensectomy and vitrectomy for young children undergoing cataract surgery was complete. Unfortunately, many surgeons in the developing world are still facing the high complication rates seen in the 1950s in the United States and Europe. Until vitreous suction cutting devices are made available to centers in these locations, young children will not benefit from the improvements in prognosis produced by this automation. A recent study from India demonstrated the need for a vitrectomy even in children 5 to 12 years of age, despite using modern techniques such as optic capture of the IOL through a posterior capsulorrhexis.11
The second major revolution in the treatment of childhood cataracts has been the introduction of the IOL. Although Choyce placed an IOL in the eye of a child after traumatic cataract surgery as early as 1956,12 IOL implantation in children did not become routine until the 1990s.13,14 Currently, IOLs are widely used for children beyond their first birthday. Preliminary results of the study of unilateral congenital cataracts indicate that IOL implantation in the first 6 months of life may produce better visual acuity but at the expense of a higher risk complications.15,16
Many adult cataract surgery techniques, such as clear corneal incisions, hydrodissection, foldable IOLs, and manual curvilinear anterior (and posterior) capsulorrhexis, have been applied to children beyond the age in which amblyopia occurs. In addition, new techniques designed specifically for children, such as posterior optic capture, vitrectorhexis, and pars plana pseudophakic posterior capsulectomy, have been introduced.
Anesthesia
General anesthesia is required in young
children. During the surgery, if the level of anesthesia changes to a lighter
plane, the Bell's phenomenon will become active. For this reason, a 4-0 silk
traction suture beneath the superior rectus muscle is recommended. Also,
because the keratometry and globe axial length measurements will often be
possible only after the child is under general anesthesia, a consignment of
IOLs is needed to avoid two separate anesthesias (one for the IOL calculations
and another for the surgery after the necessary IOL has been ordered and
received). Lastly, because Valsalva maneuvers and coughing are common during
the awakening from general anesthesia, secure suturing of wounds is important
in children even when leakage seems minimal at the conclusion of surgery.
Incisions
Wound configurations that are
self-sealing in adults will often leak when used in children. Children have
thinner and less rigid sclera and the corneal tissue is less likely to
self-seal in children. Also, children tend to traumatize their eyes more often
than adults in the early postoperative period. Synthetic, absorbable 10-0
sutures are recommended. If a rigid IOL is implanted, a scleral tunnel wound is
usually used. For foldable IOL insertion, either a corneal tunnel or a scleral
tunnel can be used. While the temporal wound location presents the same
advantages in children as it does in adults, the location is more easily
traumatized. Children do not usually have deep-set orbits and an over-hanging
brow. Therefore, the superior approach is easier in children than in adults.
This approach allows the wound to be protected by the brow and the Bell's
phenomenon in the trauma-prone childhood years.
Viscoelastics
Viscoelastics are often referred to
as ophthalmic viscosurgical devices (OVDs) because their intended surgical role
is viscosurgery. A viscoadaptive, such as Healon 5 (Pharmacia Corporation), or
a super viscous OVD, such as Healon GV (Pharmacia Corporation) is recommended
for pediatric cataract surgery to facilitate the difficult intraocular
manipulations that must be performed. These OVDs are cohesive, help maintain
anterior chamber stability, and help offset the low scleral rigidity and
increased vitreous upthrust found in pediatric eyes. In special situations
(e.g., a compromised endothelium), it may be helpful to also use a lower
viscosity dispersive agent, such as Viscoat (Alcon Laboratories) in combination
with the cohesive OVDs. Cohesive OVDs are also indispensable for secondary IOL
implantation in aphakic children. The viscoelastic substances help to dilate
the poorly functioning pupil and reduce the trauma of releasing extensive
posterior synechiae.
Anterior Capsule Management
The anterior capsule is
highly elastic in the pediatric patient and poses challenges in the creation of
a capsulotomy. Although a manual continuous curvilinear capsulorrhexis (CCC) is
ideal for adults, it is more difficult to perform in young eyes. However, this
procedure is still the gold standard because it resists tearing once completed
successfully.17 Because of the increased elasticity of the pediatric
anterior capsule, more force is required when pulling on the capsular flap
before tearing begins. Control of the capsulectomy and prevention of extensions
out toward the lens equator are inversely related to the force needed to
generate the tear. As a result, inadvertent extensions out to the lens equator
(known as a runaway rhexis) are common in children. When performing a manual
CCC in a child, the following technical recommendations are offered:
Although a CCC is a reasonable option for children older than 2 years of age, it is difficult for a surgeon to attempt on an infant eye. Vasavada and Chauhan failed to create an intact CCC using manual techniques in 80% of infants on whom this technique was attempted.18 Alternative anterior capsulotomy methods as discussed below will be more consistently successful than manual CCC in infants.
A mechanized circular anterior capsulectomy has been tested in both laboratory and clinical settings.19,20 This vitrectorhexis technique has been proven to be an effective alternative for CCC, which may be difficult to control in young children. This technique is best performed using a vitrector tip attached to a Venturi pump irrigation/aspiration (I&A) system. Peristaltic pump systems do not cut the capsule as efficiently as the Venturi pump mechanisms. The capsulotomy does not need to be started with a bent needle cystotome. Rather, the vitrector tip is placed through a tight fit stab incision made at the limbus using an microvitreoretinal blade. Irrigation is usually provided with a blunt tip irrigating cannulae through a separate stab incision.
A cut rate of 150 to 300 cycles per minute is recommended. The cutting port is oriented posteriorly and the center of the anterior capsule is aspirated up into the cutting port to create an initial opening. Any nuclear or cortical material that spontaneously exits the capsular bag anteriorly is aspirated easily without interrupting the capsulectomy technique. The capsular opening is enlarged using the cutter in a gentle circular fashion. The cutter remains just anterior to the capsular edge, aspirating the capsule up into the cutting port rather than engaging the capsular edge directly.
Visualization of the capsular edge during enlargement of the capsulectomy is excellent because the aspirating capability of the vitrector continuously removes lens cortex as it enters the anterior chamber. Also, this technique can be easily performed even when the cataract is white and mature. A smooth, round capsulectomy can be produced, which resists radial tearing. The more elastic the anterior capsule, the smoother the edge of the vitrectorhexis appears. The vitrectorhexis technique works best in young patients in whom the manual CCC is more difficult. The vitrectorhexis is less ideal in an older child because the capsule elasticity begins to approach that of an adult capsule. In these older children, the vitrector edge appears more scalloped and tears easily. However, the manual CCC is easier to complete successfully in an older child whose anterior capsule is more adult-like. For the surgeon, it is most advantageous to perform a vitrectorhexis in young children and a manual CCC in older children.
A third option for creating an anterior capsulotomy in a child is through the use of high frequency endodiathermy. The Kloti radio frequency endodiathermy has been fit with a 0.6-mm diameter handpiece and tip designed for anterior capsulectomy. A high frequency modulation (500 kHz) signal is delivered with amperage and voltage preselected and fixed within the unit by the manufacturer. A low mean energy is delivered, which minimizes the cutting energy and decreases heat generation. The base of the needle tip is placed in contact with the anterior capsule as the tip is activated by pressing the foot pedal. The surgeon controls the capsulectomy size and shape as the tip is moved along a circular path. Gas bubbles form as the capsule is cut, but they do not usually interfere with visualization of the capsulectomy edge. The procedure is performed under viscoelastic. The capsule edge tends to roll up slightly, which creates a larger capsulectomy than initially cut with the instrument tip. Studies have found no damage to corneal endothelial cells. Recent studies using adult cadaver and pig eyes have found the radio frequency diathermy capsulectomy edge to be less extensible when compared to an edge formed by manual CCC.21-24 The Fugo Blade has also been recently introduced as a radiofrequency unit that can be used to perform an anterior capsulectomy.25
Lens Substance Removal
Pediatric cataracts are soft
but can be somewhat "gummy." Phacoemulsification is rarely, if ever, necessary
in children. Because the anterior chamber may be unstable in these soft eyes,
phacoemulsification may even be hazardous. Lens cortex and nucleus are usually
aspirated easily with an I&A or vitrectomy handpiece. With the vitrector,
bursts of cutting can be used intermittently to facilitate the aspiration of
the more "gummy" cortex of young children. Hydrodissection is not as
consistently performed in children as it is in adults. Further study is needed
to accurately define whether hydrodissection is as beneficial in pediatric eyes
as it has proved to be in adult eyes. A recent study reported a reduction in
operative time and the amount of irrigating solution used when hydrodissection
was performed in pediatric eyes.26 Whatever handpiece is used, a
complete removal of cortical material is desired. Even if a primary posterior
capsulectomy is planned, removal of all cortical material will result in less
inflammation and potentially less cortical reproliferation. Despite meticulous
removal of equatorial lens epithelium, a Soemmering's ring will form in most
children after surgery. The quantity of new cortex making up the Soemmering's
ring seems to be inversely related to age at the time of surgery. Although this
reproliferated cortex usually remains trapped within the Soemmering's ring, it
can occasionally escape from within the capsular remnants and appear in the
central pupillary space. This complication is more common when surgery is
performed in the first year of life and also when an IOL has been placed.
Reproliferated cortex is easily aspirated at reoperation.
Primary IOL Implantation
A consensus exists that
IOL implantation is appropriate for most children older than 2 years of age
undergoing cataract surgery.4,13,27 In contrast, the advisability of
IOL implantation in infancy is still being questioned.28 The
majority of the eye's axial growth occurs during the first 2 years of
life.29 This rapid eye growth makes selection of an IOL power for an
infant difficult. In addition, increased tissue reactivity and decreased
scleral rigidity make IOL implantation more technically challenging in infants
as compared with older children or adults. Despite these complexities, IOLs are
being implanted in infants with increasing frequency. A higher reoperation rate
and an uncertain visual benefit from the primary IOL implantation have made
primary aphakia a commonly used alternative when cataract surgery is performed
in the first year of life.15,16,30
Primary IOL implantation is no longer controversial when surgery is performed in children older than 2 years of age. In-the-bag implantation is strongly recommended for children. Care should be taken to avoid asymmetrical fixation with one haptic in the capsular bag and the other in the ciliary sulcus. Asymmetrical fixation can lead to decentration of the IOL. In contrast to adults, dialing of an IOL into the capsular bag can be difficult in children. Often, the IOL will dial out of the capsular bag rather than into it. This tendency can be blunted somewhat by the use of highly viscous OVDs. Currently, foldable acrylic IOLs are used commonly in children. Some surgeons still prefer PMMA IOLs in children because of their proven track record. Recent studies have recommended the heparin surface modified variety of PMMA IOLs to reduce the incidence of posterior synechiae and lens deposits. The AcrySof acrylic IOL (Alcon, Ft. Worth, Texas) has been shown to be biocompatible for a child's eye.31 While silicone IOLs are infrequently used in children, the second-generation silicone material appears to be an acceptable alternative for older children.32 When capsular fixation is not possible, sulcus placement of an IOL in a child is acceptable. To avoid decentration, rigid PMMA IOLs, as opposed to foldable IOLs, are recommended when sulcus fixation is anticipated.
Secondary IOL Implantation
The majority of children
undergoing secondary IOL implantation have had a primary posterior capsulectomy
and anterior vitrectomy.33 If adequate peripheral capsular support
is present, the IOL is placed into the ciliary sulcus. Viscodissection and
meticulous clearing of all posterior synechiae between the iris and the
residual capsule are mandatory. An all-PMMA heparin surface modified IOL is
recommended for sulcus placement rather than a foldable acrylic lens.
Prolapsing the IOL optic through the fused anterior and posterior capsule
remnants is useful in preventing pupillary capture and ensuring lens
centration. If the capsular openings are appropriately sized for this optic
capture technique, a smaller optic PMMA lens or an acrylic foldable lens
becomes more acceptable. An exuberant Soemmering's ring formation will often
keep the anterior and posterior leaflets separated from one another, thus
maintaining a peripheral capsular bag. Whenever possible, the surgeon should
reopen the capsular bag, aspirate the material in the Soemmering's ring, and
place the IOL in the capsular bag. When secondary in-the-bag fixation (rather
than sulcus fixation) is anticipated, a foldable acrylic IOL can be more safely
implanted.34
When inadequate capsular support is present for sulcus fixation in a child, implantation of an IOL is not recommended unless every contact lens and spectacle option has been explored fully. Although their long-term safety is unknown, modern flexible, open-loop anterior chamber lenses seem to be well tolerated in children when their anterior segment is developmentally normal. Transscleral fixation of a posterior chamber IOL in children has also been well tolerated but complications such as pupillary capture, suture erosion, and refractive error from lens tilt or anteroposterior displacement have been reported. The ab externo approach is recommended for transscleral suture placement in children.35
IOL Power Selection
Selecting the best IOL power to
implant in a growing child presents unique challenges. Although Gordon and
Donzis29 have documented the axial growth pattern of normal eyes in
children, controversy still exists about whether the pseudophakic eye grows
predictably along that same curve. In the normal phakic child, there is little
change in refraction (0.9 D from birth through adulthood on average) because
the power of the natural lens decreases dramatically as the eye grows axially.
However, an IOL placed in a child's eye cannot change in power to match the
growth of the eye. An IOL chosen for emmetropia in early childhood is likely to
leave the patient highly myopic as he or she grows older. Dahan and
coworkers37 evaluated the lens choice and dioptric power in 156
pseudophakic eyes of 99 children 1 month to 8 years of age. As expected, the
younger the child at the time of implantation, the greater the myopic shift
over time. To reduce the necessity of an IOL exchange later in childhood, they
suggested that an infant should receive 80% of the IOL power needed for
emmetropia. A toddler or a young child should receive 90% of the power needed
for emmetropia. This would lead to initial hyperopia but allow a gradual move
to emmetropia or mild to moderate myopia in adulthood. Knight-Nanan and
coworkers38 recommended the use of an IOL that is lower than one
needed for emmetropia by 6 D to compensate for the expected myopic shift when
implanting in infants younger than 1 year of age. For children older than 2
years of age, data are available to help the surgeon predict the growth of the
eye on average.29,36,39
When performing surgery on children between 2 and 8 years of age, many surgeons have advised selecting an IOL power that will leave mild to moderate hyperopia, milder with increasing age.41,42 Awner and colleagues44 have suggested aiming for a postoperative refraction of 4 D for children younger than 2 years of age, 3 D for children 2 to 4 years of age, 2 D for children 4 to 6 years of age, 1 D for children 6 to 8 years of age, and emmetropia for children older than 8 years of age at the time of implantation. Other clinicians have advocated aiming for emmetropia regardless of age when operating on children older than 2 years of age. This approach avoids potentially amblyogenic residual hyperopia but is likely to eventually lead to the development of significant myopia.
Modern theoretical IOL formulas are usually used in adults to calculate the IOL power most likely to achieve the desired postoperative refraction. Andreo, Wilson, and Saunders45 applied the Sanders-Retzlaff-Kraff (SRK) II, SRK-T, Holladay, and Hoffer Q formulas to measurements from 47 consecutive IOL implantations in children. The eyes were divided into three groups: short (less than 22 mm in axial length), medium (axial length greater than equal to 22 mm but less than 24 mm), and long (24 mm or more). While the average error (1.2 D to 1.4 D for all formulas) was larger than usually expected in adults, no formula seemed to perform better than any other. The errors were below the target refraction as often as above it. All axial length and keratometry measurements were made under anesthesia to avoid error from poor patient cooperation.
Management of the Posterior Capsule
The advent of
vitreous suction cutting devices for removing the center of the posterior
capsule and a portion of the anterior vitreous during the initial cataract
surgery in young children dramatically decreased the need for secondary
surgery. Pediatric ophthalmologists are accustomed to removing a portion of the
posterior capsule and the anterior vitreous at the time of lensectomy.
Therefore, as IOL implantation has been added to the surgical procedure,
pediatric ophthalmologists often remain advocates of primary posterior
capsulectomy and anterior vitrectomy. However, adult cataract surgeons are
often more reluctant to perform a primary posterior capsulectomy and vitrectomy
when operating on children for fear of increasing the risk of retinal
detachment or cystoid macular edema. These complications are exceedingly rare
after pediatric cataract surgery with or without a primary capsulectomy and
vitrectomy. It is usually necessary to use Nd:YAG laser posterior capsulotomies
in children when the posterior capsule is left intact. This procedure also
carries a risk of retinal detachment and cystoid macular edema. In addition,
larger amounts of laser energy are often needed in children as compared with
adults, and the posterior capsule opening may close, requiring repeated laser
treatments or a secondary pars plana membranectomy.
Previous studies have shown that a posterior capsulectomy without a central vitrectomy would be unlikely to prevent the development of a secondary membrane.46 In fact, the opacification rate was not significantly decreased by a posterior capsulectomy alone. Only when an anterior vitrectomy was added did the opacification rate fall. In a prospective and randomized study, Vasavada and Trevidi47 showed that visual axis obscuration across the anterior vitreous face occurred in 70% of those eyes in which vitrectomy was not performed after posterior CCC in children 5 to 12 years of age. No eye developed visual axis obscuration when a posterior CCC was combined with an anterior vitrectomy. Gimbel and DeBroff 48 recommended performing a posterior manual capsulorrhexis with IOL optic capture in an attempt to prevent secondary membrane formation without necessitating a vitrectomy. Subsequent studies, however, have reported secondary opacification despite the use of Gimbel's technique.49,50 In another attempt to obviate the need for a vitrectomy, Atkinson and Hiles51 recommended leaving the posterior capsule intact, even in young children, and performing an Nd:YAG laser posterior capsulotomy under a second general anesthesia in the early postoperative period before opacification occurs. Subsequently, however, the same group reported a 41% closure of the laser capsulotomy when this protocol was followed.
Postoperative Medications
When pediatric cataract
surgery is performed under general anesthesia, a patch and shield are usually
placed over the eye for the first postoperative night. Immediately at the end
of surgery, a drop of dilute povidone-iodine 5% is placed on the operative eye.
An antibiotic/steroid ointment and atropine ointment are placed on the eye
prior to the patch and shield. The eye is examined on the first postoperative
day. Topical atropine (0.5% in children younger than 1 year of age, and 1%
thereafter) is instilled once per day for 2 to 4 weeks. Prednisolone acetate is
used topically six times per day for 2 weeks and then three to four times per
day for an additional 2 weeks. An antibiotic drop is used for 1 week. Any
residual refractive error is corrected after the wound stabilizes and the
synthetic absorbable sutures dissolve.
Follow-up
The eye patch and shield are removed on
the first postoperative day. The use of glasses or a shield during the day and
a shield at night is recommended for at least 1 week postoperatively.
Postoperative examinations are scheduled at 2 weeks, 4 weeks, 3 months, and 6
months postoperatively. Beyond 6 months, the postoperative visits are
customized for each patient based on amblyopia treatment and other
considerations. Yearly examinations under anesthesia should be considered in
children undergoing cataract surgery to measure intraocular pressure, examine
the peripheral retina, monitor eye growth using A scan ultrasound, examine the
position of the IOL, and detect any secondary membrane or after-cataract
formation. Once children become old enough and cooperative enough to undergo
these examinations awake, the serial EUAs become unnecessary. Since children
with cataracts often have other ocular abnormalities, careful follow-up is
needed for a lifetime. Aphakic or pseudophakic glaucoma is a particular concern
when microphthalmia is present. An attempt should be made to gradually gain the
child's trust enough to measure the intraocular pressure at each visit. A
marked and unexpected myopic shift can also be a sign of glaucoma in a child.
Amblyopia treatment is also paramount during the follow-up of children
undergoing cataract surgery. Attention to and compliance with amblyopia
treatment will affect the visual outcome of these children to a greater extent
than the surgical decisions discussed in this tutorial.
The surgical management of cataracts in children is markedly different from adults. The eyes are not only smaller because of age but many are also microphthalmic. Decreased scleral rigidity and increased vitreous upthrust make surgical manipulations within these eyes more difficult. The anterior chamber is often unstable, the capsule management requires special considerations, and the propensity for postoperative inflammation is increased. Ocular growth makes selection of an IOL power difficult. Children do not always comply with postoperative instructions. Examinations of the eye after surgery are also often incomplete. The long expected life span after surgery for children deserves consideration when surgical decisions are made. These special patients are uniquely challenging. The best surgical techniques for children will evolve most efficiently with optimal cooperation and collaboration between pediatric ophthalmologists and adult cataract surgeons.
Posted Aug. 2003