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It may all come down to timing
The visual prognosis for children with congenital cataracts has improved dramatically since it was first recognised that cataract surgery during infancy is critical for a good visual outcome1,2; however, the optimal time to perform cataract surgery in a child with a congenital cataract is still in question. Anecdotal reports have noted excellent visual outcomes in neonates undergoing cataract surgery during the first week of life1,3; however, a subsequent analysis of 45 children with dense unilateral cataracts, who underwent cataract surgery, found that the visual outcome was the same regardless of when the surgery was performed during the first 6 weeks of life.4 While the same analysis has not been performed on children with bilateral congenital cataracts, it has been proposed that the critical period for treating children with bilateral congenital cataracts may extend to 8 weeks of life.2,5,6 Paediatric ophthalmologists are now trying to determine the optimal time to perform cataract surgery to reduce the high incidence of complications that have been reported following cataract surgery during infancy.
One of the most serious complications that occurs following paediatric cataract surgery is glaucoma. It is usually open angle and has been reported to develop in up to one third of children after a lensectomy and vitrectomy.7–11 Known risk factors for aphakic glaucoma include microcornea, persistent fetal vasculature, and cataract surgery during infancy. Parks et al8 reported that 54% of the children in their series who developed aphakic glaucoma underwent cataract surgery when they were younger than 2 months of age. Rabiah11 reported that 37% of children undergoing cataract surgery when 9 months of age or younger developed glaucoma compared to only 6% of children undergoing surgery thereafter. Vishwanath et al reports in this issue of the BJO (p 905) that 50% of children undergoing bilateral lensectomies during the first month of life developed glaucoma in one or both eyes after a 5 year follow up compared to only 15% of children undergoing cataract surgery thereafter. Lundvall and Kugelberg5 also reported that 80% of the children in their series of children with bilateral congenital cataracts who developed glaucoma underwent cataract surgery during the first 4 weeks of life. Finally, Watts and coworkers12 reported that aphakic glaucoma was more prevalent in children undergoing surgery when 14–34 days of age. While it is possible that eyes with congenital cataracts requiring early surgery are more prone to develop glaucoma than eyes that acquire cataracts later in childhood, it is also likely that early surgery increases the risk of these eyes developing glaucoma. For this reason, Vishwanath and coworkers have proposed that cataract surgery should be deferred until after the first 4 weeks of life.
It would appear that the optimal time to remove a dense congenital cataract in an infant and to initiate optical treatment is when the child is 4–6 weeks of age
The pathophysiology of aphakic open angle glaucoma is poorly understood. Its aetiology has been attributed to damage to the trabecular meshwork by inflammation, the loss of mechanical support of the trabecular meshwork, or a toxic substance gaining access to the trabecular meshwork from the vitreous humour.13 It has been reported to occur after both limbal and a pars plicata based lensectomies, suggesting that the surgical approach is not the critical factor in determining its occurrence.14
Children are more commonly being optically corrected with intraocular lenses following cataract surgery.15 Asrani and coworkers13 have reported a decreased incidence of open angle glaucoma in older children undergoing primary IOL implantation following cataract surgery. Recent studies, however, have noted a high incidence of open angle glaucoma in children undergoing IOL implantation during the first 4 weeks of life.16–18
A final factor to consider is the safety of general anaesthesia during infancy. The immaturity of an infant’s cardiovascular, pulmonary, and gastrointestinal systems, as well as their liver, kidneys, and thermoregulation puts them at greater risk from general anaesthesia.19 The most life threatening risk to an infant is postoperative apnoea. The risk of postoperative apnoea has been shown to be higher in preterm infants less than 44 post-conception weeks of age.20 For this reason, it has been recommended that all non-essential surgery for preterm infants be delayed until they are older than 44 post-conception weeks of age.21 While an increased risk of postoperative apnoea in a full term infant following general anaesthesia has not been established, waiting until an infant is older to perform cataract surgery allows all of the different systems in an infant to mature to some degree and should be safer.
From the available data, it would appear that the optimal time to remove a dense congenital cataract in an infant and to initiate optical treatment is when the child is 4–6 weeks of age. To remove the cataract before 4 weeks of age appears to increase the risk of the eye developing aphakic glaucoma, whereas waiting beyond 6 weeks of age compromises the visual outcome.
Note in Proof
It may all come down to timing
Supported in part by NIH Core Grant EY06360 and Research to Prevent Blindness, Inc.