Retinopathy of prematurity
Congenital cataract
How to Treat – Paediatric eye – the first 12 months
Retinopathy of prematurity
Figure 1. A fundus photograph with features of retinopathy of prematurity including dilated and tortuous posterior pole vessels, haemorrhages and incomplete vascularisation of the retina( arrows indicate the limit of vascularisation).
THE vascular supply of the retina begins to develop in the fourth month of gestation. Vessels arise from the optic disc and extend peripherally, reaching the ora serrata, the outermost point of the retina, by month eight or nine, and capillary remodelling continues until three months’ post-term. This process is regulated by interleukin growth factor-1( IGF-1).
When a baby is born prematurely, the immature retinal vasculature shifts from an in-utero environment( low oxygen tension, high IGF-1) to an ex-utero one( high oxygen tension and low IGF- 1). This is especially so if the child requires resuscitation or supplemental oxygen.
The sudden onset of hyperoxia and loss of IGF-1 causes normal retinal vessel development to cease abruptly. The underlying retina continues to develop though, and over several weeks, the increased metabolism within the retinal cells creates a hypoxic environment within the eye. This new hypoxia can drive the retinal vessels to begin growing again( neovascularisation), but they grow in an abnormal and disorganised way— towards the vitreous rather than towards the ora serrata. In serious cases, this can lead to traction on the retina and ultimately, a total retinal detachment causing permanent blindness.
The most significant risk factors for the development of this disease are low gestation, low birth weight and use of supplemental oxygen. 1 While every neonatal intensive care unit will have its own guidelines, the current recommendation from the American Academy of Ophthalmology is that all infants born at 32 weeks’ gestation or less, or at a birthweight of 1500g or less, or for any reason at the neonatologists’ discretion, are screened for this condition. 2
Screening requires examination of both eyes after dilation of the pupils, with a binocular indirect ophthalmoscope.
The ophthalmologist will recommend either ongoing screening or treatment based on the following: the extent to which the retina is vascularised( referred to as the‘ zone’); the stage of any disease at the limit of vascularisation
( graded from no retinopathy of prematurity [ Stage 0 ] to total retinal detachment [ Stage 5 ]); and the presence or absence of any dilation or tortuosity of the vessels at the posterior pole( plus disease)( see figure 1).
The frequency of ongoing screening depends upon the severity of the disease seen, and is usually every one or two weeks until the retina is fully vascularised. Treatment is indicated if the disease meets the criteria for‘ type 1 retinopathy of prematurity’, as defined by the Early Treatment of Retinopathy of Prematurity Trial. 3 Treatment is by laser retinal photocoagulation therapy to the area
Figure 2. Type 1 retinopathy of prematurity is treated with indirect laser retinal photocoagulation under general anaesthesia or sedation.
of non-vascularised retina( see figure 2). More recently, intravitreal anti-vascular endothelial growth factor( anti-VEGF) therapy has been used with success in the treatment of disease close to the posterior pole( zone 1). Retinal detachment requires surgical repair and the outcomes are often poor.
Congenital cataract
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CATARACT refers to any opacity within the lens of the eye( see figure 3). About one in 250 infants will have some type of lens opacity, varying from mild and visually insignificant, to severe and completely obscuring the red reflex. 4
Congenital lens opacities may be unilateral or bilateral. Unilateral cataract is usually isolated and not associated with systemic disease. In contrast, bilateral cataract may be inherited in an autosomal dominant manner or may occur in association with systemic conditions, including metabolic disease, skeletal syndromes or congenital infections( such as TORCH infections— Toxoplasmosis, Other [ syphilis, varicella-zoster, parvovirus B19 ], Rubella, Cytomegalovirus, and Herpes infections).
For this reason, all children with bilateral cataract should be examined by a paediatrician and have investigations to screen for genetic, metabolic and infective causes.
An assessment of the red reflex at birth and at the six-week check facilitates prompt diagnosis, referral and timely management. Any abnormality of the red reflex( absence, asymmetry, unusual colour, dullness or a‘ black spot’ within it) or any whiteness( leukocoria) or dullness within the
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pupil can be a sign of intraocular abnormality, including cataract.
Early detection and management is crucial in optimising the child’ s visual outcome. A delay in diagnosis and treatment means the visual cortex is deprived of normal visual input during a critical period of development. The visual system often cannot recover after a delay in diagnosis and treatment. Roving eye movements and nystagmus are late signs of congenital cataract( presenting at approximately 3-4
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months of age) and their presence is associated with a poorer visual outcome.
Visually significant congenital cataracts are managed surgically. Surgery is performed as soon after four weeks of age as possible. Surgery before four weeks is associated with a higher risk of aphakic glaucoma( a form of secondary glaucoma associated with having no lens inside the eye).
Surgery is performed under general anaesthesia and differs significantly from the technique
Figure 3. Bilateral congenital cataracts in a newborn—( A) Right eye,( B) Left eye.
used in adults: A circular opening is created inside the anterior lens capsule; the entire cataractous lens is removed; a circular opening is made in the posterior lens capsule; the anterior and central vitreous body is removed by vitrectomy; intraocular antibiotics are injected into the eye to prevent infection; and all surgical wounds are tightly closed with sutures. Some surgeons will choose to place an intraocular lens at the time of initial surgery. Others will leave the child aphakic and instead rely on contact lenses and / or glasses, which can be changed easily to adapt their focusing power as the eye grows. An intraocular lens can be inserted as a secondary procedure when the eye has grown fully or if the child begins to refuse contact lenses or glasses.
An infant who is left aphakic( with contact lenses or glasses used for refractive correction) will have the same vision at one year and at 4.5 years post-surgery as one who has a lens implanted. However, aphakic infants have a statistically significantly reduced chance of needing more unplanned surgery within the first year, and a lower chance of an adverse post-operative event. 4
Where there is asymmetry of vision after surgery or where the cataract was unilateral, amblyopia treatment in the form of parttime occlusion therapy is needed postoperatively. To achieve good visual outcomes, the occlusion therapy often needs to continue for years, and demands occlusion periods longer than the standard two hours per day.
This intensive, long-term treatment can be very challenging for families and they may benefit from regular support and encouragement. cont’ d page 20
18 | Australian Doctor | 28 July 2017 www. australiandoctor. com. au