Australian Doctor Australian Doctor 28th July 2017 | Page 18

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 .

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

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