Peripheral retinal ablation for threshold retinopathy of prematurity in preterm infants

Advances in perinatal medicine have led to increased survival of extremely low birth weight infants and an increase in the incidence of retinopathy of prematurity (ROP). This is a vascular proliferative disorder of the immature retina in premature infants that can result in impairment of vision and a high (> 47%) chance of blindness if untreated (threshold ROP). Normally the retina has a complete system of blood vessels by 40 weeks. Injury to the developing retinal capillaries occurring before or during birth and in the days following delivery stimulates new vascularization, which is the observable retinopathy. This can result in successful revascularization of the retina (regression of the ROP) or progression to neovascular membranes in the vitreous, subsequent scarring and retinal detachment. The incidence and severity of retinopathy is inversely related to gestational age. Treatment involves removal (ablation) of the part of the retina without blood vessels to preserve central macula vision. Cryoablation and laser techniques are used. The review authors identified two randomised trials involving 291 and 28 premature infants with threshold ROP, reported in the 1980s. Both used cryotherapy for peripheral retinal ablation, reducing the incidence of adverse ophthalmic outcomes. Unfavorable retinal structure at less than 12 months and in early childhood at 5½ years (234 infants) was reduced by some 18 to 20%. Therefore, the number of eyes with threshold ROP needed to treat (NNT) to avoid one unfavorable outcome is around five. The risk of poor visual acuity in early childhood was reduced from 63 to 51% (NNT 8).

The advantage of retinal ablation in these eyes outweighs short term morbidity associated with the therapy. This includes an increase incidence of apnoea and bradycardia both during the procedure and in the following one to three days. The visual fields in sighted eyes were slightly smaller in the group receiving cryoablation as compared to the control group. It is important to note that compared to normal, eyes with ROP that spontaneously recovered also had a reduction in visual field. At this stage, long term outcomes remain unknown.

Authors' conclusions: 

Peripheral retinal ablation reduces the incidence of adverse ophthalmic outcome in premature infants with threshold ROP. In sighted eyes, peripheral retinal ablation may reduce the size of the visual field. At this stage, long term outcomes remain unknown.

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Background: 

This section is under preparation and will be included in the next issue.

Objectives: 

In premature infants with threshold retinopathy of prematurity (ROP) does peripheral retinal ablation, by any means, reduce the incidence of adverse ophthalmic outcome?

Search strategy: 

The standard search strategy of the Cochrane Neonatal Review Group was used. This included a search of the Cochrane Neonatal Group Register of Clinical Trials, MEDLINE, EMBASE, previous reviews including cross references, abstracts from pediatric and ophthalmologic meetings, letters and expert informants. Search terms included "Retinopathy of Prematurity" [MeSH Terms], "Retrolental Fibroplasia" [All Fields] and "Lightcoagulation" [All Fields] or "Cryosurgery" [All Fields]. In addition, a personal bibliographic database was used as a cross-reference.

Selection criteria: 

All trials in human premature infants with threshold ROP utilizing random or quasi random allocation to either peripheral retinal ablation of the avascular retina, by any means, or concurrent control group with independent outcome assessment were initially selected for review. Following methodologic review, only studies using random allocation were selected for data extraction.

Data collection and analysis: 

Relevance and validity were assessed by the two authors and consensus reached. Each author extracted clinical outcomes from valid reports independently. Data analysis was conducted according to the standards of the Cochrane Neonatal Review Group.

Main results: 

Two randomised trials were identified. Data from these studies show that peripheral retinal ablation reduces the risk of (1) early unfavorable retinal structure from 47.9% to 28.1% (absolute risk reduction 19.8% [95% CI 27.9 - 11.8%]), (2) unfavorable retinal structure in early childhood from 44.3% to 26.3% (absolute risk reduction 18% [95% CI 27.0 - 9.1%]) and (3) unfavorable visual acuity in early childhood from 63% to 50.6% (absolute risk reduction 12.2% [95% CI 21.2 - 3.1]). In addition, visual fields in sighted eyes were slightly smaller in the treated (51.3° ± 11.8°) group as compared to the control (58.2°± 14.5°) group.

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