Retinopathy of prematurity

Question 1 (10 marks)

a) Define the screening criteria for retinopathy of prematurity and state when the first examination should occur. (4 marks) Screening is offered to infants with a gestational age of 30 weeks or less or a birth weight of 1500 g or less, with some guidelines adding selected unstable infants with a higher gestational age or birth weight [2]. The first retinal examination should be performed at 31 weeks postmenstrual age or 4 weeks of chronological age, whichever is later [2].

b) Describe the three axes used to classify ROP and define plus disease. (3 marks) ROP is classified by zone, stage, and the presence of plus disease [4]. The zones are concentric circles centred on the optic disc: Zone I is posterior with a radius twice the disc-to-fovea distance, Zone II extends to the nasal ora, and Zone III is the temporal crescent [4]. Plus disease is venous dilation and arteriolar tortuosity of the posterior retinal vessels greater than or equal to the standard published photograph [4].

c) This infant's findings (Zone II stage 3 with plus) meet Type 1 criteria. Outline the management. (3 marks) This infant has Type 1 ROP, which requires treatment within 72 hours [1]. The options are laser photocoagulation of the avascular retina or intravitreal anti-VEGF therapy, chosen on the basis of zone, the infant's systemic state, and the reliability of follow-up [1]. After treatment the infant needs close surveillance for recurrence or reactivation, particularly if anti-VEGF is used [3].

Question 2 (10 marks)

a) Explain the two-phase model of ROP pathogenesis. (4 marks) In Phase 1, the relative hyperoxia of extrauterine life combined with loss of placental insulin-like growth factor 1 suppresses vascular endothelial growth factor and IGF-1 signalling, causing arrested growth and regression of developing retinal capillaries and enlarging the avascular retina [4]. In Phase 2, the metabolically active avascular retina becomes hypoxic and releases a surge of vascular endothelial growth factor; as IGF-1 recovers with growth, abnormal disorganised neovascularisation is driven, forming the ridge and risking tractional detachment [4].

b) Compare laser photocoagulation with intravitreal bevacizumab for ROP. (3 marks) Laser ablates the avascular retina and removes the vascular endothelial growth factor source but destroys peripheral retina, causing myopia and visual-field loss [1]. Intravitreal bevacizumab neutralises the vascular endothelial growth factor surge directly and the BEAT-ROP trial showed it was superior to laser for Zone I stage 3 disease with plus, while also causing less myopia than laser [3].

c) List four pitfalls in ROP management that lead to poor outcome. (3 marks) First, missing or delaying a scheduled retinal examination in an eligible infant [2]. Second, deferring screening because the infant looks well or is growing [2]. Third, treating after the Type 1 threshold rather than at it, allowing progression toward detachment [1]. Fourth, inadequate follow-up after anti-VEGF, missing late reactivation of disease [3].