Retinopathy of Prematurity
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Direct answer
A baby born at twenty-nine weeks weighing 1,200 grams goes on a retinal examination timetable, not a waiting list: retinopathy of prematurity (ROP) is a vasoproliferative disease of the immature retina in which normal vessel development arrests and abnormal neovascularisation takes over, capable of detaching the retina and blinding for life. Indian guidelines screen preterm neonates of roughly 34 weeks gestation or less, or birth weight of about 1,750 to 2,000 grams and below (criteria vary slightly between bodies and many units screen more liberally), with the first examination at four weeks of postnatal age or 31 weeks post-conceptional age, whichever is later. Disease is described by zone (one to three, centred on the disc), stage (one to five) and plus disease; Type 1 ROP — the treatment trigger — must receive laser photocoagulation of the avascular retina, or intravitreal anti-VEGF in selected posterior disease, within about 48 hours of diagnosis.
What you must remember
- Pathophysiology: premature birth halts vascularisation; extrauterine relative hyperoxia downregulates VEGF, then the growing avascular retina turns hypoxic and VEGF surges, driving neovascularisation.
- Screening criteria (India): gestational age about 34 weeks or less, and/or birth weight about 1,750 to 2,000 grams or less, with sicker, more immature babies screened by clinical judgement; first screening at 4 weeks postnatal age or 31 weeks post-menstrual age, whichever is later.
- Zones: zone one is a circle of twice the disc-to-macula distance around the disc; zone two extends to the nasal ora serrata (equator temporally); zone three is the remaining temporal crescent — the more posterior the disease, the more dangerous.
- Stages: stage 1 a flat demarcation line; stage 2 an elevated ridge; stage 3 ridge with extraretinal fibrovascular proliferation; stage 4 partial detachment (4A extrafoveal, 4B involving the fovea); stage 5 total funnel detachment.
- Plus disease: venous dilation and arteriolar tortuosity at the posterior pole — the single most important treatment trigger, outweighing stage alone; aggressive posterior ROP is its rapidly progressing, worst-behaved variant.
- Type 1 ROP (treat): zone one, any stage with plus; zone one, stage 3 without plus; zone two, stage 2 or 3 with plus. Type 2 ROP (observe) sits just below these thresholds.
- Treatment: laser to the avascular retina within about 48 hours of Type 1 disease; intravitreal anti-VEGF (bevacizumab) for zone one and aggressive posterior disease, with late recurrence demanding prolonged follow-up.
- Follow-up and sequelae: checks every one to two weeks until mature; regressed ROP still leaves lifelong myopia, strabismus and detachment risk; oxygen targeting is the nursery-side preventive.
Screening a 30-weeker from day one to discharge
A girl born at 30 weeks and 1,350 grams spends her first week on oxygen, enrolled for ROP screening at birth — eligibility is demographic, not symptomatic. At a postmenstrual age of 31 weeks and postnatal age of four weeks (the later clock), a trained ophthalmologist examines with the indirect ophthalmoscope and scleral depression. The right eye shows a ridge at the vascular-avascular boundary in zone two: stage 2 without plus, rescheduled in one week. Next visit, the ridge has thickened and posterior veins are dilated and tortuous: stage 2, zone two, with plus — Type 1 ROP, treatment within 48 hours. Under sedation, confluent laser covers the entire avascular retina, sparing the ridge; parents are counselled that treatment arrests most disease, that weekly follow-up continues until vascularisation, and that childhood myopia is likely. Had vessels simply kept growing, checks would space to two-weekly and discharge follow when zone three vascularises.
Where the exam frames it
Three recurring templates: a vignette giving gestational age and birth weight, asking whether screening is indicated and when it begins; a photograph or description asking to name the stage (line, ridge or proliferation); and a threshold question — which findings convert observation into treatment. The Type 1 criteria are the heart of the matter, and plus disease is the keyword examiners weight most heavily, because posterior vascular change predicts progression better than peripheral stage. The India-specific angle: neonatal care keeps saving tinier babies, creating more at-risk retinas, and screening is being folded into government child-health initiatives including Rashtriya Bal Swasthya Karyakram in several states. Finally, the mid-twentieth-century epidemic followed unrestricted oxygen — target, do not maximise, oxygen saturation.
Frequently asked questions
Which babies require ROP screening in India?
Preterm infants of roughly 34 weeks gestation or less and/or birth weight of about 1,750 to 2,000 grams or less, with the first examination at four weeks postnatal age or 31 weeks post-menstrual age, whichever is later.
What is plus disease in ROP?
Dilation and tortuosity of the posterior pole retinal vessels — the treatment-triggering sign that accompanies Type 1 ROP regardless of peripheral stage.
What defines Type 1 ROP?
Zone one any stage with plus, zone one stage 3 without plus, or zone two stage 2 or 3 with plus — the threshold requiring treatment within about 48 hours.
Why is laser applied to the avascular retina rather than to the ridge?
Ablating the ischaemic peripheral retina removes the VEGF drive feeding the neovascular ridge; the ridge itself is left to regress.
What are the late ocular sequelae of regressed ROP?
Myopia (the commonest), strabismus, amblyopia and the risk of retinal detachment — lifelong ophthalmic follow-up is advised.