Retinopathy of Prematurity: Screening, Classification and Follow-up
Key Takeaways
ROP screening uses gestational, postnatal and postmenstrual ages; apply the current national timetable.
Classify each eye by zone, stage, extent and vascular severity, including aggressive disease.
Treatment criteria precede historical threshold disease; borderline disease requires prompt specialist discussion.
Anti-VEGF regression requires prolonged surveillance for persistent avascular retina and delayed reactivation.
Prematurity creates a surveillance problem
Retinopathy of prematurity (ROP) is disordered retinal vascular development in an incompletely vascularised retina. Premature birth interrupts normal development; oxygen exposure and systemic illness influence a later hypoxic drive to abnormal vascular proliferation. Screening aims to find sight-threatening disease before tractional detachment. An infant may have no externally visible warning sign, so screening eligibility and scheduled follow-up cannot depend on apparent vision or absence of leukocoria.
Distinguish gestational age at birth, postnatal age and postmenstrual age, which combines gestational and postnatal age. Local eligibility varies because neonatal populations and care differ. The UK guideline revised in October 2024 screens infants born before 31 weeks or with birth weight below 1501 g and also recommends considering those born at 31+0 to 31+6 weeks. For birth before 31 weeks, the first examination is in the 31+0–31+6 postmenstrual week or at four completed postnatal weeks, whichever is later. For eligible infants born from 31 weeks, it is in the 36+0–36+6 postmenstrual week or four completed postnatal weeks, whichever is sooner. These are UK rules, not a universal EBO-wide timetable. See the RCPCH 2024 guideline.
Classify each eye completely
The third International Classification, ICROP3, describes zone, stage, extent and vascular severity, with aggressive disease, regression and reactivation recorded. Zone I is centred on the disc with radius twice the disc-to-fovea distance. Zone II extends to the nasal ora; zone III is the remaining temporal crescent. The most posterior disease determines zone, including a notch into a more posterior zone. Do not label an eye zone III without adequate examination of the nasal retina.
| Stage | Finding |
|---|---|
| 1 | Demarcation line at the vascular–avascular junction |
| 2 | Elevated ridge |
| 3 | Extraretinal neovascular proliferation, including flat neovascularisation |
| 4A / 4B | Partial detachment with fovea attached / detached |
| 5 | Total detachment, further described by configuration and anterior changes |
Plus disease reflects increased vascular dilation and tortuosity; pre-plus lies between normal and plus on a spectrum. ICROP3 emphasises the overall posterior vascular appearance rather than a rigid photographic-quadrant shortcut. Aggressive ROP replaces “aggressive posterior ROP” because rapid aggressive disease is not confined to one posterior location. It may progress without passing neatly through all conventional stages. Record clock-hour extent and the appearance in each eye. The original ICROP3 publication supplies classification rather than a complete treatment protocol.
Referral and treatment
Traditional ETROP type 1 treatment criteria include zone I ROP with plus at any stage, zone I stage 3 without plus, and zone II stage 2 or 3 with plus. Protocols can differ at borderline disease: UK guidance specifically describes zone II stage 2 with plus as requiring treatment consideration or review within a week or less. Aggressive disease and rapid change require prompt discussion with the treating specialist. Do not wait for historical “threshold” clock-hour criteria in an eye meeting contemporary treatment criteria.
Laser treats avascular retina and reduces its angiogenic drive, at the cost of peripheral retinal destruction and potential refractive consequences. Intravitreal anti-VEGF can allow further vascularisation and is particularly useful in selected posterior or aggressive disease, but it introduces uncertainty about systemic exposure and delayed reactivation. Agent, dose and authorisation depend on current national guidance and product information. Do not transfer adult retinal injection doses to a premature infant.
Discuss these trade-offs with parents and neonatologists and arrange appropriate analgesia, monitoring and respiratory support for the chosen procedure. Detachment may require specialist vitreoretinal surgery; prognosis depends on stage and anatomy. The RCOphth treatment guidance should be used alongside screening guidance.
Safe examination and continuity
A dilated binocular indirect examination or validated wide-field imaging pathway must assess the relevant peripheral retina. Imaging can miss peripheral disease, so a screening programme must specify how incomplete views and final assessments are handled. Use age-appropriate mydriatic preparation, comfort measures and cardiorespiratory monitoring. A distressed or unstable infant needs senior coordination, not an unexplained missed examination. Record findings, images when available, the next examination and who owns follow-up.
After anti-VEGF, apparent disappearance of plus or stage 3 does not establish permanent cure. Persistent avascular retina and later reactivation require prolonged surveillance under the treatment protocol. Discharge or transfer between hospitals must include the exact examination plan and contact responsible for arranging it. Parents need clear instructions about the importance of attendance, with practical support if appointments are difficult.
Later childhood assessment addresses myopia, astigmatism, amblyopia, strabismus and possible late retinal complications. A treated infant with attached retinas may still need substantial visual support. In an exam case, state the complete classification, whether referral is urgent, the available treatment options and the surveillance obligation; treatment without follow-up is an incomplete answer.
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