Paediatric Retina · Surgeon Series
The retina of a
premature baby is
still being built.
Retinal blood vessels finish growing only around full term. A baby born early has an unfinished retina, and what happens next — quiet completion or a wave of abnormal vessels that peels the retina off — is decided over a handful of weeks, visible only on a dilated examination nobody outside the nursery ever sees.
severely impaired by ROP (2010)
Type 1 disease
most dangerous territory
Section 01 — The Mechanism
Two phases, and only
the second one
does the damage.
Retinopathy of prematurity is often described as "eye damage from oxygen in incubators." That description is old, partial and misleading. ROP is a developmental disorder of retinal blood vessels, and understanding it requires holding two opposite events in mind, separated by weeks.
In normal gestation, retinal vessels sprout from the optic disc at around the fourth month and creep outward across the retina, reaching the nasal edge earlier and the temporal edge last, at roughly term. A baby delivered at 27 weeks therefore arrives with a large rim of peripheral retina that has no blood supply yet and was never supposed to need one at that point.
Phase 1 — vaso-obliteration. After birth the baby moves from the low-oxygen environment of the womb into room air or supplemental oxygen, which is comparatively hyperoxic for that retina. Relative hyperoxia suppresses the growth factors driving vessel extension. The advancing vascular front stalls, and some already-formed vessels regress. The retina is now not just unfinished but arrested.
Phase 2 — vaso-proliferation. As the infant grows, the metabolic demand of that avascular peripheral retina rises while its blood supply does not. It becomes genuinely hypoxic and responds the way ischaemic retina always responds: by releasing vascular endothelial growth factor (VEGF) and related mediators. Vessels now regrow, but disorganised — piling into a ridge at the junction with vascularised retina and, in severe disease, breaking out of the retinal plane into the vitreous as fragile fronds that bleed, contract and drag the retina off its wall.
ROP happens because preterm birth interrupts retinal vessel growth mid-way. First the relatively oxygen-rich postnatal environment halts that growth and leaves peripheral retina without blood supply; then, as the baby grows, the starved retina floods the eye with VEGF and vessels return in a destructive, disorganised form. Most ROP regresses on its own. A minority progresses to a stage where abnormal tissue contracts and detaches the retina, and that outcome is irreversible. Because the dangerous phase is silent, painless and invisible to parents and to an undilated look at the eye, the entire clinical strategy rests on one thing: examining the right babies, on schedule, until the retina is finished.
Section 02 — Interactive
How an examiner reads
a retina: zone, stage, plus.
Every ROP examination produces three pieces of information, and the treatment decision falls out of their combination. Set the zone, stage and plus status below and watch the classification — and the treatment threshold — resolve.
Zone answers how far did normal vessels get? — measured as a circle centred on the optic disc. Zone I is a small posterior circle with a radius of twice the disc-to-fovea distance; Zone II is the annulus extending out to the nasal ora serrata; Zone III is the residual temporal crescent beyond it. Posterior disease is worse disease, because a Zone I eye has almost no vascularised retina and an enormous ischaemic drive behind whatever is seen at the ridge.
Stage answers what does the junction look like? — a flat white demarcation line is stage 1, a ridge with volume is stage 2, a ridge with fibrovascular tissue growing off it into the vitreous is stage 3, partial retinal detachment is stage 4 (4A sparing the fovea, 4B involving it) and total detachment is stage 5, which the third edition of the international classification subdivides further by the configuration of the funnel.
Plus disease answers how active is it right now? — and it is recorded at the posterior pole, not at the ridge. Dilated, tortuous arterioles and venules near the disc indicate high blood flow driven by high VEGF. Pre-plus describes abnormality insufficient for plus. The third edition explicitly reframes this as a continuous spectrum rather than a yes/no photograph comparison, which matters because plus disease is the variable that most often converts an observation decision into a treatment decision.
Section 03 — Who Gets Screened
Different countries
draw the line
in different places.
Screening criteria are not a universal biological constant. They are a bet about where the disease will show up in a given population's babies, and the bet differs between health systems with different neonatal survival profiles and different oxygen-monitoring capability.
The 2018 joint policy statement from the American Academy of Pediatrics, the American Academy of Ophthalmology and AAPOS recommends screening infants with a birth weight of 1500 g or less, or a gestational age of 30 weeks or less, together with selected larger and more mature infants whose neonatal course was unstable in the judgement of the treating team. That threshold reflects a setting where very preterm infants receive tightly titrated oxygen and continuous saturation monitoring.
India's national newborn eye-screening guidance deliberately casts a wider net — commonly cited as screening babies born at about 34 weeks or below, or weighing about 2000 g or below, with further widening for risk factors. The reason is empirical rather than precautionary: Indian series have repeatedly described severe, treatment-requiring ROP in bigger and more mature babies than Western criteria would ever have captured, a pattern often shorthanded as "bigger baby ROP" and generally attributed to variability in oxygen delivery and monitoring across a very large and heterogeneous neonatal care landscape.
| Element | AAP / AAO / AAPOS 2018 policy | India — national newborn eye-screening guidance |
|---|---|---|
| Birth weight trigger | ≤1500 g | Approximately ≤2000 g |
| Gestational age trigger | ≤30 weeks | Approximately ≤34 weeks |
| Larger/older babies | Screened selectively, on the neonatal team's judgement of unstable course | Screened where risk factors are present; wider net by design |
| First examination | Conventionally around 4 weeks chronological age or 31 weeks postmenstrual age, whichever is later, with the exact week set by gestational age at birth | |
| Endpoint of screening | Full retinal vascularisation, or unambiguous regression, or completion of treatment follow-up — not a fixed number of visits | |
The logistics problem, and telemedicine
Screening is not limited by knowledge; it is limited by there being an ophthalmologist trained in indirect ophthalmoscopy physically present in a neonatal unit on the right week. That is a hard constraint in rural and district hospitals everywhere. Wide-field retinal imaging by trained non-physician technicians, with images read remotely, has been deployed at scale to close exactly that gap — the KIDROP programme in Karnataka being one of the better-documented models, reporting screening of infants in outreach centres far from any retinal specialist. The model does not replace an examiner; it relocates the examiner's eye.
Section 04 — The Treatment Threshold
Type 1 disease, and
the trial that moved
the line earlier.
For most of the modern history of ROP, treatment waited for "threshold" disease as defined by the CRYO-ROP trial of the late 1980s — the first study to show that ablating the avascular peripheral retina reduced unfavourable outcomes at all. The question that took another fifteen years to answer was whether waiting that long was itself costing vision.
The Early Treatment for Retinopathy of Prematurity (ETROP) randomised trial answered it. Published in 2003, it compared treatment at the older threshold against earlier treatment of high-risk pre-threshold eyes, and found better structural and visual acuity outcomes with the earlier intervention. Its practical legacy is the Type 1 / Type 2 vocabulary still used at every cotside today.
| Category | Findings | Conventional action |
|---|---|---|
| Type 1 ROP | Zone I, any stage, with plus disease — or Zone I stage 3 without plus — or Zone II stage 2 or 3 with plus disease | Treat, conventionally within about 72 hours |
| Type 2 ROP | Zone I stage 1 or 2 without plus — or Zone II stage 3 without plus | Do not treat yet; re-examine at a short interval and treat on progression to Type 1 |
| Aggressive ROP (A-ROP) | Rapid, flat, ill-defined disease with prominent plus, not progressing through orderly stages | Treat urgently — conventional stage-based waiting is unsafe here |
The 72-hour figure is a clinical convention drawn from the pace at which Type 1 disease actually moves, not a regulatory rule or a number the trial randomised against. The underlying point stands regardless of the exact figure: this is one of the few situations in ophthalmology where an appointment slipping by a week can change a child's lifelong visual outcome.
to treat Type 1
for the first exam
classification
Section 05 — Laser or Injection
Burn the periphery,
or block the signal.
Once treatment is indicated there are two established options, and they attack the same disease from opposite ends. Laser removes the tissue producing the growth-factor signal. Anti-VEGF neutralises the signal and leaves the tissue in place. Neither is a universally correct answer.
Laser photocoagulation ablates the avascular peripheral retina, typically under near-confluent burns delivered by indirect laser in a single sitting. It ends the ischaemic drive permanently, which is its great strength: once the peripheral retina is ablated it cannot restart the process. The costs are equally permanent — peripheral visual field is sacrificed by design, and treated eyes tend toward myopia, often high myopia, in later childhood.
Intravitreal anti-VEGF injects a very small dose of an anti-VEGF agent into the vitreous, suppressing the proliferative drive and allowing peripheral vessels to resume growing in a more normal pattern. The BEAT-ROP trial, published in the New England Journal of Medicine in 2011, randomised infants with stage 3+ ROP to intravitreal bevacizumab or conventional laser and found a significant advantage for bevacizumab specifically in Zone I disease — the very population where laser performs worst because so much retina must be destroyed. The RAINBOW trial, published in The Lancet in 2019, compared ranibizumab against laser in very low birthweight infants and supported ranibizumab as a treatment option, with ranibizumab subsequently gaining regulatory approval for ROP in several jurisdictions.
| Dimension | Laser photocoagulation | Intravitreal anti-VEGF |
|---|---|---|
| Mechanism | Destroys the ischaemic retina producing VEGF | Neutralises circulating intraocular VEGF |
| Peripheral retina | Permanently ablated — field loss by design | Preserved; vascularisation can continue outward |
| Zone I disease | Difficult — a very large area must be treated | Trial evidence favours anti-VEGF in this specific subgroup |
| Reactivation | Uncommon once ablation is adequate | Documented, sometimes weeks to months later — demands longer, disciplined follow-up |
| Refractive outcome | Tendency toward myopia, frequently high | Generally less myopigenic in comparative reports |
| Open questions | Field loss quantification in later life | Systemic VEGF suppression in a developing infant; optimal dose |
| Practical demands | Laser equipment, anaesthetic support, one definitive sitting | Sterile injection setting; mandatory extended surveillance |
Illustrative visualisation of the direction of difference described across the trial literature and subsequent reviews (BEAT-ROP 2011, RAINBOW 2019 and related work) — see References. Not pooled meta-analytic effect sizes, and not a substitute for a clinician's judgement in an individual eye.
Section 06 — The Oxygen Trade-off
Less oxygen means
less ROP. It also
meant more deaths.
Because phase 1 of ROP is driven by relative hyperoxia, the obvious prevention strategy is to target lower oxygen saturations in preterm infants. This was tested properly, and the result is one of the most uncomfortable findings in neonatal medicine — and an important corrective to any account of ROP that treats oxygen as a simple dial to turn down.
The SUPPORT trial, published in the New England Journal of Medicine in 2010, randomised extremely preterm infants to a lower (85–89%) or higher (91–95%) oxygen saturation target. The lower-target group had substantially less severe retinopathy. The same group also had higher mortality. The NeOProM collaboration's prospective meta-analysis of the individual trials, published in JAMA in 2018, pooled this evidence and reported the same direction: lower saturation targeting was associated with a higher risk of death, alongside a lower risk of treated retinopathy.
The practical consequence for ophthalmology is unglamorous and unchanged: because oxygen exposure cannot be reduced to zero risk without cost elsewhere, ROP will keep occurring in surviving preterm infants, and screening remains the intervention that actually prevents blindness.
Section 07 — Afterwards
Regression is not
the same as discharge.
Most ROP regresses. That is the single most reassuring fact in this subject and the one most often mistaken for the end of the story. An eye that had ROP — treated or spontaneously regressed — remains a different eye, and the follow-up schedule should reflect that.
A baby born at 33 weeks weighing 1750 g, ventilated briefly for respiratory distress and discharged home in good condition, would fall outside a screening criterion set at 30 weeks or 1500 g. Under India's wider criteria the same baby is screened, and it is precisely in this band that Indian series have described treatment-requiring disease — including aggressive forms that do not wait for an orderly progression through stages.
The failure mode here is not misdiagnosis. It is that the examination never happens, because nobody was told the baby needed one. By the time a parent notices something wrong with a two-year-old's vision, phase 2 finished eighteen months earlier.
For parents, the actionable version is short: if a baby was born preterm, ask explicitly whether a retinal examination has been scheduled, get the date in writing before discharge from the neonatal unit, and keep it even if the baby looks perfectly well — because at the stage where it is still fixable, the baby always does.
Section 08 — FAQ
Frequently asked questions
about retinopathy of prematurity.
Retinopathy of prematurity (ROP) is a disorder of the developing retinal blood vessels in babies born preterm. In the womb, retinal vessels grow outward from the optic nerve and normally reach the edge of the retina only near full term. A baby born early has an incompletely vascularised retina. After birth the relatively oxygen-rich environment first slows or halts that vessel growth, leaving peripheral retina without a blood supply. As the baby grows, that starved retina releases growth factors including VEGF, and vessels then regrow abnormally — as a ridge of tissue and, in severe disease, as fragile vessels that grow into the vitreous, scar and pull the retina off. It is a two-phase disease, and the damaging phase is the second one.
Thresholds differ by country. The American Academy of Pediatrics joint 2018 policy recommends screening infants with a birth weight of 1500 g or less or a gestational age of 30 weeks or less, plus selected larger or more mature infants whose clinical course has been unstable. India's national newborn eye-screening guidance uses a deliberately wider net — commonly cited as all babies born at about 34 weeks or less, or weighing about 2000 g or less — because Indian series have repeatedly reported severe ROP in bigger, more mature babies than Western criteria would capture. Any premature baby who received prolonged supplemental oxygen or had a stormy neonatal course should be examined regardless of where the numbers fall.
The first dilated examination is conventionally timed at about four weeks of chronological age or about 31 weeks postmenstrual age, whichever comes later, with the exact first-visit week set by gestational age at birth. The reason for anchoring to postmenstrual age is that ROP follows the retina's developmental clock more closely than the calendar since delivery. Follow-up intervals — typically one, two or three weeks — are then set by what the examiner finds, and screening continues until the retina is fully vascularised or the disease has clearly regressed.
Zone describes how far normal vessels have grown, measured from the optic disc. Zone I is the small posterior circle centred on the disc, Zone II the annulus beyond it, and Zone III the remaining temporal crescent. The more posterior the disease, the more dangerous it is, because less retina has been vascularised. Stage describes what the junction between vascularised and non-vascularised retina looks like: stage 1 a flat demarcation line, stage 2 a raised ridge, stage 3 a ridge with extraretinal fibrovascular proliferation, stage 4 partial retinal detachment and stage 5 total detachment. Plus disease — abnormal dilation and tortuosity of the posterior pole vessels — is recorded separately and is the single strongest indicator of activity.
Type 1 ROP is the treatment threshold defined by the Early Treatment for Retinopathy of Prematurity (ETROP) randomised trial: Zone I with any stage plus plus disease, Zone I stage 3 without plus disease, or Zone II stage 2 or 3 with plus disease. ETROP showed that treating at this earlier point produced better visual and structural outcomes than waiting for the older, more advanced threshold criteria. Treatment is conventionally advised within roughly 72 hours of the diagnosis being made because Type 1 disease can progress to retinal detachment over days, not months.
Both are in routine use and the choice is case-specific. Laser photocoagulation ablates the avascular peripheral retina, removing the source of the growth-factor drive; it is definitive, it does not depend on a drug reaching the eye, and its main cost is a permanently ablated peripheral retina and a tendency toward myopia. Intravitreal anti-VEGF blocks the drive chemically and allows peripheral vessels to continue growing; the BEAT-ROP trial found bevacizumab advantageous over laser specifically for Zone I stage 3+ disease, and the RAINBOW trial supported ranibizumab as an alternative to laser. The trade-off with anti-VEGF is that disease can reactivate weeks later, so follow-up must be longer and more disciplined, and questions about systemic VEGF suppression in a developing infant have not been fully closed.
Many do. Mild ROP frequently regresses spontaneously with no lasting visual consequence. But a history of ROP — treated or regressed — carries a higher lifetime rate of myopia, often high myopia, and also of strabismus, amblyopia, glaucoma and late retinal detachment, so these children need ophthalmic follow-up through childhood rather than a single discharge visit. Advanced disease that reaches stage 4 or 5 has a far worse prognosis; surgery for a detached premature retina can restore anatomy in some cases but rarely restores good functional vision, which is exactly why the screening window matters so much more than the surgical one.
References & Evidence Base
Peer-reviewed
citations.
Continue Reading
Related guides
from Beyond Vision.
Paediatric Retina · Surgeon Series
The retina of a
premature baby is
still being built.
Retinal blood vessels finish growing only around full term. A baby born early has an unfinished retina, and what happens next — quiet completion or a wave of abnormal vessels that peels the retina off — is decided over a handful of weeks, visible only on a dilated examination nobody outside the nursery ever sees.
severely impaired by ROP (2010)
Type 1 disease
most dangerous territory
Section 01 — The Mechanism
Two phases, and only
the second one
does the damage.
Retinopathy of prematurity is often described as "eye damage from oxygen in incubators." That description is old, partial and misleading. ROP is a developmental disorder of retinal blood vessels, and understanding it requires holding two opposite events in mind, separated by weeks.
In normal gestation, retinal vessels sprout from the optic disc at around the fourth month and creep outward across the retina, reaching the nasal edge earlier and the temporal edge last, at roughly term. A baby delivered at 27 weeks therefore arrives with a large rim of peripheral retina that has no blood supply yet and was never supposed to need one at that point.
Phase 1 — vaso-obliteration. After birth the baby moves from the low-oxygen environment of the womb into room air or supplemental oxygen, which is comparatively hyperoxic for that retina. Relative hyperoxia suppresses the growth factors driving vessel extension. The advancing vascular front stalls, and some already-formed vessels regress. The retina is now not just unfinished but arrested.
Phase 2 — vaso-proliferation. As the infant grows, the metabolic demand of that avascular peripheral retina rises while its blood supply does not. It becomes genuinely hypoxic and responds the way ischaemic retina always responds: by releasing vascular endothelial growth factor (VEGF) and related mediators. Vessels now regrow, but disorganised — piling into a ridge at the junction with vascularised retina and, in severe disease, breaking out of the retinal plane into the vitreous as fragile fronds that bleed, contract and drag the retina off its wall.
ROP happens because preterm birth interrupts retinal vessel growth mid-way. First the relatively oxygen-rich postnatal environment halts that growth and leaves peripheral retina without blood supply; then, as the baby grows, the starved retina floods the eye with VEGF and vessels return in a destructive, disorganised form. Most ROP regresses on its own. A minority progresses to a stage where abnormal tissue contracts and detaches the retina, and that outcome is irreversible. Because the dangerous phase is silent, painless and invisible to parents and to an undilated look at the eye, the entire clinical strategy rests on one thing: examining the right babies, on schedule, until the retina is finished.
Section 02 — Interactive
How an examiner reads
a retina: zone, stage, plus.
Every ROP examination produces three pieces of information, and the treatment decision falls out of their combination. Set the zone, stage and plus status below and watch the classification — and the treatment threshold — resolve.
Zone answers how far did normal vessels get? — measured as a circle centred on the optic disc. Zone I is a small posterior circle with a radius of twice the disc-to-fovea distance; Zone II is the annulus extending out to the nasal ora serrata; Zone III is the residual temporal crescent beyond it. Posterior disease is worse disease, because a Zone I eye has almost no vascularised retina and an enormous ischaemic drive behind whatever is seen at the ridge.
Stage answers what does the junction look like? — a flat white demarcation line is stage 1, a ridge with volume is stage 2, a ridge with fibrovascular tissue growing off it into the vitreous is stage 3, partial retinal detachment is stage 4 (4A sparing the fovea, 4B involving it) and total detachment is stage 5, which the third edition of the international classification subdivides further by the configuration of the funnel.
Plus disease answers how active is it right now? — and it is recorded at the posterior pole, not at the ridge. Dilated, tortuous arterioles and venules near the disc indicate high blood flow driven by high VEGF. Pre-plus describes abnormality insufficient for plus. The third edition explicitly reframes this as a continuous spectrum rather than a yes/no photograph comparison, which matters because plus disease is the variable that most often converts an observation decision into a treatment decision.
Section 03 — Who Gets Screened
Different countries
draw the line
in different places.
Screening criteria are not a universal biological constant. They are a bet about where the disease will show up in a given population's babies, and the bet differs between health systems with different neonatal survival profiles and different oxygen-monitoring capability.
The 2018 joint policy statement from the American Academy of Pediatrics, the American Academy of Ophthalmology and AAPOS recommends screening infants with a birth weight of 1500 g or less, or a gestational age of 30 weeks or less, together with selected larger and more mature infants whose neonatal course was unstable in the judgement of the treating team. That threshold reflects a setting where very preterm infants receive tightly titrated oxygen and continuous saturation monitoring.
India's national newborn eye-screening guidance deliberately casts a wider net — commonly cited as screening babies born at about 34 weeks or below, or weighing about 2000 g or below, with further widening for risk factors. The reason is empirical rather than precautionary: Indian series have repeatedly described severe, treatment-requiring ROP in bigger and more mature babies than Western criteria would ever have captured, a pattern often shorthanded as "bigger baby ROP" and generally attributed to variability in oxygen delivery and monitoring across a very large and heterogeneous neonatal care landscape.
| Element | AAP / AAO / AAPOS 2018 policy | India — national newborn eye-screening guidance |
|---|---|---|
| Birth weight trigger | ≤1500 g | Approximately ≤2000 g |
| Gestational age trigger | ≤30 weeks | Approximately ≤34 weeks |
| Larger/older babies | Screened selectively, on the neonatal team's judgement of unstable course | Screened where risk factors are present; wider net by design |
| First examination | Conventionally around 4 weeks chronological age or 31 weeks postmenstrual age, whichever is later, with the exact week set by gestational age at birth | |
| Endpoint of screening | Full retinal vascularisation, or unambiguous regression, or completion of treatment follow-up — not a fixed number of visits | |
The logistics problem, and telemedicine
Screening is not limited by knowledge; it is limited by there being an ophthalmologist trained in indirect ophthalmoscopy physically present in a neonatal unit on the right week. That is a hard constraint in rural and district hospitals everywhere. Wide-field retinal imaging by trained non-physician technicians, with images read remotely, has been deployed at scale to close exactly that gap — the KIDROP programme in Karnataka being one of the better-documented models, reporting screening of infants in outreach centres far from any retinal specialist. The model does not replace an examiner; it relocates the examiner's eye.
Section 04 — The Treatment Threshold
Type 1 disease, and
the trial that moved
the line earlier.
For most of the modern history of ROP, treatment waited for "threshold" disease as defined by the CRYO-ROP trial of the late 1980s — the first study to show that ablating the avascular peripheral retina reduced unfavourable outcomes at all. The question that took another fifteen years to answer was whether waiting that long was itself costing vision.
The Early Treatment for Retinopathy of Prematurity (ETROP) randomised trial answered it. Published in 2003, it compared treatment at the older threshold against earlier treatment of high-risk pre-threshold eyes, and found better structural and visual acuity outcomes with the earlier intervention. Its practical legacy is the Type 1 / Type 2 vocabulary still used at every cotside today.
| Category | Findings | Conventional action |
|---|---|---|
| Type 1 ROP | Zone I, any stage, with plus disease — or Zone I stage 3 without plus — or Zone II stage 2 or 3 with plus disease | Treat, conventionally within about 72 hours |
| Type 2 ROP | Zone I stage 1 or 2 without plus — or Zone II stage 3 without plus | Do not treat yet; re-examine at a short interval and treat on progression to Type 1 |
| Aggressive ROP (A-ROP) | Rapid, flat, ill-defined disease with prominent plus, not progressing through orderly stages | Treat urgently — conventional stage-based waiting is unsafe here |
The 72-hour figure is a clinical convention drawn from the pace at which Type 1 disease actually moves, not a regulatory rule or a number the trial randomised against. The underlying point stands regardless of the exact figure: this is one of the few situations in ophthalmology where an appointment slipping by a week can change a child's lifelong visual outcome.
to treat Type 1
for the first exam
classification
Section 05 — Laser or Injection
Burn the periphery,
or block the signal.
Once treatment is indicated there are two established options, and they attack the same disease from opposite ends. Laser removes the tissue producing the growth-factor signal. Anti-VEGF neutralises the signal and leaves the tissue in place. Neither is a universally correct answer.
Laser photocoagulation ablates the avascular peripheral retina, typically under near-confluent burns delivered by indirect laser in a single sitting. It ends the ischaemic drive permanently, which is its great strength: once the peripheral retina is ablated it cannot restart the process. The costs are equally permanent — peripheral visual field is sacrificed by design, and treated eyes tend toward myopia, often high myopia, in later childhood.
Intravitreal anti-VEGF injects a very small dose of an anti-VEGF agent into the vitreous, suppressing the proliferative drive and allowing peripheral vessels to resume growing in a more normal pattern. The BEAT-ROP trial, published in the New England Journal of Medicine in 2011, randomised infants with stage 3+ ROP to intravitreal bevacizumab or conventional laser and found a significant advantage for bevacizumab specifically in Zone I disease — the very population where laser performs worst because so much retina must be destroyed. The RAINBOW trial, published in The Lancet in 2019, compared ranibizumab against laser in very low birthweight infants and supported ranibizumab as a treatment option, with ranibizumab subsequently gaining regulatory approval for ROP in several jurisdictions.
| Dimension | Laser photocoagulation | Intravitreal anti-VEGF |
|---|---|---|
| Mechanism | Destroys the ischaemic retina producing VEGF | Neutralises circulating intraocular VEGF |
| Peripheral retina | Permanently ablated — field loss by design | Preserved; vascularisation can continue outward |
| Zone I disease | Difficult — a very large area must be treated | Trial evidence favours anti-VEGF in this specific subgroup |
| Reactivation | Uncommon once ablation is adequate | Documented, sometimes weeks to months later — demands longer, disciplined follow-up |
| Refractive outcome | Tendency toward myopia, frequently high | Generally less myopigenic in comparative reports |
| Open questions | Field loss quantification in later life | Systemic VEGF suppression in a developing infant; optimal dose |
| Practical demands | Laser equipment, anaesthetic support, one definitive sitting | Sterile injection setting; mandatory extended surveillance |
Illustrative visualisation of the direction of difference described across the trial literature and subsequent reviews (BEAT-ROP 2011, RAINBOW 2019 and related work) — see References. Not pooled meta-analytic effect sizes, and not a substitute for a clinician's judgement in an individual eye.
Section 06 — The Oxygen Trade-off
Less oxygen means
less ROP. It also
meant more deaths.
Because phase 1 of ROP is driven by relative hyperoxia, the obvious prevention strategy is to target lower oxygen saturations in preterm infants. This was tested properly, and the result is one of the most uncomfortable findings in neonatal medicine — and an important corrective to any account of ROP that treats oxygen as a simple dial to turn down.
The SUPPORT trial, published in the New England Journal of Medicine in 2010, randomised extremely preterm infants to a lower (85–89%) or higher (91–95%) oxygen saturation target. The lower-target group had substantially less severe retinopathy. The same group also had higher mortality. The NeOProM collaboration's prospective meta-analysis of the individual trials, published in JAMA in 2018, pooled this evidence and reported the same direction: lower saturation targeting was associated with a higher risk of death, alongside a lower risk of treated retinopathy.
The practical consequence for ophthalmology is unglamorous and unchanged: because oxygen exposure cannot be reduced to zero risk without cost elsewhere, ROP will keep occurring in surviving preterm infants, and screening remains the intervention that actually prevents blindness.
Section 07 — Afterwards
Regression is not
the same as discharge.
Most ROP regresses. That is the single most reassuring fact in this subject and the one most often mistaken for the end of the story. An eye that had ROP — treated or spontaneously regressed — remains a different eye, and the follow-up schedule should reflect that.
A baby born at 33 weeks weighing 1750 g, ventilated briefly for respiratory distress and discharged home in good condition, would fall outside a screening criterion set at 30 weeks or 1500 g. Under India's wider criteria the same baby is screened, and it is precisely in this band that Indian series have described treatment-requiring disease — including aggressive forms that do not wait for an orderly progression through stages.
The failure mode here is not misdiagnosis. It is that the examination never happens, because nobody was told the baby needed one. By the time a parent notices something wrong with a two-year-old's vision, phase 2 finished eighteen months earlier.
For parents, the actionable version is short: if a baby was born preterm, ask explicitly whether a retinal examination has been scheduled, get the date in writing before discharge from the neonatal unit, and keep it even if the baby looks perfectly well — because at the stage where it is still fixable, the baby always does.
Section 08 — FAQ
Frequently asked questions
about retinopathy of prematurity.
Retinopathy of prematurity (ROP) is a disorder of the developing retinal blood vessels in babies born preterm. In the womb, retinal vessels grow outward from the optic nerve and normally reach the edge of the retina only near full term. A baby born early has an incompletely vascularised retina. After birth the relatively oxygen-rich environment first slows or halts that vessel growth, leaving peripheral retina without a blood supply. As the baby grows, that starved retina releases growth factors including VEGF, and vessels then regrow abnormally — as a ridge of tissue and, in severe disease, as fragile vessels that grow into the vitreous, scar and pull the retina off. It is a two-phase disease, and the damaging phase is the second one.
Thresholds differ by country. The American Academy of Pediatrics joint 2018 policy recommends screening infants with a birth weight of 1500 g or less or a gestational age of 30 weeks or less, plus selected larger or more mature infants whose clinical course has been unstable. India's national newborn eye-screening guidance uses a deliberately wider net — commonly cited as all babies born at about 34 weeks or less, or weighing about 2000 g or less — because Indian series have repeatedly reported severe ROP in bigger, more mature babies than Western criteria would capture. Any premature baby who received prolonged supplemental oxygen or had a stormy neonatal course should be examined regardless of where the numbers fall.
The first dilated examination is conventionally timed at about four weeks of chronological age or about 31 weeks postmenstrual age, whichever comes later, with the exact first-visit week set by gestational age at birth. The reason for anchoring to postmenstrual age is that ROP follows the retina's developmental clock more closely than the calendar since delivery. Follow-up intervals — typically one, two or three weeks — are then set by what the examiner finds, and screening continues until the retina is fully vascularised or the disease has clearly regressed.
Zone describes how far normal vessels have grown, measured from the optic disc. Zone I is the small posterior circle centred on the disc, Zone II the annulus beyond it, and Zone III the remaining temporal crescent. The more posterior the disease, the more dangerous it is, because less retina has been vascularised. Stage describes what the junction between vascularised and non-vascularised retina looks like: stage 1 a flat demarcation line, stage 2 a raised ridge, stage 3 a ridge with extraretinal fibrovascular proliferation, stage 4 partial retinal detachment and stage 5 total detachment. Plus disease — abnormal dilation and tortuosity of the posterior pole vessels — is recorded separately and is the single strongest indicator of activity.
Type 1 ROP is the treatment threshold defined by the Early Treatment for Retinopathy of Prematurity (ETROP) randomised trial: Zone I with any stage plus plus disease, Zone I stage 3 without plus disease, or Zone II stage 2 or 3 with plus disease. ETROP showed that treating at this earlier point produced better visual and structural outcomes than waiting for the older, more advanced threshold criteria. Treatment is conventionally advised within roughly 72 hours of the diagnosis being made because Type 1 disease can progress to retinal detachment over days, not months.
Both are in routine use and the choice is case-specific. Laser photocoagulation ablates the avascular peripheral retina, removing the source of the growth-factor drive; it is definitive, it does not depend on a drug reaching the eye, and its main cost is a permanently ablated peripheral retina and a tendency toward myopia. Intravitreal anti-VEGF blocks the drive chemically and allows peripheral vessels to continue growing; the BEAT-ROP trial found bevacizumab advantageous over laser specifically for Zone I stage 3+ disease, and the RAINBOW trial supported ranibizumab as an alternative to laser. The trade-off with anti-VEGF is that disease can reactivate weeks later, so follow-up must be longer and more disciplined, and questions about systemic VEGF suppression in a developing infant have not been fully closed.
Many do. Mild ROP frequently regresses spontaneously with no lasting visual consequence. But a history of ROP — treated or regressed — carries a higher lifetime rate of myopia, often high myopia, and also of strabismus, amblyopia, glaucoma and late retinal detachment, so these children need ophthalmic follow-up through childhood rather than a single discharge visit. Advanced disease that reaches stage 4 or 5 has a far worse prognosis; surgery for a detached premature retina can restore anatomy in some cases but rarely restores good functional vision, which is exactly why the screening window matters so much more than the surgical one.
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Retinopathy of Prematurity (ROP): Screening Windows, Zones, Stages & Treatment (2026 Guide)