Retinopathy of prematurity
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Retinopathy of Prematurity (ROP)
Definition & Pathophysiology
ROP is a proliferative vasculopathy affecting the developing retina of premature, low-birthweight infants and is one of the leading causes of childhood blindness worldwide.
The retina has no blood vessels until the 4th month of gestation; vascular complexes then grow from optic disc hyaloid vessels toward the periphery. The nasal retina is fully vascularized by ~8 months gestation, but the temporal periphery vascularizes at or up to 1 month after term delivery. Prematurity interrupts this process in two phases:
- Hyperoxic phase (supplemental O₂ in NICU): Retinal vessels undergo vasoconstriction and obliteration — vascular growth is arrested.
- Hypoxic/vasoproliferative phase: The growing, metabolically active avascular retina becomes hypoxic, triggering VEGF-driven abnormal neovascularization at the vascular–avascular junction.
— Kanski's Clinical Ophthalmology, 10e; Harriet Lane Handbook, 23e
Risk Factors
| Major | Additional |
|---|---|
| Gestational age ≤30–32 weeks | Supplemental oxygen use |
| Birth weight <1,500 g | Neonatal sepsis |
| Prematurity (degree correlated to risk) | Hypoxemia / hypercarbia |
| — | Anaemia, low vitamin E |
| — | Failure to thrive |
| — | Caucasian race, male sex |
Risk factors are additive when concurrent. — Wills Eye Manual; Kanski's
Classification (ICROP 3rd Edition, 2021)
Zones (centred on the optic disc)
- Zone I: Posterior pole — radius = 2× the disc-to-fovea distance. Worst prognosis.
- Zone II: From zone I edge to the nasal ora serrata.
- Zone III: Residual temporal crescent anterior to zone II.
The zone of the most posterior ROP lesion defines the zone. An incursion 1–2 clock hours into a more posterior zone = a "notch."
Stages
| Stage | Description |
|---|---|
| 1 | Thin flat grey-white demarcation line at vascular–avascular junction |
| 2 | Ridge — elevated, has height and width; small neovascular tufts may appear posterior to it |
| 3 | Extraretinal fibrovascular proliferation extending into vitreous from ridge (mild/moderate/severe); peaks ~35 weeks post-conceptual age |
| 4A | Partial retinal detachment — extrafoveal |
| 4B | Partial retinal detachment — involving fovea |
| 5 | Total retinal detachment |
"Plus" Disease
At least 2 quadrants of posterior pole venous engorgement and arterial tortuosity. Denoted with "+", e.g., Stage 3+. Advanced plus disease also shows iris vascular engorgement, poor pupil dilation, and vitreous haze.
Pre-plus disease: Intermediate vascular changes insufficient to diagnose plus disease.
Aggressive posterior ROP (AP-ROP): Rapidly progressive zone I disease with extensive plus disease; may skip stages and progress directly to stage 5. Hemorrhages at the vascular–avascular junction may be present.
Type Classification (Treatment Guidance)
| Type | Criteria | Action |
|---|---|---|
| Type 1 (high-risk, treat) | Zone I, any stage with plus; Zone I, stage 3 without plus; Zone II, stage 2 or 3 with plus | Treat within 48–72 hours |
| Type 2 (watch closely) | Zone I, stage 1–2 without plus; Zone II, stage 3 without plus | Close follow-up |
— Wills Eye Manual; Kanski's Clinical Ophthalmology
Fundus Images
Staging Reference
Stage 3 ROP — Ridge with Extraretinal Proliferation
Progression Stages 1–3 and Laser Treatment
Screening
| Criterion | Detail |
|---|---|
| Indication | All infants with birth weight ≤1,500 g or gestational age ≤30 weeks |
| Also screen | Infants >30 wks with unstable clinical course / cardiorespiratory support |
| First exam timing (≤27 wks GA) | At 31 weeks postmenstrual age (PMA) |
| First exam timing (≥28 wks GA) | At 4 weeks chronologic age |
| <25 wks GA | Consider at 6 weeks chronologic age (earlier if severe comorbidities) — to detect AP-ROP |
Examination is by dilated indirect ophthalmoscopy.
— Harriet Lane Handbook, 23e; Wills Eye Manual
Treatment
Type 1 ROP / Threshold Disease
Laser photocoagulation (preferred over cryotherapy) — near-confluent ablation of the avascular peripheral retina. Must be done within 48–72 hours of diagnosis.
Anti-VEGF Therapy
Intravitreal bevacizumab (0.625 mg / 0.025 mL) is an emerging option, particularly for:
- Zone I cases (very posterior disease)
- When laser is not available
Long-term systemic effects in preterm infants are not yet fully established. If anti-VEGF is used, extended follow-up is mandatory due to risk of recurrence after 65–70 weeks PMA if retinal vascularization remains incomplete.
Stages 4–5 (Retinal Detachment)
Surgical repair by vitrectomy.
— Wills Eye Manual; Kanski's Clinical Ophthalmology
Cicatricial (Regressed) Disease
~20% of infants with active ROP develop cicatricial complications:
- Temporal vitreoretinal fibrosis
- Straightening of vascular arcades
- Macular dragging (disc and macula dragged temporally)
- Falciform retinal fold
- Retinal detachment / total detachment ("retrolental fibroplasia")
- Secondary angle-closure glaucoma (forward displacement of iris-lens diaphragm)
More posterior and more advanced active disease → worse cicatricial sequelae. — Kanski's Clinical Ophthalmology
Follow-Up Schedule
| Finding | Follow-up interval |
|---|---|
| Zone I, no ROP; zone I stage 1–2; zone II stage 3; AP-ROP concern | ≤1 week |
| Posterior zone II, immature; zone II stage 2; zone I regressing | 1–2 weeks |
| Zone II, no ROP; zone II stage 1; zone II regressing | 2 weeks |
| Zone III stage 1–2; zone III regressing | 2–3 weeks |
Discontinue acute screening when: Zone III vascularization attained without prior zone I/II ROP; PMA ≥50 weeks with no disease worse than zone II stage 3; or full vascularization to the ora serrata (for anti-VEGF–treated eyes).
Lifelong annual follow-up is indicated due to increased lifetime risk of myopia, strabismus, amblyopia, macular dragging, cataracts, glaucoma, and retinal detachment. — Wills Eye Manual
Differential Diagnosis
- FEVR (Familial Exudative Vitreoretinopathy): Hereditary, often asymmetric, no prematurity history
- Incontinentia pigmenti: X-linked dominant (girls); skin, CNS, dental anomalies
- Other causes of leukocoria (retinoblastoma, Coats disease, etc.)
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