Retinal Vascularization Development in Premature Infants
The 2003 American Thoracic Society/American Journal of Respiratory and Critical Care Medicine statement on chronic lung disease demonstrates that retinal vessels begin growing at approximately 16 weeks of gestation and do not reach the edge of the retina (ora serrata) until full term, making premature infants born with incomplete retinal vascularization highly susceptible to injury. 1
Key Developmental Timeline
The evidence clearly establishes the incomplete nature of ocular development at birth in premature infants:
- Retinal vessel growth initiates at 16 weeks of gestation and progresses outward from the optic nerve toward the peripheral retina 1
- Premature infants are born long before retinal vessels reach the ora serrata, leaving large areas of avascular retina 1
- The incomplete vessels are highly susceptible to injury from prolonged elevated arterial oxygen (days of exposure) and other severe physiologic stressors 1
Clinical Implications of Incomplete Vascularization
The immature retinal vasculature creates a biphasic injury pattern:
- Initial injury phase: Occurs when incomplete vessels are exposed to hyperoxia or other stressors, causing a delay in normal vascularization 1
- Neovascularization phase: After injury, vessels grow excessively in response to vascular growth factors produced by the now-metabolically demanding avascular retina, manifesting as retinopathy of prematurity (ROP) 1
Oxygen Management Considerations
The incomplete retinal development creates a clinical dilemma in managing premature infants with chronic lung disease:
- Maintaining adequate arterial oxygenation to prevent cor pulmonale can conflict with the need to carefully manage oxygen levels when the retina remains incompletely vascularized 1
- High arterial oxygen levels slow normal vascularization, while marginally low oxygen aggravates neovascularization following initial injury 1
Screening Implications
First ROP screening should occur at 31-33 weeks postmenstrual age or 4 weeks chronological age, whichever is later, as recommended by the American Academy of Pediatrics 2. This timing reflects the period when incomplete vascularization places infants at highest risk for developing threshold disease requiring treatment 2.
The evidence demonstrates that extreme prematurity is the single most important risk factor for both ROP and incomplete retinal development, with incidence and severity increasing as gestational age at birth decreases 1.