Type 1 retinopathy of prematurity in zone I represents the most severe type of ROP and has the worst prognosis. It is unknown whether low-dose bevacizumab will be successful in these severe cases. Also unknown is the timing and extent of peripheral retinal vascularization after low-dose bevacizumab compared with the standard dose. The current study will evaluate whether doses of 0.063 mg and 0.25mg are effective as treatment for type 1 ROP, with ROP and retinal vessels all in zone I.

Infants with type 1 ROP and no prior treatment for ROP will be randomly assigned (1:1) to treatment with either intravitreous bevacizumab 0.063 mg or either intravitreous bevacizumab 0.25 mg. Study exams will be at 1 day, 4 days (if no improvement on day 1), 1, 2, 3, and 4 weeks, and at 2 and 4-months post-treatment (and re-treatment when indicated). Additional study exams will occur at adjusted age 6 and 12 months. Non-study examinations will be at clinician discretion and are likely to occur more often. The primary outcome will be treatment success within each dose group, defined as improvement by the day 4 exam and no recurrence of type 1 ROP or severe neovascularization requiring additional treatment within 4 weeks of injection. Important secondary outcomes include safety and efficacy. refractive outcomes, and the extent of retinal vascularization at 2 and 4 months post-injection between the two dose groups.

Inclusion Criteria:

The study participant must have at least one eye meeting all of the inclusion criteria in order to be eligible to participate:

1. Birth weight < 1251 grams
2. Newly diagnosed (within 2 days) type 1 ROP in zone I in one or both eyes

Exclusion Criteria:

Participants meeting any of the following exclusion criteria will be excluded from study participation.

1. Previous treatment for ROP
2. Stage 4 or 5 ROP in either eye
3. Treatment could not be done within 2 days of diagnosis of type 1 ROP
4. Investigator unwilling to randomize or parent unwilling to accept randomized assignment to either treatment
5. Transfer to another hospital anticipated within the next 4 weeks where exams by study-certified examiners are not available. If hospital discharge is anticipated within the next 4 weeks, parents unable or unwilling to return to the PEDIG site for outpatient follow-up visits.
6. Active ocular infection or purulent nasolacrimal duct obstruction in either eye

One eye will be excluded, and other eye may be eligible, if either of the following are present:

• Visually significant ocular anomaly (e.g., cataract, coloboma)
• Opacity that precludes an adequate view of the retina

In accordance with the NIH data sharing policy, a de-identified database is placed in the public domain on the Pediatric Eye Disease Investigator Group (PEDIG) public website after the completion of each protocol and publication of the primary manuscript.

Data will be made available after publication of each primary manuscript.

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