How Is ROP Diagnosed and Staged?
An instrument called a binocular indirect ophthalmoscope is used to examine for ROP. Eye drops are used to dilate the pupils before examination, allowing for a better view of the retina. A stabilizing device may be used to hold the eyes open during the examination. Photographs of the retina may also be taken.1,2
ROP is classified by describing 3 key features2,5
- Zone: refers to the location of retina affected
- Stage: refers to severity of disease, ranging from stage 1 (mild) through 5 (severe)
- Appearance of retinal blood vessels: refers to the presence or absence of “plus” disease
Although development of ROP typically occurs in both eyes, each eye may have different zone, stage, and plus disease classifications.4,5
Area of the retina affected: "Zone"
Zone 1 includes the center of the retina, the area of the retina responsible for the clearest, straight-ahead (central) vision. Zones 2 and 3 are each further away and are responsible for side (peripheral) vision. Because of the effect on central vision, ROP is more of a threat to vision in zone 1 than zone 3.5
Severity of disease: “Stage”
There are five stages of severity of ROP. Higher numbered stages represent more severe disease and threat to vision than lower numbered stages.5
Appearance of blood vessels: evaluating for “plus” disease
ROP is also classified by the shape of the retinal blood vessels. If the blood vessels are wider or twisted, it may indicate more severe disease, called “plus.” Plus disease can indicate a worsening of ROP.2,5
References
- Fierson WM, American Academy of Pediatrics Section on Ophthalmology; American Academy of Ophthalmology; American Association for Pediatric Ophthalmology and Strabismus; American Association of Certified Orthoptists. Screening examination of premature infants for retinopathy of prematurity. Pediatrics. 2018;142(6):e20183061.
- American Association for Pediatric Ophthalmology and Strabismus. Retinopathy of Prematurity. Last updated April, 2023. https://aapos.org/glossary/retinopathy-of-prematurity
- Inoon A. Look into their eyes. MediScene. 2007;42(07). https://www.sundaytimes.lk/070715/MediScene/ms_7.html
- Molinari A, et al. Classifying retinopathy of prematurity. Community Eye Health. 2017;30:55-56.
- Chiang MF, Quinn GE, Fielder AR, et al. International Classification of Retinopathy of Prematurity, Third Edition. Ophthalmology. 2021;128(10):51-68.
- University of Maryland Medical Center. Retinopathy of Prematurity (ROP). https://www.umms.org/ummc/health-services/ophthalmology/pediatric/rop
- Safer Care Victoria. Retinopathy of prematurity (ROP). Last updated February 17, 2021. https://www.safercare.vic.gov.au/clinical-guidance/neonatal/retinopathy-of-prematurity-rop
- Bozell C. Normal fundus image. Retina image bank. 2018;28545. https://imagebank.asrs.org/file/28545/normal-fundus-image
- Ells AL. Stage 3 ROP. Retina Image Bank. 2018;28486. https://imagebank.asrs.org/file/28486/stage-3-rop
All URLs accessed December 23, 2025.
