Retinopathy of prematurity is a condition affecting preterm and low birth weight babies. It typically affects babies born before 32 weeks gestation. Abnormal development of the blood vessels in the retina can lead to scarring, retinal detachment and blindness. Treatment can prevent blindness, which is why screening is so important.
Pathophysiology
Retinal blood vessel development starts at around 16 weeks and is complete by 37 – 40 weeks gestation. The blood vessels grow from the middle of the retina to the outer area. This vessel formation is stimulated by hypoxia, which is a normal condition in the retina during pregnancy. When the retina is exposed to higher oxygen concentrations in a preterm baby, particularly with supplementary oxygen during medical care, the stimulant for normal blood vessel development is removed.
When the hypoxic environment recurs, the retina responds by producing excessive blood vessels (neovascularisation), as well as scar tissue. These abnormal blood vessels may regress and leave the retina without a blood supply. The scar tissue may cause retinal detachment.
Assessment
The retina is divided into three zones:
- Zone 1 includes the optic nerve and the macula
- Zone 2 is from the edge of zone 1 to the ora serrata, the pigmented boarder between the retina and ciliary body
- Zone 3 is outside the ora serrata
The retinal areas are described as a clock face, for example “there is disease from 3 to 5 o’clock”. The areas of disease are described from stage 1 (slightly abnormal vessel growth) to stage 5 (complete retinal detachment).
“Plus disease” describes additional findings, such as tortuous vessels and hazy vitreous humour.
Screening
Babies born before 32 weeks or under 1.5kg should be screened for ROP. Screening is performed by an ophthalmologist. Screening starts at:
- 30 – 31 weeks gestational age in babies born before 27 weeks
- 4 – 5 weeks of age in babies born after 27 weeks
Screening should happen at least every 2 weeks and can cease once the retinal vessels enter zone 3, usually at around 36 weeks gestation.
Examination
All retinal areas need to be visualised. Screening involves monitoring the retinal vessels as they develop and looking for plus disease.
Treatment
Treatment involves systematically targeting areas of the retina to stop new blood vessels developing.
First line is transpupillary laser photocoagulation to halt and reverse neovascularisation.
Other options are cryotherapy and injections of intravitreal VEGF inhibitors. Surgery may be required if retinal detachment occurs.
Last updated January 2020