Retinopathy of prematurity (ROP) is a condition of the eye that threatens sight, and is seen typically in children whose body weight is at or below 1250 grams, or who are born before the 31st week of pregnancy is completed.
The risk of developing ROP increases as the gestational age at which the baby is born goes down. The incidence is going up because of the increased survival of very low birth weight babies with modern technology.
This condition is among the major causes of childhood visual impairment. Its effects occur in both eyes, and may last throughout life in the form of poor sight and blindness. However, in the 90% of cases where the deficiency of vision is very mild, normal vision may be regained. The remaining 10% of infants with ROP remain severely visually challenged or are legally blind.
Stages of ROP
ROP occurs in different stages, namely:
Stage 1: A mild degree of retinal vessel growth, which is often associated with transient visual impairment
Stage 2: Moderately abnormal retinal vessel growth, again often transient, which eventually resolves spontaneously
Stage 3: Severely abnormal retinal growth, in which the blood vessels grow towards the center of the eye rather than along the retinal surface. This is often associated with plus disease, an advanced phase of stage 3, in which the retinal vessels themselves become dilated and tortuous. The threatened outcome with plus disease in stage 3 is retinal detachment. Few infants with stage 3 disease escape with normal vision.
Stage 4: Partial detachment of the retina, due to traction produced by scar tissue on the retinal surface. This in turn is the result of subretinal hemorrhage from the abnormal and fragile vessels.
Stage 5: Complete retinal detachment, which results in serious visual loss or blindness. This is the final stage of the disease.
Complications of ROP
Most infants who have ROP develop either stages 1 or 2, and grow up to have normal vision. However, ROP is still associated with a higher chance of complications in later life such as:
- Retinal detachment
For this reason, such patients require lifelong follow up.
Causes of ROP
ROP is due to a failure of the retinal vessels to grow to the edges of the developing retina, because of very preterm delivery.
Retinal development is normally completed within the last trimester of pregnancy.
In babies born before 31 weeks, the retinal vessels have not reached the periphery of the retina, which is therefore deprived of adequate blood supply.
The resulting chemical signals from the retina are presumed to stimulate vascular growth, resulting in the appearance of fragile abnormal new vessels on the retina.
These break and bleed easily and result in the formation of retinal scars, which lead to the occurrence of retinal detachment.
Other factors which contribute to the incidence of ROP include:
- Blood transfusions
- Respiratory distress
- Poor medical status of the infant
- Heart disease
- High carbon dioxide levels in the blood
- Hypoxemia and acidosis
Diagnosis and Treatment
Since ROP does not produce any symptoms, regular examination of the eyes of premature infants is the only way to detect it.
The treatment of ROP is limited to techniques which destroy the peripheral relatively avascular parts of the retina, and thus prevent neovascularization of this region.
Laser photocoagulation is used to produce controlled burns, while cryotherapy uses a freezing probe (cryoprobe) to achieve the same aim of irreversible death of the cells in this region.
This is effective in limiting abnormal vascular growth in the retina and preserving macular vision. However, it is achieved at the cost of destroying much of the peripheral visual field.
Scleral buckling and vitrectomy are other approaches which are used at later stages (4 or 5).
In a few cases which conform to strict guidelines, an anti-VEGF molecule called bevacizumab is injected into the eye to arrest and prevent the growth of the abnormal vessels. This molecule may have serious effects on lung and brain development because of its activity against vascular growth, which is why its use is restricted.
If retinal detachment occurs in spite of treatment, it may be left alone if only partial detachment has occurred. However, if it threatens to progress and involve the macula, measures may be taken to reattach the retina, such as laser or cryoretinopexy.