Retinopathy of Prematurity
Retinopathy of Prematurity (ROP) is a potentially blinding condition that affects premature infants and is caused by the abnormal growth of blood vessels in the retina. The retina is a thin tissue that lines the inside of the eye, and that is responsible for receiving light and turning it into neurological messages to be sent to the brain. Infants born before 31 weeks gestation and weighing less than 2.75 pounds have a high probability of having ROP. The smaller the infant is at birth, the higher the chances of the infant having ROP. Most ROP resolves without causing retinal damage, but if severe, this condition can cause the retina to detach from the inside of the eye, and possibly blindness.
What causes ROP?
The development of ROP may be due to the presence of several risk factors. The eye starts to develop at approximately 16 weeks gestation, when the retinal blood vessels begin to form at the level of the optic nerve in the back of the eye. These vessels grow from the central retina to the periphery, providing oxygen and vital nutrients to the developing retina.
The eye develops rapidly during the last 12 weeks of pregnancy, so that by the time a full-term baby is born, growth of the retinal blood vessels is largely complete. However, if a baby is born prematurely, normal blood vessel growth stops before the vessels are able to reach the retinal periphery. Hence, the retinal periphery may not get enough oxygen and nutrients.
It is believed that at this point, the retina sends signals to other retinal areas for support and nourishment causing the growth and spread of new abnormal blood vessels. These new malformed blood vessels are delicate and can leak, leading to retinal scarring, contraction, and ultimately a retinal detachment. Retinal detachment is the main cause of vision loss in ROP.
Are there other risk factors for ROP?
Outside of birth weight and how early a baby is born, other factors that play a role in the potential development of ROP include anemia, blood transfusions, respiratory difficulties, and general health of the baby.
Are there other complications related to ROP?
Infants with ROP are more likely to develop retinal detachments, myopia(nearsightedness), strabismus (crossed eyes), amblyopia (lazy eye) and glaucoma. These conditions are often responsive to treatment.
What are the stages of ROP?
There are five stages of ROP from mild (stage I) to severe (stage V).
Stage I: There are very few, abnormal blood vessels. Many babies who develop stage 1 improve with no intervention and ultimately achieve normal vision. At this stage, ROP resolves on its own with no progression.
Stage II: The abnormal growth of blood vessels is more severe as compared to stage I; however, many premature infants who develop stage II still manage to improve without any treatment and are able to develop normal vision without any progression of ROP.
Stage III: The abnormal blood vessel growth can now be classified as severe. These abnormal vessels begin to grow and spread toward the center of the eye instead of following their normal pattern along the surface of the retina. Some babies with stage III ROP improve with no intervention and are able to acquire normal vision. However, if ROP worsens and the retinal vessels become enlarged and distorted, treatment for the condition becomes a consideration, especially since prevention of retinal detachment is a priority.
Stage IV: During this stage, the retina is partly detached due to the expansion of the abnormal leaky blood vessels, and consequent scarring and traction of the retinal surface.
Stage V: This is the most severe stage. At this endpoint in the disease, the retina is completely detached and immediate surgery to avoid permanent blindness becomes a priority.
Many babies do not go past Stage I or Stage II of ROP, but others who progress through Stages III to V require treatment in order to prevent or reduce the growth of abnormal blood vessels, and consequently to reduce the risk of subsequent retinal detachments.
How is ROP treated?
Treatment of advanced ROP often involves laser therapy or cryotherapy. Laser therapy causes burns in the peripheral retina, whereas cryotherapy involves using freezing temperatures to destroy parts of the retinal periphery. The objective of both of these therapies is to destroy areas of the retinal periphery in an effort to slow or reverse the growth of abnormal blood vessels and protect the area of the retina responsible for clear central vision.
Other treatments for the later stages of ROP include scleral buckle, and vitrectomy. Scleral buckle involves placing a tight silicone band around the eye to reduce traction on the retinal scar tissue, and to allow the retina to flatten down onto the wall of the eye. This procedure is reserved for stage IV and V ROP, and infants who receive a scleral buckle eventually need to have the band removed to allow the eye to continue to grow.
Vitrectomy involves removing the vitreous gel that fills the eye and gives it its shape, and replacing it with a saline solution. With the vitreous gone, scar tissue on the retina can be surgically removed, reducing retinal traction and allowing the retina to lay flat against the wall of the eye. Vitrectomies are typically only performed on stage V ROP.