Prematurity

Retinopathy of Prematurity (ROP), also known as retrolental fibroplasia (RLF) is an eye disease that occurs in some premature babies. It is during the final 12 weeks of a full-term delivery (28-40 weeks gestation), that the fetal eye undergoes a vigorous period of growth. The blood supply to the fetal retina starts at the optic nerve at 16 weeks of gestation. The vessels then gradually grow out over the surface of the retina, till they reach the anterior (front) edge, and stop their progression at about the time of birth.

With premature infants, the retinal vessels cease their normal pattern of growth, and new abnormal vessels begin to develop. There appears to be a barrier preventing the further growth of normal vessels, a barrier beyond which the normal vessels cannot pass. The retina anterior to, or in front of this "barrier" lacks an adequate oxygen supply, and probably exudes chemical signals that stimulate new vessel growth. As more and more of these new vessels grow in response to the chemical signals, they form arterio-venous shunts at the location of the barrier on the surface of the retina.

This shunt gradually enlarges, becoming thicker and more elevated. The new vessels are accompanied by fibroblasts, which produce fibrous scar tissue. Eventually, a ring of scar tissue is formed which is attached to the retina and to the vitreous gel, and which may extend for 360 degrees around the inside of the eye. When this scar tissue contracts, it pulls on the retina and produces a traction retinal detachment. If enough scar tissue forms and causes enough traction, the retina become completely detached, and the infant is blind. An international classification of ROP has been developed to standardize evaluation and research in this disease. This classification is not just a way to pigeonhole patients; learning about this classification is very helpful in understanding the disease process and rationale for treatment.

Fortunately, most premature infants do not develop ROP, and most infants with ROP improve spontaneously. However, the risk of severe visual loss is high enough to warrant ROP screening programs at most newborn intensive care units. If ROP does develop, it usually occurs between 34 and 40 weeks after conception, regardless of gestational age at birth. One might expect an infant born at 23 weeks gestation to have ROP at a younger age than an infant born at 33 weeks. However, both infants would probably develop ROP at about the same gestational age (37 weeks) rather than at the same chronological (post-natal) age.

The treatment of ROP is usually laser treatment. The laser treatment is applied to the retina anterior to the vascular shunt that does not yet have a blood supply. The purpose of the treatment is to eliminate the abnormal vessels before they lay down enough scar tissue to produce a retinal detachment. Other treatment options include cryopexy, scleral buckle, and vitrectomy.

Most infants with mild retinopathy of prematurity that resolves will have no remaining scar tissue. These infants usually develop normal central vision. However, some infants who undergo regression may have late complications of ROP, including strabismus (crossed eyes), amblyopia ("lazy eye"), myopia (near-sightedness), glaucoma and late onset retinal detachment.