Retinopathy of Prematurity: An Epidemiological Perspective
By John T. Flynn, MD
Vast improvements in neonatal care over the past few decades have resulted in the saving of many premature babies who never would have survived just 20 or 30 years ago. Extremely low birth weight babies are living today at a rate of 85-90 percent - and in the best nurseries in the US, well in excess of 90 percent. With the exportation of modern neonatology to developing nations, many more babies are surviving there, too.
In developing countries, Retinopathy of Prematurity (ROP) is often not identified and treated. This is the case in much of Central and South America, so much so that at the Bascom Palmer Institute, once or twice a month - and sometimes as often as three or four times - an 18-month or two-year-old child with stage 5 retinopathy of prematurity could be seen. No eye doctor had seen these children. In general, this is because ophthalmology has not kept pace with neonatology. In developing countries, ROP is largely ignored by ophthalmologists.
ROP - A Disease of Developing Retinal Blood Vessels
When you first look in a premature baby's eye, very early at around 26 or 27 weeks, nothing can be seen by the examiner because everything is very hazy. Huge developmental processes are occurring; a capillary meshwork that will give rise to mature arteries and veins is developing. But ROP wipes out the tissue of the capillary meshwork. The two tissues left, the mesenchyme and the pluri-potent tissue, unite to form the classical lesion of ROP. When the haze clears and ROP is present, you see characteristic dilated, tortuous vessels at the back of the eye leading to the optic nerve. This tissue no longer grows in the retina, but rather, escapes into the vitreous. It starts to pull the entire retina, like a rug, across the inner surface of the eye and tears the retina off its bed of pigment epithelium.
Fluorescein Angiograms - The First Images of an ROP Lesion
The first picture of what ROP looks like was captured by a fluorescein angiogram.
The lesion in the retina can be seen, along with the avascular retina, the vascularized retina, and the circumferential tissue at the retinal vasculature, which is circular in nature and centered on the optic disk. The tissue fills with fluorescein and leaks due to a lack of tight junctions between cells, as capillaries require tight junctions.
The Stages of ROP - Opening International Discussions
Steps are just beginning to facilitate communication among ophthalmologists around the world to identify early cases of ROP. Among them is the creation of a universal classification system that allows us to discuss ROP with ophthalmologists worldwide.
The classification of the disease has allowed us to have a syntax, grammar and vocabulary, so that we can speak the same language with German, Hungarian or Japanese ophthalmologists about ROP. And speaking the same language gave rise to an international classification system, laying the foundation for further international collaboration.
A second step is the use of digital imaging to share images of neonates' eyes at risk for end-stage ROP. Digital imaging has provided a means for non-ophthalmologists to help screen for ROP by using a digital camera and a high-speed modem that can instantaneously send a high-quality image to an ROP expert.
Digital cameras can now take a picture of a baby's fundus (the fundus of the eye includes the retina, macula, fovea, optic disc and retinal vessels) and send it anywhere in the world almost instantaneously over a high-speed modem to be read by ROP experts. These pictures don't necessarily have to be taken by an ophthalmic photographer with several years of training; neonatal nurses can learn how to take them, enabling ROP to be identified in neonatal intensive care units where there are no ophthalmologists. This represents a major advance in the field, as the nursery can be alerted when a baby has a serious disease and requires immediate treatment by an ophthalmologist.
The following chart shows the prevalence of ROP in countries that supply statistics.
Retinopathy of Prematurity: Outcome/100,000 Live Births | |||
|
Country |
ERA |
Type of Study |
Outcome/ |
|
England |
1/84 - 12/87 |
Retro, |
12.4 Blind, SVI |
|
Sweden |
17 years |
Retro, |
10.9 Blind, SVI |
|
Holland |
1975-85 |
Retro, |
4.2 versus 5.1 |
|
Nordic Countries (4) |
17 years |
3.8M Children of 17M Total Pop. |
12 - Denmark |
Unfortunately, U.S. statistics are not particularly sound. In England, 12.5 per hundred thousand live births experience either blindness or severe visual impairment. While this may not seem like many, consider that we're speaking of a very special and very small population of premature infants. In Holland, the prevalence was lower earlier on than it is today. This is probably due to that fact that between 1975 and 1985, fewer tiny babies were born.
A major aspect of ROP that we don't understand - and that remains a challenge to the young people who are coming into ophthalmology - is that in 90+ percent of cases of ROP the condition gets better on its own. Diabetic retinopathy doesn't get better on its own. Nor does sickle cell retinopathy. We don't understand the mechanism behind this phenomenon. We have no cure for the disease, but when it improves, we call it regression.
To paraphrase Winston Churchill: We are not at the end of the story of retinopathy of prematurity, nor at the beginning of the end, but, rather, at the end of the beginning of the story.
By John T. Flynn, MD, Chief of the Division of Pediatric Ophthalmology, Edward S. Harkness Eye Institute, Columbia University, New York, NY
From Lighthouse International's EnVision newsletter (Summer 2002 issue)