May 2010

 

OPHTHALMOLOGY NEWS

 

OCT helps to identify retinoschisis


by Maxine Lipner Senior EyeWorld Contributing Editor

   

New sight-threatening complication detected

retinal scans Diagnosing ROP with retinal scans; OCT may play a new role in diagnosing vision changes Source: Michael F. Chiang, M.D.

Using a hand-held spectral domain optical coherence tomography (OCT) imaging device may help practitioners to pinpoint sight-threatening changes such as retinoschisis in infants with progressive retinopathy of prematurity (ROP), according to Thomas C. Lee, M.D., associate professor of ophthalmology, University of Southern California, and director, Retina Institute, Children’s Hospital Los Angeles. In a recent study published in the January 2010 issue of Archives of Ophthalmology, investigators found that use of the device helped to identify eyes with sight-threatening retinoschisis.

ROP is an all-too-common phenomenon among neonates. “Of children born weighing less than 1250 grams, 10% will develop ROP that’s advanced enough that in the absence of treatment 50% will go blind,” Dr. Lee said. “About one out of every 100 kids can go blind from ROP despite going to the [neonatal intensive-care unit], getting screened, and getting laser treatment. Depending on how young the child is, the rate of blindness can approach 30% –50% despite laser treatment.”

For children born prematurely the difficulty is that the eye is not yet fully vascularized. “At 30 weeks of gestation vascular development starting at the optic nerve radiating outward is incomplete,” Dr. Lee said. Such vascular development can then become arrested. Some suspect that this has something to do with being exposed to atmospheric oxygen. “When a baby sees atmospheric oxygen its body is being exposed to a much higher level than it would be if it were still in the womb,” Dr. Lee said. “In the womb oxygen tension runs 2%. Once the baby hits the atmosphere that jumps to 18%—that’s a nine-fold increase.”

Chaotic blood vessel growth

The pattern of blood vessel development in these ROP-affected children is altered. “The growth of blood vessels into the retina slows down,” Dr. Lee said. “It’s not so much that the blood vessels stop growing, they’re just not growing in the right direction.” Many times the blood vessels start to pile up. “They don’t know where to go so these sprouting blood vessels at the interface at the leading edge of the vascular retina start to grow in a very chaotic manner that’s not directional,” he said. “They basically stop and accumulate in that one area.”

As the child develops, the blood vessels can begin to grow off the retina, which can sometimes lead to a tractional retinal detachment. “It usually takes about 10-20 years in a diabetic to develop enough scar tissue and fibrosis to cause traction,” Dr. Lee said. “ROP is 20 years worth of diabetes in 3 weeks—a child can go blind from ROP in a matter of 7 days.”

Patients who fail laser treatment are at a heightened risk. “The reason that they fail is that the scar tissue starts to tug on the retina and it’s a very subtle detachment,” Dr. Lee said. “By the time the detachment is obvious it’s too late.”

As a result, Dr. Lee finds that typical methods for screening the eye with an indirect ophthalmoscope are usually ineffective. “I describe using an indirect ophthalmoscope like being on top of a 10-story building and trying to read the license plates of the cars below,” he said. However, the hand-held spectral domain OCT offers much more clarity. “Its images are on the order of 5-7 microns and it’s done very quickly,” Dr. Lee said. “Using this is like reading license plates but now you’re on the street level and you’re looking right at the car.”

While initially investigators thought that the OCT technology would be useful in identifying subtle retinal detachments in ROP eyes, they soon realized that there might be something else at work. “It became clear that these weren’t necessarily retinal detachments,” Dr. Lee said. “That’s where it completely changed how we look at this disease.”

Unlike a typical retinal detachment where the retina remains intact, in many of these cases the tissue was disturbed. “Some of the children were having traction that was developing in such a way that it was actually filleting the retina in half much like you would a fish,” Dr. Lee said. “That’s an irreversible, permanent degree of damage.”

Identifying retinoschisis

In the recent retrospective consecutive case series of three patients with progressive ROP, despite laser photocoagulation using the OCT, investigators identified presumed retinoschisis in all five study eyes. One eye that was identified as having exudative retinal detachment following laser photocoagulation was excluded from the study. This has implications for how practitioners may proceed in these progressive cases. “We’re recognizing that we can’t do this surgery thinking that we’ll recover vision if there’s retinoschisis,” Dr. Lee said. “It also lowers my threshold for going in because I know right away that I’ve already lost vision in the retina and I don’t want to lose more.” The OCT can be used to help parents understand the implications of what is occurring in the retina. “With the OCT I can show them what’s going on in the child’s eye, like a movie,” Dr. Lee said. “When they see this movie the light bulb goes on in their head and they say, ‘You can take care of this problem now.’”

Dr. Lee hopes that practitioners will come away from the study knowing that there are very subtle yet dangerous changes that happen in these children’s eyes that can be difficult to detect. “I think that clinicians must be aware that children who have had laser treatment who remain active may be developing retinoschisis where you would otherwise say the retina still looks attached,” he said. “Clinicians shouldn’t be under the impression that just because there isn’t detachment there isn’t some other form of damage.”

Editors’ note: Dr. Lee has no financial interests related to his comments.

Contact information

Lee: 323-361-2299, thlee@chla.usc.edu

OCT helps to identify retinoschisis OCT helps to identify retinoschisis
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