"This study was important because it identified when we should operate and intervene to prevent retinal detachment and total blindness without placing the infant at risk of surgical trauma and its consequences," said Dr. Mary Elizabeth Hartnett, associate professor of ophthalmology in UNC's School of Medicine.
The new findings appeared in the April issue of the journal Retina. Hartnett is the study's lead author.
Retinopathy of prematurity (ROP) is an eye disease causing 550 cases of blindness annually in the United States and many more worldwide. "Prevention of progression to retinal detachment is preferable to surgery to reattach a totally detached retina because even with successful surgery to reattach a totally detached retina, vision can be extremely poor," Hartnett said.
Preterm infants less than 2.7 pounds or less than 28 weeks gestational age are particularly at risk from ROP, since they are born with an immature retina with incomplete blood vessel development, Hartnett said. This leaves a retina area without a blood or oxygen supply, and this ischemic situation then stimulates new blood vessel growth, or angiogenesis.
"But this angiogenesis grows in the wrong part of the eye," Hartnett said. "When the blood vessels grow they grow into the vitreous, the clear gel above the retina. The blood vessels are immature and leak substances that cause scarring and later retinal detachment." The current recommended treatment for severe ROP preceding stage 4 or retinal detachment is laser ablation of the ischemic retina, a process thought to destroy tissue that produces substances causing unwanted angiogenesis into the vitreous.
"These treatments help reduce the risk of retinal detachment by at least 50 percent," she said. "But that still leaves a certain number of infants that develop stage 4 ROP, which is early, partial retinal detachment. What we want to do is prevent stage 5 ROP, total retinal detachment."
Not all stage 4 ROP progresses to retinal detachment, Hartnett added, and the surgery poses risks such as infection, bleeding and surgical trauma. "So, this study sought to determine which infants, who had laser treatment for severe ROP and who didn't have regression of disease, needed to have surgery to prevent progressive stage 4 ROP and subsequent risk of blindness."
The researchers reviewed the retinal eye exam charts of infants who had been treated with laser but still developed stage 4 ROP. They found that the infants had specific features within the eyes two weeks before the development of progressive stage 4 ROP that should tell the surgeon to consider surgery: an increased extent of elevated tissue at the junction of the normal retinal blood vessels and the area of retina without blood vessels, dilated blood vessels in half the retina or more (called plus disease), and increasing vitreous cloudiness.
The extent of the abnormal blood vessels growing into the vitreous previously had always been considered an indication of disease progression. Surprisingly, this study did not support that feature as predictive of later retinal detachment.
"Instead, if unwanted intravitreous angiogenesis is found, that should clue the surgeon into looking for areas missed during the laser treatment and to treating these areas," Hartnett said.
"The findings in this study need to be confirmed with a larger prospective study, if that is possible, given that stage 4 ROP is not a very common condition. For now, this study provides guidance to the ophthalmologist monitoring infants who received laser treatment for severe ROP as to when surgery may be necessary to prevent progressive stage 4 ROP, total retinal detachment, and blindness."
By JAN MCCOLM
UNC School of Medicine