November 17, 2000

Eye surgeries repair defects of prematurity

Featured Image

Dr. Khaled Tawansy performs an eye surgery on patient Kayla House as Dr. Terry Semchyshyn assists. (photo by Dana Johnson)

Eye surgeries repair defects of prematurity

Illustration by Dominic Doyle

Illustration by Dominic Doyle

Four-month-old Kayla House lies swaddled, draped and under sedation in a dark operating room. A tiny speculum props open her tiny right eye, its pupil dilated to the size of a small marble.

Kayla and her twin sister Katelynn were born at 25 weeks gestation. In a regular screening in Vanderbilt University Hospital’s neonatal intensive care unit Dr. Khaled Tawansy, assistant professor of Ophthalmology and Visual Sciences, detected in Kayla retinopathy of prematurity, (ROP), detachment of the retina caused by the irregular growth of blood vessels in the eye.

Peering through a microscope, Tawansy penetrates the sclera, the white of Kayla’s eye, through a narrow anatomical window between the retina and lens into the vitreous gel and detached retina.

Tawansy joined VUMC in January 1999 following fellowship training in surgical retina at the University of British Columbia and medical retina with Dr. Gass at Vanderbilt. He trained in Boston and Detroit with two of the pioneers of pediatric vitrectomy, the surgical procedure that offers the best hope for allowing Kayla’s eyes to develop functional vision. During the year, Tawansy learned two techniques – one a closed procedure, the one Kayla will receive. The other, an “open sky” technique, is for more advanced stages of ROP and involves the removal of the cornea, opening the eye’s anatomy for more direct access to the destructive scar tissue and creating a larger workspace. Recently, Tawansy developed his own hybrid technique for the most challenging cases, a combination “open-closed” approach.

Techniques aside, Kayla stands a good chance at normal retinal development and fairly good vision because the ROP was detected early.

“We try to intervene as soon as possible because prognosis depends largely on the stage of retinopathy at surgery,” Tawansy said. Within days, the detachment can evolve from partial to complete, and from open funnel to closed funnel, he said.

Normal vascularization of the retina is usually complete around the 40th week of fetal development. Vessels begin their growth at the optic nerve and progress outward to the peripheral retina. Premature children are exposed to ambient oxygen that temporarily halts normal vessel development. Later, growth factors produced by the oxygen-deprived nonvascular retina stimulate new proliferation at the leading edge of the intrinsic vessels. Most of the time retinal vascularization resumes normally, but half of the children born before 26 weeks or weighing less than 1250 grams will develop some manifestation of ROP. In these cases the vessels begin to grow inside the vitreous – the jelly-like substance inside the eyeball. The vessels become fibrous and contractile and pull on the retina.

Nationally, about 2,000 kids each year suffer blindness or severe visual impairment from ROP, Tawansy said. But the majority of children with ROP about 85 percent will spontaneously resolve, avoiding retinal problems without intervention The remaining 15 percent will suffer retinopathy sufficient to require a laser procedure that sacrifices the avascular retina, eliminating the ischemia that drives intravitreal vessel growth. This procedure works for at least half of the kids. The others will require one of Tawansy’s techniques.

In advanced ROP, the retina has detached and becomes plastered to the back of the lens or the ciliary processes in the front of the eye. Entering the eye through the sclera is too dangerous, Tawansy said, because the retina is in folds that can not be visualized and may be torn. So the cornea is removed, and the “open-sky” allows a two-handed dissection of the vessels and fibrous tissue from front to back.

Kayla’s retina had only begun to be tugged away from its supportive pigment layer. The first step of correction, the laser procedure, had been performed by Dr. Robbin Sinatra, assistant professor of Ophthalmology and Visual Sciences. It significantly decreases the incidence of total retinal detachment, Tawansy said, and most children develop near-normal sight after laser.

Kayla’s left eye responded well to the laser treatment, but the irregular vascularization in the right eye was farther along and had begun to pull the retina. Still, her ROP was caught early enough to allow Tawansy to perform the less invasive closed procedure.

Tawansy threads an irrigating light through one port and a vitreous cutter through the other. The scope illuminates the tangled contracting vessels, like the satellite view of a confluence of young rivers. In minute movements, Tawansy cuts away the culprit tissue without disturbing the lens, and the retina relaxes to its normal position.

In the most advanced stages of ROP dissection of the abnormally growing vessels and fibrous vitreous material is required from the front to the back of the eye. The retinal folds in the front make a closed approach risky, yet the open-sky approach makes reaching the back of the eye difficult, Tawansy said. Hence his new combined open-closed technique.

There is some debate about when to perform vitrectomy, or if to perform it at all in children with advanced detachment, Tawansy said. “In those that have appropriate laser and have early surgery when the retina is partially detached, our success at reattachment can exceed 90 percent,” he said. The emphasis is on timely screening in the neonatal intensive care units. In children with advanced detachments and no laser children who generally have not been screened – the rate of reattachment with aggressive surgery is 30 percent to 40 percent, Tawansy said.

“We feel strongly that it is important to do everything possible even for these children with advanced disease, because they are able to make maximal use of any bit of functioning retina that we can salvage,” he said. A child’s vision can be progress from no having no light perception to having light perception, or from seeing hand motion to 20/800 vision. “The difference and the impact on the children’s function throughout their lifetime are enormous,” he said. Consequently, he has developed his combination open-closed method. He has performed this surgery successfully on three eyes this year.

On the day of Kayla’s vitrectomy her mother, Jennifer Neighbors, realized the risks her new daughter faced. “If we didn’t do the surgery, she might be blind. But if we did the surgery there was a chance it would help, or it might not,” she said.

A week later, in a follow-up visit, Kayla’s retina had settled and looked quiet. The traction was relieved and the destructive new vessels were regressing.