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Possible mechanism behind retinal damage in severe stage 5 ROP recently recognized
Poor visual results even when the retina is reattached may be due to retinal vascular compromise or occlusion.
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MONTREUX, Switzerland – Reduced or occluded retinal circulation due to distortion of retinal vessels may be a principal cause of irreversible retinal damage in severe retinopathy of prematurity. This may lead to poor visual results even when the retina is reattached, according to a presentation at the Club Jules Gonin meeting here.
“It’s a mechanism that has not been recognized previously, and that is triggered by retinal traction,” said Michael T. Trese, MD, of Royal Oak, Mich. “We refer to it as the ‘garden hose’ phenomenon, because the intrinsic blood vessels of the retina are kinked and bent just like a garden hose. The flow is reduced or blocked and the retina acquires a characteristic whitish appearance.”
Garden hose phenomenon
Dr. Trese said current methods of managing ROP produce increasingly good results. In stage 4A, thanks to timely screening, peripheral ablation and lens-sparing vitrectomy, a 90% reattachment rate and satisfactory visual results have been achieved. A 2.5-year follow-up of a large group of these stage 4A ROP infants showed a mean visual acuity of 20/55.
“Unfortunately, some children still go on to closed-funnel stage 5 ROP. In approximately half of these cases the retina can be reattached in the posterior pole or reattached completely, but only 30% of the eyes achieve some form of visual results,” Dr. Trese said.
A factor recognized as contributing to these poor visual outcomes is blood invading the subretinal space and irreversibly damaging the retinal pigment epithelial cells and photoreceptors. Also, pseudoamblyopia certainly plays a role, he said.
“The garden hose phenomenon, however, might be the main cause of the disappointing results we get from those eyes even when the retina has been reattached.”
The hyaloid vasculature and the tunica vasculosa lentis are embryologic blood vessels that regress in normal development. In ROP eyes, Dr. Trese explained, they are still present. They progressively gather strength and pull the retina. Consequently, the vessels that travel within the retina are kinked and squeezed in many different directions.
“The traction and distortion in ROP is much greater than in any adult tractional disease, and we think it can lead to severe vessel compromise, which is commonly observed in the retinal circulation during vitreosurgery,” he said. “In a very severe closed-funnel stage 5 eye, even when the retina is reattached it appears atrophic, the retinal vessels are attenuated, the optic nerve is pale and the retinal pigment epithelium is mottled. Some of this RPE mottling can be due to blood in the subretinal space, but to a greater extent we think it may be due to retinal vascular compromise or occlusion.”
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Surgical intervention
Despite compromised retinal vasculature, the pseudoamblyopia and blood in the subretinal space, some of these eyes can still achieve vision with vitreous surgery, according to Dr. Trese.
“We use a technique called lamellar dissection,” he said while showing a video illustrating his surgical technique.
“First, we remove the lens and the posterior lens capsule. You can see that the tissue is particularly white and there is no great change in the vasculature even though the capsule has been removed. Then we start to dissect the retrolenticular tissue using two sharp needles to open it in a cross-handed fashion to avoid peripheral stretching. At this point we use an infusion spatula and forceps to remove the tissue layer by layer,” he said.
Even while tissue is removed, no change in terms of color of the retinal tissue is visible, he noted.
“We won’t see many blood vessels at all, even if we are removing the tissue one layer at a time. This proves that the whitish appearance is not due to tissue overlying the vessels,” he said.
It is only when the stalk tissue is peeled that the retinal circulation begins to fill.
“When stalk tissue has been freed, particularly centrally, blood vessels start to fill. The stalk is then removed, fluid-air exchange is applied and we can see a quite good vasculature in the retina, which will provide some vision for these children.”
Early intervention
The best treatment, however, remains prevention.
“Having discovered this new mechanism of retinal damage, we have one more reason to prevent eyes from developing this condition,” Dr. Trese said. “While with early intervention results can be very good, without vitrectomy the same eyes have a 92% chance of going on to closed-funnel stage 5 ROP. In developing countries, where screening is not performed as thoroughly and accurately, these stage 5 eyes are seen regularly. Vitreous surgery should be timed to avoid this.”
Dr. Trese reminded those present that ROP has been identified by the World Health Organization as the leading cause of pediatric blindness worldwide.
“It’s a very significant public health problem in both developed and developing countries; the problem exists wherever there is a neonatal ICU that’s good enough to keep small babies alive,” he said.
For Your Information:
- Michael T. Trese, MD, can be reached at Associated Retinal Consultants, 3535 W. Thirteen Mile Road, Suite 632, Royal Oak, MI 48073; (248) 288-2280; fax: (248) 288-5644; e-mail: MTTrese@associatedretinalconsultants.com.