OCT yields new information on juvenile retinoschisis

Indianapolis-In vivo imaging studies using optical coherence tomography (OCT) are providing new insight into the pathology of X-linked juvenile retinoschisis, according to Hua Gao, MD, PhD.

The fovea in one patient was examined using OCT. This revealed that the primary pathology, schisis, was located in the outer plexiform layer. Another patient was examined subsequently; schisis in the fovea was similarly localized to the outer retina.

Describing the OCT findings in more detail, Dr. Gao noted that in the 19-year-old patient, the inner nuclear layer and ganglion cell layer were condensed into a single layer and there were large foveal cystoid spaces present in the outer plexiform layer. The cystoid spaces were generally of uniform thickness and they were crossed by multiple, vertically oriented, bridging strands. Focal atrophic changes were seen in the retinal pigment epithelium.

"In some areas, the strands crossing the cystoid spaces were very evenly spaced so as to create an image resembling a ladder resting on its side," he said.

In the younger brother, cystoid changes were also identified in the outer plexiform layer, but the extent of the changes differed between the right and left eyes consistent with their different levels of vision. In the left eye, which still had relatively good vision of 20/60, there was only limited schisis in the foveal center. Vision was poor in the fellow eye and the OCT revealed changes in the fovea center that were spreading toward the perifoveal region.

Disease progression "The differences observed between the two eyes provide us with some understanding about where the retinal changes begin in the fovea and how they progress over time in individuals affected by this hereditary disease," Dr. Gao said. "Retinoschisis appears to start in the foveal center and spread toward the perifoveal area."

Considering the OCT findings from his patients, other recent reports from investigators using OCT, as well as the histopathologic studies, Dr. Gao has postulated that mutational differences in the retinoschisin gene may give rise to different phenotypes.

"Retinoschisis in this disease occurs because of a missense mutation of retinoschisis, a protein obviously produced in the retina and probably in the photoreceptors," Dr. Gao said. "Although the function of retinoschisin is still unknown, it appears that it is transported within the retina between different layers, possibly from the photoreceptors to the inner retina, i.e., the nerve fiber layer.

"Perhaps, however, retinoschisin handling is affected differently depending on the mutation, so that it becomes trapped at different layers in the retina, giving rise to a variable pathologic picture," he said.