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OPG brain scan
Brain MRI showing the optic nerve segmentation in red.
By Kristen Mulvihill 
Scheie Vision Annual Report 2019

In March 2019, the Children’s Hospital of Philadelphia (CHOP) received a $3.5 million grant from the National Institutes of Health (NIH) titled Biomarkers of Vision Loss in Children with Optic Pathway Gliomas. Robert Avery, DO, MSCE, Assistant Professor of Ophthalmology and Assistant Professor of Neurology, is the Principal Investigator of this five-year study. 

Optic pathway gliomas (OPGs) are one of the most common brain tumors in children, representing approximately two to five percent of pediatric brain tumors. Nearly 75 percent of OPGs occur in children younger than 10 years old. These slow progressing tumors emerge in or around the optic nerve, which transmits visual information from the eye to the brain; the optic chiasm, the X-shaped structure formed by the intersection of the optic nerves from each eye; and/or the optic tract, an extension of the optic nerve. OPGs can disturb the function of the visual pathway and lead to severe vision loss.

Most often, OPGs are treated with chemotherapy, which is used to stop the progression of the tumor and stabilize or improve the child’s vision. In this study, Dr. Avery and colleagues are aiming to discern why some children respond well to chemotherapy, with their vision stabilizing or recovering, while others respond poorly, with their vision declining after treatment. 

The long-term goal of the project is to improve the clinical care and visual outcomes of children with OPGs by better understanding the timing and causes of vision loss. More specifically, this proposal aims to determine whether optical coherence tomography (OCT) measures are accurate biomarkers for vision, thereby defining an optimal treatment window for vision loss. 

OCT is a non-invasive imaging technology that uses light waves to take cross-sectional images of the optic nerve and retina. Dr. Avery and colleagues plan to study the OCT measures of circumpapillary retinal nerve fiber layer (cpRNFL) and ganglion cell-inner plexiform layer (GCIPL) thickness, as both measures are important for the detection and ongoing monitoring of optic nerve damage. 

Traditional OCT machines will be used in older, more cooperative children. Some of the younger patients will undergo handheld OCT while they are being sedated for their clinical MRI scan. Analyzing OCT measures will allow for a reproducible and objective evaluation of the entire visual pathway, ensuring consistency across studies and centers regardless of the child’s ability to comply with standard vision testing.

The researchers hypothesize that the location and magnitude of cpRNFL and GCIPL thickness will be closely correlated to visual function. Based on previously published research, both measures will start to decline before visual function declines, thus identifying a prime treatment window to prevent or slow vision loss.

“We are looking at these biomarkers in both a cross sectional analysis as well as a longitudinal analysis,” explained Dr. Avery. “Specifically, can we use these OCT measures to detect impending vision loss that is heralded by a slowly declining cpRNFL and/or GCIPL, allowing us to initiate chemotherapy earlier and hopefully improve visual outcomes. This type of data would be especially helpful for our young children who cannot cooperate with standard vision testing.”

Given the complexity of vision loss from OPGs, they are also utilizing electrophysiology measures (i.e. photophic negative response and visual evoked potential), along with advanced MRI techniques such as diffusion tensor imaging, and volumetric measures of the visual pathway. They also hypothesize that children who recover their vision during OPG treatment will display specific electrophysiologic and MRI features when compared to children who do not experience visual recovery after treatment.

“We are trying to understand why some children respond well to treatment with chemotherapy, with their vision stabilizing or improving, compared to others who respond poorly, with their vision worsening,” said Dr. Avery. “This may help us decide whether to treat kids with more aggressive therapy up front if they have features to suggest they will not respond well to standard treatments.”

This study will significantly impact the clinical management and visual outcomes of children with this common type of brain tumor. By understanding the timing and causes of vision loss in children with OPGs, this research will allow for earlier treatment to prevent vision loss, and will help develop new treatments, including neuroprotective therapies.

To accomplish this large study, Dr. Avery is fortunate to have expert collaborators from Penn Ophthalmology (Dr. Gui-shuang Ying), and Neuro-Oncology (Dr. Michael Fisher) and advanced MRI analytics (Drs. Jeffrey Berman and Ritto Datta) from CHOP. Additional study sites and collaborators are from Boston Children’s Hospital (Dr. Gena Heidary) and The Hospital for Sick Children in Toronto (Dr. Arun Reginald).
 
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