We appreciate the interest by Chang and associates about our recent article published in the journal. The authors also highlight the results of their study. While both studies share the same goal of improving our understanding of optic pathway glioma (OPG) in children, the primary outcome measures and interpretations differed between studies.
As discussed in an expert review and an accompanying editorial, clinicians caring for children with OPG are faced with a number of challenges, most notably determining what is the best method to screen/detect OPG in children with neurofibromatosis type 1 (NF-1) and how to follow their clinical examination to determine disease progression. Answering these questions is further complicated by the difficulties with vision testing in young children, especially those with NF-1, which can be inconsistent and relies heavily on their cooperation. Chang and associates suggest that optical coherence tomography (OCT) may have the potential to be used as a screening test for OPG, instead of magnetic resonance imaging. Their study reported a decreased retinal nerve fiber layer (RNFL) and macular thickness in children with NF-1 and OPG as compared to NF-1 children without OPG. However, in our study, despite having an OPG, children with normal visual acuity and visual fields were found to have normal RNFL thickness. Thus, we would not recommend the use of OCT as a screening tool for known OPG in this population.
Instead, our study focused on understanding the “structure-function” relationship between RNFL thickness and visual acuity in children with and without OPG. Children with abnormal visual acuity and/or visual fields had decreased RNFL thickness whereas those with normal vision had normal RNFL thickness. If RNFL could serve as an objective quantitative biomarker of vision that does not rely on patient cooperation, this could be an ideal way to monitor disease progression of known OPG. However, our cross-sectional study design only provided preliminary data that suggest RNFL has the potential to be a biomarker of vision.
We agree that a sufficiently powered longitudinal study is needed to assess whether OCT is helpful in the management and outcome of pediatric OPG. At Children’s National Medical Center in Washington, DC, we are currently enrolling children with NF-1 as young as 18 months with and without OPG in a longitudinal study using hand-held spectral-domain OCT. However, until a large multicenter longitudinal study is completed, OCT in children with OPG remains a research tool and is not recommended to be part of the clinical evaluation.