Purpose <p>To evaluate the correlation between tumour volume and retinal nerve fibre layer (RNFL) thickness in patients with optic pathway glioma (OPG).</p> Methods <p>Patients with OPG receiving clinical care at King Khalid University Hospital and undergoing contrast-enhanced brain magnetic resonance imaging (MRI) as well as optical coherence tomography (OCT) RNFL measurement within three months of MRI testing were enrolled. All participants had undergone visual acuity (VA) testing and complete ophthalmic evaluation. Tumour volume was calculated using the ABC/2 method on high-resolution T1-weighted MRI images. Linear regression models were used to evaluate the relationship between RNFL thickness and OPG volume.</p> Results <p>Sixteen participants with and without neurofibromatosis type 1 (NF1) were included. The median age was 6 years (IQR: 3–11). Twelve of the participants were male. Eight patients (50%) had VA of 20/100 or worse in at least one eye. The majority of the patients had isolated optic nerve gliomas (37.5%). The median tumour volume was 1696.25 mm³ (IQR: 313.5- 5082.5mm³), and the median OCT RNFL thickness was 69 μm (IQR: 60–93 μm). There was a significant negative correlation between OCT RNFL thickness and tumour volume (rs[13] = .939, p &lt; .001). Subgroup analysis showed a strong negative association between OCT measurement and isolated optic nerve glioma (rs[6] = .943, p = 0.05).</p> Conclusion <p>This study provides some evidence that a thinner RNFL on OCT is correlated with larger volume OPGs. The negative correlation was more significant in isolated optic nerve gliomas. Further prospective trials to explore the prognostic value of this correlation are needed.</p>