Williams, T David, and A DiPasquale. “Direct Ophthalmoscopy Toward the Retinal Periphery: A Quantitative Study”. Canadian Journal of Optometry 43, no. 2-3 (September 1, 1981): 4. Accessed November 30, 2024. https://openjournals.uwaterloo.ca/index.php/cjo/article/view/4163.