Beyond Eye Changes in Ocular Toxicity Studies: Practical Considerations for Sampling and Evaluation of Extraocular Visual Pathways, and Common Findings.

This article focuses on the comprehensive evaluation of extraocular visual pathways in ocular toxicity studies, emphasizing the need to assess not only the eye but also connected central nervous system (CNS) structures due to potential primary or secondary toxicities from ocular therapeutics. It provides practical guidance on sampling and trimming key visual pathway components—including the optic nerve, optic chiasm, optic tract, lateral geniculate nucleus, superior colliculus, and visual cortex—in commonly used preclinical species such as nonhuman primates, rabbits, and rats. The article highlights additional nervous system structures relevant to ocular drug effects, such as the ciliary ganglion and oculomotor nerve, particularly in the context of adeno-associated virus (AAV) gene therapies. It also discusses the utility of special stains, immunohistochemistry, and in situ hybridization for detecting subtle neurotoxic changes and localizing therapeutic agents within ocular and CNS tissues. The authors conclude that consistent and bilateral evaluation of visual pathways is essential for accurate safety assessment of ocular therapeutics, given the complex anatomical and physiological connections between the eye and brain.