Ocular toxicity assessment from systemically administered xenobiotics: considerations in drug development

The eye is a unique sensory structure, which must be evaluated for toxicity to determine the safety of drugs, industrial chemicals, and consumer products. Changes in the structure and/or function of ocular tissues following systemic administration of a potential new drug in preclinical animal models can result in significant delays in the development of a new therapeutic and in some cases lead to termination of the development. The ability to detect and characterize ocular toxicity in preclinical models and to predict risk in patients is critically dependent on the preclinical testing strategy, the availability and use of state-of-the-art ocular safety assessment tools, and the knowledge of drug mechanism of action and the current regulatory environment. This review describes the design and execution of toxicity studies with the incorporation of current methods for in vivo assessment of ocular toxicity, including methods for detecting early changes in the eye. In addition, anatomical differences among laboratory animals, preparation of globes for examination, and iatrogenic and spontaneous ocular findings are described that can affect interpretation of toxicological findings. Finally, the correlation between nonclinical outcomes and clinical evaluations is discussed in terms of expected therapeutic uses, indications, and regulatory consequences of ocular effects.