Before an ophthalmic drug candidate reaches its first nonclinical study, someone has to answer a deceptively simple question: which animal do we test it in? The answer depends on where the drug will be delivered, how it will be dosed, and how closely the model’s eye anatomy needs to mirror our own. Get it wrong, and downstream toxicology and pharmacokinetic data may not translate, an expensive problem to discover late in development.
Species selection is one of the earliest and most consequential decisions a nonclinical team makes. Its effects ripple forward through study design, the endpoints that are feasible to collect, and ultimately how persuasive the regulatory package looks by the time it reaches a reviewer. Because the downside of a poor choice often does not surface until much later, in a failed translational readout or a tough question from an agency, experienced developers tend to back their species choice with mechanistic reasoning as well as published precedent rather than convention alone.
For anyone new to ocular preclinical work, there’s good news: the field is well documented. A handful of references show up again and again on the desks of experienced ophthalmic drug developers, and together they cover the great majority of species-selection questions that arise.
It’s worth noting that species selection should also keep the sponsor’s Target Product Profile (TPP) in view. The label claims and indication(s) it defines are what will unlock access in a given sector, not just what will satisfy regulators.
Foundational References
“Safety Evaluation of Ocular Drugs” (Ramos et al.) is widely regarded as one of the most comprehensive reviews of ocular toxicology available, with detailed comparisons of rabbit, dog, minipig, and nonhuman primate eye anatomy and physiology, including how species differ in cornea, retina, vitreous, and aqueous humor dynamics, and what that means for interpreting toxicology findings.
A companion volume, “Safety Evaluation of Ocular Drug Delivery Formulations,” offers a more practical, hands-on guide to species selection for local ocular toxicity studies. One of its more counterintuitive points: rabbits can actually be more sensitive than dogs or monkeys to intravitreal inflammation, simply because of differences in vitreous volume and clearance.
Rounding out the foundational trio, “Nonclinical Regulatory Aspects for Ophthalmic Drugs” is probably the best regulatory-focused review available. It walks through species selection from an FDA/ICH perspective, and explains why, especially for biologics, pharmacologic relevance often matters more than tradition.
Best References for Intravitreal Programs
For teams working specifically on intravitreal programs, two more references are essential. Del Amo and Urtti’s “Rabbit as an Animal Model for Intravitreal Pharmacokinetics” remains required reading for retinal drug developers. Despite real anatomical differences between rabbit and human eyes, rabbit intravitreal PK turns out to be reasonably predictive of human PK, and the paper provides quantitative scaling approaches for clearance and half-life.
A more recent industry-consortium perspective, published through the International Consortium for Innovation and Quality (IQ), extends that conversation by discussing the role of different preclinical species in translational PK/PD and dose prediction, and how species choice influences model predictivity.
Regulatory Documents You Should Know
No preclinical reading list is complete without the regulatory texts themselves. ICH M3(R2) lays out the general nonclinical safety framework that underpins most drug development programs. ICH’s biologics-focused guidance is critical reading for anyone working with antibodies, gene therapies, or other large-molecule ocular candidates, and it explicitly favors pharmacologically relevant species over the traditional rodent/nonrodent pairing.
FDA pharmacology/toxicology reviews for approved ophthalmic drugs (such as Lucentis®, Eylea®, Macugen®, and Vabysmo®) are also worth a careful read, since they often provide concrete, real-world examples of how species choices were justified and evaluated in regulatory context.
These reviews are publicly available through FDA’s Drug Approval Package database. Reading a handful end to end can be one of the fastest ways to see how a species justification actually reads once it has been accepted by the agency, and is often more directly illustrative than guidance documents, which tend to remain more general and principle-based.
A Top-Five Starter Library
If you were building an ophthalmic drug development library today, five references would cover most of the ground: Ramos et al.’s “Safety Evaluation of Ocular Drugs;” “Nonclinical Regulatory Aspects for Ophthalmic Drugs;” Del Amo and Urtti’s rabbit intravitreal PK paper; the IQ Consortium’s intravitreal development paper; and FDA’s pharmacology/toxicology reviews for recently approved retinal therapeutics. Together, this short list resolves roughly 90% of the species-selection questions that come up in ophthalmic preclinical development.
References
Ramos, M.F., Attar, M., Stern, M.E., Brassard, J.A., Kim, A.S., Matsumoto, S., Vangyi, C. (2017). Safety Evaluation of Ocular Drugs. In A Comprehensive Guide to Toxicology in Nonclinical Drug Development, 2nd ed., pp. 757 to 811. Elsevier. https://doi.org/10.1016/B978-0-12-803620-4.00029-3
Short, B.G. (2008). Safety Evaluation of Ocular Drug Delivery Formulations: Techniques and Practical Considerations. Toxicologic Pathology, 36(1), 49 to 62. https://doi.org/10.1177/0192623307310955
Weir, A.B., Wilson, S.D. (2012). Nonclinical Regulatory Aspects for Ophthalmic Drugs. In Weir, A., Collins, M. (eds), Assessing Ocular Toxicology in Laboratory Animals, pp. 259 to 294. Humana Press. https://doi.org/10.1007/978-1-62703-164-6_7
Del Amo, E.M., Urtti, A. (2015). Rabbit as an Animal Model for Intravitreal Pharmacokinetics: Clinical Predictability and Quality of the Published Data. Experimental Eye Research, 137, 111 to 124. https://doi.org/10.1016/j.exer.2015.05.003
ICH M3(R2) (2009). Guidance on Nonclinical Safety Studies for the Conduct of Human Clinical Trials and Marketing Authorization for Pharmaceuticals. International Council for Harmonisation.
ICH S6(R1) (2011). Preclinical Safety Evaluation of Biotechnology-Derived Pharmaceuticals. International Council for Harmonisation.
FDA Drug Approval Package pharmacology and toxicology reviews: Lucentis, BLA 125156 (2006); Macugen, NDA 021756 (2004); Eylea, BLA 125387 (2011); Vabysmo, BLA 761235 (2022). Available at accessdata.fda.gov.