What is a major challenge in using dogs as models for ocular surface disease?

• A. Dogs cannot identify mild disease; owners present with moderate-to-severe disease.
• B. There is no variability in disease progression, making standardization easy.
• C. Client compliance is never an issue.
• D. There are numerous large-scale trials in dogs.

Answer: (A)

The key idea is recruitment bias due to how dogs are brought to veterinary care for ocular surface disease. Dogs can’t report subtle or early signs, so owners tend to notice and seek help only when symptoms become noticeable or bothersome. That means animals enrolled in studies or presenting for care are more often moderate to severe cases, not mild ones. This skews the sample toward later stages of disease, making it hard to study early disease mechanisms, progression from mild to severe, and responses to early interventions. It also introduces variability tied to how long the disease has been present and prior treatments, which can confound outcomes and limit how well findings apply to the full spectrum of disease. In other words, the biggest hurdle is that reliance on owner recognition leads to a lack of representation of mild disease, compromising generalizability and the ability to evaluate early treatment effects.