What is the normal tear volume on a dog's ocular surface?

• A. ~30 μL
• B. ~65 μL
• C. ~100 μL
• D. ~10 μL

Answer: (B)

The amount of tear film that normally covers the dog's eye is the reservoir that keeps the ocular surface moist and supports a stable tear film between blinks. In dogs, this tear reservoir is about tens of microliters, with around 65 μL commonly cited as a normal value. This level reflects the balance between tear production by the lacrimal glands and drainage through the nasolacrimal system, as well as distribution across the cornea via blinking. If tear volume were significantly lower, the surface dries more quickly, increasing the risk of keratoconjunctivitis sicca and corneal ulcers. If tear volume is too high or drainage is impaired, tearing and overflow can occur. While individual dogs vary, 65 μL is the best estimate for a typical canine tear film reservoir.