In the equine eye, where is the tapetum and what is its color?

• A. Tapetum dorsal: Often blue-green; Non-tapetum ventral: Usually dark
• B. Tapetum ventral: Often blue-green; Non-tapetum dorsal: Usually dark
• C. Tapetum dorsal: Usually dark; Non-tapetum ventral: Often blue-green
• D. Tapetum ventral: Usually dark; Non-tapetum dorsal: Often blue-green

Answer: (A)

Tapetum lucidum is the reflective layer behind the retina that boosts night vision by reflecting light back through the photoreceptors. In horses, this reflective layer sits on the dorsal (upper) part of the retina, so you see a blue-green glow when light hits the eye. The ventral (lower) retina lacks the tapetum, appearing dark because there is no reflective layer there. This combination—dorsal blue-green tapetum with a dark non-tapetal ventral retina—is why the described pattern is correct.