Jason Bradwell's 365/366 Photo a Day Blog

Testing indicates that a cat's vision is superior at night in comparison to humans, and inferior in daylight. Cats have a tapetum lucidum, which is a reflective layer behind the retina that reflects light that passes through the retina back into the eye. While this enhances the ability to see in low light, it appears to reduce net visual acuity, thus detracting when light is abundant. In very bright light, the slit-like iris closes very narrowly over the eye, reducing the amount of light on the sensitive retina, and improving depth of field. The tapetum and other mechanisms give the cat a minimum light detection threshold up to seven times lower than that of humans. Variation in color of cats' eyes in flash photographs is largely due to the reflection of the flash by the tapetum.