Form 2WT, at Waimate High School, asks :-

People say that cats are colour-blind or only see black and white? If this is true how do they know this?

Claudia Ugarte, who is studying small animals at Massey University's Department of Veterinary Clinical Sciences, responded.

Cat's eyes are made to be useful at night, because that is the time of the day when cats are more active. At night the light is poor and it is not easy to see colour. Even cartoonists know this, almost. In Asterix comics the moonlight night scenes are always shown in just blue and white.

Eyes have the function of telling the brain when light is incident on them. The tiny light receptors at the back of the eye are of two sorts, cones which detect colour in bright light and rods which are very efficient in registering poor light but dont detect colour. Night-hunting animals such as cats have more rods than cones so cannot tell the brain about colours.

However cats may be able to see some colour. They have shown responses to different colour lights. The way we can tell this is happening is by measuring electric currents running between the eyes and the brain. This is the way that the eyes tell the brain when light is coming through and what colour it is. But we also know that cats have mostly rods at the back of their eye so they cannot be very good at seeing colour. For this reason they are called colour-blind.