Dogs don't see life through rose-coloured glasses, nor in black and white
For a few months now, I’ve been treating six-year-old Samuel, who has the beginnings of myopia.
- For a few months now, I’ve been treating six-year-old Samuel, who has the beginnings of myopia.
- He’s very quick for his age and often asks me questions about tests I give him, and about what I see inside his eyes.
- However, as an optometrist, I can offer some insights that might help answer Samuel’s question.
Cones and rods
- The retina, the sensitive part that lines the back of the eye, has two types of photon receptors: cones and rods.
- The cones, in the centre of the retina (fovea), perceive bright light and are responsible for colour perception.
- There are three types of cones.
- The brain combines the signals emitted by each of these cones to form the colour it perceives.
And what about animals?
- For example, birds have a fourth opsin that allows them to see ultraviolet (UV) light.
- Humans cannot perceive this light because our crystalline (internal) lens filters UV rays.
- UV rays influence birds’ behavioural decisions, including foraging and their choice of a mate.
- This is an advantage when it comes to spotting prey, as they can distinguish their heat even at night.
Back to Scotch
- The vision of dogs — such as our friend Scotch — is quite different.
- As a result, dogs have a wider field of vision (250 to 280 degrees), but less simultaneous vision.
- This is equivalent to the vision of a very myopic person not wearing glasses.
- And as an added bonus, they have an extra layer of the retina, called the tapetum lucidum — or carpet.
- So it’s possible, depending on the colour of the ball, that Scotch will not see it, and as a result, will gaze up at Samuel with a lost look.