Understanding Reptile Vision, Part 1: Understanding Sight – October 2013

By Jennifer Greene

Hopefully, you have at least a basic understanding of how sight works.  In case you don’t, simply speaking the way humans perceive the world is through reflected light on objects around us.  For the majority of vertebrates, this is how sight works.  Light from the sun, a light bulb, moonlight, etc is reflected off of objects around us, and our eyes take in that light and send signals up to our brain indicating what it is we’ve seen. There’s different wavelengths of light – which most of you already know.  There’s visible light, which is the colors we see as humans, and then there’s wavelengths like UVA, UVB, UVC, and so on.  There’s also infrared light – which is, essentially, the same as heat.

Infrared, visible light, the UVB spectrum, these are a small portion of the BIG range of wavelengths that the sun and various light/energy sources can emit.  As far as we’re concerned, though, those are the relevant wavelengths for us to pay attention to.

The cells that send the signals up to our brain each fire when they encounter the type of light they’re designed to perceive, so your sight is only as good as the number of cells in your eyes.  And from there, your sight is only as good as the number of cells designed to pick up the various types of light out there.

The common way for vertebrates to see is through the use of two types of sight cells – rods and cones.  Rods simply pick up light, period, and fire when visible light hits them.  Cones pick up different colors of light, and there are various types of cones for the various colors or wavelengths of visible light out there.  In low light situations, rods work best, as they will just fire if there is light – so all of your rod cells are going to work to detect light when there isn’t much there.  Cone cells only fire when they are triggered by the specific type of light they’re designed to pick up – so they are not as effective as rod cells in low light, as there is often not enough reflected light of a specific color to make them fire.

This is extremely simplified; vision and lighting are complicated topics, and if you’d like to research it more, I highly recommend it.

As a result of the way the cells work, it is common and expected for most nocturnal species to have large numbers of rod cells in their eyes, allowing them to pick up even tiny amounts of reflected light at night and giving them excellent night vision.  Some owls, for example, have night vision up to 100 times better than what we can see – and this is due to the large number of rods in their eyes.

When it comes to daytime vision and cone cells, though, that’s where sight can get really interesting.  Different animal groups have different types of cones, and the way the cones work can vary immensely from animal type to animal type.

In mammals, it is common for them to only have 2 types of cones.  They are usually blind to the difference between the colors of red and green, a color range humans can detect because we have 3 types of cones.  Human color detection is better than most mammals, but it can only be called “better” in that range of comparison.  When you start to look at other vertebrates, the limits of our own sight become much more obvious.

Birds and many tropical fish can see into the Ultraviolet, or UV range, giving them the ability to perceive colors we can’t even comprehend.  Can you imagine a new color that has never existed before?  That’s a color that birds and many fish see all the time!

In that same group of exceptional sight, many reptiles have at least 4 types of cone cells, with some having 5.  This means they can perceive color even better than we can in most cases, and for species with the best color perception, they can see a range of colors that even birds and fish can’t.

This is definitely a generalization, and is not meant to imply that reptiles can all see with clarity and distance that we can – but they can perceive a wider range of colors than our senses can, and this should be considered when maintaining captive collections.

Obviously, not all reptiles require full spectrum lighting, or even much in the way of specialized lighting.  Commercialized breeding of several species has shown that specialized lighting is not necessary for the maintenance of some species, and this video and article series is not intended to dispute that.  Rather, this is a look at how reptiles perceive their world, and how we as keepers can better modify our lighting and cage setup to reflect the natural conditions our reptiles are likely to experience.  For the single pet reptile or for dedicated enthusiasts determined to closely replicate nature as best they’re able, information on reptile sight is just one aspect of husbandry to consider.

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