Antonyweeks
Well-Known Member
So I was taking out the owner of a permission I have. She is a vetinary surgeon and an eye specialist (lecturing and so on about eyes in animals). Being the pleb I am I said that deer see in grey. At which point Hayley said "really?". Anwyay she suggested that she do some research. This is the email she sent me earlier. Very interesting I think. I'm sure some of you already know all this. For me though was informative:
Regarding deer ophthalmology, this lead me to a fantastic rabbit hole of research this afternoon, as it is not a species I have ever treated and I was projecting based on other ruminants. Vision disorders are virtually unreported in deer (contagious diseases of eyes yes, but not blindness), presumably because blind deer can not forage, find mates etc and the problem dies with the deer. So now that I know I am unlikely to make a career as a cervid ophthalmologist, forgive me if I harp on about eyeballs for a bit
I can confirm that deer see in colour.
Various behavioural studies have shown that deer can tell the difference between green and grey at standardised brightness. Now the geeky science……
Photoreceptors are cells in the retina that convert packages of light (photons) into electrical impulses, which our brain interprets as pictures. Deer retinas are mostly made up of rod photoreceptors, which gives them good motion detection and better contrast in low light levels. As mostly crepuscular animals, that are prey species, natural selection has likely given them a drive towards night vision over colour and visual acuity.
It is said that deer have a rod:cone ratio ten times higher than ours. Hence lower visual acuity and possibly muted colours, but better night vision and movement detection. They may see clearly at 10 metres away what you would pick out at 100 metres away, but if that object is moving ever so slightly they will catch that movement way before you. Thank goodness deer don’t drive cars!
Deer also have a tapetum lucidum- a shiny reflective layer behind the retina that increases internal reflection within the eye, so boosting their ability to see in dim light. Effectively this means light passes through the retina twice (”forwards” from the light source and “backwards” when reflected by the tapetum) to maximise absorption. The tapetum is what gives you the eye-shine effect when you look at them with e.g. car headlights.
They do have cone photoreceptor cells in the retina as well - these contain pigments that “fire” at different wavelengths of light and give them higher visual acuity. The photopigments found in cervid retinas allow them vision in the blue and green range of light only. This means that they likely see colours as a red-green colour blind human would. This is similar to horses and other ruminants.
As a digression it is reported that arctic reindeer may see into the UV spectrum as an adaption for seeing well in the snow……
Deer have horizontal oval pupils which allow them to scan a wide horizon more effectively (more light ingress in the “corners” of the eye) rather than focus on a small area through a round pupil. Their widely lateralised eyes (on the side of their head, not both facing forwards) means they have a wider field of view for surveillance (approximately 300 degrees rather than our 180 degrees) at the expense of stereopsis (the ability to compare images from left and right eye and judge distance). The higher ability to detect movement (rods) combined with the detection of blue versus green (which equals sky versus grass i.e. a horizon) is another useful adaption for environmental threat vigilance.
Deer also have a visual streak in their retina. This is the equivalent to the human macula - an area of higher cone photoreceptor density that we can use to concentrate our focus. In deer this is orientated as a horizontal oval area of the retina which lines up with the pupil to maximise surveillance of a large area laterally (at the expense of vision far above or below the horizon). The trade-off for not being able to see red wavelengths and resultant shift in colour sensitivity (blue/green only) in the visual streak compared to humans likely allows them to discriminate different plants well across a plain/field/woodland floor.
Hopefully this explains why you should move very slowly or stand still (they detect movement well, but can not judge distance very effectively and any change in contrast compared to the horizon will be perceived as a threat), can more readily shoot from above or below them (off their visual streak), and why it doesn’t matter if you wear red camo gear to stalk.
Regarding deer ophthalmology, this lead me to a fantastic rabbit hole of research this afternoon, as it is not a species I have ever treated and I was projecting based on other ruminants. Vision disorders are virtually unreported in deer (contagious diseases of eyes yes, but not blindness), presumably because blind deer can not forage, find mates etc and the problem dies with the deer. So now that I know I am unlikely to make a career as a cervid ophthalmologist, forgive me if I harp on about eyeballs for a bit
I can confirm that deer see in colour.
Various behavioural studies have shown that deer can tell the difference between green and grey at standardised brightness. Now the geeky science……
Photoreceptors are cells in the retina that convert packages of light (photons) into electrical impulses, which our brain interprets as pictures. Deer retinas are mostly made up of rod photoreceptors, which gives them good motion detection and better contrast in low light levels. As mostly crepuscular animals, that are prey species, natural selection has likely given them a drive towards night vision over colour and visual acuity.
It is said that deer have a rod:cone ratio ten times higher than ours. Hence lower visual acuity and possibly muted colours, but better night vision and movement detection. They may see clearly at 10 metres away what you would pick out at 100 metres away, but if that object is moving ever so slightly they will catch that movement way before you. Thank goodness deer don’t drive cars!
Deer also have a tapetum lucidum- a shiny reflective layer behind the retina that increases internal reflection within the eye, so boosting their ability to see in dim light. Effectively this means light passes through the retina twice (”forwards” from the light source and “backwards” when reflected by the tapetum) to maximise absorption. The tapetum is what gives you the eye-shine effect when you look at them with e.g. car headlights.
They do have cone photoreceptor cells in the retina as well - these contain pigments that “fire” at different wavelengths of light and give them higher visual acuity. The photopigments found in cervid retinas allow them vision in the blue and green range of light only. This means that they likely see colours as a red-green colour blind human would. This is similar to horses and other ruminants.
As a digression it is reported that arctic reindeer may see into the UV spectrum as an adaption for seeing well in the snow……
Deer have horizontal oval pupils which allow them to scan a wide horizon more effectively (more light ingress in the “corners” of the eye) rather than focus on a small area through a round pupil. Their widely lateralised eyes (on the side of their head, not both facing forwards) means they have a wider field of view for surveillance (approximately 300 degrees rather than our 180 degrees) at the expense of stereopsis (the ability to compare images from left and right eye and judge distance). The higher ability to detect movement (rods) combined with the detection of blue versus green (which equals sky versus grass i.e. a horizon) is another useful adaption for environmental threat vigilance.
Deer also have a visual streak in their retina. This is the equivalent to the human macula - an area of higher cone photoreceptor density that we can use to concentrate our focus. In deer this is orientated as a horizontal oval area of the retina which lines up with the pupil to maximise surveillance of a large area laterally (at the expense of vision far above or below the horizon). The trade-off for not being able to see red wavelengths and resultant shift in colour sensitivity (blue/green only) in the visual streak compared to humans likely allows them to discriminate different plants well across a plain/field/woodland floor.
Hopefully this explains why you should move very slowly or stand still (they detect movement well, but can not judge distance very effectively and any change in contrast compared to the horizon will be perceived as a threat), can more readily shoot from above or below them (off their visual streak), and why it doesn’t matter if you wear red camo gear to stalk.
