A horse’s night vision
|April 29, 2009
|Posted by Melinda under Uncategorized
“There is one area in which the equine eye is definitely superior to the human eye–night vision. Generally speaking, a horse’s night vision is a good 50% better than a human’s… Why? Because the equine eye contains a reflective panel on its retina. This panel pulls in what little light is available at night, enabling that horse to have far better night vision than its rider.” (click here for the article)
“Rod photoreceptors dominate in number over cones in the horse. The rods are responsible for the very good night vision of horses, and the cones are responsible for daytime vision and the limited color vision (horses see blue colors best). ” (click here for the article)
I can remember is high school physics doing an experiment comparing the rods and cones in the eye. Cones are responsible for color and daytime vision, rods are responsible for night time vision. In horses, rods predominate over cones. It takes time for the rods in our eyes to “activate”. We sat at our desks with our heads down and our fingers pressed over our eye lids to prevent any light from coming in. After 10 minutes the teacher led us outside (our fingers still pressed over our eyelids) into a bright sunny day. On cue we opened our eyes and then closed them VERY quickly – just a blink. There was an impression of the landscape inside our eyelids, kind of like a negative of a picture. No real colors, but an accurate landscape! You could do this 2 or 3 times until the light “deactivated” the rods and our eyes switched over the “cone” vision.
At Mariposa this year many many MANY people were using flashlights. It’s typical to use flashlights during horse watch to untangle animals (the fire danger of using a candle lantern is very high), however, usually no light is needed. Apparently everyone decided they couldn’t wait the 10 minutes for their rod vision to kick in and insisted on walking around everywhere with flashlights. Although I did ask several people very politely not to shine them in my face (people unconsciously shine light where they are looking) I didn’t think much about it (other than to be annoyed) until I tried to water my ambulance horses ~3:30am.
The campfires were very bright however I tried hard not to look at them and kept the horses tilted away from them. We met 2 people on the way to the water trough that shined their flashlights in my face and at the horses. I noticed afterwards that Buttercup was spooking at things (an overhead fly, fly ropes, the forge etc.) that an old campaigner shouldn’t have been concerned with. My rod (night vision) returned fairly quickly, and in humans, as long as there is some light, we can use our limited cone (day/color vision) vision to see in the not-so-dark. I know from my endurance experience that horses can see much better than I can so I wasn’t concerned and led them up to the water trough. Imagine my surprise when neither horse could apparently find the water trough that was right in front of the them! Gunsmoke walked into in and stumbled over it when I tried to show her where it was. It was 10 minutes, standing in front of the trough in total darkness, before they were able to find the trough and drink. Their night vision had been destroyed by a combination of the campfires and the LED flashlights shined in our faces on the way to the water trough.
Why did it take so long for the horses’s superior night vision to return? How was it destroyed so completely when mine stayed “adequate”?
This is my own personal hypothesis and I don’t have time to look anything up right now, so please take it with a grain of salt. Here is what I do know:
1. Horses have superior night vision to humans based upon the number and concentration of rods versus cones.
2. Humans have superior color and day vision due to the number and concentration of cones versus rods.
3. Rods work in low light conditions. Too much light causes the rods to deactivate and the cones to take over
4. Horses have a reflective “plate” in their eyes that can collect the available light in low light conditions (other animals have this as well – it’s why their eyes “glow” and look like foil at night when light catches them at a certain angle). They can see in extremely low light conditions due to this light “collector”, which then works with the rods.
Here is my hypothesis: If a human is working in low light conditions, their rods are working. If they are suddenly exposed to a flashlight in the face, the rods are partially deactivated until they are in the dark long enough to “reactivate”. During that time of reactivation, humans use their limited cone vision in the dark. Depending on the amount of light present, this may work well, or not so well. At Mariposa, I was able to see after the flashlight incident because of the number of campfires, stars etc was sufficient for my cone vision until my rods starting working again. If a horse is exposed to the same conditions as the human, they can see better than the human as first, because of their superior rod vision. The reflective plate in their eye is busy collecting all the light available and giving them even BETTER night vision. Insert flashlight to the face. The reflective plate makes the amount of light entering the eye even worse than the human. The horses’s rod vision is completely destroyed, until it can recharge some time later. The horses limited cone vision cannot make up for the loss in rod vision and the horse is effectively blind until the rods recharge.
What do you think? If this is true, it has serious implications for night riding and the endurance riding I do. I’m going to start having much less patience for people who shine lights in my horses direction. The endurance rides I have attended where the start was before dawn were actually very good. The headlamps are small, everyone is used to working with lights and horses and I can’t remember more than once or twice being shined in the face by another person, even in a start of 100+ people. Most people do NOT get on their horses with the headlamp on which minimizes the amount of light flashing around. Additionally, everyone using a flashlight usually keeps in pointed straight down at their side. At Mariposa I lost count of the number of times I got flashed in the face by a very strong LED flashlight.
In the future I know that I will be much more careful where my light falls when working around horses. I’m also going to be a lot less tolerant of other people who continually shine flashlights at my horse. If I’m riding a single track on the side of the cliff at night, I’m relying on my horses’s vision. Someone that screws that up might get me killed. There are some endurance riders who feel they must use a headlamp during the night for theirs and their horses’ safety. I will make sure that they end up far enough in front of me that their light doesn’t bother me or my horse. After my experience last weekend, it’s no longer a matter of preference, it’s a matter of safety.
Thought of the Day
Does anyone have any comments? Personally experience? Actual knowledge instead of my best guess? I would love to hear it!
I took a lot of pictures at Mariposa, here is just a few. There’s a “real” after-action report coming up with even more pictures.