24 Mar Your Retina Sees Backwards
Images on your retina are reversed. Your retina “sees” everything backwards. Your brain reorients you. This image reversal is an adaptive advantage providing us with tremendous peripheral vision and the ability to view objects much larger than just a few millimeters.
Everything is Upside Down…and Reversed
The simplest illustration of how your retina sees is shown above. If you look at the eye chart, it gets turned upside down and reversed on the retina.
The image the retina “sees” is completely reversed.
The brain has to then reorient the image to allow you to see things “right side up” (and re-reversed).
Keyholes are Actually Pupils
Imagine you were looking through a keyhole trying to spy on someone inside a room. As you are scanning the room, looking at the right side of the room to the left side of the room, you really need to move your head/body in the opposite direction. This is the only way you can “see” the entire room.
The important point is that you can see the entire room through a very tiny hole. In the eye, the analogous part is the pupil.
Images need to be reversed so we can see objects much larger than the size of our pupil and so that we may have peripheral vision.
The Washington Monument is Upside Down
Using an example of the Washington Monument may help a bit. The image of the top of the monument must travel through your pupil and is focused on the inferior, or bottom, portion of your retina. The image of the base of the monument is focused (along with all the flags) on the superior, or top, portion of your retina.
What Does This Mean?
By reversing the image, we are able to visualize objects much larger than our eye. If you look at the light rays, colored in blue (see above), you will notice that the distance between the light rays emanating from the top and the bottom of the chart get closer together as they approach the eye. At some point, they actually cross and reverse.
The image of the eye chart is getting smaller, too. The light rays get smaller allowing the entire image to fit through the pupil and form a complete image on the retina, albeit upside down and reversed.
Without this reversal, we would have a very limited view of our world. It would be similar to viewing the world through a drinking straw.
(Note: For those of you who have had retinal detachment surgery involving gas injection, or macular hole surgery with gas or an intravitreal injection with an air bubble, this explains why the “gas/air” appears toward the bottom of your vision when looking straight ahead. With your head erect, the gas rises to the top of your eye, giving you the impression that the gas is on the floor,)
iolePosted at 12:00h, 23 April
i believe the picture on the retina is not properly represented.
from the same point of view, the letter K should be upside-down and on the left.
Randall V. Wong, M.D.Posted at 05:21h, 26 April
Thanks! I agree!
OmarPosted at 12:27h, 31 May
Randall V. Wong, M.D.Posted at 00:06h, 03 June
Bill SvensonPosted at 22:44h, 22 October
Is there a difference between the receptors on the upper part of the retina vs. the lower. I have a problem with reflected sunlight, like from a pool surface, it causes irritation even agression if prolonged?
Randall V. Wong, M.D.Posted at 00:34h, 26 October
Not so sure about this. I am wondering if the reflected light gives a ton of glare?
JoannaPosted at 01:40h, 01 December
I just randomly came across your blog by searching retinas on google. I like it! I was wondering, though, if you could maybe give me an opinion- I have this problem where I see a copy of almost everything I look at, see halo-like lights around objects and people, and I see the “snow” that one gets when pulling the cable out of a TV. Any ideas on whether it’s hallucinations or an eye problem? Thanks! Sorry, I know this is a lot to read/think about.
Randall V. Wong, M.D.Posted at 06:40h, 07 December
You have the symptoms of cataracts. See your eye doctor for her opinion. Obviously, I’m only guessing as I can’t examine you.
ChristopherPosted at 13:22h, 13 August
I have double vision (i think that’s what its called) where any object I look at is like its being drug down my vision and a little to the left, not just a duplicate, but an actual drag, would prisms help with this? also, do they make something that keeps the shape of one’s eye in form, when i open my eye and pull my eye brow up and cheek down, the shape of my eye changes and i can see MUCH more clearly. i’d love your thoughts.
Randall V. Wong, M.D.Posted at 17:27h, 17 August
Not sure I quite understand your description. Regardless, I’d seek the evaluation of a pediatric ophthalmologist for “double vision.”
Pediatric ophthalmologists take care of children with crossed eyes and adults who suffer double vision.
Stephen PaulPosted at 01:50h, 01 September
This is something I thought I understood until reading above that images are (in addition to being projected upside-down) reversed on the retina. I’m having some difficulty understanding the delivery of visual content to the different hemispheres now. In the image above, and assuming that fixation is centered between the letters K and H, K should be part of the left visual field and H part of the right visual field. When ONLY flipped upside down on the retina of the right eye for example, this puts the K on the temporal side which projects ipsilaterally and the H on the nasal portion of the retina to go contralaterally. HOWEVER, if the image is also reversed… then wouldn’t that mean that the left visual field (K) would fall on the nasal portion of the retina to now project contralaterally? I’m having trouble understanding how the right visual field can project contralaterally if images are also reversed. Can you help me to better understand this?
Randall Wong, M.D.Posted at 15:08h, 07 October
Your understanding is correct! The K is absolutely “backwards.” Sorry for the late reply. r
GrahamPosted at 07:13h, 09 February
Thanks for the explanation. I currently have 3rd nerve palsy (is improving) but it does explain why when I open my left eye, even though it is slightly fixed looking downwards and to the left, the image I see is to the right of what my right eye sees. Eyes and what the brain does makes for a fascinating subject to study.
Randall Wong, M.D.Posted at 03:01h, 28 February
Thanks for following. r