B The focal length of the eye and image inversion

  • B
  • Thread starter Thread starter anuttarasammyak
  • Start date Start date
AI Thread Summary
The discussion centers on the relationship between the focal length of the eye, image inversion, and visual perception after eye surgery. It highlights that the brain processes images from the retina in an inverted manner, regardless of whether a person is nearsighted or farsighted. Participants share personal experiences with visual perception changes, particularly when using corrective lenses and observing laser speckle patterns. The conversation also touches on the challenges of coordinating movements and visual orientation, especially when viewing oneself in mirrors or on video calls. Overall, the thread explores the complexities of how the eye and brain interact to create our visual experience.
anuttarasammyak
Gold Member
Messages
2,922
Reaction score
1,515
After my surgery this year, gas remained in my eye for a while. The light air bubbles appeared to sink to the bottom, and I realized that the brain was processing the information to invert the up/down/left/right image transferred to the retina.

I have a question about optics and ophthalmology. Does the inversion of the image transferred to the retina depend on the position of the intraocular focal point of the lens of the eye? For example, in people with farsightedness, the focal point is behind the retina, so does an uninverted image transfer to the retina? Incidentally, I am nearsighted.
 
Science news on Phys.org
No, the image is inverted for all of us. Draw a standard ray diagram for a pair of thin lenses with a couple of off-axis points in the same object plane. Now consider shifting the screen backwards and forwards through the image plane. You'll induce blur in each point, but the points won't swap position.

If you look at a laser dot on a wall you will see laser speckle, and if you move your head you will see the speckle pattern flow. I am told that whether it flows in the same direction or the opposite direction to your head movement does depend on long- or short-sightedness. I have not had the opportunity to test that claim.
 
  • Like
Likes Lnewqban, hutchphd and anuttarasammyak
Thank you @Ibix. I was caught up in a false association between focus and inversion.
 
Ibix said:
I have not had the opportunity to test that claim.
In fact I have and it is absolutely true. I am farsighted and have reading eyeglasses that make me effectively nearsighted. The movement of the speckle (from a laser pointed on a matt surface wall at distance 3m) is easy to see and changes direction when glasses are removed. I know of no practical utilizations of this effect but intend to play with it soon and do some research. Will append any interesting findings here.
 
  • Like
Likes anuttarasammyak and Ibix
kuruman said:
And then there is the Erismann experiment.
The only time I encounter this organically is when trimming my "back burns" in the mirror. If I keep at it long enough, eventually I can coordinate my movements.
hutchphd said:
In fact I have and it is absolutely true. I am farsighted and have reading eyeglasses that make me effectively nearsighted. The movement of the speckle (from a laser pointed on a matt surface wall at distance 3m) is easy to see and changes direction when glasses are removed. I know of no practical utilizations of this effect but intend to play with it soon and do some research. Will append any interesting findings here.
Well now I have to try this.
 
anuttarasammyak said:
After my surgery this year, gas remained in my eye for a while. The light air bubbles appeared to sink to the bottom, and I realized that the brain was processing the information to invert the up/down/left/right image transferred to the retina.
Note that you only see objects within your eye sharply, if they are close to the retina. Otherwise they are blurred across a large part of the image. So there is bias to which objects you even notice. And the visual location of those object is inverted, because of how the brain interprets the signals from different locations on the retina.
 
Last edited:
DaveC426913 said:
The only time I encounter this organically is when trimming my "back burns" in the mirror. If I keep at it long enough, eventually I can coordinate my movements.
I can coordinate the movements of the right hand, but not (or only with difficulty) the left. Is this common?
 
mjc123 said:
I can coordinate the movements of the right hand, but not (or only with difficulty) the left. Is this common?
Well, presumably it's affected by your handedness. I'm a leftie and I can't even operate scissors right-handed without a mirror.
 
  • #10
DaveC426913 said:
Well, presumably it's affected by your handedness. I'm a leftie and I can't even operate scissors right-handed without a mirror.
I always get disoriented when I see myself on a store's surveillance monitor because I instinctively interpret what I see as my mirror image. I guess the equivalent would be for you to try operating scissors while looking at a live selfie video. :oldsmile:
 
  • Like
Likes sophiecentaur and DaveC426913
  • #11
kuruman said:
I always get disoriented when I see myself on a store's surveillance monitor because I instinctively interpret what I see as my mirror image.
On a Zoom call with several others, you may notice that your image is arranged to be the familiar mirror-inverted but everyone else is 'right way round'. (And, of course they all see you the right way round.) We accept those things without thinking but, when talking to family kids on FaceTime , if you're trying to be smart and move about up close to the screen, it's not obvious where to put your face so that you are 'nose-to nose'. Such is the interesting life of a grandad!!
 

Similar threads

Replies
9
Views
3K
Replies
1
Views
2K
Replies
12
Views
4K
Replies
8
Views
2K
Replies
1
Views
2K
Replies
7
Views
3K
Replies
36
Views
7K
Back
Top