Why Two Eyes? Flashcards
20 years from now, remember that you can enhance pt’s visual performance through VT by helping them improve
Oculomotor, vergence, acommodative control and visual attention.
The human visual system can detect differences in light at the ___ level
nanometer
Why is the eye an ideal detector?
A normal, fully dark adapted human eye must be presented with only 1 photon to each photoreceptor (8-10) in order to detect it.
is 0.25 diopter significant?
Yes. It may be to some patients. Accommodation is dynamic and 0.25D can shift the range enough to make the patient more comfortable.
Similarly, vergences are dynamic.
Stereo originates from what greek word?
Solid. 3D. can be used in vision context or hearing context.
Stereo in vision
The perception that an object has 3 dimensions (length, width, depth) that we get because each of our eyes views the object from a slightly different vantage point.
we can trick the brain into perceiving 3D if we showing each eye a flat picture.
As long as we meet the requirements the brain needs to see in 3D so the “depth cell” receives a stimulus it likes.
3 Requirements to see in 3D
- Two eyes, frontally located and horizontally separated so that fields overlap.
- Eyes must be aligned and pointed at the same object.
- Equally clear vision in the two eyes. (cataracts, glaucoma, ARMD, refractive error) Even if eyes are aligned, if one picture is blurry, the brain has difficulty putting the two pictures together to make 3D vision.
How can you determine that the eyes aren’t aligned by using a pen light?
Look at purkinje images on the eye.
How do you trick the brain into seeing 3D?
- Must present two different targets of the same picture to each eye separately
- Must get each eye to see the picture from a slightly different angle.
The brain doesn’t care how its near and far cells are stimulated. But they need to be stimulated, the brain will see one target with depth.
Wheatstone stereoscope
Pt looks inside machine with 2 mirrors angled 45 degrees. The same picture is presented to each eye.
Brewster Stereoscope
Used high power plus lenses. Pt’s eyes separated by septum. 2 similar photos are presented to the patient’s right and left eye. Slightly different horizontally. More portable than wheatstone.
Anaglyphs
Filters allow some wavelengths to enter and blocks others. Use glasses with cyan and blue filters. Brain gets 2 separate ghost images that slightly vary horizontally. Brain will fuse and interpret 3D
Polarizing lenses used to create 3D
Left and right eyes see different images based on polarizing the light reflecting off movie screen.
More expensive
Colors are more life like
Free fusion
A device-free way of presenting separate targets of the same picture to the two eyes.
Normal, crossed (visual axis intercepts in front of the card), uncrossed (visual axis intercepts behind the plane)
Does the brain need contour lines to see depth?
NO, it also doesn’t even need to two totally separate targets.
