Stereopsis Flashcards
First degree fusion
Patient is NOT fusing. First step in becoming a fully fused, binocular being, is for both eyes to be on. Achievement of first degree fusion.
Eyes are bi-ocular. Eyes are gathering, brain is perceiving. They just may not be making it into one.
Second degree fusion
Flat fusion- using both eyes to make 1 uniform image, but no depth perception.
Third degree fusion
Depth perception, or stereopsis. Highest level of binocular vision.
Monocular depth perception cues and examples
Visual clues seen with one eye that can be used to determine where something is located in space, relative to the person.
Examples:
Relative size. Larger? perceived to be larger.
Light and shade
Overlapping
Binocular depth perception cues
Visual clues seen with both eyes that can be used to determine where something is located in space.
Determined by disparity, or slight differences between the two images of both eyes. Each eye being stimulated in a corresponding point of the fovea.
Global stereopsis
The most advanced- forms or shapes. The visual system does not have any monocular cues. Completely dependent on being binocular and using retinal correspondence.
If you have a constant trope or supresser, they will not see the forms ever.
Local stereopsis
Lesser level of stereo advancement. Patient takes advantage of monocular cues.
Ex: pt with only one eye can achieve some level of local stereopsis. Ex: wirt circles.
Stereoacuity
What we measure when local stereopsis- Wirt circles. As you go 1-10, the disparity of the perceived raised image grows smaller and smaller and smaller. Measured in seconds of arc (“)
If the patient cannot see stereo, what is causing it? Should look at:
Binocularity- must determine if the patient is monocular, biocular, or binocular.
Their refractive error- especially with large amounts of anisometropia (unequal refractive power)?
Strabismus? Do they suppress?
Age? Stereopsis is a learned trait. Young kids may not know how.
Anisometropia
Unequal refractive power
