Introduction To Binocular Vision Flashcards
What is binocular single vision?
‘Simultaneous use of two eyes to give one mental image’
What happens if you do not have binocular single vision (BSV)?
Basically double vision (in the case of a face it would look like four eyes on a face)
What is the advantage of having two eyes?
You have a spare eye if pathology happens to one. Wider field of view.
What are the advantages of binocular single vision (BSV - I.e using two eyes to produce one image)?
—>Binocular summation - both eyes contributing to one image means there is an enhanced visual acuity, contrast sensitivity and motion perception. —> Stereopsis (ability to perceive depth). This means you have enhanced visual motor skills. (To test this try joining the tip of a vertically held pencil to another vertically held pencil - with both eyes open one can do it easily but with one eye covered it’s incredibly difficult to measure depth).
What is stereopsis?
Depth perception
What do you need to develop normal BSV?
You need Normal retinal correspondence (NRC).
How can the impact of binocular vision in regards to stereopsis be tested ?
The Pencil tip test. With both eyes open it’s very easy to connect the tip of a pencil to another pencil somebody else is holding (vertically) whereas with only one eye open this is increasingly difficult.
What is retinal correspondence?
It means that every single point on the retina corresponds to a point in space.
What is Normal Retinal Correspondence?
A Binocular condition in which the fovea and areas on nasal and temporal retina correspond and have a common visual direction with the fovea and nasal retina areas of the other eye.
What’s the cyclopean?
It’s an imaginary eye - it basically represents how vision is seen if we only had one eye in the centre of our head (same as the image produced at the moment from the summation from both eyes)
What is the theoretical horopter?
An imaginary line in which each point has an exact corresponding retinal point thus is seen as a single image.
What is the theoretical/geometrical horopter in the horizontal plane come to be known as ?
Veith-Mülleer circle
What is Panums fusional space?
The small area around the horopter in which corresponding and almost corresponding objects are still seen singularly.
What is stereopsis caused by?
The disparity of the almost corresponding points (i.e. those close to the horopter line) (as a pose to the single points i.e. those exactly on the horopter), which are fused together into one single image. This gives that 3D depth effect.
What happens when objects fall out of Panam’s fusional area?
All objects outside of Panum’s fusional space give rise to physiological (normal) diplopia.
This type of diplopia exists when you have binocular vision
What is crossed double vision refered to as and how can we identify it?
Crossed double vision is referred to as Heteronymous double vision.
In this example if you get the patient to close one eye the image moves to the other side.
(False image is on the same side as the healthy eye).
What happens in homonymous diplopia?
When you get the patient to close one eye
(False image is on the same side as the affected eye).
What are worths grades?
- Simultaneous Perception
- Fusion - Sensory Fusion
- Motor Fusion
- Stereopsis
How does normal retinal correspondance work?
Normal retinal correspondence (NRC) is a binocular condition in which both foveas work together as corresponding retinal points, with resultant images fused in the occipital cortex of the brain.
I.e Fovea of the right eye corresponds to the fovea of the left eye. The nasal elements of the right eye correspond to the temporal elements of the left eye. The temporal elements of the right eye correspond to the nasal elements of the left eye.
What happens in pathological diplopia associated with manifest strabismus in adults?
Imagine the patient is looking at a tree and the patient has esotropia of the right eye (i.e. right eye turns inwards). The tree would land on the fovea of the left eye but not on the fovea of the right eye - In this case the tree stimulates the left nasal retina.
As the nasal retina is stimulated it projects temporally.
How does supression in those that have strabismus occur?
Important to note –>This happens in children under 8 and that if this didnt happen the child would be experiencing Pathologic diplopia.
The human brain is extremely clever and realises we are getting double vision and that this isn’t useful thus it literally just ignores the double vision that would be occuring - this only happens though when both eyes are open!
