Binocular Single Vision

Question 1

What is BSV?

Answer 1

Simultaneous use of two eyes to give one mental image

Question 2

Why do we have 2 eyes?

Answer 2

• Spare eye -> if something happens to one

- Wider FoV -> as eyes wider apart

Question 3

Advantages of BSV?

Answer 3

• Binocular summation -> enhanced VA, CS and motion perception
• Ability to perceive depth - stereopsis

Question 4

What is Normal Retinal Correspondence (NRC)?

Answer 4

Every single point on the retina corresponds to a certain point in space.
When in the RE: T corresponds to LE: N
When in the LE: T corresponds to RE: N

Question 5

What is the Horopter?

Answer 5

An imaginary line - where any object laying on this line stimulates exactly corresponding retinal points and are seen singly/ as one image.

AKA - Vieth-Muller Circle

Question 6

What happens if an object does not stimulate exactly corresponding points?
What is the area known as?

Answer 6

The small area around the Horopter in which points are almost corresponding but are not seen singly.
The area is known as Panum’s Fusional Area.

Question 7

What is Panum’s Fusional Area/Space?

Answer 7

It is the disparity of the almost corresponding points which are fused into one single image and results in stereopsis.

Question 8

What happens to objects that fall outside Panum’s Area?

Answer 8

The objects give rise to physiological (normal) diplopia. This type of diplopia exists when you have binocular vision - therefore anything outside is not seen singly.

Question 9

What are the grades (Worth’s grades) of BSV?

Answer 9

• Simultaneous perception
• Fusion: sensory fusion and motor fusion
• Stereopsis

Question 10

What is simultaneous perception?

Answer 10

Ability to perceive two images simultaneously, one from each retina.

Question 11

What is sensory fusion?

Answer 11

Integration of two similar images, one formed on each retina into one image within the brain.

Question 12

What is motor fusion?

Answer 12

Maintenance of sensory fusion through a range of vergence movements.

Question 13

What is stereopsis?

Answer 13

The perception of relative depth of objects by the fusion of relative disparity of images from the two eyes.

Question 14

What happens when one of your eye turns? (Strabismus)

Answer 14

The Px will have one of the following:

• Confusion - NRC
• Diplopia - NRC
• Suppression - NRC
• Abnormal Retinal Correspondence - ARC
• Normal straight eyes - No Strabismus

Question 15

What is confusion?

Answer 15

Confusion is when the fovea of the fixating eye receives the image of the fixated image and the fovea of the strabismus eye receives a different image. The two images are superimposed.

Question 16

What is pathological diplopia?

Answer 16

The inability to fuse corresponding foveal images.
Occurs in manifest strabismus when the fovea of the fixated object stimulates a non-corresponding peripheral area in the strabismic eye.

Question 17

What is suppression?

Answer 17

The mental inhibition of the image in front of the eye which is deviated off when both eyes are open.

Question 18

Why does suppression occur?

Answer 18

In order to avoid: Diplopia and Confusion.

They usually do not have stereopsis.

Question 19

What is abnormal retinal correspondence?

Answer 19

Its a binocular condition.
The sensory adaptation in which the fovea and areas on nasal and temporal retina correspond and have a common visual direction with an area other than the fovea with the deviating eye. i.e. the psuedofovea.
No stereopsis.
Overcomes: diplopia and confusion.

Question 20

Why is Abnormal Binocular Single Vision (ABSV) useful?

Answer 20

• Will also have a form of stereopsis

- Will also have a form of binocular summation

Question 21

What happens in constant strabismus?

• Children?
• Adult? >8y/o

Answer 21

• Children: Suppression (NRC) - treat for cosmesis. ARC - usually dont treat, just monitor.
• Adult: Confusion (NRC) and Diplopia (NRC) - usually treat with prisms, lenses and surgery.