2. Development of BSV

Question 1

What is essential for normal BSV? (6)

Answer 1

1. Normal development of the globes (babies can be born with one or both very small eyes or only one eye, BE not used together hence no BSV).
2. Normal development of orbits (Problems include restricted skull growth).
3. Normal visual pathways (Anomalies associated with visual pathway lead to poor/ no visual acuity)
4. Normal overlap of visual fields (larger the distance between 2 eyes, smaller the overlap)
5. Normal decussation of retinal fibers (Abnormal condition includes ocular albinism).
6. Presence of NRC (retinal areas in the RE correspond to retinal areas in the LE).

Question 2

Grades of BSV

Answer 2

1. Simultaneous perception
2. Sensory Fusion
3. Motor Fusion
4. Stereopsis

Question 3

1. What is simultaneous perception
2. How is it demonstrated?

Answer 3

1. Ability to appreciate 2 separate images as the same time, one formed on each retina.
2. Using synoptophore

Question 4

1. What is Sensory Fusion
2. How is it demonstrated? At near & distance?

Answer 4

1. Ability to perceive 2 similar images one image on each retina and interpret them as one.
2. Using Baglioni glasses, Worths lights or synoptophore

Question 5

1. What is motor fusion
2. How is it demonstrated?

Answer 5

1. Ability to maintain sensory fusion through a range of vergence movements, it allows us to maintain single vision as we converge or diverge to fix on objects at different distances.
2. 20^ BO prism test (on babies) or prism fusion range (adults).

Question 6

On CT px has phoria, but they complain of double vision explain in terms of grades of BSV?

Answer 6

Px has enough BSV to maintain sensory fusion but not enough to motor fusion. Hence, when eyes move around they can’t hold that sensory fusion.

Question 7

Normal vs Suppressing eye with 20^ BO Prism Test

Answer 7

Normal: Eye under prism moves in and other eye moves out, and px has diplopia. then the eye not under prism moves back in to fuse images and eliminate diplopia.
Suppression: Eye under prism doesn’t move, hence eye under prism is suppressing. Or if eye not under the prism doesn’t move back in, suggests diplopia not recognized hence eye not under the prism is suppressing.

Question 8

Normal prism fusion range, distance & near?

Answer 8

Distance: 45BO- 18BI
Near: 20BO- 8BI

Question 9

Why does stereopsis occur?

Answer 9

Due to the distance between 2 eyes. It is the binocular appreciation of depth. Fusion of 2 separate images leads to 3D images.

Question 10

What instrument can assess all grades of BSV?

Answer 10

Synoptophore

Question 11

What are sensory obstacles of BSV?

Answer 11

1. Poor VA in one eye, hence barrier to fusion.
2. Sensory strabismus is adults
3. Vision loss at birth for children.

Question 11

Near VS Distance Stereopsis tests

Answer 11

NEAR: lang, TNO, Wirt, Frisby
Distance: Synoptophore, Frisby Davie 2

Question 12

Fusional obstacles for BSV?

Answer 12

Any latent deviation (phoria) - fusional reverse not enough to cope with the size of deviation. Due to commitent phoria, cranial nerve palsy, myogenic or mechanical problems, refractive error.

Question 13

2 obstacles of BSV other than sensory and fusional obstacles?

Answer 13

Extraneous- factors outside the eye like ptosis or over occluding.
Cortical obstacles- Failure to achieve binocularity (trauma, tumor, infection)

Question 14

What happens following failure of fusion and the development of heterotropia?

Answer 14

1. Pathological diplopia
2. Confusion