Week 8 - BSV revision

Question 1

Binocular vision definition + Normal vs abnormal BV

Answer 1

• Binocular Vision: the ability to use both eyes at the same time.

• Normal Binocular Vision: Bifoveal.
No manifest deviation/No heterotropia.

• Abnormal Binocular Vision: There is a small manifest deviation/small heterotropia but BSV is demonstrated

Question 2

Worth’s Grades of BV

Answer 2

1. Simultaneous Perception: The ability to perceive an image from each eye at the same time. Includes diplopia.
2. Fusion: Sensory Fusion and Motor Fusion
   • Sensory Fusion: The ability to appreciate two similar images from either eye and view them as one.
   • Motor Fusion: Maintain a single image during vergence movements.
3. Stereopsis: Perception of relative depth of an object.

Question 3

Investigations into grades of BV: Simultaneous perception

Answer 3

• Bagolini Glasses
• Worth Lights

Question 4

Investigations into grades of BV: Fusion

Answer 4

Sensory
• Bagolini Glasses
• Worth Lights

Motor
• Prism Reflex Test
• Prism Fusion Amplitude
• Synoptophore

Question 5

Investigations into grades of BV: Stereopsis

Answer 5

Frisby- Near and Distance
TNO
Randot Test
Wirt Test
Lang’s Two-Pencil Test

Question 6

Normal correspondence is expected in:

Answer 6

• Normal Retinal Correspondence (NRC)
Both fovea have a common visual direction: The nasal points of one eye correspond to the temporal point of the other eye.

NRC is expected:
• Normal BSV
• Intermittent strabismus e.g. Intermittent distance exotropia and convergence excess esotropia.
• Acquired strabismus with onset after visual development period e.g.
cranial nerve palsy.

Question 7

Abnormal retinal correspondence

Answer 7

• Sensory adaptation in manifest strabismus, allows for BSV. Lesser quality BSV than NRC BSV.

• Monocular condition: disappears when fixing monocularly.

• The fovea of one eye has the common visual direction with an extrafoveal area of the other eye. Usually associated with central suppression scotoma.

• 2 Types of ARC:
- Harmonious: The angle of anomaly= angle of strabismus
- Unharmonious: The angle of anomaly is greater than zero but
Less than the angle of deviation.

Question 8

Prism Fusion Range Revision

Answer 8

• When a prism is placed in front of an eye, the target is shifted towards the apex of the prism.
• To maintain BS, the eye must make a corrective movement.
• If a base out prism is used- the corrective movement is inwards.
• If a base in prism is used- the corrective movement is outwards.
• The largest prism which can maintain BSV: Fusion range

Question 9

Relationship between Heterophoria and PFR

Answer 9

• “Normal” ranges of PFR for N/ DIST and BI/BO are not always sufficient dependent on patients underlying phoria.
• Heterophorias have a compensatory range which controls the deviation.

Exophoria= Base Out
Esophoria= Base In

• Sheard’s criterion says that the compensatory range should be at least double the size of the heterophoria.
- Example: Exophoria of size 10^B|= 20^BO fusion required.
- 30^BO at near= “Normal” PFR. However, if patient has an exophoria of 20^BI they required 40^BO to maintain comfortable BSV. This patient may still decompensate from phoria> tropia even with “normal” PFR.