Mechanical Vs Neurogenic

Question 1

Things to compare between the 2

Answer 1

• deviation
• diplopia
• head posture
• ocular movements
• Hess chart
• globe retraction
• pain on movement
• forced duction
• saccadic eye movement
• iop

Question 2

Deviation in PP

Answer 2

Neurogenic
- deviation in PP can be marked

Mechanical
- often little deviation in PP

Question 3

Diplopia

Answer 3

Neurogenic
- except 3rd, diplopia is the same in all positions of gaze

Mechanical
- diplopia can reverse

Question 4

Head posture

Answer 4

Neurogenic
- head tilt usually

Mechanical
- head elevation or depression

Question 5

Ocular movements

Answer 5

Neurogenic
- amount of movement elicited is often greater on duction than version
- movement ceases gradually in direction affected
- maximum limitation in direction of affected muscle

Mechanical
- duction and versions equally affected
- movement ceases suddenly

Question 6

Hess chart

Answer 6

Neurogenic
- field of affected eye is smaller
- proportional spacing between inner and outer field

Mechanical
- outer field very close to inner field in direction that’s most affected
- usually limited up/down/left/right
- no contracture of ipsilateral antagonist

Question 7

Retraction of globe

Answer 7

Neurogenic
- none

Mechanical
- retracts when turned in opposite direction of the mechanical lesion

Question 8

Forced duction

Answer 8

Neurogenic
- full passive movement unless secondary muscle contracture

Mechanical
- limited passive movement in direction opposite to the lesion
- sometimes in both directions

Question 9

Saccadic eye movement

Answer 9

Neurogenic
- reduced peak saccadic velocity

Mechanical
- normal

Question 10

IOP

Answer 10

Neurogenic
- remains unchanged

Mechanical
- raised when looking away from site of the lesion - difference in more than 5mmHg between 2 opposite directions of gaze is significant