Convergence

Question 1

What is disjugate eye movement?

Answer 1

The eyes move in the opposite relative direction

Question 2

What is conjugate eye movement?

Answer 2

The eyes move in the same relative direction

Question 3

What is ‘normal convergence’?

Answer 3

Near point of convergence of less than or equal to <10cm without effort is considered normal

Question 4

What’s the ‘near triad’?

Answer 4

Convergence = closer = fatter lens (accommodation)
Far objective = no accommodation = lens thinner
Near objective = pupil miosis

Question 5

What unit is convergence measured in?

Answer 5

• Prism Dioptres
• Degrees
• cm
• Meter angle (equivalent to dioptre of accommodation used in clinical research)

Question 6

What do we need to know to work out required convergence?

Answer 6

Need to know a person’s IPD and know the target distance

Question 7

What’s the average adult IPD in females and males?

Answer 7

52 - 76mm
Female average is 62mm
Male average is 65mm

Question 8

When do we use zero convergence?

Answer 8

When looking at a target at infinity or with an IPD of 60mm at 6cm

Question 9

How much convergence is required for a distance target?

Answer 9

Less convergence

Question 10

How much convergence is required for a wider IPD?

Answer 10

More convergence required

Question 11

How much convergence is required for a narrower IPD?

Answer 11

Less convergence required

Question 12

If 1PD of convergence moves an image 1cm at 1m, how many cm does an image move at 0.5m and 2m?

Answer 12

0.5m = 0.5cm
2m = 2cm

Question 13

If a target is 1m away and IPD is 6cm, how much must the target move?

Answer 13

To view target 1m the image must move 3cm + 3cm
RE converges 3PD for 3cm
LE converges 3PD for 3cm
So total convergence required is 6PD

Question 14

If a target is 0.5m away and IPD is 6cm, how much must the target move?

Answer 14

As 1PD of convergence moves an image 0.5cm at 6m this means we’d need 12PD convergence in total (6PD in each eye)

Question 15

If a target is 2m away and IPD is 6cm, how much must the target move?

Answer 15

As 1PD convergence moves an image 2cm at 2m, 6/2 = 3PD so 1.5PD in each eye

Question 16

What are the 4 types of convergence?

Answer 16

Tonic Convergence
Accommodative Convergence
Proximal Convergence
Fusional Convergence

Question 17

What is Tonic Convergence?

Answer 17

Passive state of vergence of the eyes in the absence of a stimulus maintained by the tonus of the EOMs (which are never without neural activity)

It’s the ability to hold position of convergence without a target when the anatomical position of rest is divergence. When awake this new tonic convergence is seen due to innervation of eye muscles; it can be eliminated by occlusion or deep anaesthesia and decreases with age

Question 18

What is Accommodative Convergence?

Answer 18

Convergence is induced when accommodation occurs; it’s induced by ‘blurred retinal image’

Accommodation Convergence/ Accommodation
Measures changes in AC in PD induced when the patient exerts or relaxes 1PD of A; normally 4:1

Question 19

What is Proximal Convergence?

Answer 19

When convergence is stimulated by the awareness of nearness of an object.

Question 20

Why might measurements on a synoptophore differ compared to a prism cover test?

Answer 20

Due to proximal convergence; from over-convergence on synoptophore due to artificial viewing causing an increased ET angle and decreased XT angle (but Georgievski, 1995 found no difference on PCT on synoptophore vs. free space)

Question 21

What is Fusional Convergence?

Answer 21

Stimulated by disparate (separate) images to maintain bifoveal fixation and avoid diplopia (to ensure that the images hit the corresponding retinal areas in each eye)

• Positive (convergence) = when insufficient convergence from other components
• Negative (divergence) = when too much convergence from other elements

Question 22

What is Relative Fusional Convergence?

Answer 22

Allows accommodation or convergence to be flexible e.g. in refractive error or heterophoria
It’s the maximum vergence movement enabling a patient to see a comfortable clear image and is represented by the first point of blur and so can be improved with exercises. Measured by the prism fusion range and it’s convergence response in excess of accommodation or vice versa

Question 23

What’s near point of convergence (NPC)?

Answer 23

NPC is the closest point at which an object can be seen as one during bifoveal vision and doesn’t change with age

Question 24

How is near point of convergence measured?

Answer 24

Free space or the RAF rule

Question 25

How do we measure NPC in free space?

Answer 25

Test with refractive correction and use a small fixation target that’ll be moved steadily toward the nose with the patient reporting when they see 2 and record the NPC in cm. (it’s an estimate)

Question 26

What must you be aware of watching during NPC testing in free space?

Answer 26

Important to watch the eyes for when convergence breaks as there could be a suppression response instead of diplopia

Question 27

How do we measure NPC in RAF rule?

Answer 27

Tested with refractive correction using the line & dot on the drum.
The rod is held in a slightly depressed position and report when the line splits into 2 . Need to report 3x to reveal fatigue. It’s recorded in cm, record what happened at break point and whether effort is involved.

Question 28

What’s impaired convergence?

Answer 28

Convergence insufficiency
Convergence Paralysis
Convergence Spasm