Convergence & depth of field

Question 1

What is convergence as related to eye movements?

Answer 1

Both visual axes move nasally to place the image of the near objects on the fovea.

Question 2

Which of the extraocular muscles are mainly responsible for producing convergence?

Answer 2

Medial recti muscle

Question 3

What is the effect of convergence on the pupil?

Answer 3

Miosis

Question 4

Define near point convergence

Answer 4

The nearest point to which the eyes can converge

Question 5

Describe how the position of the Near Point of Convergence can be found

Answer 5

*Px looks at object on midline with both eyes open
*Object brought closer until target doubles
*The distance from the eyes to this point is the NEAR POINT OF CONVERGENCE
*If practitioner notices eyes stop adducting before an image doubles this will be the NEAR POINT CONVERGENCE

Question 6

What would be considered a normal range of values for this measurement?

Answer 6

50-100mm

Question 7

Advantage of a meter angle as a unit of convergence

Answer 7

*Doesn’t require a PD
*It is numerically equivalent to accommodation in dioptres

Question 8

How is depth of field affected by pupil size

Answer 8

The smaller the pupil, the larger the depth of field. If the pupil is larger, the depth of field will be reduced.

Question 9

Convergence as related to eye movements

Answer 9

Both visual axes move nasally to place the images of the near objects on the fovea

Question 10

Which extraocular muscles are mainly responsible for producing convergence?

Answer 10

Medial recti muscle

Question 11

Effects of convergence on the pupil

Answer 11

Miosis

Question 12

Near point of convergence

Answer 12

The nearest point to which the eyes can converge

Question 13

How position of Near Point of Convergence may be found

Answer 13

*Px looks at an object on midline
with both eyes open

*Object is brought closer until
the target doubles

*The distance from the eyes to
this point is the ‘near point of
convergence’

*If practitioner notices the eyes
stop adducting before an image
doubles, this would be the NCP

Question 14

Range for normal convergence

Answer 14

From 50 - 100 mm

Question 15

Advantages of meter angles as a unit of convergence

Answer 15

*Doesn’t require a PD
*Numerically equivalent to
accommodation in dioptres

Question 16

Negative spectacle lens and convergence

Answer 16

Negative spectacle lens will reduce the amount of convergence needed

Question 17

Convergence

Answer 17

*Describes a movement of the visual axes nasalwards from primary position of gaze.

*In primary position the visual axes are initially parallel.

*A convergence movement causes the visual axes to intersect in front of the eyes (this usually means the two visual axes intersect at the fixation point)

*Assuming R&L symmetry each eye converges by the same angle when the fixation point is on the median line.

Question 18

Relative convergence

Answer 18

*Is the amount of convergence or (divergence) that a subject can exert for a fixed amount of accommodation.

*Its measured by placing prisms of increasing strength in front of px’s eyes while they view a target at a specified distance.

*Prism base OUT will cuse convergence & as the prism power is increased, at acertain point, accommodation will be stimulated, causing the target to blur.

*The strength of the prism that causes this to occur is known as the blur point.

*If prism power is increased further, eventually the subject will no longer be able to converge to overcome the prism & diplopia (double vision) will occur. This is known as the break point.

*Prism base IN will cause the eyes to diverge