accommodation

Question 1

define accommodation

Answer 1

• the process of when the refractive power of eye increases to provide clear near vision
• when not exerted: relaxed
• decrease in power (near to distance): negative accommodation

Question 2

outline ocular changes during accommodation

Answer 2

1. ciliary muscle contracts (moves forward and inwards)
2. relaxes tension on zonules
3. releases distorting force on capsule
4. capsule adopts more spherical shape

Question 3

define far point (punctum remotum, Mr)

identify location for emmetropia, myopia and hyperopia

Answer 3

• furthest point from the eye that an object is in focus (with accom fully relaxed)

emmetropia: infinity
myopia: in front
hyperopia: behind

Question 4

define near point (punctum proximum, Mp)

identify location for emmetropia, myopia and hyperopia

Answer 4

• nearest point to the eye that an object can be brought into focus (with accom fully exerted)

emmetropia: in front
myopia: in front
hyperopia: “anywhere” -> depends on amplitude of hyperopia and accommodation

Question 5

define range of accommodation (2)

ie. range of near vision

Answer 5

• linear distance from the far point to the near point

- clincally more meaningful for patients

Question 6

define amplitude of accommodation (2)

Answer 6

• maximum amount the eye can change power during accommodation
  ie. dioptric range from the far point vergence to near point vergence when accommodation is maximally exerted

Question 7

define accommodative demand (1)

Answer 7

the accommodation required to bring the image of a near object to the retina

Question 8

define focusing error (1)

Answer 8

the dioptric difference between near point and a near object when accommodation is insufficient to meet accommodative demand

Question 9

define accomodative reserve (1)

Answer 9

• portion of accomodation amplitude not engaged at near working distance to ensure comfortable prolonged near vision

Question 10

define presbyopia (2)

how is caused (2)

Answer 10

• age-related decrease in accommodation
• inability of the eye to accommodate for objects at close range
• result of:
  1. lens stiffening
  2. change in stiffness gradient
  (nucleus more stiff than cortex)
  3. slackening of zonules

Question 11

subjective measurment influences (4)

Answer 11

• alertness of patient
• awareness of nearness
• depth of focus
• tolerance to blur (ie. visual acuity)