topic 4: accommodation and presbyopia

Question 1

what happens in accomodation?

Answer 1

When the ciliary muscles contract, it relaxes tension from the suspensory zonules of Zinn and allows the crystalline lens to take on a more curved shape.

The increased radius of curvature of the crystalline lens gives it a higher refractive power. This process is known as accommodation.

Question 2

What stimulates the eye to accommodate to a near target?

Answer 2

1. blur retinal image
2. chromatic aberration
3. convergence

Question 3

what is the formula for accommodation exerted?

Answer 3

A = K – L

Where K = distance ocular refraction
L = object vergence

Question 4

how to calculate far point?

Answer 4

1/K

1= RI of air
K= ocular refraction

Question 5

how to calculate near add?

Answer 5

1) measure the amplitude of accommodation
2) halve that value to find out the amount of accommodation that the patient can realistically exert for sustained periods of near work.

3) calculate the amount of power needed for the working distance (1/ working distance),
and prescribe the amount of near addition needed if the value in (2) is insufficient.
take power needed -accommodation

Question 6

what is near point?

Answer 6

The near point is the point in space where light rays will be focused on the retina when maximum accommodation is exerted.