Mechanism Of Accommodation

Question 1

Structures involved in accommodation

Answer 1

• ciliary body (muscle)
• choroid
• iris
• anterior and posterior zonules
• crystalline lens (lens capsule)

Question 2

The ciliary body is part of the:

Answer 2

Intermediate tunic

Question 3

What type of muscle is the Ciliary muscle? What innervates it?

Answer 3

Smooth muscle.

Mainly PNS through the short cilary nerves.
-causes contraction

SNS is believed to cause relaxation through the long ciliary nerves.

Question 4

Why do both the SNS and PNS innervate the ciliary muscle?

Answer 4

For smooth accommodative tracking

Question 5

What acts as the ciliary muscle’s antagonist?

Answer 5

The ciliary muscle. Because it is innervated by both PNS and SNS

Question 6

3 muscle fiber groups of the Ciliary Muscle

Answer 6

Longitudinal/Brucke’s

Radial

Circular/annular/circumferential

Question 7

What does the longitudinal muscle fiber group do? What’s an alternate name?

Answer 7

It pulls the ciliary body anteriorly

Brucke’s muscle

Question 8

The longitudinal bundle originates from what type of structures? What does it attach to?

Answer 8

Epichorioidal stars

The outer surface of the choroid. It continues forward to the sclera spur and it’s tendons continue beyond into the trabeluar meshwork.

Question 9

During Accommodation, what happens to all 3 ciliary bundles?

Answer 9

They contract!

Question 10

Which group of fibers of the ciliary muscle has the greatest contribution to changing lens shape during accommodation?

Answer 10

The annular fibers.

Question 11

What is the ciliary muscles’ primary function?

Answer 11

To release resting tension on the zonular fibers during accommodation

Question 12

What happens to the sclera spur and trabecular meshwork during accommodation? What drug could also cause this?

Answer 12

SS moves posteriorly and enhances the flow across the TM, increasing effective filtration area.

Pilocarpine, PNS topical drug

Question 13

What happens to the sclera spur and trabecular meshwork during relaxation? What drug could also cause this?

Answer 13

SS returns to its anatomic position and decreases flow across the TM, decreasing effective filtration area.

Atropine, topical SNS drug

Question 14

What structures form a continuous carpet over the innner surface of the pars plant?

Answer 14

Zonular fibers

Question 15

Zonules, elastin based fibers, are secreted by…

What is their primary function?

Answer 15

Nonpigmented ciliary epithelium

To stabilize the lens

Question 16

What are the 2 types of zonules? Which type has 3 groups?

Answer 16

Anterior zonules (anterior group, equatorial group, posterior group)

Posterior zonules

Question 17

Where do the posterior zonules attach?

Answer 17

To the ILM covering the NPCE near ora serrata

Aid in pulling the ciliary muscle back to its unaccommodated state

Question 18

Where do the anterior zonules attach?

Answer 18

The anterior capsule surface (zonular lamella), equator, and posterior capsule

Few fibers actually penetrate the capsule

Question 19

What structure supplies the major force to accommodate the lens?

Answer 19

The lens capsule

Question 20

At resting state, there is ___D of tonic accommodation

Answer 20

1.5 D

Question 21

What are the 3 physiologic responses of the Accommodative Triad/Near Reflex?

Answer 21

1. Pupillary constriction
2. Convergence of the eyes
3. Accommodation

Question 22

Age related loss of accommodation

Answer 22

Presbyopia

Question 23

2 ways to correct presbyopia

Answer 23

Bifocals and contact lens