Accommodation

Question 1

What is the refractive index of the cornea?

Answer 1

n= 1.376

Question 2

what is the refractive index of aqueous humor?

Answer 2

n=1.336

Question 3

what is the refractive index of the lens?

Answer 3

sufaces n=1.386

center n=1.406

Question 4

what is the refractive index of the aqueous humor?

Answer 4

n=1.336

Question 5

Where does the optical power of the cornea come from?

Answer 5

The optical power of the cornea comes from the change in refractive index and the positive radius of curvature.

Question 6

T/F: The posterior lens surface does not move with accommodation and the posterior lens surface curvature does not change.

Answer 6

FALSE!

The posterior lens surface increases in curvature and moves backward with accommodation.

Question 7

What is depth of field?

Answer 7

The range over which a target can be moved toward or away from the eye without a perceptible change in the blur or focus of the image.

Question 8

What is depth of focus?

Answer 8

Depth of focus is the focusing error that can be tolerated without an appreciable decrease in acuity or change in blur or focus of the image on the retina.

Question 9

How is Depth of Focus is dependent on pupil size?

Answer 9

Small pupil = Larger depth of focus

Large pupil = Smaller depth of focus

Question 10

T/F: With accommodation the pupil size decreases, increasing the depth of focus.

Answer 10

True

Question 11

What is senile miosis?

Answer 11

Reduction in pupil size with aging

Question 12

Tonic (residual) accommodation accounts for about how much diaptors?

Answer 12

About 1.5 diopters

Question 13

What occurs during the The Accommodative Triad?

Answer 13

1. the pupil constricts
2. the eyes converge
3. the eyes accommodate

Question 14

T/F: An accommodative stimulus presented monocularly results in a binocular accommodation and convergence response.

Answer 14

True

Question 15

What is blur-driven accommodation?

Answer 15

Placeing a (-) lens in front of an eye, the eyes accommodate to overcome the defocus. (to induce accommodation)

Question 16

What happens when there is pharmacologic stimulation of accommodation?

Answer 16

Topical application of muscarinic cholinergic agonist (pilocarpine) to the eye results in stimulation of the ciliary muscle.
This results in pupil constriction but convergence does not occur.

Question 17

What is accommodative esotropia?

Answer 17

occurs in uncorrected hyperopes as a consequence of needing to accommodate to even see distant objects in focus

Question 18

What is cycloplegia?

Answer 18

Blocking accommodation
with either Atropine, cyclopentolate, tropicamide
Competitively bind to the same muscarinic receptors as the agonists: prevent agonist binding and block accommodation

Question 19

What chemicals can be used to induce cycloplegia?

Answer 19

Atropine, cyclopentolate, tropicamide

Question 20

What is a push-up method?

Answer 20

A way of measuring accommodation. Patient reports when a near letter chart is no longer in sharp focus as it is brought closer to the eye.

It is a subjective evaluation

Question 21

What is the accurate objective measurement of accommodation?

Answer 21

Refractometers

Question 22

T/F:

2/3 of accommodative amplitude is lost between ages 15-35

Answer 22

True!

Question 23

Objective measurement of accommodation shows linear decline of ≈( ? )D per decade

Answer 23

2.3D

Question 24

What is the Lenticular Sclerosis theory?

Answer 24

Says that the crystalline lens gets harder with increasing age and thus is a cause for presbyopia.

Question 25

What is the Geometric Theory theory?

Answer 25

Says presbyopia is a consequence of the altered geometry of the lens/zonular relationship

Young lens:
The anterior zonular connections are near the lens equator and exert strong influence on the curvature of the lens
Aged lens:
The connections are farther forward, so there is not effective relaxation of the force with ciliary muscle contraction

Question 26

What is the Disaccommodation Theory?

Answer 26

says presbyopia is caused by a gradual failure of the lens to be held in an unaccommodated form at rest

Question 27

What is the multifactoral theory?

Answer 27

Says presbyopia results not from any single causal factor, but through global deterioration of accommodative function of many aspects of the accommodative apparatus

Question 28

What are some optical compensation for presbyopia? (name 4)

Answer 28

Spectacle lenses (reading glasses)
Contact lenses (mono-vision)
Corneal refractive surgical procedures
Or artificial intraocular lenses (IOLs).