Accomodation

Question 1

What is accomodation

Answer 1

A dynamic change in the power of the eye. It provides the ability to change the point of focus of the eye from distant to near objects

Question 2

T/F The optical power of the lens decreases with accomodation.

Answer 2

False. It increases, the focal length decreases

Question 3

How is accomodation measured

Answer 3

in diopters (1/m)

Question 4

How is increased optical power achieved

Answer 4

Due to increased surface curvature and increased thickness of the lens

Question 5

How do myopes use accomodation

Answer 5

Myopes can focus clearly on objects closer than optical infinity without accomodation

Question 6

How do hyperopes accomodate

Answer 6

They focus on objects through an accomodative increase or with + powered lenses. They accomodate for near and far

Question 7

The optical power of the cornea is attributable to what combination?

Answer 7

The positive radius curvature and higher refractive index than the surrounding air

Question 8

T/F The posterior lens surface does not move with accomodation

Answer 8

False! The posterior lens surface increases in curvature and moves backward with accomodation

Question 9

What is depth of field

Answer 9

The range at which the target can be moved forward or backward and still maintain clarity

Question 10

What is depth of focus

Answer 10

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

Question 11

What is depth of focus dependent on

Answer 11

Pupil size! Larger depth of focus = small pupil

Smaller depth of focus = large pupil

Question 12

does pupil size increase or decease with age

Answer 12

Decrease. This helps with reading and decreased need for add in presbyopic correction

Question 13

What happens with accomodation at rest

Answer 13

The eye is focused for distance, and the zonules apply an outward tension on the lens. This hold the lens in a flattened and unaccomadated state

Question 14

What refers to tonic (residual) accommodation

Answer 14

At rest, the eyes have some residual or resting level of accomodation amounting to approximately 1.5 diopters

Question 15

What does the Accomodative Triad refer to

Answer 15

1. Pupil constricts
2. The eyes converge
3. The eyes accommodate

Question 16

Accomodation is a binocular process

Answer 16

TRUE

Question 17

What does a minus lens do to your eye (blur-driven accomodation)

Answer 17

Decreasing the power of the eye, the eyes accomodate to overome the defocus. Keep adding minus lenses until you can no longer see the object. Object gets minified

Question 18

T/F Accomodation is blur driven

Answer 18

True

Question 19

What happens when you place a base out prism in front of the eyes

Answer 19

The pupils constrict and the eyes converge; accomodation occurs

Question 20

how can accomodation be induced

Answer 20

Through pharmacologic stimulation. Topical application of muscarinic cholingergic agonist (pilocarpine) to the eye results in stimulation of the ciliary muscle

Question 21

T/F pupil constriction occurs with pharmacologic stimulation, but convergence does not

Answer 21

TRUE

Question 22

What is accomodative esotropia

Answer 22

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

Question 23

How can accomodation be pharmacologically blocked?

Answer 23

Atropine, cycloentolate, tropicamide. Competitively bind to the same muscarinic receptors as the agonists and prevent agonist binding and block accomodation

Question 24

What refers to blockage of accomodation

Answer 24

cylcoplegia

Question 25

How do you measure accomodation

Answer 25

Through the push-up method. Patient reports when a near letter chart is no longer in sharp focus as it is brought closer to the eye. Convert it to diopters

Question 26

What can influence the push up method

Answer 26

1. Depth of focus
2. VA
3. Contrast sensitivity of the eye
4. Contrast of the image

Question 27

Are the minus lens to blur method and push up method subjective

Answer 27

YES

Question 28

What would be the clinical method to get the most accurate measurement of accomodation

Answer 28

Static or dynamic refractometers: Units that can calculate the power of your eye

Question 29

What is presbyopia

Answer 29

The age related loss in accomodative ability; results in nearly complete loss in accomodative ability by about 50 yrs of age.

Question 30

What does objective measurement of accomadation show

Answer 30

Linear decline of 2.3 D per decade. 2/3 of accomodative amplitude is lost between ages 15-35

Question 31

What are some surgical options for presbyopia

Answer 31

Corneal refractive surgery, cataract surgery, accomodative IOL.

Question 32

What factos lead to presbyopia

Answer 32

1. Loss of muscle fibers and increase in connective tissue
2. The contractile forces DO NOT decrease, actually at its max at the age presyopia is manifest
3. The ciliary muscle ages: The inner apex of the unaccomodated ciliary muscle resides further forward and inward toward anteroposterior axis in the aging eye. At rest, it is less able to hold or pull the lens into its flattened and unaccomodated configuration.

Question 33

What is the aging process in the lens capsule aka the fisher theory

Answer 33

Thickness of the anterior lens capsule increases from 11 micrometers at birth to 20 micrometers at 60 years then decreases slightly thereafter. Fisher suggested that the force transmitted per unit thickness decreases by half at age 60 but that the increased thickness compensates for the loss of elasticity, however the capsule gets brittle

Question 34

What is the growth rate of the lens

Answer 34

Increases more than 1.5 x over the human life span.. the equatorial diameter of the lens also increases with age.

Question 35

T/F In young lenses become accomodated. Adult presbyopic lenses do not undergo a change in shape

Answer 35

TRUE

Question 36

How much does the lens become hard and how does this affect presbyopia

Answer 36

• A more than 4 fold exponential increase
• Lens is no longer pliable so that capsular forces can act on it to flatten and unaccomodate it and increase the curvatures into a more accomodated state

Question 37

As the eye ages what happens

Answer 37

Nothing changes in terms of the length of the eye, but lens increases in thickness, anterior chamber depth decreases

Question 38

What are some theories of presbyopia

Answer 38

Lenticular Sclerosis: The crystallin lens gets harder with increasing age.
Geometric Theory: Presbyopia is a consequence of the altered geometry of the lens/zonular relationship.
Disaccomodation Theory: Presbyopia is caused by a gradual failure of the lens to be held in an unaccomodated form at rest.

Question 39

What is the most important theory and valid theory that leads to presbyopia

Answer 39

Lenticular Sclerosis