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Ocular Physiology 2 > Accomodation > Flashcards

Flashcards in Accomodation Deck (39)
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1

What is accomodation

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

2

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

False. It increases, the focal length decreases

3

How is accomodation measured

in diopters (1/m)

4

How is increased optical power achieved

Due to increased surface curvature and increased thickness of the lens

5

How do myopes use accomodation

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

6

How do hyperopes accomodate

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

7

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

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

8

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

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

9

What is depth of field

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

10

What is depth of focus

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.

11

What is depth of focus dependent on

Pupil size! Larger depth of focus = small pupil
Smaller depth of focus = large pupil

12

does pupil size increase or decease with age

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

13

What happens with accomodation at rest

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

14

What refers to tonic (residual) accommodation

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

15

What does the Accomodative Triad refer to

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

16

Accomodation is a binocular process

TRUE

17

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

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

18

T/F Accomodation is blur driven

True

19

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

The pupils constrict and the eyes converge; accomodation occurs

20

how can accomodation be induced

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

21

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

TRUE

22

What is accomodative esotropia

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

23

How can accomodation be pharmacologically blocked?

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

24

What refers to blockage of accomodation

cylcoplegia

25

How do you measure accomodation

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

26

What can influence the push up method

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

27

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

YES

28

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

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

29

What is presbyopia

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

30

What does objective measurement of accomadation show

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