Accommodation and Presbyopia Flashcards Preview

Ocular Physiology #2 > Accommodation and Presbyopia > Flashcards

Flashcards in Accommodation and Presbyopia Deck (55)
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2

what happens to the lens in accommodation

the optical power increases (focal length decreases) by increasing the surface curvature and thickness

3

what is accommodation measured in

diopters (1/meter)- a measure of the vergence of light

4

what is accommodation

a dynamic change in the power of the eye- change in the focus from distance to near

5

what mediates accommodation

contraction of the ciliary muscle, release of zonular tension at the equator and "rounding up" of the lens (force exerted by capsule)

6

can a person with myopia focus at near or distance without accommodation

they can focus clearly on objects closer than optical infinity without accommodation

7

what has a higher refractive index: the cornea or aqueous humor

the cornea (n= 1.376 and aqueous humor n= 1.336)

8

can a person with hyperopia focus at optical infinity without accommodation

no, they are only able to focus clearly on objects at optical infinity only through an accommodative increase or with a (+) lens

9

where does the optical power of the cornea come from

the change in refractive index and the positive radius of curvature

10

do both the anterior and posterior sides of the lens increase in curvature with accommodation

yes- although historically it was thought the posterior did not move

11

what is depth of field

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

12

what is depth of focus

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

13

what is depth of focus dependent on

the pupil size

14

what size pupil is the depth of focus larger

a small pupil has a larger depth of focus but a smaller field of view

15

what happens to the depth of focus during accommodation

the pupil size decreases during accommodation, which will increase the depth of focus

16

why would there be a decreased need for presbyopic correction as a person ages

their pupil size decreases with aging (senile miosis) which give a pinhole effect and increases the depth of focus

17

where is the eye focused when the eye is at rest

for distance

18

what are the lens and zonule positions when the eye is at rest

the zonules apply an outward tension on the lens and it is in a flattened and unaccommodated state

19

name the 3 parts of the accommodative triad or near reflex

1. pupils constrict
2. eyes converge
3. eyes accommodate

20

what is blur-driven accommodation

place a (-) lens in front of an eye and the eyes will accommodate to overcome the blur/defocus

21

what is tonic accommodation

when the eye is at rest it has some residual or resting level of accommodation- about 1.5 D due to muscle tone

22

how can you induce blur with a BO prism

it increases the vergence- causing pupil constriction, convergence, and accommodation occurs

23

how can you induce accommodation with pharmacologic stimulation

use of a topical muscarinic cholinergic agonist (pilocarpine) results in stimulation of the ciliary muscle causing pupil constriction but not convergence

24

what is accommodative esotropia

occurs in uncorrected hyperopes because they need to accommodate to see distance objects and it over-converges the eyes

25

what drops can block accommodation

cycloplegia drops- atropine, cyclopentolate, tropicamide

26

how do cycloplegic drops work

they competitively bind to the same muscarinic receptors as the agonists: preventing the agonist from binding and block accommodation

27

what is the push-up method

a way to measure accommodation: the patient reports when a near letter chart is no longer in sharp focus as it is brought closer to the eye

28

what is a downside of the push-up method for measuring accommodation

it is a subjective evaluation of best image focus and can overestimate the amount of accommodation

29

what can influence the push-up method

depth of focus, visual acuity, contrast sensitivity of the eye and contrast of the image

30

what is the minus lens to blur method

a subjective measurement of accommodation amplitude by placing a (-) lens in front of one or both eyes to blur a distant letter- stimulating accommodation

31

what is a problem with the minus lens to blur method

it minifies the letters and can underestimate the amount of accommodation