Accommodation and Presbyopia Flashcards Preview

Ocular Physiology #2 > Accommodation and Presbyopia > Flashcards

Flashcards in Accommodation and Presbyopia Deck (55)
Loading flashcards...

what happens to the lens in accommodation

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


what is accommodation measured in

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


what is accommodation

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


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)


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

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


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

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


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


where does the optical power of the cornea come from

the change in refractive index and the positive radius of curvature


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


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


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


what is depth of focus dependent on

the pupil size


what size pupil is the depth of focus larger

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


what happens to the depth of focus during accommodation

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


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


where is the eye focused when the eye is at rest

for distance


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


name the 3 parts of the accommodative triad or near reflex

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


what is blur-driven accommodation

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


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


how can you induce blur with a BO prism

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


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


what is accommodative esotropia

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


what drops can block accommodation

cycloplegia drops- atropine, cyclopentolate, tropicamide


how do cycloplegic drops work

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


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


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


what can influence the push-up method

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


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


what is a problem with the minus lens to blur method

it minifies the letters and can underestimate the amount of accommodation