Accommodation and Presbyopia Flashcards
What is accommodation?
A dynamic change in the power of the eye
What does accommodation provide the eye?
The ability to change the point of focus of the eye from distant to near objects
Does the optical power of the lens increase of decrease with accommodation
Increase
What unit is accommodation measured in?
Diopteres
What is a diopter and how is it measured?
a reciprocal meter
measure of the vergence of light
How is accomodation mediated?
◦Contraction of the ciliary muscle
◦Release of zonular tension at the equator
◦“Rounding up” of the lens (force exerted by capsule)
How is the increased optical power in accommodation achieved?
Through the increased anterior and posterior lens surface curvatures and increased thickness of the lens
Myopes can focus clearly on objects _____ than optical infinity with accommodation
closer
Hyperopes can focues clearly on objects at ____ ___ only through an accommodative increase or with + lens
optical infinity
What is the refractive index of the cornea?
About 1.376
The refractive index of the aqueous humor is about?
1.336
Because the refractive indexes of the aqueous humor and cornea are so close the optical affective is?
relatively little
The optical power of the cornea comes from?
The change in refractive index and positive radius of curvature
the anterior and posterior surface of the lens add or subtract to the optical power of the eye
add
The posterior lens surface increases or decreases in curvature and moves backward or forward with accommodation?
Increases
Backward
What is the depth of field?
The range over which a target can be moved toward or away from the eye without a perceptible change in blur or focus of the image
What is the depth of focus?
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
Depth of focus is dependent on?
Pupil size
What does a small pupil say about depth of focus? large pupil?
Small - larger depth of focus
Larger - smaller depth of focus
Does the pupil size increase or decrease with accommodation?
Decreases (increasing depth of focus)
Does pupil size increase ot decrease with aging? What is this referred to?
Decreases
Senile Miosis
(decreased need for add in presbyopic correction- increased depth of focus)
When the eye is at rest focused on distance the resting tension on the zonular fibers spanning the anterior zonule applies what?
An outward directed tension on the lens squator throgh the lens capsule
(holds lens in relatively flattened and unaccommodated state)
At rest, the eyes have some residual or resting level of accommodation amounting to approx. _____ D. What is this called?
1.5 D
tonic accommodation (residual)
What is the accommodative triad?
◦1. the pupil constricts
◦2. the eyes converge
◦3. the eyes accommodate
An accommodative stimulus presented ______ results in a binocular accommodation and convergence response.
Monocularly
A convergence stimulus in one eye results in ____ _____, _______, and ______ in both eyes.
Pupil Constriction
Convergence
Accommodation
If a myopic blur is presented to one or both eyes which lens will cause the eyes to accommodate to overcome the imposed defocus?
negative lens
If a base-out prism is placed in front of the eye will vergence increase or decrease?
Increase
What can accommodation be induced through?
Pharmacologic stimulation
(muscarinic cholinergic agostists)
(pupil constriction ill also occur but no convergence)
Accommodative esotropia most often occurs in?
Uncorrected persons with hyperopia as a consequence of a need to accommodate even to see distance objects in focus
What can block accommodation?
Cycloplegia
induced byt topical application of muscarinic antagosists
The push-up method in accommodation requires the patient to report?
When a near letter chart can no longer be maintained in sharp focus as the chart is gradually brought closer to the eye
What is the minus lens to blur method?
◦Placing negatively powered trial lenses in front of one or both eyes to blur a distant letter chart stimulating accommodation
◦
◦Letter size is minified - problem
What are surgical options for persons with presbyopia?
◦Corneal refractive surgery
◦Cataract surgery
◦Accommodative IOLs
As we age, there is a (loss/gain) of muscle fibers and (increase/decrease) in connective tissue?
Loss
Increase
In aging, the contractive force does not (increase/decrease); it (increases/decreases) and is at its max at the age presbyopia manifests
Decrease
Increases
Where does the inner apex of the unaccommodated ciliary muscle reside in the aging eye?
Further forward and inward toward the anteroposterior axis
What is presbyopia?
The age-related loss in accommodative ability; results in nearly complete loss in accommodative ability by age 50
How much of accommodative amplitude is lost between ages 15-35?
2/3
What is the thickness of the lens capsule at birth and at age 60?
11 um at birth
20 um at age 60 (decrease slightly thereafter)
Force transmitted per unit of thickness by ____ at age 60
half
What does increased thickness of the lens compensate for?
The loss of elasticity
Does the equatorial diameter of the lens increase?
Yes
When young lenses are removed from the eye they (do/do not) accommate?
Do
When older lenses are removed from the eye they (do/ do not) change in shape
do not
How much does the hardness of the lens increase of the life span?
four-fold (doesnt stop at age 50)
The lens substance must remain suffiecintly pliable so the capsular foces can act on it to ____ it (______) and ______ it (______)
Flatten it (unaccommodative)
Curve it (accommodative)
Lenticular sclerosis
Most commonly articulated explanation for presbyopia
lens becomes harder with increasing age
Where are the anterior zonular connections in the young lens?
Near the lens equator and exert strong influence on the curvature of the lens
Where are the anterior zonular connections in the aged lens?
Farther forward than equator, not effective relaxation of the force with ciliary muscle contraction
What does the disaccommodation theory suggest?
Not caused by a failure of the lens to accommodate but instead a gradual failure of the lens to be held in the unaccommodated form at rest
What is the multifactorial theory?
Presbyopia results not from any single causal factor, but through global deterioration of accommodative function
Presbyopia is not an end point, but a time point in a gradual, progressive continuum of deterioration of the accommodative structures
Optical compensation for presbyopes is achieved with?
◦Spectacle lenses
◦Contact lenses
◦Corneal refractive surgical procedures
◦Or artificial intraocular lenses (IOLs).
