Optics: Accommodaiton Flashcards
What is accommodation?
The ability of the eye to change its power to bring objects of interest at different distances into focus
In the unaccommodated form, the zonules…
Pull on the lens and flatten it
When changing focus from far to near vision, the ciliary muscle ______, _________ the tension on the zonules
Contracts, reducing
What allows the lens to take on a more round shape?
The elastic properties of the lens capsule
Less curvature =
Less power
When the eye accommodates, what happens to the anterior surface of the lens?
It moves forward and takes a hyperbolic form
What is the amplitude of accommodation (accommodation range)?
The distance between the far and near points
What four structures bring about changes in optical power?
-ciliary
-choroid
-zonules
-crystalline lens
Changes in lens when going from distant to near target:
-anterior movement of choroid
-ciliary constricts
-zonules loosens
-lens less curved
-optical power increases
Changes in lens when going from near to distant target:
-posterior movement of choroid
-ciliary relaxes
-zonules tighten
-lens flattened
-optical power decreases
Lens diameter ___________ with accommodation?
Decreases
Does lens diameter change throughout life?
No
As accommodation occurs, the lens surface curvature becomes _________, lens thickness _________, and anterior chamber ___________
Steeper, increases, decreases
Which lens surface has more movement?
The anterior surface
Which structure involved in accommodation is the active structure? Where does it get its input?
Ciliary, receives its input from the midbrain
The choroid, zonules, and crystalline lens are ________ structures
Passive structures
What makes the choroid, zonules, and crystalline lens passive?
The receive their in-out from the ciliary body
What is sensory cue to accommodation?
The reference frame used to drive accommodation
Two different categories of accommodation cues:
-retinotopic cues
-spatiotpoic cues
What are retinotopic cues?
-Retinal blur and binocular retinal image disparity
-the eye is reference for accommodation
What are Spatiotopic cues to accommodation?
-Target proximity
-use the entire body area reference to accommodate
What is the range for retinotopic accommodation cues?
Smaller and finer ranges
What is the optimal stimulus for retinotopic cues?
Near demand
How often are retinotopic cues sampled?
Continuously to fine tune the near response
What is the operating range of spatiotopic accommodation cues?
Larger and coarser range
What is the optimal stimulus for spatiotopic accommodation cues?
Far demand
How often are spatiotopic cues sampled?
Intermittently at the beginning of the near response
What is blur driven (reflex) accommodation?
The automatic adjustment of the refractive state to maintain and sharp and focused retinal image in response to blur input
What assists in blur-driven or reflex accommodation?
Microsaccades, voluntary accommodative effort is also needed
What amount of blur is reflex accommodation responsible for?
Up to 2D
Which mode of accommodation is the largest and most important component for both monocular and binocular viewing conditions?
Blur-driven (reflex) accommodation
What is Disparity-driven (vengeance) accommodation?
Accommodation induced by the instinct to fuse images
*second major component
Which two modes of accommodation are retinotopic?
-blur-driven (reflex)
-disparity-driven (vergence)
What is Proximity-driven accommodation?
Accommodation due to the influence or knowledge of apparent nearness of an object (within 3m)
What is proximal accommodation stimulated by?
Perceptual cues
What is tonic accommodation?
-Seen in the absence of blur, disparity, and proximal inputs
-presumably reflects baseline innervation and stable input
Range of tonic accommodation
1D
Reduced VA at near is correlated with ________________ and reduced VA at far is correlated with _____________
Accommodative lag, accommodative lead
Accommodative triad:
-accommodation in both eyes
-constriction of pupils
-convergence of eyes
What does convergence achieve?
Single, fused image of the near object as viewed with both eyes
What does constriction of the pupil do?
Increases the depth of field
Uncorrected myope must accommodate ________ the emmetrope
Less than
Accommodation required by an emmetropic eyes is _________ the stimulus of accommodation
Equal to
When an eye is corrected with a contact lens the required accommodation is ________ the stimulus to accommodate
Equal to
When an object is located at the far point, will that person be accommodating?
No
An uncorrected hyperope must accommodate ___________ the emmetrope
More than
An uncorrected myopic patient may continue to…
Have acceptable near vision even as they age and lose the accommodative ability (bc the far point is closer)
What is the near point of accommodation?
How near an object can be to the eye and still be imaged clearly on the retina
