Accommodation Flashcards
Accommodation
process to make and maintain a focused retinal image
changes lens power and lens curvature
What causes the lens changes in accommodation?
Ciliary Muscle
Ciliary Muscle
parasympathetic innervation
contracts to cause lens changes and releases resting tension of zonules
Edinger-Westphal Nucleus
where parasympathetic pathway starts
3 physiological changes in accommodation
Triad or Near Reflex
eye accommodation
pupil constriction
eyes converge
Change in pupil size
controls light
modifies depth of focus
varies any optical aberration
Reflex Accommodation
auto adjustment to maintain focused retinal image
response to blur
important for scanning eye movements
Vergence Accommodation
induced during fusional vergences
leads to convergence accommodation/ convergence ratio (CA/C)
Proximal Accommodation
refocusing from perceived nearness of target
stimulated by targets w/in 3 m of person
Tonic Accommodation
“Lead of Accommodation”
resting level of accommodation (0.5 - 1.5D)
due to baseline stable parasympathetic innervation
reduces with age
Factors that affect Accommodation
blur, convergence, proximal issues, pharmacology, minus lens, disease
Retinal image factors that affect Accommodation
contrast, spatial frequency, retinal image motion
Non-retinal factors that affect Accommodation
mood, voluntary effort, target luminance, training
Optical Cues that affect Accommodation
offer info about directionality, astigmatism, aberrations
Non-optical cues that affect Accommodation
size, proximity, apparent distance, depth cues
Aberrations
occur when peripheral rays do not coincide with the central and on axis rays
Depth of Focus
variation in image distance that is tolerable without defocus
Muscarinic blockers
inhibit accommodation by preventing acetylcholine from binding
Tropicamide and Cyclopentolate
Presbyopia
age related loss of accommodative amplitude
40-45 yrs
complete loss of accommodation by 50-55
2.5D loss per yr
Factors that lead to loss of Accommodation
lens thickness and size increase, springiness of capsule decreases (thickens), anterior surface curvature increases
zonule # decreases
What remains the same when a person starts to lose accommodation?
Ciliary muscle function
zonule elasticity
motor neuron pathway
Accommodation Excess
treated with distance correction and VT
Accommodation Infacility
correction and VT
Accommodation Insufficiency
correction and plus lenses
