Accommodation Flashcards
What structures are involved in accommodation
Ciliary body and muscle Choroid Iris Anterior zonules Posterior zonules Crystalline lens and lens capsule
The ciliary muscle is what kind of muscle
Smooth muscle
The PNS has what affect on the ciliary muscles
Contraction
The SNS has what affect on the ciliary muscle
Relaxation
What are the 3 muscle groups in the ciliary muscle
Longitudinal
Radial
Circular
What happens to the ciliary muscle fibers in accommodation
All contract
Causes a gradual rearrangement of the fibers
What muscle fibers have the greatest contribution to changing the lens shape during accommodation
Circular fibers
What happens to the TM during accommodation
Sclera spur moves posteriorly and enhances flow across the entire trabecular mesh work by opening up flow channels, which increases effective filtration area
What happens to the TM during relaxation
The scleral spur moves to its original position. Decrease flow across TM by closing flow channels. Decreases effective filtration area
Where do the zonular fibers insert at
Valleys of Kuhnt on the pars plicata of the ciliary body
What are the zonules made of
Elastin based fibers
What secretes the zonules
Nonpigmented ciliary epithelium
What is the function of the zonules
Stabilize the lens
What are the zonule groups
Anterior
Anterior
Equatorial
Posterior
PosteriorWhat is the function of the posterior zonules
Aid in pulling the ciliary muscle back to its unaccommodated state position after accommodation has ceased
What is the mechanism of accommodation
Looking at distance the eye is at rest
There is resting tension on the anterior zonules that pull the lens outward and keep it flat.
Contraction of the ciliary body pulls the inner face of the ciliary body forward and places stress on the posterior zonules while releasing tension on the anterior zonules.
The capsule molds the lens into a more spherical shape
Lens diameter decreases and lens thickness increases.
Anterior curvature increases and so does anterior chamber depth
What is the mechanism of relaxing accommodation
The elasticity of the ciliary muscle to the choroid and tension on the posterior zonules pulls the ciliary body posterior
Resting tension on anterior zonules is returned
Posterior zonules relax
What supplies the major force to accommodate the lens
The lens capsule
What does the lens content do
Reduce the rate of capsule movement and retard the extent of change in the lens
What is the resting state of accommodation
1.5D of tonic accommodation
What are the 3 physiological responses of the accommodative process
Pupillary constriction
Convergence of the eyes
Accommodation
What nucleus in important in accommodation
EW nucleus
What is presbyopia
Age related loss of accommodation
When is presbyopia complete
50 years of age
What is the cause of presbyopia
Multifactorial
How do you correct presbyopia
Bifocals or contact lenses
