Ocular: Accommodation Flashcards
What structures are involved in accommodation?
-Cilliary body (ciliary muscle)
-choroid
-iris
-anterior and posterior zonules
-crystalline lens (lens capsule)
What type of muscle is ciliary muscle?
Smooth muscle
Ciliary muscle is mainly innervated by
Parasympathetic innveration
The ciliary muscle has a little bit of sympathetic innervation that is believed to be used for..
Inducing relaxation (of accommodation)
Why does the ciliary muscle have both sympathetic and parasympathetic innervation?
-smooth accommodative tracking
-ciliary muscle acts as its own antagonists
What are the three muscle fiber groups of the ciliary muscle?
-longitudinal(burke’s)
-radial
-annular (circumferential)
The ciliary muscle fibers transition in what order?
Longitudinal orientation -> radial -> annular
where does longitudinal bundle originate?
Epichoroidal spurs that attach the muscle to the outer surface of the choroid
The longitudinal bundle continues froward to the ..
Scleral spur and continues beyond into the trabecular mesh work
During accommodation all 3 fiber bundles in the ciliary muscle _____.
Contract
Why are annular fibers said to have the greatest contribution to changing lens shape during accommodation?
During contraction, there is a general rearrangement of the fibers to transition into annular fibers at the expense of the longitudinal and radial fibers
The primary function of the ciliary muscle is releasing _____ _____ on the anterior zonular fibers during accommodation
Resting tension
During accommodation, the scleral spur moves _________ and opens up _____ _______
posteriorly, flow channels
The opening of flow channels enhances the _____ _______ and increases the _____ ____ ____.
Trabecular meshwork, effective filtration area
when the ciliary muscle is relaxed the scleral spur goes back and causes a decrease in what?
flow across the trabecular meshwork
Zonula fibers form a continuous carpet over the inner surface of the ___ _____.
Pars plana
Zonular fibers are channeled into the valleys between adjacent processes in the ____ ____.
Pars plicata
Zonules are made up of what protein?
Fibrillin
Zonules are secreted by the
Nonpigmented ciliary epithelium
What is the primary function for the zonules?
To stabilize the lens
Posterior zonules are attached to the ____ covering the _____.
ILM, NPCE (idk what they mean or id type them out….i think second is non-pigmented ciliary epithelium….might be internal limiting membrane for the first…)
After accommodation has ceased, the posterior zonules aid in what?
pulling the ciliary muscle back into its unaccommodated (resting) state position
Anterior zonules attach at what three parts of the lens?
-Anterior capsule surface
-equator
-posterior capsule
Do many zonule fibers actually penetrate the capsule?
Nope!
Steps of accommodation:
-innervation to ciliary muscle
-ciliary muscle contracts
-ciliary muscle moves inward and anterior
-zonules relax and tension decreases
-lens capsule molds to crystalline lens
-lens becomes more round/spherical
-lens power increase
-eye changes focus from distance to near
Why is the lens capsule important?
It supplies the major force to accommodate the lens, which allows the lens to reduce the rate of capsule movement and prevent configuration change
How many diopters of tonic accommodation are in the resting state?
1.5D
Three physiologic responses to the accommodative process
-pupillary constriction
-convergence
-accommodation
Where does the nerve that causes the ciliary muscle to contract originate?
The EWN
Presbyopia is…
Age related loss of accommodation and is completed by age 50
How can presbyopia be multi-factorial?
Due to the global determination of the accommodative apparatus, no single factor is the cause
