Anatomy of the Accommodative Apparatus Flashcards
what structures are involved in accommodation
ciliary body, ciliary muscle, choroid, zonules, lens capsule, and lens
what division of neural innervation dominates accommodation, parasympathetic or sympathetic
parasympathetic, causes contraction of the ciliary muscles
what does the sympathetic innervation involve in accommodation
it relaxes the ciliary muscle
why are there both parasympathetic and sympathetic innervation involved in accommodation
to allow for smooth accommodative tracking
does contraction of the ciliary muscle result in contraction of all 3 muscle fibers: longitudinal, radial, and circular
yes
which muscle, longitudinal, radial or circular have the greatest influence on changing the lens shape
the circular (annular)
where are the zonules produced and anchored
in the valleys of the ciliary processes
what is the purpose of the posterior zonules
to aid in pulling the ciliary muscle back to its unaccommodated position after the need for accommodation has ceased
how many types of anterior zonules are there
3: anterior, equatorial, and posterior fiber groups
what is the current theory of accommodation based on
the work of Helmholtz
is there tension on the anterior zonules when the eye is at rest (unaccommodative state- distance vision)
yes- they pull the capsule of the lens at the equator
is the lens flat or round in the unaccommodatative state
it is pulled flat
what happens to the anterior zonules when the ciliary muscle contracts and the eye is accommodating
the tension releases on the anterior zonules but tension is placed on the posterior zonules
what shape is the lens during accommodation
is it spherical
what does the lens capsule do during accommodation
it molds the shape of the lens into the spherical shape when the anterior zonules are released
what happens to the anterior chamber during accommodation
the depth decreases due to the forward movement of the lens
once the lens is done accommodating, what happens to the zonules
the posterior zonules pull the ciliary muscle back towards its unaccommodative state and the tension to the anterior zonules is restored (flattening the lens)
what is the major force for the lens to change shape
the lens capsule
what physiological responses happen during accommodation process
pupillary constriction, convergence, and accommodation
what are the physiological responses refered to as
the accommodative triad or near reflex
what neurological responses regulate accommodation
parasympathetics that travel in the oculomotor nerve from the Edinger-Westphal nucleus in the brain
after the parasympathetics synapse in the ciliary ganglion, where do the continue to travel
via the short posterior ciliary nerves as postganglionic parasympathetics to innervate the ciliary muscles and the iris sphincter
