Lecture 15 (dr. chase) Flashcards
what pathway causes accommodation of the ciliary muscle?
parasympathetic (Ach makes the muscle contract)
what pathway causes the ciliary muscle to relax for distance viewing?
the sympathetic system (NE makes the muscles relax)
what happens to the lens shape as we accommodate?
the lens bulges
what is depth of field?
the amount a target can be moved and still give a clear image on the retina
what is depth of focus?
the range on the retina where an image will still be clear
what is the monocular DOF range?
from 0.46 to 0.81
what happens to depth of focus as the pupil diameter increases?
the depth of focus gets smaller (a smaller pupil has a larger depth of focus)
does the push-up method overestimate or underestimate accommodation?
overestimates (by 2D)
does retinoscopy overestimate or underestimate?
it overestimates accommodation (by 2D)
what is the hofstetter equation for the average amplitude of accommodation?
18.5 - 0.3age
what happens to the push-up amplitude with age?
it gradually decreases - about 0.25D every year you age
what is the equation for Hofstetter’s minimum amplitude of accommodation?
15 - 0.25age
what predicts symptom severity of amplitude of accommodation?
only accommodative lag
what is seen with static accommodative target?
under-accommodation or lag
how much accommodation can a person with accommodative insufficiency use until they cannot function anymore?
about 3D - need a 4-5D stimulus to really push their system and see it clinically
does accommodative insufficiency have a steady, constant accommodative lag?
no - it is very unstable and the target is always blurry
does a patient with accommodative fatigue or ill-sustained accommodative have a constant lag?
no - over time they have a larger lag as the time increases
what is a normal cpm for accommodative facility for monocular and binocular?
monocular = 10 cpm binocular = 8 cpm
what is the normal result for an amplitude-scaled facility test (binocular) - adjusted for distance and lens power?
binocular = 14cpm
how does tonic accommodation affect the facility test?
some people have 2.5D of tonic accommodation (instead of 0D) and the flipper will not change accommodation stimulus
what is the far-near response seen by autorefraction?
initially the eyes will lead (over accommodate) then they will lag by about 1D while viewing a target
what is accommodative gain?
parasympathetic (cholinergic), muscarinic receptor in ciliary muscle and has a 1-2 sec response time
what is slow adaptation?
sympathetic (adrenergic), beta2 receptor in ciliary smooth muscle, 20-40 sec response time and has low magnitude (1.5-2D max)
inhibitory signal is dependent upon parasympathetic gain
when does the amplitude of accommodation start decreasing?
after age 30 (35-40 = critical ages for presbyopia)
why do myopes maintain better amplitudes?
myopia reduces the amount of accommodation needed - system is already focused at near
which is responsible for presbyopia - the lens or ciliary muscle?
lens = becomes crystalized and looses elasticity (no a linear decline)
when do you treat presbyopia?
when the patient complains of symptoms (asthenopia)
does amplitude predict symptoms?
no - only accommodative lag
