Accommodation Flashcards
(30 cards)
What system is stimulated in positive accommodation?
Parasympathetic nervous system
What occurs in positive accommodation?
Ciliary contraction Ciliary body moves forward Ligament tension is released Lens becomes more convex Increase in dioptric power
What occurs in negative accommodation?
Tension on ciliary muscle is released
Capsule flattens
Decrease in dioptric power
What are the 4 types of normal accommodation?
Reflex accommodation
Tonic accommodation
Convergence-accommodation
Psychic or near accommodation
What stimulates reflex accommodation?
The quality of retinal images
What system operates reflex accommodation?
Parasympathetic nervous system
What is the pathway in the PSNS to increase the power of the lens?
CN III
Short posterior ciliary nerves
Ciliary body
On what is tonic accommodation dependent?
The tone of the ciliary body
What removes the appreciation of blur?
Darkness
With which type of accommodation is night myopia or empty field myopia associated?
Tonic accommodation
Convergence-accommodation is also known as ___?
Relative accommodation
When trying to measure accommodation, we can use minus lenses to do what? Plus lenses?
Induce accommodation
Relax accommodation
What is psychic accommodation?
Accommodation induced by the awareness of nearness of a targe
What are some examples of psychic accommodation?
Using: Microscopes Auto-refractor Eyestrain Charts less than 20ft
Accommodating slightly less than the needed amount is called what?
Accommodative lag
Accommodating slightly more than is needed is called ___?
Accommodative lead
Most people show an accommodative lag of how much?
+0.50D
We expect intermittent accommodation at 5-8” for how long?
Short periods of time
We expect sustained reading at 40 cm for how long?
At least 2 hours
What are the two suggestions about the normal amplitude of accommodation made my Donders?
It decreases with age
There is biological variation
What is the Hofstetter formula for minimum expected accommodative amplitude?
15-(0.25)(age)
What is the Hofstetter formula for average expected accommodative amplitude?
18.5-(0.40)(age)
What is accommodative facility?
Ability to repeatedly stimulate and relax accommodation with ease
What is the expected normal finding when testing accommodative facility?
Adults - 10 cycles per minute binocularly
Children - 5 cpm binocularly
