Accommodation Flashcards
Process by which the dioptric power of lens changes to maintain a focused image on fovea
Normal Accommodation (consensual and equal)
List the components of the near triad
convergence, accommodation, miosis
What are the two types of accommodation
Positive accommodation (focus) and Negative accommodation (defocus)
What 4 things occur in positive accommodation with parasympathetic nervous system (PSNS) stimulation
ciliary muscle contraction, ciliary body moves forward, ligament tension is released, and lens becomes more convex (increased dioptric power)
What 3 things occur in negative accommodation
tension on ciliary muscle is released, capsule flattens, and dioptric power decreases
What are the 4 types of NORMAL accommodation
reflex, tonic, convergence, and psychic/near
What stimulates reflex accommodation
the quality of retinal images (blurred or defocused signals)
What does tonic accommodation depend on
the tone of the ciliary body
What is convergence accommodation (aka: relative accommodation)
as the convergence angle is changed the accommodation must increase to see a target nearer and nearer
What are strong drivers for near work induced myopia
low illumination and low CA/C ratio (convergence-accommodation /convergence
How can you measure accommodation
push-up method, minus lens induction, or plus lens relaxation
If your patient reports blur at 5cm what is the amplitude of accommodation
(1/.05m) = 20D
List three standards for push-up method
monocularly, habitual Rx, target 1-2 lines larger than best near acuity
What is psychic accommodation
accommodation induced by the awareness of nearness of targets (microscopes, auto-refractor, eyestrain, charts less than 20ft away
Why is accuracy of accommodation not perfect
the stimulus is not always equal to the response of accommodation (lead/more than needed and lag/less than needed)
What two things did Donder suggest about normal amplitude of accommodation
it decreases with age and biological variation
What is lag for majority of normal people
+0.50D
if a patient reports blur, what type of accommodation are they experiencing?
maximal accommodation is reached
what type of accommodation is strongly controlled by convergence and fusion? And also somewhat controlled by the shift of spectral sensitivity and chromatic aberration?
tonic accommodation
when measuring accommodation with minus lenses when would you stop introducing minus lenses to the patient, while they are maintaining convergence at distance?
until the patient first reports blur (PRA= positive accommodation relative to convergence)
with plus lenses, what signals the limit when accommodation is relaxed?
convergence stimulus of accommodation (NRA)
Is the stimulus to accommodation always equal to the response in accommodation?
no… not Perfect
describe intermittent accommodation
5-8” for short periods of time
for how long should a person be able to sustain reading at 40 cm?
2 hours
according to donders table at what age does a person experience 4.5 D of accommodation and 0 D of accommodation respectively?
40 and 75
Average expected accommodative amplitue
18.5-(0.30)(age)
maximum expected accommodative amplitude
25-(0.40)(age)
minimum expected accommodative amplitude
15-(0.25)(age)
what is accommodative facility?
the ability to “rock” back and forth accommodation from a distance to a near target
how is accommodative facility tested?
using +/- 2.00 D Flippers and polaroid lenses. Done binocularly and reading bar is used to check for suppression
during accommodative facility test, when would you test the eyes monoculary?
if patient records less than 8 cycles per minute. (in monocular test you dont use bar reader nor polaroid glasses)
what range should monocular reading fall under during the accommodative facility test?
4 cpm for each eye
expected results for children 8-12 in accommodative facility test?
5 cpm binocularly
7 cpm monocularly
expected results for adults 13-30 in accommodative facility test?
10 cpm binocularly
11 cpm monocular
how is accommodative insufficiency measured?
the “push up” method (near point accommodation). Record: blur/break/recovery
accommodative excess
abnormally high lead (ex. 5D accommodation required, yet the accommodative response is more 5.75D). see this in younger patients
accommodative spasms
inability to relax from the accommodative lead, some of which is experienced by the patient as an interference with distance vision (near-to-far-blur)
accommodative infacillity
facility of accommodation may be reduced so that focusing from near to distance may cause blur that last more than a few seconds or a sustained blur after reading for 20 mins (difficult or blur at distance after reading)
