Accommodation Flashcards
What is the refractive index of the cornea?
n= 1.376
what is the refractive index of aqueous humor?
n=1.336
what is the refractive index of the lens?
sufaces n=1.386
center n=1.406
what is the refractive index of the aqueous humor?
n=1.336
Where does the optical power of the cornea come from?
The optical power of the cornea comes from the change in refractive index and the positive radius of curvature.
T/F: The posterior lens surface does not move with accommodation and the posterior lens surface curvature does not change.
FALSE!
The posterior lens surface increases in curvature and moves backward with accommodation.
What is depth of field?
The range over which a target can be moved toward or away from the eye without a perceptible change in the blur or focus of the image.
What is depth of focus?
Depth of focus is the focusing error that can be tolerated without an appreciable decrease in acuity or change in blur or focus of the image on the retina.
How is Depth of Focus is dependent on pupil size?
Small pupil = Larger depth of focus
Large pupil = Smaller depth of focus
T/F: With accommodation the pupil size decreases, increasing the depth of focus.
True
What is senile miosis?
Reduction in pupil size with aging
Tonic (residual) accommodation accounts for about how much diaptors?
About 1.5 diopters
What occurs during the The Accommodative Triad?
- the pupil constricts
- the eyes converge
- the eyes accommodate
T/F: An accommodative stimulus presented monocularly results in a binocular accommodation and convergence response.
True
What is blur-driven accommodation?
Placeing a (-) lens in front of an eye, the eyes accommodate to overcome the defocus. (to induce accommodation)
What happens when there is pharmacologic stimulation of accommodation?
Topical application of muscarinic cholinergic agonist (pilocarpine) to the eye results in stimulation of the ciliary muscle.
This results in pupil constriction but convergence does not occur.
What is accommodative esotropia?
occurs in uncorrected hyperopes as a consequence of needing to accommodate to even see distant objects in focus
What is cycloplegia?
Blocking accommodation
with either Atropine, cyclopentolate, tropicamide
Competitively bind to the same muscarinic receptors as the agonists: prevent agonist binding and block accommodation
What chemicals can be used to induce cycloplegia?
Atropine, cyclopentolate, tropicamide
What is a push-up method?
A way of measuring accommodation. Patient reports when a near letter chart is no longer in sharp focus as it is brought closer to the eye.
It is a subjective evaluation
What is the accurate objective measurement of accommodation?
Refractometers
T/F:
2/3 of accommodative amplitude is lost between ages 15-35
True!
Objective measurement of accommodation shows linear decline of ≈( ? )D per decade
2.3D
What is the Lenticular Sclerosis theory?
Says that the crystalline lens gets harder with increasing age and thus is a cause for presbyopia.
What is the Geometric Theory theory?
Says presbyopia is a consequence of the altered geometry of the lens/zonular relationship
Young lens:
The anterior zonular connections are near the lens equator and exert strong influence on the curvature of the lens
Aged lens:
The connections are farther forward, so there is not effective relaxation of the force with ciliary muscle contraction
What is the Disaccommodation Theory?
says presbyopia is caused by a gradual failure of the lens to be held in an unaccommodated form at rest
What is the multifactoral theory?
Says presbyopia results not from any single causal factor, but through global deterioration of accommodative function of many aspects of the accommodative apparatus
What are some optical compensation for presbyopia? (name 4)
Spectacle lenses (reading glasses) Contact lenses (mono-vision) Corneal refractive surgical procedures Or artificial intraocular lenses (IOLs).
