Accommodation And Presbyopia Flashcards
You have a -2.oo D myopic patient that has an accommodative amplitude of 8 D. What is their near point?
2+8=10
1/10=0.1m
10cm
Your emmetropic patient wants to read their computer monitor at 0.8m. What us the minimum accommodation necessary to see the monitor clearly. Assume +-0.25D depth of focus
4/5=5/4=1.25D
1.25-0.25=1.00D
You have a +2.00D uncorrected hyperope with an accommodative amplitude of 6D. What is a comfortable close distance for them for long periods of time (1/2 their AA)
+2.00 hyperopia
6D AA (3 for comfort)
3-2=1D left
1m
Normal aging process of the eye
Presbyopia
The age related continuous but gradual loss of accommodation
Presbyopia
The function whereby the converging power of the optical. System of the eye is increaes so that light diverging from a near source may be brought to a focus upon the retina
Accommodation
A process whereby the young eye is able to change the point of focus from a distance object to a near object
Accommodation
Other terms for presbyopia
- normal decreasing elasticity of the crystalline lens that leads to loss of accommodation
- accommodation insufficiency
- accommodative insufficiency
- presbyopia
Who is at risk for presbyopia
Anyone over the age of 35
Signs and symptoms of presbyopia
- hard time reading small print
- having to hold things at arms distance
- problems seeing objects that are close to you
- headaches
- eye strain
Needing optical correcting to the best distance correction to achieve an acceptable near VA (add on top of distance vision)
Objective hyperopia
Needing optical correction to the presenting distance correction to achieve acceptable near VA
Functional presbyopia
How many people world wide have presbyopia
1 billion
How many people lack adequate presbyopia correction
Half
What is the projected number of presbyopes in 2020
1.37 bil;lion
Symptom of presbyopia
- ocular discomfort with sustained near work
- drowsiness during near work
- holding stuff further away
- asthenopia related to excessive accommodative efforts
- transient diplopia or esophoria
What is the most recent theory of accommodation that says that the ciliary muscle relaxes and zonular fibers at ‘resting’ tension cause lens to contract and increase dioptric power?
Herman von helmholtz
What are some debunked theories of accommodation
- accommodation causes increase in zonular tension
- no need for active focusing because if the interval of sturm
- pupil size changes result in accommodation
- corneal curvature changes
- shift in lens position
- change in axial length of the eye
What state are the zonules relaxed in
Accommodation
What state are the zonules tense
Relaxed
When is there always tension on the zonules
When relaxed
In what state is the lens under tension at the equator from the ciliary body?
Relaxed
What does the tension on the lens in the relaxed state do
Keeps the surfaces flat so that for an emmetropic eye distant objects focus on the retina
In what state is the ciliary muscle constricted and the tension on the equator of the lens is relaxed?
Accommodated
Surface curvature of the lens in accommodation
Increases
Power of the lens in accommodation
Increases
What are the different types of accommodation
Reflex
Vergence
Proximal
Tonic
What are the two major types of accommodation
Reflex and vergence
Automatic adjustment of refractive state to obtain and maintain a sharply defined and focused retinal image in response to a blur input.
Reflex accommodation
How much dioptric power is reflex accommodation
Up to 2.00D blur
What assists in reflex accommodation
Small scanning eye movements, or microsaccades, assist in the process
What is the largest and most important component of accommodation under both monocular and binocular viewing conditions
Reflex accommodation
Induced by the innate neurological linking and action of disparity (fusional) vergence
Vergence accommodation
What gives rise to the convergence accommodation/convergence (CA/C) ratio?
Vergence accommodation
What is the second major component of accommodation
Vergence accommodation
Due to the influence of knowledge of apparent nearness of an object
Proximal accommodation
Stimulated by targets within 3m of the individual
Proximal accommodation
When does proximal accommodation become quite large?
With near viewing, providing up to 80% of the total near response without other cues
What is proximal accommodation stimulated by
Perceptual cues
Why is it sometimes hard to measure wavefront abberations for LASIK sometimes
Because of proximal accommodation
Reveled in the absence of blur, disparity, and proximal inputs
Tonic accommodation
How is tonic accommodation measured
By removal of the other three inputs (large dark room)
What is the mean tonic accommodative level in young adults
About 1D with a range from nearly 0 to 2.00D
What kind of accommodation reduces with age
Tonic accommodation.
