Accommodation And Presbyopia II Flashcards
A -2.00D myope is overminued. She wears a -4.00D spec correction. If she has an 8D Amp of accommodation, what is the location of her near point when wearing her glasses?
16cm in front of her eyes
She is a +2.00D with her glasses. Take that away from the 6D amp of accommodation and you get 6. Inverse that and you get 16cm in front of her eyes
You measure the Rx. Of a 5 year old in an autorefractor. Your ret showed +1.ooD. The autorefractor show -3.00D. Which form of accommodation might account for the different results
Proximal accommodation
Your 45 year old patient says he has no problems with either reading or distance. You measure the spec Rx as:
OD: -1.00 -0.25 +180. +1.00
OS: +0.25 -0.50x170. +1.00
Objective presbyopia
Which is the most correct theory of the method for accommodation
Ciliary muscle contraction cause relaxation of the lens zonules
What does accommodation do
Causes zonules to relax. The lens balls up, increases space between ciliary body and lens
Lens capsule with age
Becomes less pliant
What does the lens capsule becoming less compliant have to do with accommodation
Causes progressive decrease in accommodative capacity
What could defeat efforts to produce an accommodative IOL placed inside the lens capsule
The lens capsule becoming more pliant with age
Shrinkage. Fibrotic tissue condenses and shrinks together and forms small hole
Phimosis
Primary factors leading to presbyopia
- The modulus of the elasticity of th elens capsule decreases with age
- The modulus of the elasticity of the lens substance increases slightly
- The lens size/volume increases progressively with age
Why does the modulus od the elasticity of the lens capsule decrease with age
It becomes progressively less stiff and mroe compliant
Why does the modulus of the elasticity of the lens substance increase slightly with age
- the lens substance becomes stiffer, more plastic, and more sclerotic-like with age
- thus the energy required to deform the lens substance itself increases with age, with this energy being proportional to the modulus of elasticity
What factor contributes to 44% of the loss of accommodation
The modulus of the elasticity of the lens substance increases slightly
The lens size/volume increases progressively with age and presbyopia
- this makes the lens capsule function less effectively
- it is more difficult to deform a larger body than to deform a smaller body, especially with a concomitant change in shape
What factor contributes to 55% of the loss of accommodation
The lens size/volume increases progressively with age
What are the two main factors that cause presbyopia
The size increases and becomes stiffer (lens)
What is presbyopia not caused by
Zonular elasticity
Ciliary muscle power
Control pathways and structures
Zonular elasticity and age
Remains constant
Ciliary muscle power and age
Increases from youth to 45
Control pathways and structures of the eye throughout presbyopia
Remain constant
What two structures change and cause presbyopia
Lens and lens capsule
When does amp of accommodation start dropping
About 50
When is amp amp accommodation about 0
75
Mean amp of accommodation
18.5-(0.30*age)
Minimum amp of accommodation
15-(0.25*age)
Max amp of accommodation
25-(0.40*age)
What might be a common add given to a 50 year old patient
+1.50D
Minimum expected amp for 40-44 years
5.00 to 4.00
Range of near adds for 40-44
+0.75 to +1.00
Minimum expected amp for 45-49
3.75 to 2.75
Range of ad powers for 45-49
+1.00 to +1.50
Minimum amp of accommodation for 50-54
2.50 to 1.50
Range of adds powers for 50-54
+1.50-+2.00
Minimum amp for 55-59
1.25 to 0.25
Range of add for 55-59
+2-+2.50
Minimum amp for 60 and over
0
Range of adds for 60 and over
+2.25 to +2.50
Disparity between retinal defocus and accommodative mechanism
Lag/lead accommodation
How can lag/lead accommodation be measured
Ret
What can lag/lead accommodation reveal problems with
Accommodation
Lead accommodation
Looking in front of the ret
Lag accommodation
Looking behind the ret
What are some accommodation problems that will cause lead/lag accommodation
Presbyopia, accommodative insufficiency
Accommodative spasm
Focusing so much on something in front of you that when you look up at something in the distance, it looks blurry
Accommodative spasm
What are some things that could cause accommodative spasm
Latent hyperopia
Pseudomyopia
When refracting someone with accommodative spasm, what is something you might have to do
Fogging repeatedly, cyclo, or sudden unfogging (-/+2.00Ds trial lens
How fast someone can look between a -2.00 and a +2.00 at a neat object and tell you that is it “clear”
Accommodative facility
Number of complete cycles in 60 seconds of going between -2 and +2
Accommodative facility
What is a normal accommodative facility in adults
12cpm
Is acommodative facility better monocularly or binocularly
Monocular
What is a persons accommodation when there is a -2.00 40cm in front of them
-4.50
What is a persons accommodation when there’s s a +2.00 40cm in front of them
0.5D
Accommodation of an emmetropes is approximately equal to
The stimulus to accommodate
If something is 40cm away, it will take 2.5D to accommodate
What can reduce stimulus in emmetrope accommodation
Depth of field
What could provide stimulus to over and under accommodate in emmetropes
Aberrations
______ need to accommodate less
Myope
_______ need to accommodate more
Hyperope
Accommodation with CL
Same as emmetropic
Accommodation with glasses
Use vertex distance of glasses to calculate accommodative demand at the cornea
