Accommodation Flashcards
What is accommodation?
Change in refractive power of the crystalline lens, resulting from contraction of the ciliary muscle
What happens when the ciliary muscle contracts?
Central aperture diameter decreases, and the tension in the zonules decreases which allows the lens to bulge forward
What are the changes that occur in the crystalline lens during accommodation?
- Equatorial diameter decreases
- Anterior pole moves forward
- Central anterior radius of curvature decreases
- Central posterior radius of curvature decreases slightly
- Central thickness increases (distance from anterior to posterior pole)
- Lens sinks
How is stimulus to accommodation calculated?
Required power- unaccommodated power
What causes the stimulus to accommodation to vary?
The refractive error
Does the stimulus to accommodation change for an axial myope vs refractive myope or refractive hyperope vs refractive hyperope?
NO- it is the same stimulus
What contributes to accommodation?
- Tonic accommodation
- Proximal accommodation
- Convergent accommodation
- Blur-driven accommodation
What is tonic accommodation?
Caused by underlying tonus of the ciliary smooth muscles which never fully relaxes
What is the average/ mean tonus value?
0.50D
What is the average convergent accommodation to convergence ratio?
(CA/C)
0.40D/6 prisms
What is blur driven accommodation?
Accommodation to clear retinal blur
What is proximal accommodation?
Accommodation due to the awareness/ nearness of an object
When does the accommodative stimulus = accommodative response?
1D
When is the accommodative response more than the accommodative stimulus?
What is this known as?
<1D stimulus= LEAD of accommodation
When does the accommodative response become more than the accommodative stimulus?
What is this known as?
> 1D stimulus= LAG of accommodation
