Intraocular Lens Flashcards
Surgical solution for vision loss due to cataract formation
Vision correction with cataract surgery (monofocal IOL)
What can you achieve with a monfocal IOL
20/20 vision at distance Image quality (or resolution efficiency)
Continuous vision for presbyopia
- higher spectacle independence (far, inner, near correction)
- continuous vision (bifocal,trifocals, EDF, monovision)
What are the different kinds of IOLs
- surgical solution for vision loss due to cataract formation
- continuous vision solution for presbyopia
- accommodating vision or similar to nature crystalline lens
When does a spherical lens work
Smaller apertures
What happens with a larger aperture and a spherical lens
Generates higher spherical aberrations, which in turn affects the image quality
Why is an aspherical lens better
Provides higher image quality with minimal SA
What does the MTF of perfect lenses do with increasing refractive power
Increases at a certain spatial frequency
What does the MTF of lenses with aberration do with increasing refractive power
The modulation (or resolution) decreases with increasing refractive power above a certain limit
Symmetrical IOLs with RI of 1.46 and a 3.0mm aperture show what on MTF?
Perfect modulation up to about +15.0D
For power up to +25.0D, the modulation remains constant, and for powers above +25.0D…
There is a significant loss of modulation (contrast)
Increased curvature of IOL
Increased power, increased aberrations
What is the ISO standard for MTF of IOL?
About 0.4
Monofocal IOL
- distant vision correction
- non accommodative lens
- very high image quality
What kind of IOL has very high image quality
Monofocal IOL
What is the equation for determining the power of the IOL needed in an eye
F(IOL)=A-2.5xAxial Length-0.9xK reading
A is a constant that reflects what the manufacturers have learned about the IOL position
Find the correct power for an IOL for someone with axial length 23mm, K reading of 43.5D, and A=118.2
F(IOL)=(118.2)-2.5(23)-0.9(43.5)
+21.6D
Why is axial length so important in determine the power of the IOL?
If you are off by just 1mm, will be off by 2.5D, which is a very big difference
What is the minimum resolution of an IOL for ISO standards
60
IOLs and spec independence
In spite of high image quality achieved with monofocal IOLs, it only provides correction for distance vision and doesn’t provide ‘spectacle independence’
What kind of IOL provides distant and near vision
Bifocal IOL
What kind of optics does a bifocal IOL use
Refractive fresnel optics
What gives the add power in a biofical IOL
Fresnel
What gives the base power of a biofocal IOL
The monofocal part of the lens
