Lec 10 Presbyopic CL Flashcards
Current methods to correct presbyopia with CL
CLs for single vision + SVN
Mono vision CL
Multifocal/bifocals
Modified mono vision
How to test which eye should get the distance correction with mono vision (lens method not triangle)
Plus tolerance test
- px full distance correction and looks at VA chart at distance
- BE open, put +0.5D or +1 over RE and then LE
- the more comfortable eye is near eye so non dominant
Advantage of mono vision
Cheap
Easy way to provide distance and near
Uses standard technique for lens selection and fitting
Effect of mono vision on vision performance
VA loss of 1/2 a line
Stereo loss of 40sec arc
Contrast sensitivity loss 7%
Px may need hear turn
No peripheral loss
Types of multifocal and bifocal lenses
Translating/alternating (ONLY RGP version works)
Simultaneous
- concentric optics
- aspheric optics
- diffractive optics
How does a rigid translating bifocal work
Near seg is on lower part of lens so relies on lens moving up on downgaze
This translating movement can be achieved by a prism ballast or truncation
How to fit a rigid translating bifocal
Use bifocal trial lens
Get good NaFl pattern and centration
Find where near seg is relative to lower pupil margin in primary gaze and in downgaze
Advantage of RGP bifocals
Good distance and near VA
no contrast loss
No BV loss
Not really affected by pupil size
Disadvantage if translating RGP bifocals
Hard to get adequate translation
Discomfort from prism or truncation
Less o2 from prism
Need trial set
What’s simultaneous vision
When more than 1 power is presented at the same time so 2 images projected on retina with one in focus and other blurred
Uses higher cortical suppression of non focused image
What are concentric bifocals
Have 2 or more optic zones covering the pupil with a centre D and N surround
OR
centre N and D surround
What are aspheric designs for simultaneous vision
There’s a blend of powers allowing less spherical aberration(?)
In a concentric design what happens as you increase the add power
And clinical pearl
The distance zone decreases
So to fit more add pose there can be more Crowding/aberrations into the distance zone
Don’t underplus the distance Rx or else need higher add
How are aspheric RGPs for presbyopia designed
(Back surface aspheric)
- note front surface aspheric just gives higher add on front
Back surface aspheric
- higher asphericity to cause increase in add
- central pooling steep which can cause corneal moulding
- limit +1.5 add
- requires some translation to see full add power
Compare between aspheric RGP and translating RGPS
Aspheric easy fit and often fit steeper than K VS translating harder and fit flatter
Aspheric may have visual compromise but translating doesn’t if positioned well
Aspheric good intermediate vision but translating NONE
aspheric possible fit empirically but translating = diagnostic fit
Advantage of simultaneous vision
Easy to fit and refit lens wears
Diagnostic lenses allow trial wear which is important for checking adaptation
Disadvantage of simultaneous designs
Change in pupil affects ratio of distance and near
Glare increases with dim light
Loss of VA/Contrast
Decentration causes aberrations like coma
What’s a modified mono vision
Using multifocal CL unconventionally
Good for astig in one eye, px needing high add,
Example of modified mono vision for astig
SV toric + multifocal intermediate and near
- need this as not much multi focal that gives both add and corrects for astig
Example of modified mono vision for high add that does lots of near work
SV near + multifocal with low add (distance and intermediate)
high add in absolute presbyopes means distance area is crowded so by giving SV near u done need high add anymore
Example of modified mono vision for px with high Add and wants good range
Multifocal distance + multifocal near
High add in near eye gives good near but also gives range while low add in distance also gives good range and distance
Example of modified mono vision for high add px and works mainly at distance
SV distance + multifocal with high add
SV distance good for distance and then the high add gives some range and good near
