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Starting Trial Lens
Topography Fitting: Take the
central K's and a reading at the 4mm temporal area.
Manual
Keratometer Fitting:
Take
central K's and then get temporal measurements or use pre-surgery K
readings.
The
base curve of the Special Reverse Geometry lens will be 1 diopter steeper
than the flat central K. To determine the amount of reverse curve needed,
calculate the difference between the base curve and the 4mm temporal
measure i.e. central K's of 40.00/42.00 and 4mm temporal K of 44.00.
Select a trial lens of 41.00 with 3 diopters or the Series B lens.
Flat
K = 40.00
One D
steeper than flat central K of 40.00D + 1 = 41.00D
Base
curve is 41.00D
Difference
between base curve of 41.00D and temporal K of 44.00 = 3D
Try a
series B Special Reverse Geometry lens that has a 3D reverse curve.
Desired
Fluoroscein Pattern:
An alignment pattern is the ultimate
goal, but that is difficult to achieve. Get as close to alignment
pattern as possible. You want to see minimal vaulting in the central
region. The lens is made from Menicon Z®
material for good oxygen transmission and good wetting so metabolic wastes
are washed away.
In our example, if the mid-peripheral
area is pinched off, you need less reverse curve so go to a Series A.
This increases the lift. If the mid-peripheral area is showing
pooling, you need more reverse curves so go to a Series C. This
decreases the lift.
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