|
This design is best suited for Post Lasik and Post RK corneas that show the flat, central ablation zone with steeper cornea curvature from the mid-periphery out. The standard lens diameter is 11.2 mm with a 9.0 mm back optic zone and a reverse secondary curve option.
Post Lasik: The topography at right shows the classic flat central zone created by ablating the cornea.
RK Corneas: Some of these corneas will have the flat central zone and others will not. If the topography shows the flat central area surrounded by a steeper peripheral area, use a reverse geometry lens. If it does NOT have the flat appearance in the center, use the standard Dyna Intra-Limbal lens design.
Post Penetrating Keratoplasty - Sunken Grafts: The graft area sinks resembling a Post Lasik topography. A reverse geometry option is needed.
Starting Trial Lens:
Select a trial lens with a base curve one diopter steeper than the flat central K and 2 diopters of reverse curve (Series A, least reverse radius).
Diameter Selection:
The standard Dyna Intra-Limbal Special Reverse Geometry lens is 11.2 mm in diameter with a 9.0 mm BOZ. The lens is designed to fit intra-limbal and to achieve 0.5 mm to 1.0 mm of movement. With adequate edge lift, light limbal involvement is acceptable. The overall diameter should be approximately 0.2 mm to 0.5 mm smaller than the cornea and the lens may need to be smaller or larger than 11.2 to meet this criteria. Dyna Intra-Limbal lenses come in diameters 10.4 mm to 12.5 mm.
Desired Fluorescein Pattern:
The best fit will exhibit an alignment pattern in the center, the reverse curve area, and the edge. First, find a base curve that aligns the central cornea, then look at the secondary curve area. If the mid-periphery needs to be changed, consider changing the Series rather than changing the base curve.
Example: If there is pinch off in the mid-periphery, decrease the amount of reverse curve by going from a Series B to a Series A lens. If there is pooling in the mid-periphery, increase the reverse curve amount by going from a Series A to a Series B or Series C lens.
Finally, evaluate the edge profile for adequate lift. The edge profile should show about 0.2 mm of clearance. Overall lens movement will be 0.5 mm to 1.0 mm. The ultimate fluorescein pattern will be as alignment looking as possible.
It is important to remember that this design needs to be carefully evaluated in
three areas: 1st the base curve, 2nd the reverse curve area, and 3rd the edge
Edge Profile:
The desired edge lift should be about 0.2 mm wide. The Dyna Intra-Limbal system starts with a standard edge lift. Flatter or steeper edge lifts are available in a step system. You can order any edge profile in steps 1 through 15 flatter and 1 through 10 steps steeper. All changes are computer modeled so that reproducibility is insured.
Examples: Should the standard edge profile show pinch off, start with a 1 Flat edge lift. This should be adequate in most cases. Flatten the edge lift until a 0.2 mm edge width is achieved. The same is true in reverse. If the standard edge profile shows too much edge lift, steepen the edge until a 0.2 mm edge width is achieved.
Many times one or more of the four quadrants may have touch or stand-off. In these cases, the Quad Sym PC Option allows for increasing or decreasing the edge in any or all quadrants.
Do NOT try to decrease the edge lift by adding more reverse curve.
This will cause mid-peripheral seal-off.
Other Design Options:
Multifocal Option: Front aspheric optics can be added for presbyopic correction. The base curve is not affected.
Toric Options: Bitoric and front toric designs are available.
|
