Lens Dynamics, Inc.

It is not often that truly “new designs” are presented to the contact lens practitioner. The US is at that juncture with Quadrant Specific Technology.

Has a patient presented with a flat or steep area in only one quadrant on the cornea? Have you ever wished you could split the back surface in two with one half being steep and the other half being flat? Most contact lens fitters working with irregular corneas have faced these problems. The contact lens laboratories have not been able to provide designs that would address these corneal irregularities.

Figure 1

NEW KID ON THE BLOCK:

Past lathing technology allowed labs to only cut spherical or aspheric back surfaces and back or bitoric designs. New software engineering in the US will allow labs, with the newest lathes, to alter the back surface of a gas permeable lens to match some highly irregular surfaces. This lathing process has been working in Europe for several years and is popular among the keratoconus practitioners there.

So what is this voodoo? ( Figure 3) Cut a circle into 4 slices or quadrants. Going counter-clockwise, Quad 1 is 0 to 90 degrees; Quad 2 is 90 to 180 degrees, etc. Looking at Figure 1

we see a very flat area in Quad 2 with Quad 1 being slightly steeper than Quads 3 and 4. This cornea needs a 6.00 mm in Quad 1, 7.80 mm in Quad 2, and 6.20 in Quads 3 & 4.

Figure 3

The biggest problem in the past with this type of lathing has been matching the front radii cuts to the various back surface radii to produce the required power. Computer ray tracing and data points analysis has made this software possible.

FITTER BEWARE:

As in any new technology, marketing can get very creative and confuse the real issues. Let’s adopt some standard language so everyone knows what is actually being ordered and manufactured. Quadrants 1 to 4 seem innocent enough for calling out the area(s) needing special treatment.

Power is another issue. This is like bitorics where we can have “drum readings” or call out the primary power with the amount of cylinder for the opposite meridian. In Quadrant Specific lenses this is a bit more detailed. In the Figure 1 example, there will be three different front radii cuts because we have 3 different base curve radii. The simple approach is to call out the power based on the major quadrant base curve and the lab can figure the radii cuts needed in the minor quadrants to get the proper power. In Figure 1, the major quadrants are Quads 3 & 4 at 6.20 mm and needed a power of -11.00.

What to order: Quadrant Specific Design, B.C.s, Quad 1- 6.00mm, Quad 2- 7.80mm, Quads 3 & 4- 6.20mm. power -11.00 at 6.20 radius, 11.2/9.4, standard edge.

The Whole Piece or Just the Crust?

There has been partial quadrant specific technology available in the U.S. Lens Dynamics has made the Flat/Steep Option for several years. Tru-Form recently offered the QuadraKoneä Design. These designs address the PERIPHERAL AREA only. They could more correctly be called PC Quadrant Specific designs. These work quite well with edge stand off or edge pinch off in a specific edge area. THIS IS THE CRUST.

When you need the entire piece of the pie as in Figure 1, the affected area needs a change in the entire quadrant from center to edge. This cornea demands the Whole Piece of the Pie.

Case History:

Figure 4 shows a left eye after two RK procedures. The practitioner tried a spherical Dyna Intra-Limbal of 11.2 / 9.4 and experienced either excessive touch or excessive pooling depending on the BC tried. Final solution was Quadrant Specific Design with Quad 2 being three Diopters flatter than Quads 1, 3 & 4.

Figure 4

About the author:

Al Vaske is President of Lens Dynamics, Inc. specializing in keratoconus and other irregular corneas. Mr. Vaske is a frequent lecturer world wide on these corneas. Currently Mr. Vaske is a Board member of the Contact Lens Manufacturing Association and a former Associate Board member of CLSA.

Last Updated 5/7/2008