EyeWitness Fall 2010 - 21

the cornea from mechanical rubbing. It can also solve the issue of lens displacement, which tends to be a recurring problem with PMD patients who wear smaller, more traditional keratoconic designs. New technology has brought this lens option back into play recently. SynergEyes offers higher Dk and better bonding between the gas permeable lens and soft skirt junction than its predecessors. The GP portion of the lens has an aspheric posterior surface with a diameter of 8.40mm and an overall lens diameter of 14.5mm. The optimal fit of this lens design is different than that of the standard GP fit and the fitter should look for a steeper fluorescein pattern. In achieving the appropriate movement and tear exchange, this design should have a tear layer of approximately 30 microns which is generally achieved by fitting 1.25D steeper than the typical corneal GP lens. SynergEyes also offers different soft skirt fits to accommodate varying horizontal visible iris diameters (HVIDs). The soft skirt portion of this lens design will appear as any standard soft lens fit. This lens is best fit with the use of a diagnostic set and practitioner certification is required prior to purchase.

KeraSoft IC
Currently available in Europe, KeraSoft® IC is a soft lens design developed specifically for irregular corneas including patients with PMD. Along with the ability to fit a steeper central base curve than most standard soft lens designs, this unique lens allows the fitter to flatten or steepen the peripheral portion of the lens independently from the base curve. The peripheral portion of the lens can be adjusted up to four steps steeper or flatter, and specified either as the entire peripheral circumference or in particular sectors/quadrants with sector management control (SMC). This is the first silicone hydrogel to incorporate SMC. Each step of peripheral change is equal to that of a 0.20mm base curve change. Being able to control the fit even more precisely on an irregular cornea allows this lens to provide better stability and reduce rotational problems associated with standard soft lenses, providing better overall optics and visual acuity. This stability factor, as well as an optimal Dk, allows prior GP patients who have had to decrease wearing time due to discomfort to return to normal wear with KeraSoft IC. The desired fit is similar to that of a standard soft lens. The axis marking is at 6 o’clock and readily drops back into this position after the blink. The fitter should not be surprised to find that 3mm of movement is not uncommon with this lens design. As usual, once the best fitting lens has been determined, the over-refraction is then performed. Topography can be used to assess the amount of corneal cylinder and axis present and to help determine the estimated amount of cylinder and axis correction required. The wide range of parameters available, including up to 15.00D of cylinder correction, should allow for a good visual end point. Some patients may find improved visual comfort with this lens modality versus that of a standard diameter GP lens, due to reduced photophobia provided by the larger optic zone, less aberrations from decreased tear pooling, and wave front optics incorporated into every lens. This design is fit with the use of topography and an 8-lens diagnostic set. KeraSoft IC is not currently available in the United States. The challenges of highly asymmetric corneas and large refractive cylinders common to pellucid marginal degeneration create fitting issues of lens displacement, bubble entrapment, and corneal insult from inappropriate tear exchange or mechanical rubbing. Having a variety of lens options to address these concerns is extremely helpful. Regardless of which design becomes the final lens, the desired outcome should be the same; a well fitting lens that will provide the patient with adequate acuity, all day comfort, and minimal interference to the cornea.

Quadrant Control
A new and exciting option with GPs is quadrant control lens design. Quadrant control allows the lens to align over the flat superior portion of a PMD cornea and fit the inferior steep portion. This increases lens stability and comfort, as well as eliminating displacement issues caused by inferior edge lift. Most design options available utilize the quadrant control aspect of the lens in the peripheral portion. Some will allow the fitter to specify which particular quadrant needs steepening, while others will only allow the inferior portion to be steepened. The type of control available depends on the design offered by each manufacturer. Lens Dynamics offers Quad-Sym BC technology that changes from the center out in four quadrants, requiring a different front radii to be generated in each quadrant in order to achieve the needed Rx across the entire lens surface. TruForm’s QuadraKone™ design maintains the central optical zone and base curve while utilizing a controllable quad aspheric periphery to allow peripheral changes in four meridians. The fitter would start with a standard keratoconic lens design and look for good centration with slight touch over the steep portion of the cornea. Next, the peripheral design is evaluated. Look for areas of excessive pooling, typically found inferiorly in patients with PMD. These areas of increased lift would be the quadrant in which a steeper peripheral curve would be indicated, generally requiring a steepening of 3 to 4 diopters. Quadrant control designs are most often fit with diagnostic lenses and the aid of topography.

EyEWitnEss FALL 2010

c o n ta c t l e n s s o c i e t y o f a m e r i c a

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EyeWitness Fall 2010

Table of Contents for the Digital Edition of EyeWitness Fall 2010