contact lens focus

Expand Your Keratoconic Fits

Lens meets needs of a broad spectrum of keratoconus patients

NATALIE COREY, O.D. AND SUSAN KOVACICH, O.D., F.A.A.O.

Many patients with irregular astigmatism, including keratoconic patients with oval, decentered and globus cones, post-refractive surgery patients or those with pellucid marginal degeneration, must wear RGP contact lenses (CL) for the best visual acuity (VA). After CL failure due to fit or discomfort, we often must tell these patients CL wear isn't an option. The good news: The ClearKone hybrid lens, from SynergEyes, Inc., is now a viable option for many of these patients.

Lens design and fitting

The ClearKone incorporates a reverse geometry RGP center, which completely vaults an irregular cornea without touch or bearing on the cornea, surrounded by a traditional hydrogel skirt. By vaulting the cornea with the reverse geometry RGP portion, the tear layer behind the CL creates a new optical surface, which enhances vision and decreases aberration. This is because reverse geometry allows for a greater vault with a flatter base curve and lower overall power. The soft skirt, meanwhile, provides centration and comfort.

The CL is available in 11 vault values and three skirt curve radii. The vault values are independent of corneal curvature and are fit via elevation or height rather than base curve. To fit the ClearKone, you must become certified by completing fit training with a SynergEyes, Inc. product specialist. And since the CL must be fit diagnostically vs. empirically, a fitting set is required.

The ideal fit of the ClearKone hybrid CL: complete apical clearance and even fluorescein thinning between the RGP border, or inner landing zone (ILZ), and the soft skirt junction, or outer landing zone (OLZ). Excessive CL touch or bearing on the cornea causes patient discomfort and results in a failed fit. Touch may occur if the RGP vault is too shallow or when corneal irregularity occurs in the peripheral cornea — often a problem with an inferior cone or pellucid marginal degeneration.

Identify each ClearKone by a laser mark on the skirt that shows the vault value and a letter that shows the skirt curvature, S (steep), M (medium) or F (flat).

SynergEyes, Inc. recommends starting with the 250-micron (M) vault with a medium skirt curve for all patients. Then, make adjustments to the vault value in 50M to 100M increments. Assess the fluorescein pattern immediately after CL insertion to rule out insertion bubbles and then again after three-tofive minutes of wear to ensure a correct fit. (Touch or bearing of the central RGP and tightening of the skirt are best evaluated after three-to-five minutes of wear.)

If a large, central insertion bubble presents, remove the CL, and reinsert it (with saline in the bowl of the lens). If you observe excessive fluorescein pooling under the RGP portion at the three-minute mark, decrease the vault value. If CL bearing appears on the cone's apex, increase the vault value. The ideal fit is the vault value 100M over the value you first observed bearing. Change the skirt curve as needed to produce the ideal fluorescein pattern at the ILZ and OLZ.

ClearKone

MATERIAL: Paflucon D Center (Hemiberfilcon A skirt)
WATER CONTENT: 27% (soft skirt)
DK/T: 100 (RGP Center)
WEARING SCHEDULE: Daily wear
REPLACEMENT: Six-month
DIAMETER: 14.5mm
VAULT: 100 to 600 in 50 micron steps
SKIRT CURVE RADII: Steep, Medium, Flat
POWERS: +5.00D to −20.00D (0.50D steps above +2.50D and −8.50D)

Patient experience

A now 37-year-old male was diagnosed with bilateral keratoconus in 2001. His keratometry (K) readings at diagnosis were 58.24/49.23D @ 018 OD and 43.67/43.48D @ 055 OS. Through several years, his condition has progressed rapidly, making it necessary to frequently refit him with several different keratoconic CLs. By 2009, his K readings had advanced to OD 64.0/53.0 @ 022 and 71.00/58.1 @ 168; the latest CL on his right eye began showing apical bearing. Further, he reported both CLs were uncomfortable due to the keratoconus progression. The cone was more centrally located in the left eye, so we adjusted the OS fit to both patient and practitioner satisfaction, while the right eye's cone was more irregular, making that fit a continual problem. We tried several large diameter, semi-scleral, and scleral CLs OD, but all OD CLs demonstrated central touch with peripheral bubbles and patient discomfort. So, the patient eventually opted to discontinue OD wear.

In early 2010, the patient returned for his annual exam. His K readings were 66.10/60.50D @ 035 OD and 74.30/60.90D @ 164 OS. He said his vision OS had been worsening through the past year. His uncorrected VA OD was 20/400, and his VA with his habitual CL OS was 20/30. Given the advanced state of the patient's keratoconus and the recent availability of the ClearKone, we chose this CL as the next lens option.

His topographies demonstrated large areas of central steepening OU. We determined the best ClearKone was 600S, −13.00D OD and 550S, −10.00D OS. Both CLs provided complete apical clearance with the proper amount of ILZ thinning. At the patient's follow-up visit, he noted "excellent" comfort OU and was correctable to 20/30 OD and 20/25 OS.

Because the ClearKone's reverse geometry of the RGP lens portion allows for complete vaulting of the cone apex with less minus power, it results in fewer induced aberrations. Also, we've found that its hybrid design enhances patient comfort and improves centration. These two components make this CL ideal for patients who have failed in CL wear due to the cone's location or severity. OM