A New Hybrid Option for Keratoconus
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRé, FAAO
Keratoconus is a condition of obscure etiology that occurs in approximately 1 in 2,500 to 1 in 5,000 people. Reference to the condition appears in the British literature as early as the mid-1700s, and today the condition occurs in almost every region and every ethnicity worldwide.
Types of Keratoconus
In clinical practice, we've identified three distinct forms of keratoconus: Puberty onset, late onset and form frust. The puberty onset form of the condition begins in early adolescence at about ages 14 to 16. It's usually bilateral with one eye affected worse than the other. Clinical experience has shown that often, the earlier in life the keratoconus occurs, the more severe the condition becomes.
In late onset keratoconus, the earliest signs and symptoms begin in the late 20s or early 30s. It frequently affects both eyes to a similar degree, and unlike puberty onset keratoconus, its progression is often significantly less severe and rarely requires surgical intervention.
Form frust is an extremely mild and non-progressive form of keratoconus that can occur anytime throughout life. The condition manifests as a central or paracentral zone of irregular astigmatism of unknown etiology.
|Figure 1. SynergEyes for keratoconus|
The clinical management of keratoconus often varies with the severity of the condition and can range from non-surgical options, such as glasses and contact lenses, to surgical interventions, including corneal cross-linking, intra-stromal inlays and penetrating keratoplasty. Contact lenses have been the preferred method to optically manage the condition since 1888, and today a wide range of lens designs and materials is available for keratoconus.
Hybrid lenses (a GP center and soft peripheral skirt) first appeared in 1985 as the Saturn lens, with the later generation Softperm (CIBA Vision) design launching in 1989. In September 2001, a California-based research group began developing a new high-Dk hybrid lens that today is called SynergEyes (SynergEyes, Inc.). The lens incorporates an 8.2mm aspheric high-Dk rigid center (Paragon HDS 100, Dk 100) and a 31-percent water non-ionic soft lens skirt. The overall diameter of the lens is 14.5mm.
A Hybrid Lens Case
We've successfully fit the SynergEyes KC lens for keratoconic patients such as FJ, a 34-year-old male who had a history of discomfort and decreased wearing time with his traditional GPs.
The fitting procedure begins by selecting a diagnostic lens with a base curve radius equal to the steepest K reading. We placed high-molecular-weight fluorescein into the bowl of the lens and placed the lens on the eye. The GP portion of the lens should exhibit slight apical clearance or "feather touch" across the apex of the cone and midperipheral lens bearing (Figure 1). The soft lens skirt should exhibit 0.25mm of blink-induced movement.
Today FJ enjoys 20/25 vision OU and all-day lens wear.
Patrick Caroline is an associate professor of optometry at Pacific University and is an assistant professor of ophthalmology at the Oregon Health Sciences University. He is also a consultant to Paragon Vision Sciences and SynergEyes, Inc. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for Alcon Labs, CooperVision and SynergEyes, Inc.