contact lens case reports
Intacs and Keratoconus
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
Gene Reynolds, MD, OD, PhD, first proposed intrastromal corneal rings in the 1980s. The original concept was a 360-degree ring that could be implanted into the periphery of the cornea to manipulate the central cornea's shape. Expanding the ring would flatten the central cornea while constricting the ring would steepen it. This evolved into two 150-degree arches of varying thickness to control the amount of central corneal flattening (Figure 1).
The product, Intacs (Addition Technology, Inc.), received FDA approval in 1999 as a refractive surgery device/technique. In 2004 its approval expanded to treat keratoconus under a Humanitarian Device Exemption, because at that time Intacs demonstrated a good safety record internationally and no treatment options, other than penetrating keratoplasty, existed for keratoconus patients who were intolerant to contact lenses.
Figure 1. Evolution of the intrastromal rings from a 360-degree ring to two 150-degree PMMA segments.
Figure 2. Anterior segment OCT of the patient's right eye.
A male patient reported a long history of contact lens intolerance secondary to unilateral keratoconus. He underwent Intacs surgery to his right eye in 2006. His postoperative Ks were OD 51.37 @ 161/54.37 @ 71. His non-keratoconic left eye had Ks of 43.62 @ 90/43.87 @ 180 with a refractive error of plano and a visual acuity of 20/20. He was referred to our practice for lens management of his high anisometropia and central irregular astigmatism.
We performed anterior segment OCT on the patient's right eye (Figure 2). You can easily see the central corneal thinning, the profile and depth of the ring segments and the posterior budge adjacent to the Intacs.
Many lens options are available to manage his refractive error, and after a diagnostic fitting we selected the aspheric, 10.4mm diameter I Kone lens design from Valley Contax. The final parameters were 52.00D base curve, –8.00D power, 10.4mm diameter with an ultimate visual acuity of 20/25. The lens periphery in Figure 3 was steepened slightly to reduce peripheral edge lift. Despite his history he wears the new lens 16 hours a day and enjoys restored binocular vision.
Figure 3. White light and fluorescein pattern view of the patient's right eye.
Clinical experience with Intacs shows that the best results are in patients who have mild forms of keratoconus. However, these patients are often easily managed with the vast armamentarium of lens options at our disposal. It also remains questionable whether the post-Intacs topography is easier to fit with lenses. CLS
Patrick Caroline is an associate professor of optometry at Pacific 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 CooperVision and SynergEyes, Inc.