How Intracorneal Rings Affect Lens Fitting for Keratoconus
How Intracorneal Rings Affect Lens Fitting for Keratoconus
BY LORETTA B. SZCZOTKA-FLYNN, OD, PHD, MS, FAAO
It has been stated that intrastromal corneal ring segments improve contact lens tolerance in keratoconus patients (Ertan, 2007). Instrastromal ring segments are also touted to improve best-corrected visual acuity and uncorrected visual acuity as well as to delay the need for keratoplasty by reshaping the cornea. What evidence supports that these devices improve the fitting of contact lenses after their surgical placement? This month's column will explore the available published data in this regard.
Intracorneal Rings and Keratoconus
There are several models of intracorneal rings; the most commonly used is Intacs by Addition Technology. This additive technology alters the corneal structure by an arc-shortening effect as the material is added to the corneal periphery. The ideal result is a reduction of corneal asymmetry and convexity of the cone, which improves best-corrected spectacle acuity and uncorrected visual acuity.
The results in keratoconus are variable. Some of the larger studies report that about 85 percent of patients gain at least one line in uncorrected or best-corrected visual acuity; however the majority of those patients do not improve more than three lines of uncorrected or best-correct visual acuity (Ertan, 2007). Central keratometry can flatten by about 6D, and the cone apex can move toward the geographic corneal center (Dauwe, 2009), which is partially responsible for the reduced irregular astigmatism in some patients. The best results occur in keratoconus patients who have moderate or early disease; once the mean keratometry readings exceed 55D, the results are poor (Alio, 2006).
Any invasive corneal surgery for keratoconus, including intracorneal ring implantation, is almost always reserved for patients who are contact lens intolerant. Surveying the literature, few patients actually return to contact lenses after Intacs inserts. This is likely reflective of excellent selection by surgeons and realistic expectations by patients. Although their acuity may not be improved to their best potential, patients accept the improvement that the device has provided for them without relying on contact lenses.
In the only published case series of contact lenses fit after intrastromal corneal ring segment surgery, only three patients were referred for contact lens fitting in a two-year time period at a large, university-based contact lens practice at the University of California, Los Angeles (UCLA) (Nepomuceno, 2003). Two of the three were fit to large-diameter GP lenses, and one patient was fit with a soft toric lens. In other case reports surveyed, some form of GP lens fitting (often piggyback) was recommended to achieve the best-corrected visual acuity (Uçakhan, 2006; Smith, 2008). Although there is no denominator to calculate incidence, and the publication of reports describing complicated contact lens fitting in these patients may be a form of publication bias, the literature (and meeting abstracts) mostly describe specialty GP contact lens fitting after intracorneal ring implantation. This is consistent with my experience in a specialty university-based contact lens practice. That is, it is rare for soft contact lenses to work well postoperatively.
Fitting GP Lenses
The peripheral circumferential corneal elevation above the ring segment inserts causes mechanical barriers when fitting rigid contact lenses (Figure 1). Although successful fits can be achieved, it is not without a significant number of diagnostic lenses and multiple design changes. For example, in the UCLA study up to seven diagnostic lenses were used before a final fit was achieved. In my practice, specialty GP lenses have always been employed after intracorneal ring inserts, either in a piggyback, semi-scleral, or hybrid design. Rarely can a small-diameter GP lens be used alone because of mechanical impingement and epithelial breakdown in the area immediately above the inserted segments. In the UCLA study, one of the three subjects was fit to a semi-scleral lens, as was the patient in Figure 2. These lenses work very well and have become the lens of choice after intracorneal ring segment implantation in my practice because they can vault the cornea, preventing impingement on the epithelium above the inserts and redistributing the pressure to the sclera. Of course, they correct residual ametropia and irregular astigmatism as well.
Figure 1. Topography of a keratoconus patient before and after undergoing intracorneal ring segment surgery. PHOTOS COURTESY OF MICHAEL A. WARD, MMSC, FAAO
Figure 2. Semi-scleral lens on a patient who has intracorneal ring segments.
Because the average patient has moderate disease before undergoing Intacs or other intracorneal ring implantation, there are more contact lens options for this group of patients (that are also easier to fit with fewer complications) before surgery compared to after. That is, although GP lenses provide the best acuity, they are much more difficult to fit after surgery compared to before. Patients who won't settle for less than their best acuity are obviously not candidates for intracorneal ring segments because the complicated fitting postoperatively overshadows the potentially improved spectacle-corrected and uncorrected acuity.
A case example from my clinic involved a GP intolerant patient who was moderately successful in a hybrid lens for keratoconus. He sought out and proceeded with placement of Intacs and postoperatively did not achieve substantially improved best-corrected spectacle acuity. After surgery, he was refit to another hybrid lens, this time with more difficulty on my part as the ring segments posed some issues with erosions during the fitting process. Nonetheless, although the fitting was more complex, the patient claims improved post-surgical comfort and tolerance.
Fitting Soft Lenses
You can fit soft lenses after intracorneal ring segment implantation if the astigmatism has been reduced and/or has become more regular. Fitting soft lenses is straightforward and poses no significant additional concerns for contact lens fitters. My experience indicates that the ring segments, although elevated in the corneal periphery, do not necessarily disrupt the draping, centration, movement, or tolerance of soft toric or spherical lenses.
One case report described a patient who had an unsuccessful postoperative result and was initially fit with a piggyback lens system that resulted in good vision. She chose to sacrifice vision for comfort and was ultimately fit in a spherical soft lens that provided 20/40 visual acuity (Uçakhan, 2006).
The opportunity to be fit with a soft lens is an ideal result for a patient who is intolerant to GP lenses, but is not always practically achieved following intracorneal ring inserts. In my opinion, the patient should never proceed to intracorneal ring segment surgery expecting to wear a soft lens postoperatively—it is more like icing on the cake. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #174.
Dr. Szczotka-Flynn is an associate professor at the Case Western Reserve University Dept. of Ophthalmology & Visual Sciences and is director of the Contact Lens Service at University Hospitals Case Medical Center. She has received research funding from Ciba, Vistakon, Alcon, and CooperVision.
Contact Lens Spectrum, Issue: May 2010