A New Option for Fitting Post-Surgical Corneas
A New Option for Fitting Post-Surgical Corneas
A new reverse curve hybrid lens offers practitioners another option for successfully fitting irregular corneas.
By Michael DePaolis, OD, FAAO
Dr. DePaolis practices at Visionary Eye Associates in Rochester, New York, and is an adjunct faculty member of the University of Rochester Medical Center.
Our practice has witnessed a steady increase in the number of patients who require optical correction after refractive surgery. It's not surprising given the rapid ascent of LASIK and the fact that more than 10 million Americans have undergone some form of corneal refractive surgery. This trend may be further accentuated as this modality gains popularity and patients are offered additional incentives to consider refractive surgery.
While refractive surgery has become an extremely safe and effective modality, perfect results are not inevitable.
Post-Surgical Patient Population
In 2006, 1.2 million LASIK procedures were performed in the United States alone (2006 Comprehensive Report on The Global Refractive Surgery Market). The majority of these procedures were successful with a positive outcome. However, due to the intrinsic nature of refractive surgery and the innate variability of wound healing, some patients experience unexpected outcomes and challenges. In fact, estimates indicate that 2 percent of post-refractive surgery patients need further visual correction.
Most patients who have a suboptimal refractive surgical outcome or who have developed post-surgical ectasia are distraught and reticent to undergo additional surgery. Additionally, many of these individuals have a history of contact lens intolerance and are skeptical of returning to this modality. For these and other reasons, post-surgical oblate corneas can be a technical and emotional challenge for contact lens prescribers.
Figure 1. SynergEyes PS lift options demonstrate how adjusting the Lift allows fine tuning of the lens design to optimize fit.
We all have these special patients in our practices, whether we see only a handful every year or a consistent number on a weekly basis. While each patient presents a unique challenge, a common thread is the significant role contact lenses play in managing the visual needs of this growing population.
Post-Surgical Fitting Challenges
Post-refractive surgery irregular corneas can be challenging from both an anatomical and a visual needs perspective. Spectacle correction often fails to address the complex optical issues these patients experience, and soft contact lenses, while achieving a successful physical fit, generally do not provide stable visual correction. Simply put, rigid lens optics are necessary to optimize visual acuity and minimize diurnal fluctuations.
Figure 2. Apical clearance with the SynergEyes PS lens.
Contemporary GP designs provide us with a variety of reverse geometry options that are available in high-DK materials, but these don't always meet all the criteria for a successful fit. A successful post-surgical contact lens must provide an acceptable physiological fit, optimal vision and an acceptable level of comfort. It's often poor comfort — especially in an individual who had hoped to eliminate contact lens wear — that limits GP lens success in this population. While intolerance is often ascribed to the rigid nature of GP lenses, post-surgical dry eye also plays a major role.
A New Hybrid Lens Option
The re-emergence of hybrid contact lens technology with the SynergEyes line of contact lenses (SynergEyes, Inc., www.synergeyes.com, 877-733-2012) has provided clinicians with a viable alternative to traditional lens designs. Through the development of a patented technology, SynergEyes has effectively addressed a number of deficiencies historically associated with hybrid lens designs. The SynergEyes design allows prescribers to fit a more diverse population, in addition to providing greater oxygen transmission in a more durable platform. Over the past two years, I believe this design has distinguished itself as a viable option for patients who have high astigmatism, keratoconus and pellucid marginal degeneration and for other irregular cornea patients.
SynergEyes PS Lens In January, SynergEyes introduced its new reverse curve hybrid design, SynergEyes PS. As one of the clinical investigators working with this new design, I found that I was able to successfully fit a variety of oblate corneas, often resulting in superior vision, comfort and stability. Many of these patients had been unable to achieve the triad of physiology, vision and comfort with any other product. There's nothing quite like being able to provide functional vision for a patient who has struggled with visual impairment.
The SynergEyes PS lens is designed with an oblate posterior surface and a 6.5mm spherical posterior optical zone. Eight base curves are available in 0.2mm steps in addition to a variable secondary curve, steeper than the base curve, called "Lift" that extends across the skirt junction to 9.0mm with the choice of flat (L1), medium (L2) or steep (L3). Figure 1 shows the different Lift options. The Lift parameter allows you to raise or lower the appropriate base curve in relationship to the oblate corneal surface. Two spherical skirt curves are also available. Table 1 shows the full range of available parameters.
Fitting SynergEyes PS
SynergEyes offers a 24-lens diagnostic set to simplify the fitting process. The set includes all base curves in each of the three Lift choices and the 8.6mm skirt curve. The diagnostic lenses are plano. Place one drop of high-molecular weight fluorescein into the lens bowl prior to lens application to evaluate the lens-to-cornea fitting relationship. The objective is to achieve apical clearance over the central cornea with little or no touch in the rigid zone of the lens (Figure 2). The landing occurs in the soft skirt with light touch at the 9mm chord diameter (Figure 3).
Figure 3. Landing occurs in the soft skirt with a light touch at the 9mm chord diameter.
Mean postoperative keratometry or simulated keratometry (derived from corneal topography) provides an excellent starting point for base curve selection. SynergEyes recommends that when selecting the initial lens, once you have determined the mean K value, round down (steeper) to the nearest base curve in the diagnostic set. Use high-molecular weight fluorescein analysis for final base curve determination. The secondary Lift variable allows for further fit refinement, thereby achieving rigid lens clearance without adherence. While not employed as a primary variable, the 8.3mm skirt provides yet another mechanism to optimize fit.
SynergEyes provides a troubleshooting guide to achieve a successful fit when either bubbles or excess touch occurs. The approach is relatively straightforward and has been successful for us and for several of our patients.
Once you achieve an ideal fluorescein pattern, over-refract to determine the final lens power.
In addition to post-refractive surgery complications, our practice cares for many patients who have irregular corneas. Whether the irregularity is associated with corneal trauma, dystrophy, infection or penetrating keratoplasty, they all fall into the same challenging category. It's always exciting to have another tool, such as SynergEyes PS, to positively impact the lives of these patients. CLS
Contact Lens Spectrum, Issue: April 2008