Reader and Industry Forum
GP Custom Edge Modification for Fitting Irregular Corneas
By Thomas Devetski, OD
Rehabilitating vision in patients who have irregular corneas using contact lenses is among the most difficult tasks that contact lens practitioners face. Without question, rigid lenses provide the best potential for normal vision. But the rigid nature and spherical dimensions of a standard GP lens on an irregular cornea can lead to complications and potential lens-wear failure. Central lens-to-cornea modifications are accomplished through simple changes to the base curve and optic zone (OZ), but the peripheral fitting relationship is often difficult to perfect on these irregular corneas.
Over the past few years, specialty lens designers have introduced technology that allows for customized peripheral curve modifications. Specialty keratoconus lens designs such as QuadraKone (Truform Optics) and Rose K2 (Menicon/Blanchard Contact Lens) offer the ability to change the circumferential edge lift independent of the base curve and diameter with quadrant-specific steepening or flattening to improve the fitting relationship.
In our practice, we have used the Rose K2 lens extensively to reduce the negative impact of a less-than-ideal fitting relationship. Along with adjustable edge lift, which affects the entire lens, toric peripheral curves (TP) and Asymmetric Corneal Technology (ACT) are available to improve the fitting relationship and to allow many patients who have irregular corneas to either return to wearing GP lenses or to successfully begin wearing them. Use of these modifications can significantly improve their comfort, wearing time, and corneal health.
The purpose of this article is to demonstrate the effects of two of these modifications on patients who experienced complications from GP lenses worn for keratoconus. Patient #1 was experiencing increasing discomfort with reduced wearing time, and Patient #2 was having difficulty with lens stability—the lens was uncomfortable and would dislodge and fall out. Both had previously been successfully wearing Rose K2 contact lenses without any specialty edge modifications.
Toric Peripheral Curve
The Rose K2 TP system affects the peripheral 1mm of the lens and allows for edge lift to be increased (flattened) at polar meridians while at the same time steepening the edges at the opposite polar meridians. The standard difference between meridians is 0.8mm but can be varied from 0.4mm to 1.33mm.
The habitual lens that Patient #1 had been wearing successfully was now causing 3 o'clock and 9 o'clock staining and conjunctival injection due to edge chafing along the flat 180 meridian (Figure 1). He reported his wearing time was now reduced to two hours. Using the maximum TP value (1.33mm) with the same base curve and diameter, Patient #1 was able to regain comfort, reduce conjunctival injection and staining, and has increased his wearing time to 12 hours. The fluorescein pattern is more uniform at the periphery with better edge lift at the 3 o'clock to 9 o'clock meridian (Figure 2).
Figure 1. Patient #1's habitual lens, which caused chafing along the horizontal meridian.
Figure 2. Using the TP modification, Patient #1's lens shows a more uniform peripheral fluorescein pattern.
Asymmetric Corneal Technology
Typically, the ectasia resulting from keratoconus will present a fitting dilemma at the inferior aspect of the cornea. Attempts to match the extreme steepening at the 6 o'clock position with a standard GP edge design will result in chafing and erosion at the other clock positions or conversely, matching the normal curvature of the superior cornea leaves an area of extreme edge lift inferiorly. The ACT system allows for reduced edge lift or tightening at the 6 o'clock position independent of the rest of the lens. The system includes three grades of ACT (0.7mm, 1mm, and 1.3mm steepening) for increasing severity of edge lift.
Slit lamp examination of Patient #2 wearing her habitual lens showed that her inferior cornea had steepened, which caused the lens edge to lift off the cornea, allowing it to catch on the lower lid and eject spontaneously (Figure 3). To improve the fitting relationship, we used grade 2 ACT to create a better alignment with the inferior cornea. Patient #2 was able to wear the lens comfortably without it dislodging (Figure 4).
Figure 3. Patient #2's habitual lens with inferior edge lift that caused lens ejection.
Figure 4. Modifying Patient #2's lens using ACT allowed it to align better with the inferior cornea.
Satisfy All Patient Needs
Success or failure with specialty contact lenses is always a function of both vision and comfort. A patient who can see 20/15 but can't stand to wear the lenses for more than an hour or two is not a success. We must strive to use all means available to successfully fulfill both criteria. Utilizing customized peripheral modifications to match the contour of an irregular cornea will allow many patients who were previously unsuccessful to attain excellent vision with much improved comfort and corneal health. CLS
Dr. Devetski is currently practicing in a multi-specialty group practice in Burlington, N.C., and specializes in the fitting of medically necessary contact lenses. He was previously the director of the Contact Lens Service at the University of North Carolina School of Medicine. You can reach him at firstname.lastname@example.org.