THERE ARE U.S. Food and Drug Administration (FDA)-approved, therapeutic bandage contact lens (BCL) options that can be used for the management of pain and healing following corneal cross-linking (CXL), post-refractive surgery, or other corneal procedures. However, these commercially available silicone hydrogel (SiHy) materials are manufactured with a sagittal height (sag) range that fits the average ocular sagittal height and horizontal visible iris diameter (HVID) of 11.8mm to 12.0mm, which applies to approximately 77% of eyes (Caroline and André, 2002). They generally come in one or two base curve (BC) options and one diameter.
This means that almost one-quarter of your patient base consists of outliers for these standard BCLs based on corneal size alone. Add in the complexity of needing to place a BCL on the eye of a patient who has a steep and irregular cornea due to keratoconus or a flatter cornea due to refractive surgery, and what was thought to be a no-brainer since there are only three options (lotrafilcon A, balafilcon A, and senofilcon A) can become a head-scratcher.
Although a BCL is usually only needed for 48 to 72 hours, and sometimes no more than one week, to facilitate corneal re-epithelialization after these surgical procedures, it’s important that the BCL fully covers the cornea, has minimal movement, and can stay on the eye. Fluting at the edge of the BCL (Figure 1) or excessive movement can indicate the lens is not the appropriate diameter or sagittal depth and can add to the patient’s discomfort during the early postoperative period.
When it comes to fitting soft contact lenses (CLs), BCLs not excluded, the goal is to match the sagittal height of the cornea with the sagittal height of the CL. Corneal curvature is not the only major predictor of sagittal height; instead, it’s also impacted by corneal diameter, asphericity, and scleral shape (Young, 1992).
However, the BC, not CL-sag value, is found on the blister pack of mass-produced CLs. Ultimately the BC is “just a number”; not only is it a poor predictor of sagittal height, but it is also a poor representation of lens curvature (Ngo and Nichols, 2017). Yet, practitioners rely on the central keratometry values when choosing the BC of an initial lens even though research has indicated that it doesn’t contribute to how well a lens will fit (Young et al, 2010).
Despite this antiquated approach, there’s a high probability of “getting lucky” and a chosen BCL fitting well for a random patient. However, in irregular or surgically altered corneas, luck can run out.
The sag for 15 spherical CLs from the four major manufacturers has been measured by researchers using spectral domain optical coherence tomography (van der Worp et al, 2021). These published charts can serve to guide practitioners when selecting an approved BCL or opting to choose an alternative SiHy CL to be used off-label when a BCL is not fitting as expected.
For example, consider a patient who has a 12.5mm corneal diameter and a steeper cornea due to advanced keratoconus is undergoing CXL but the BCL keeps falling out causing patient discomfort. The chart can be referenced to choose a CL that has a substantially higher sag value versus simply choosing an alternate BCL that may have the exact BC but could, in fact, have a lower sag value (lotrafilcon A has 110µm lower sag than senofilcon A, compared to off-label fanfilcon A that has 253µm more sag than lotrafilcon A; notably, all three materials have the same 8.4 BC designation). This provides a fresh and more scientific perspective to BCL selection for postsurgical patients.
REFERENCES
1. Caroline P, André M. The Effect of Corneal Diameter on Soft Lens Fitting, Part 1. Contact Lens Spectrum. 2002 Apri;17:56.
2. Young, Graeme. Ocular Sagittal Height and Soft Contact Lens Fit. J BCLA. 1992;15(1):45-49.
3. Ngo W, Nichols JJ. How Important Is the Soft Lens Fit Anyway. Contact Lens Spectrum. 2017 Sept;32:36-38,40,41.
4. Young G, Schnider C, Hunt C, Efron S. Corneal topography and soft contact lens fit. Optom Vis Sci. 2010 May;87:358-366.
5. Van der Worp E, Lampa M, Kinoshita B, Fujimoto MJ, Coldrick BJ, Caroline P. Variation in sag values in daily disposable, reusable and toric soft contact lenses. Cont Lens Anterior Eye. 2021 Dec;44:101386.
