Well-fitting GP contact lenses provide superb optics and good comfort (following the adaptation period). The key word here is “well-fitting.” Because the lenses are rigid, they can inadvertently change the shape of the cornea if the fit is not optimal, which can lead to corneal warpage.
Corneal warpage is lens-induced irregular astigmatism with a loss of radial symmetry, a reversal of normal flattening of corneal contour, and reduced vision on post-lens-wear refraction (Calossi et al, 1996). It can be caused by excessively steep base curves, spherical lenses on toric (>2.5D) corneas, and progressing corneal ectasias. Patients are often unaware of their corneal warpage. When they are wearing the lens, the tear lens can mask astigmatism and higher-order aberrations induced from surface irregularities (Tyagi et al, 2012). Once the lens is removed, patients may be unable to differentiate their habitual blur from warpage blur. Luckily, induced corneal changes are reversible with the discontinuation of lens wear.
Cease and Refit
Warpage is easily detected with corneal topography (Figure 1). The refit process, though, is more complex. Prior to the refit, lens wear must stop to allow for corneal stabilization. The time required to reach a corneal steady state after lens discontinuation is variable and dependent on the quality of the lens fit and duration of lens wear. A longer GP history and a lower quality lens fit is associated with greater corneal warpage and longer recovery time (Tsai et al, 2004; Wang et al, 2002).
A general rule-of-thumb is to discontinue lenses for one month for every decade of wear, a schedule commonly used to obtain corneal stability in GP wearers prior to refractive or cataract surgery (Wang et al, 2002). Ideally, lens wear would be discontinued and refractions and topographies taken every two to four weeks until the data is repeatable to show corneal stability.
However, many patients cannot be taken out of their lenses as their vision is not functional without them, nor is it functional in glasses alone. One option is to fit soft lenses while waiting for the corneas to stabilize. An alternative option is to refit one eye at a time, in which the better-seeing eye could continue lens wear while the fellow eye stabilizes. The refit process can then be repeated in the other eye.
Taking this extra time is necessary because a new GP refit prior to corneal stabilization will likely change over time and provide poor visual quality. If a new pair of glasses or refitting a lens prior to stabilization is absolutely necessary, be prepared for multiple visits and changes to the optical correction of choice until the cornea stabilizes. Both fitter and patient need to have patience during this transition time. CLS
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