Cataract Surgery Preparation In RGP Contact Lens User
Contact lens development has undergone many iterations over the last few hundred years. After the introduction of rigid plastic contact lenses in polymethyl methacrylate (PMMA), the invention of the rigid gas permeable (RGP) contact lens revolutionized the use of plastics in contact lenses and helped with lens flexibility and oxygen permeability. It was initially assumed that only PMMA lenses caused corneal warpage. However subsequent studies showed that multiple types of plastic contact lens materials, including both RGPs and soft contact lenses, also caused corneal warpage and thus can affect overall corneal curvature. 
The definition of corneal warpage has evolved over time as keratography has advanced from the measurement of four paracentral points to computer-assisted videokeratography. It was first characterized by Harstein as the development of with-the-rule astigmatism with contact lens usage. Levenson also observed increased flattening of the horizontal meridian in his patients, while Levenson and Berry noted a combination of irregular and regular corneal astigmatism. Eventually, Wilson et al. defined corneal warpage as central irregular corneal astigmatism, loss of radial symmetry, and reversal of the normal pattern of progressive flattening from the center to the periphery, which is the definition that has been widely adopted in the modern literature.
Differentiating corneal warpage from keratoconus
With the advent of more advanced topographical mapping of the cornea, it was noted that there was considerable overlap in topographical corneal changes between keratoconus (KCN) and corneal warpage from RGPs, including irregular astigmatism with inferior steepening and even a scissoring reflex on retinoscopy. As RGPs are used in the correction of irregular astigmatism in KCN, it is important to distinguish the two entities in the preoperative workup of a new cataract patient. Tang et al. noted that rather than focal corneal epithelial thinning in KCN, there was focal epithelial thickening in corneal warpage, along with no significant change in pachymetry. This led to their development of the Warpage Index, used to measure the combination of anterior focal steepening and focal epithelial thickening noted in contact lens-related warpage, with a positive Index score indicating corneal warpage.
Preparing patients who use contact lenses for cataract surgery
As corneal warpage can affect corneal topographic measurements, taking accurate measurements preceding cataract surgery can be challenging. Multiple studies have been done to understand the time to recovery of the corneal warpage, with a focus on refractive stability in the context of refractive surgery. The findings for rigid contact lenses are summarized in Table 1 and for soft contact lenses in Table 2. Common consensus is that there must be stabilization of the corneal map and refraction out of contact lenses to ensure accurate intraocular lens calculations for cataract surgery. For rigid contact lens users, it is reasonable to be out of contact lenses for at least 4 weeks or for 1 month for every decade of contact lens wear and for soft contact lenses, a shorter contact lens free period of at least 2 weeks is typically adequate for the cornea to stabilize. It is important to note that time to refractive stability after contact lens wear can vary widely. This is especially important if the goal after cataract surgery is to be independent from use of contact lenses.
Table 1: Time to refractive stability with rigid contact lens use
|Study||Time to refractive stability||Definition of refractive stability|
|Wang et al.||Average of 8.8±6.8 weeks, recovery time of 1 to 20 weeks||Manifest refraction change ≤0.5 diopters (D), keratometry change ≤0.5 D, corneal topography pattern normalization|
|Tsai et al.||Majority of eyes by 6 weeks after CL discontinuation, 78% by 9 weeks (longer time period for those with longer period of CL wear)||Manifest refraction change ≤0.25 D sphere or cylinder, <25° change in orientation of axis|
|Budak et al.||5 weeks for RGPs, 2 weeks for SCLs||Manifest refraction change ≤0.5 D of sphere or cylinder|
|Pannu et al.||6 weeks||Any changes in topography or refraction|
Table 2: Time to refractive stability with soft contact lens use
|Study||Time to refractive stability||Definition of refractive stability|
|Wang et al. ||Average of 11.5±8.5 weeks (w) for soft extended-wear, soft toric 5.5±4.9 w, soft daily 2.5±2.1 w, recovery time of 1 to 20 weeks||As above (Table 1)|
|Hashemi et al.||3 days to 2 weeks, preferably wait 1-2 weeks before evaluation||Manifest refraction change ≤0.5 D sphere or cylinder, keratometry change ≤0.5 D, corneal topography pattern normalization|
|Rayess et al.||7 to 21 days, preferably wait 3 weeks before evaluation (for both hydrogel and silicone hydrogel CLs)||Manifest refraction change <0.5 D sphere or cylinder, keratometry change <0.5 D, corneal topography pattern change <0.5 D in central 3 mm|
|McKernan et al.||2 weeks||Pentacam measurements 2 weeks apart showing resolution of inferior corneal steepening (on Tangential inferior curvature)|
|Ng et al.||2 weeks by manifest refraction, 4-6 weeks by keratometry, topography or pachymetry||Manifest refraction change <0.5 D spherical equivalent or cylinder, keratometry change <0.5 D, corneal topography change <0.5 D in central 3 mm, <8mm change in pachymetry|
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