Have you ever had a patient ask why soft contact lens (CL) selection matters? This is a question I frequently encounter in clinic. I usually respond by educating my patients that while soft CLs may all look similar, they are made of different materials and have different shapes, which could negatively affect the eye if a poor selection is made (Dumbleton, 2002). Although I generally do not describe material details to my patients, a prescriber should consider CL properties such as modulus, especially when complications arise.
CL modulus (cross-sectional stress/strain) is a measure of the material’s stiffness (Horst et al, 2012). The modulus of a CL is affected by factors such as its water content (lower water content = higher modulus) and temperature (higher temperature = lower modulus) (Horst et al, 2012). Regular use of care systems may also have a variable impact on modulus (Young et al, 2010).
This information is important because a higher CL modulus increases a wearer’s risk for developing some ocular complications (Dumbleton, 2002). The following is a review of the most commonly cited conditions associated with high-modulus soft CLs.
Superior Epithelial Arcuate Lesions (SEALs) SEALs present as superficial corneal lesions that stain with sodium fluorescein (Dumbleton, 2003). A SEAL is typically a white lesion that is 0.1mm to 0.3mm wide and 2.0mm to 5.0mm long; it is also about 1mm from the superior limbus, and infiltrates may be present (Dumbleton, 2002 and 2003). SEALs are typically asymptomatic, though a minor foreign body sensation may be present (Dumbleton, 2002; Holden et al, 2001). SEALs are believed to occur from mechanical interaction/pressure between the cornea and a high-modulus soft CL (Holden et al, 2001).
Mucin Balls Mucin balls (spherical, translucent balls of mucin) typically present under the superior quadrant of the CL; they are variable in size (10μm to 100μm) (Dumbleton, 2003). Mucin balls are likely generated by stiff CLs that induce shearing/mechanical forces directed toward the ocular surface that roll mucins into balls (Tan et al, 2003). Mucin balls are typically blinked away after CL removal, though they leave a transient depression that can be accentuated with sodium fluorescein (Dumbleton, 2003).
Contact Lens-Associated Papillary Conjunctivitis (CLPC) CLPC presents with hyperemia and a variable papillary response that is more visible with sodium fluorescein staining; patients typically note foreign body sensation, itching, mucous discharge, discomfort, or excessive CL movement (Dumbleton, 2003). There is debate as to whether CLPC is due to a hypersensitivity reaction or due to mechanical interaction between the cornea and a stiff CL, though both are likely involved in the CLPC pathogenesis (Donshik et al, 2008).
Corneal Erosions CL-related corneal erosions present as areas of linear or irregular epithelial debridement that likely result from CL adhesion followed by mechanical disruption of the corneal epithelium (Dumbleton, 2002 and 2003).Affected patients may experience pain, hyperemia, watering, or photophobia (Dumbleton, 2003).
The above conditions are relatively rare, though more frequent in patients who wear extended or continuous wear silicone hydrogel CLs (Dumbleton, 2003; Holden et al, 2001). In general, these conditions should first be treated by temporarily ceasing CL use (Dumbleton, 2003). If a corneal break or infiltrate is present, antibiotic or immunosuppressive drugs may be considered, though these measures are likely unnecessary (Dumbleton, 2003).
In most cases, the conditions resolve by simply stopping CL use (Dumbleton, 2003). If the condition recurs after restarting CL use, the prescriber should consider changing to a lower-modulus material, switching to daily disposable CLs, or, in rare circumstances, ceasing CL use altogether (Dumbleton, 2002). CLS
For references, please visit www.clspectrum.com/references and click on document #262.