Corneal neovascularization (CNV) is an encroachment of new blood vessels from the limbus onto the cornea (Sweeney, 2013). CNV is a relatively common condition (prevalence ~4%) that is usually asymptomatic until the blood vessels begin to obscure the visual axis (Wong et al, 2003; Abdelfattah et al, 2015). While CNV development may stem from injury, surgery, or infection (Abdelfattah et al, 2015), CNV most commonly occurs from oxygen deprivation secondary to soft contact lens (CL) use (Abdelfattah et al, 2015). With the advent of more breathable silicone hydrogel soft CLs (Sweeney, 2013), CNV is now less common than it once was, though we should still monitor for CNV to rule out CL abuse and poorly fitting CLs.

Mechanism

CNV development typically begins with limbal hyperemia, which develops secondary to limbal hypoxia, a poorly fitting CL (tight or excessive mechanical interaction), or toxicity (Figure 1) (Sweeney, 2013). Chronic stimuli can then cause vessels to sprout from the pericorneal plexus and grow into the superficial cornea (Sweeney, 2013; Abdelfattah et al, 2015).

If the stimuli persist, fragile blood vessels (bright red and well defined) may grow deep into the corneal stroma; in severe cases, the blood vessels may hemorrhage and cause additional visual obstruction (Wong et al, 2003; Abdelfattah et al, 2015). If the stimuli are removed, the blood vessels often, though not always, regress to form ghost vessels (blood vessels that are still present without blood) (Sweeney, 2013).

Risk Factors

Each patient has a different level of susceptibility to CNV (Liesegang, 2002), though lens diameter, material, and wear schedule likely impact the risk of developing CNV (Sweeney, 2013; Abdelfattah et al, 2015). Smaller-diameter CLs are less risky compared to larger-diameter CLs because smaller-diameter CLs interact less with the limbus (Abdelfattah et al, 2015).

CLs with higher oxygen transmissibility (Dk/t) are less likely to cause CNV because more oxygen reaches the cornea with higher-Dk/t CLs (Abdelfattah et al, 2015). Similarly, continuous wear CLs are more likely to cause CNV compared to daily disposable CLs because continuous wear CLs result in more chronic oxygen deprivation (Abdelfattah et al, 2015). Likewise, higher-minus-power CLs have thicker peripheries, which also decrease oxygen transmission to the limbus (Lee et al, 2014).

There is also some evidence that dry eye patients have an increased risk for CNV because dry eye may promote the inflammatory reaction leading to CNV (Nomura et al, 2004).

Conclusion

Because chronic limbal redness is a hallmark sign of CL irritation and pre-CNV, we should regularly monitor for it (Sweeney, 2013). If marked limbal redness or CNV is noticed, switch patients to a material with a higher Dk/t or to a daily disposable. In extreme cases, discontinue CL use (Lee et al, 2014).

Furthermore, all CL wearers should be reminded that there are risks related to wearing CLs, and because of this, they should seek annual eye exams to monitor for and circumvent conditions such as CNV before they develop into a vision-threatening problem that could prevent them from wearing CLs (Lee et al, 2014). CLS

For references, please visit www.clspectrum.com/references and click on document #266.