A Hypothesis for the Aetiology of Soft Contact Lens-Induced Superior Arcuate Keratopathy

Graeme Young, Dorla Mirejovsky ICLC 20:177-180, 1993

Complications that occur with soft contact lenses are generally described as mechanical, inflammatory, infectious or multifactorial in nature. With any complication, it’s extremely important to try and determine the underlying cause in order to facilitate both prevention and treatment.

The paper published by Graeme Young and Dorla Mirejovsky in the September/October 1993 issue of the ICLC journal investigates the aetiology of soft contact lens-induced superior arcuate keratopathy, also known as epithelial splitting or superior epithelial arcuate lesions (SEAL). This paper presents a hypothesis for the formation of this particular type of keratopathy and provides two supporting clinical examples. The authors also discuss which factors might contribute to this complication and how it can be prevented from recurring.

To align properly with the cornea and perilimbal sclera, soft contact lenses are required to have a certain amount of flexure in order to drape over the steeper cornea and flatten over the sclera. The authors propose that when the elastic modulus of the contact lens material is high, or when the lens periphery is thick, the lens is unable to align to the “S” shaped contour of the eye (from the central cornea to the limbus to the sclera). Consequently, it’s forced to take on a compromised “S” shape, which does not exert pressure evenly over these areas. Specifically, pressure is exerted by the lens at a point on the peripheral cornea, at a small distance in from the limbus. In the case of the superior cornea, under the force exerted by the upper lid, the lens is pressed against the epithelium.

The authors further explain that this pressure exerted by the upper lid forces the tear fluid out from underneath the lens and causes greater than usual mechanical forces, particularly frictional force, by the blinking action of the eyelid over this area. It’s also further postulated that this pressure is exacerbated by post-lens tear film instability at the lens interface due to a lower wettability of the lens relative to the cornea.

This paper provides two examples showing low-water content soft lenses on eyes that have sustained a SEAL secondary to contact lens wear. Fluorescein was instilled behind the lenses to observe the post-lens tear film and provide insight into the lens-cornea fitting relationship. In both cases, the cornea showed an arcuate band of touch in the superior region, continuing the circumferential line of the superior arcuate staining. The authors explain that this band of touch corresponds to the area where negative pressure was the greatest, due to the extra pressure provided by the superior lid, and that this in turn led to mechanical irritation.

The hypothesis proposed by the authors for the mechanism of a contact lens-related SEAL is primarily mechanical trauma to the superficial epithelial cells as a result of inadequate lens flexure. This explanation accounts for the characteristic pattern and location of arcuate staining seen with a SEAL. Hence, the authors suggest that materials with high elastic modulus, thick lenses, designs that do not incorporate peripheral flattening, high levels of lens dehydration resulting in material stiffening, corneas of larger sagittal height and post-lens tear film instability can all lead to SEAL formation. Along the same lines, eliminating or minimizing these factors should reduce the likelihood of this complication and provide a treatment strategy.

In accordance with this hypothesis, the introduction of high-Dk silicone hydrogel lenses, due to their stiffer modulus, could increase the risk of SEAL formation. In fact, early published clinical trials with silicone hydrogels suggest a greater incidence of this complication compared to conventional hydrogel materials (1). Poor wettability and tighter fitting contact lenses have also been reported to be contributing factors (2). The feature article by Young and Mirejovsky, discussing conventional hydrogel lenses, as well as more recent published articles on high-Dk silicone hydrogel lenses (1-6), continue to help advance our understanding of SEALs, which is particularly important as new and improved materials are developed and put into the marketplace.

References:

1. Dumbleton K, Fonn D, Jones L, Williams-Lyn D, Richter D. Severity and management of contact lens related complications with continuous wear of high-Dk silicone hydrogel lenses. Optom Vis Sci 2000;77(12s):216.
2. O'Hare N, Stapleton F, Naduvilath T, Jalbert I, Sweeney DF, Holden BA. Contact lens-ocular surface interactions in superior epithelial arcuate lesions (SEALs). Cornea 2000;19(6):s110.
3. Dumbleton K. Noninflammatory silicone hydrogel contact lens complications. Eye Contact Lens 2003; Jan;29(1 Suppl):S186,9; discussion S190-1, S192-4.
4. Holden BA, Stephenson A, Stretton S, Sankaridurg PR, O'Hare N, Jalbert I, et al. Superior epithelial arcuate lesions with soft contact lens wear. Optom Vis Sci 2001; Jan;78(1):9-12.
5. Jalbert I, Sweeney DF, Holden BA. Epithelial split associated with wear of a silicone hydrogel contact lens. CLAO J 2001; Oct;27(4):231-3.
6. O'Hare N, Stapleton F, Naduvilath T, Jalbert I, Sweeney DF, Holden BA. Interaction between the contact lens and the ocular surface in the etiology of superior epithelial arcuate lesions. Adv Exp Med Biol 2002;506(Pt B):973-80.