What are mucin balls and are they of clinical significance?

Mucin balls are spherical translucent particles of debris (20 to 200 m in size) which form between the epithelium and the posterior surface of a contact lens.

Although, occasionally observed with conventional hydrogel materials, mucin balls are much more common with silicone hydrogels.

Mucin balls are blinked away following lens removal but often leave temporary depressions or imprints in the epithelium. These depressions fill with fluoroscein as occurs with dimple veiling from rigid lens wear.

Mucin ball appearance is a common patient-specific finding. Mucin balls are more likely to be present in patients who have steeper corneas (ie. a relatively flatter lens/cornea fitting relationship).

Mucin balls have been shown to have no impact on physiological response, comfort or ability to wear lenses on an extended wear basis. When excessive amounts of mucin balls are observed, patients may be managed with the use of lubricating drops and reducing the number of consecutive nights of extended lens wear. Lenses may also be removed during the day, cleaned, rinsed and reinserted.

The proposed etiology of mucin balls is a reduction of aqueous in the tear film from overnight wear, resulting in the formation of a mucin-rich viscous substance which rolls up into spheres due to the intrinsic surface tension forces associated with the cornea-lens interaction.