Conjunctival dysplastic processes probably arise secondary to chronic irritative stimuli such as solar irradiation.  Clinically, these lesions are thickened and leukoplakic(#21889).  Histopathologically, the atypical cells first appear along the basal layer and then progress to involve more and more of the epithelium until the entire epithelium is replaced by abnormal cells (#21892, #21891).  The amount of cellular dysplasia can be sub-classified as mild, moderate, and severe.  Mild atypia involves less than 25-33 % of the epithelium.  Moderate atypia involves 33-75 % of the epithelium.  Severe atypia involves greater than 75% of the epithelium.