To the Editor. —There are many patients who have seriously reduced vision due to pathological changes predominantly localized at or near the corneal surface. Thus, in ocular pemphigus and the Stevens-Johnson syndrome the epithelium can be severely irregular due to the dry keratinized epithelium, whereas the stromal scarring may be minimal and edema is usually absent. Similarly, after chemical burns an irreversibly damaged epithelium, sometimes with a vascularized pannus, may be the main cause of the visual reduction. Treatment of these conditions is notoriously difficult. Keratoplasty is usually futile. In the severe cases corneal or scleral contact lenses which would eliminate irregular astigmatism and reduce surface evaporation are often either difficult to fit or tolerate, or they are of no benefit due to the surface opacity. If the pathological epithelium in these conditions can be removed centrally and replaced permanently with a water-impermeable alloplastic membrane with a smooth surface, vision