The ocular surface disease (OSD) can be treated with prosthetic replacement of the ocular surface ecosystem (PROSE). PROSE treatment uses custom-fabricated prosthetic devices to replace or enhance the function of the ocular surface ecosystem by improving vision and supporting the ocular surface. PROSE device is also known as the Boston scleral lens or Boston scleral lens prosthetic device. A scleral lens is a large diameter lens (17.5–25 mm) of rigid material that completely vaults the corneal surface. PROSE device creates a transparent, smooth optical surface over the irregular, damaged/diseased cornea and re-establishes a healthy ocular surface environment by creating an artificial tear reservoir that provides constant lubrication and maintains oxygen supply. The steps of PROSE treatment are discussed in this chapter. The PROSE treatment can be used to treat conditions like ocular chronic graft-versus-host disease, Stevens-Johnson syndrome and toxic epidermal necrolysis, limbal stem cell deficiency, neurotrophic keratopathy, atopic keratoconjunctivitis, persistent corneal epithelial defects and lagophthalmos.