R. bras. Ci. Vet., v. 11, n. 1/2, p. 113-115, jan./ago. 2004 113 Ulcerative keratitis and keratomalacia in a dog caused by papain: a case report Paula Diniz Galera,* Robert J. Munger,** José Luiz Laus*** Abstract Corneal ulceration with keratomalacia (corneal melting) is a serious disorder that can produce blindness. A one-year-old male miniature Pinscher cross dog was presented with corneal edema caused by accidental exposure of the eye to papain (from papaya tree). Ophthalmic exam revealed severe corneal edema and keratomalacia in the left eye. This report describes the successful clinical management of the case with preservation of the cornea and vision. Keywords: melting, keratomalacia, cornea, ulcerative keratitis, papain. Resumo Ulceração corneana com ceratomalácia (melting corneano) é uma séria afecção ocular que pode resultar em perda da visão. Um cão mestiço de miniatura Pinscher, macho, com um ano de idade, foi atendido apresentando edema de córnea decorrente de exposição acidental do olho à papaína, proveniente do leite de mamão papaia. O exame oftálmico revelou edema corneano grave e ceratomalácia no olho esquerdo. Este relato descreve o sucesso do tratamento adotado, com a preservação da córnea e da visão. Palavras-chave: melting, ceratomalácia, córnea, ceratite ulcerativa, papaína. Introduction Corneal ulcers related to collagenase and proteases activity may present with progressive stromal dissolution or keratomalacia (corneal melting). Keratomalacia is a complicating component of the ulcers rather than a specific keratopathy (Whitley & Gilger, 1999). Such progressive stromal ulceration is a disorder of unique seriousness that can cause blindness (Nasisse, 1985), the physiological mechanisms responsible for melting and repair have been described (Fini et al., 1998). The physiological process of stroma dissolution caused by the activity of proteolytic substances were described (Wolfer & Gahn, 1994). Proteases and collagenases are normally produced during corneal healing to facilitate the removal of devitalized cells and debris from the cornea. Corneal epithelium cells, fibroblasts, polymorphonuclear leukocytes, some bacteria and possibly some fungi produce proteases and collagenases (Whitley & Gilger, 1999), and recent studies have identified metalloproteinase matrixes as the most active enzymes (Wagoner, 1997; Fini et al ., 1998). It has been suggested that those enzymes take part in all stages of a corneal ulceration from the beginning of the epithelial defect up to the resolution of the ulcer (Fini et al., 1998). Papain is the dry, purified latex from the Carica papaya fruit and is called “vegetal pepsin” since it contains enzymes which are similar to pepsin. However, unlike pepsin, which acts only on acid cultures (Corbett, 1982), papain acts on acid, neutral, or alkaline cultures. Papain contains several enzymes including peptidase I, which can change proteins into dipeptides or polypeptides (Robbers et al., 1997). Chemical injuries cause damage to the corneal epithelium and to the anterior segment of the eye, which can lead to permanent reduction of visual acuity (Wagoner, 1997). The initial management for corneal injuries caused by chemical substances consists of abundant irrigation to remo- ve the substance (Donzis & Mondino, 1987). Management of severe ulcerative keratitis with progressive melting demands vigorous topical therapy with control of infection and neutralization of the activity of collagenase and other proteases on the cornea (Whitley & Gilger, 1999). The efficacy of collagenase inhibitors in treating keratomalacia has been questioned (Wolfer & Grahn, 1994). Clinically they seem to have their major beneficial effect during the first 48 to 72 hours of the ulcerative process (Whitley & Gilger, 1999). Acetylcysteine, cystein, sodium citrate, tetracycline ascorbate, tetracycline, EDTA, penicillin, heparin and fresh autogenous serum have been advocated for their anti-collagenase activity (Wolfer & Grahn, 1994; Whitley & Gilger, 1999) . Acetylcysteine and serum are the most commonly utilized collagenase inhibitors in the clinical management of melting corneal ulcers. Additional adjunctive therapies to antimicrobial therapy include the application of epidermal growth factor (Swank & Hosgood, 1996), fibronectin, and tissue adhesives. Depending on the severity and progression of the corneal ulcer, surgical treatment * DVM, MSc, Associate Professor –UPIS/ Brasília, DF; Ophthalmology Unit – Department of Medicine and Surgery– College of Agricultural and Veterinarian Sciences – São Paulo State University – Jaboticabal, SP –- Brazil ** DVM, Diplomate American College of Veterinary Ophthalmologists – Animal Ophthalmology Clinic - Dallas Texas – USA *** DVM, MSc, PhD; Ophthalmology Unit – Department of Medicine and Surgery– College of Agricultural and Veterinarian Sciences – São Paulo State University – Jaboticabal, SP – Brazil http://dx.doi.org/10.4322/rbcv.2014.356