[Ocular prosthetics. Fitting, daily use and complications]. / Augenprothetische Versorgung. Anpassung, Handhabung und Komplikationen.

BACKGROUND: Ocular prosthetics make a decisive contribution to the functional, esthetic and psychosomatic rehabilitation of patients after ocular extirpation. OBJECTIVES: This article provides an overview of the fitting, daily care and complications of ocular prosthetics. METHODS: The study comprised a PubMed literature review and own clinical results. RESULTS: Ocular prosthetics made from cryolite glass or perspex can be manufactured and fitted 5-8 weeks after removal of the eye. During this period a conformer is placed within the conjunctival sac in order to prevent scar formation and shrinking of the socket. Artificial eyes can be worn continuously, only interrupted by a short but regular cleaning procedure. Artificial tears and lid hygiene improve the comfort of wearing. Glass prostheses have to be renewed every 1-2 years, while perspex prostheses need to be polished once a year. Complications, such as giant papillary conjunctivitis or blepharoconjunctivitis sicca are facilitated by poor fit, increased age and inappropriate care of the prosthetic device. In the case of socket shrinkage or anophthalmic socket syndrome, surgical interventions are needed to re-enable the use of an artificial eye. CONCLUSION: Adequate fitting, daily care of ocular prosthetics and therapeutic management of associated complications are mandatory for a durable functional, esthetic and psychosomatic rehabilitation after ocular extirpation.

The role of aspartate-235 in the binding of cations to an artificial cavity at the radical site of cytochrome c peroxidase.

The activated state of cytochrome c peroxidase, compound ES, contains a cation radical on the Trp-191 side chain. We recently reported that replacing this tryptophan with glycine creates a buried cavity at the active site that contains ordered solvent and that will specifically bind substituted imidazoles in their protonated cationic forms (Fitzgerald MM, Churchill MJ, McRee DE, Goodin DB, 1994, Biochemistry 33:3807-3818). Proposals that a nearby carboxylate, Asp-235, and competing monovalent cations should modulate the affinity of the W191G cavity for ligand binding are addressed in this study. Competitive binding titrations of the imidazolium ion to W191G as a function of [K+] show that potassium competes weakly with the binding of imidazoles. The dissociation constant observed for potassium binding (18 mM) is more than 3,000-fold higher than that for 1,2-dimethylimidazole (5.5 microM) in the absence of competing cations. Significantly, the W191G-D235N double mutant shows no evidence for binding imidazoles in their cationic or neutral forms, even though the structure of the cavity remains largely unperturbed by replacement of the carboxylate. Refined crystallographic B-values of solvent positions indicate that the weakly bound potassium in W191G is significantly depopulated in the double mutant. These results demonstrate that the buried negative charge of Asp-235 is an essential feature of the cation binding determinant and indicate that this carboxylate plays a critical role in stabilizing the formation of the Trp-191 radical cation.