Purpose-Identify recipient factors which may be related to risk of corneal graft failure Design-Multi-center prospective, double-masked, controlled clinical trial Participants-1090 subjects undergoing corneal transplantation for a moderate risk condition (principally Fuchs' dystrophy or pseudophakic corneal edema) Methods-Donor corneas were assigned using a random approach without respect to recipient factors, and surgeons were masked to information about the donor cornea including donor age. Surgery and post-operative care were performed according to the surgeons' usual routines and subjects were followed for five years. Baseline factors were evaluated for their association with graft failure.Main Outcome Measures-Graft failure, defined as a regraft or a cloudy cornea that was sufficiently opaque to compromise vision for a minimum of three consecutive months.

Free-living and parasitic protozoa are known to harbor a variety of endosymbiotic bacteria, although the roles such endosymbionts play in host survival, infectivity, and invasiveness are unclear. We have identified the presence of intracellular bacteria in 14 of 57 (24%) axenically grown Acanthamoeba isolates examined. These organisms are gram negative and non-acid fast, and they cannot be cultured by routine methodologies, although electron microscopy reveals evidence for multiplication within the amoebic cytoplasm. Examination for Legionella spp. with culture and nucleic acid probes has proven unsuccessful. We conclude that these bacteria are endosymbionts which have an obligate need to multiply within their amoebic hosts. Rod-shaped bacteria were identified in 5 of 23 clinical Acanthamoeba isolates (3 of 19 corneal isolates and 2 of 4 contact lens isolates), 4 of 25 environmental Acanthamoeba isolates, and 2 of 9 American Type Culture Collection Acanthamoeba isolates (ATCC 30868 and ATCC 30871) previously unrecognized as having endosymbionts. Coccus-shaped bacteria were present in one clinical (corneal) isolate and two environmental isolates. There was no statistical difference (P > 0.8) between the numbers of endosymbiont strains originating from clinical (26% positive) and environmental (24% positive) amoebic isolates, suggesting that the presence alone of these * Corresponding author.

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Early diagnosis and wide epithelial debridement are important elements in the successful treatment of Acanthamoeba keratitis. Recommended therapy would include the cationic antiseptic agents, chlorhexidine or PHMB in combination with propamidine isethionate and neomycin as part of triple therapy. Surgical intervention should be avoided until a medical cure has been achieved.

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