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Purpose: This study sought to determine whether intravitreal dexamethasone with vancomycin preserves retinal function in eyes with experimental Staphylococcus aureus endophthalmitis better than intravitreal vancomycin alone., Methods: Twenty-four rabbits received intravitreal injections in both eyes with S. aureus. Right eyes were treated with intravitreal dexamethasone plus vancomycin and left eyes were treated with vancomycin alone at 24, 36, 48, or 72 hours after inoculation. Evaluation was performed by slit-lamp biomicroscopy, indirect ophthalmoscopy, and electroretinogram. Vitreous humor cultures and histopathologic examinations were performed on the eyes after the rabbits were killed., Results: The combination of intravitreal dexamethasone and vancomycin resulted in significantly less inflammation than vancomycin alone at 24 and 36 hours after inoculation, but electroretinograms showed significantly better preservation only at 36 hours after bacterial inoculation. Viable bacteria were cultured from eyes treated 48 and 72 hours after inoculation., Conclusion: Intravitreal dexamethasone was found to be beneficial by electroretinography when administered 36 hours after infection. In the authors' model, a single intravitreal injection of vancomycin with or without the addition of dexamethasone was insufficient to sterilize eyes 48 and 72 hours after bacterial inoculation.

Purpose: To study the clinical, histopathologic, and immunologic responses to Staphylococcus aureus endophthalmitis in rats., Methods: Experimental Lewis rats received an intravitreal injection of viable S. aureus (65 organisms), and control rats received sterile saline. The clinical scores, cellular infiltrate, delayed hypersensitivity reaction in skin tests, and serum and vitreous enzyme-linked immunosorbent assay titers of immunoglobulin (Ig) M, IgG, and IgA to ribitol teichoic acid (RTA), the major antigenic determinant of S. aureus cell wall, were measured and compared on days 3, 7, 10, 14, 21, and 30. The differences were statistically assessed using Mann-Whitney nonparametric t-tests and analysis of variance., Results: The red reflex was abolished in the majority of rats between days 3 and 21. Ocular inflammation resolved by day 30. The vitreous of eyes injected with S. aureus showed bacterial growth on days 3 and 7, followed by a decrease in numbers on days 10 and 14 and disappearance on days 21 and 30. In the vitreous, a peak neutrophil count was observed at day 3 that rapidly declined by day 7. The number of lymphocytes and plasma cells peaked on day 3 but declined more slowly. Plasma cells and Mott cells were seen on days 10 and 14, suggesting intraocular antibody production. IgM titers to RTA increased progressively in serum and vitreous, reached a peak on day 21, and declined on day 30. A weak IgG but absent IgA response to RTA was observed in serum and vitreous. S. aureus endophthalmitis was not associated with delayed hypersensitivity to the bacteria in skin tests., Conclusions: S. aureus endophthalmitis is associated with the infiltration of neutrophils, lymphocytes, monocytes, and plasma cells in vitreous. Neutrophils, the predominant infiltrating cells, may be involved in bactericidal activity and opsonophagocytosis. In rat staphylococcal endophthalmitis, IgM rather than IgG may be the protective antibody.

Purpose: The authors studied the role of the complement system in host defense against Staphylococcus epidermidis and S. aureus endophthalmitis., Methods: Guinea pigs in the S. epidermidis model received an intravitreal injection of 7000 viable organisms, and guinea pigs in the S. aureus model received 50 viable organisms. The experimental animals in each model were decomplemented with intraperitoneal (IP) injections of cobra venom factor, whereas the control animals received IP injections of normal saline. Mean log bacterial counts in the vitreous and mean serum complement titers were compared in the experimental and control animals in each model on days 1, 2, 3, and 7., Results: In the S. epidermidis model, mean log bacterial counts in the vitreous were significantly higher in the experimental group than the control group on days 1 and 2 (P < 0.01) and on day 3 (P < 0.05). Mean serum complement titers were significantly lower in the experimental group at all days (P < 0.01). In the S. aureus model, mean log bacterial counts in the vitreous were significantly higher in the experimental group than the control group on day 2 (P < 0.05) and day 3 (P < 0.01). Mean serum complement titers were significantly lower in the experimental group on days 1, 2, and 3 (P < 0.01), but not on day 7., Conclusion: These results suggest that decomplemented guinea pigs show impaired host defense to S. epidermidis and S. aureus endophthalmitis and that this defense is restored as complement levels approach normal.

Although Staphylococcus epidermidis is the most common cause of postoperative pseudophakic endophthalmitis, little is known about the immune response to S. epidermidis-induced endophthalmitis. Using a rabbit model, the immune response to an intravitreal injection of 7000 S. epidermidis (group 1) or 30,000 S. epidermidis (group 2) organisms was investigated. Clinical evaluations showed that rabbits in group 2 had a more severe inflammatory reaction in the conjunctiva, cornea, iris, and vitreous than those in group 1. The inflammatory reaction in group 1 largely resolved by day 30; group 2 continued to show a severe inflammatory response. Histopathologic findings correlated with clinical findings, with rabbits in group 2 showing a more severe inflammatory reaction in both the anterior and posterior segments of the globe. Positive vitreous cultures for S. epidermidis were present in rabbits in group 1 on days 3, 7, 10, 14, and 21 but not thereafter. However, group 2 had higher vitreous colony counts at days 3, 7, and 14 and negative vitreous cultures thereafter. Neither group showed delayed hypersensitivity to S. epidermidis antigens (evaluated by skin tests). Serum immunoglobulin (Ig) G antibody levels to phenol-inactivated S. epidermidis and glycerol teichoic acid (GTA) increased progressively, reached a peak at days 10-14, and then declined in both groups. Serum IgA antibody levels to these antigens were not detected. Group 2 had a more prolonged IgG antibody response in vitreous and aqueous than group 1. Tear fluid showed the weakest IgG and IgA antibody response to S. epidermidis and GTA. S. epidermidis-induced endophthalmitis was associated with a humoral but not a delayed hypersensitivity response to this organism.

Staphylococcus aureus is an important cause of severe bacterial endophthalmitis. Both immunoglobulin (Ig) G and A antibody titers to ribitol teichoic acid (RTA), the major antigenic determinant of the S. aureus cell wall, were measured by an enzyme-linked immunosorbent assay in serum, tears, aqueous, and vitreous on days 3, 7, 10, 14, 21, and 30 after intravitreal injection of viable S. aureus in rabbits. Clinical examination showed vitreous opacification in all rabbits from days 7-30. Histopathologic examination showed acute inflammation on day 3 and chronic inflammation on days 7-30 in the conjunctiva, cornea, iris, ciliary body, and trabecular meshwork. The vitreous cavity contained neutrophils and necrotic cells on all days. Retinal necrosis was present on days 14-30. Lymphoid follicles with plasma cells were identified in the conjunctiva, ciliary body, and choroid. The vitreous of experimental eyes showed increasing numbers of bacteria from days 3-14, followed by a decrease in numbers on day 21 and absence of viable bacteria on day 30. Increases in IgG antibody levels to RTA were first detected in serum where they were higher than in tears, aqueous, and vitreous until day 14. Vitreous IgG antibody levels to RTA in experimental eyes exceeded all other samples on day 14 and progressively increased thereafter; the other samples declined. The IgA antibody levels were increased in tears on day 14 and in the vitreous of experimental eyes on days 14, 21, and 30. Vitreous IgG antibody levels to RTA were substantially higher than vitreous IgA antibody levels. An inverse correlation was found between vitreous IgG antibody levels and positive vitreous cultures, suggesting that the humoral immune response may be important in the spontaneous sterilization of the vitreous in this model.