Kathy McClellan

Resistance of Acanthamoeba castellanii cysts to physical, chemical, and radiological conditions.

Resistance of Acanthamoeba castellanii cysts to disinfection agents, antimicrobial agents, heat, freeze–thawing, ultraviolet radiation (UV), γ irradiation, and cellulase were evaluated in vitro. Following exposure to different agents, the cysts were removed and cultured for A. castellanii trophozoites for 3–14 days. Solutions containing 20% isopropyl alcohol or 10% formalin effectively killed A. castellanii cysts. Hydrogen peroxide (3%, AOSept Disinfectant) effectively killed A. castellanii cysts after 4 hr of exposure. Polyhexamethylene biguanide (0.02%), clotrimazole (0.1%), or propamidine isethionate (Brolene) were effective in killing A. castellanii cysts in vitro. Acanthamoeba castellanii cysts were resistant to both 250 K rads of γ irradiation and 800 mJ/cm2 of UV irradiation. Excystment of trophozoites was accelerated after exposure to 10, 100, and, 1,000 units of cellulase. These results suggest that A. castellanii cysts benefit by enhanced survival because of their resistance to very harsh environmental conditions.

Adaptive immune responses to Acanthamoeba cysts

Acanthamoeba cysts are not eliminated from the corneas of human subjects or experimentally infected animals. The persistence of Acanthamoeba cysts in the cornea indicates that either the cysts escape immunological elimination or are not recognized by the hosts immunological elements. The aim of this study was to determine the immunogenicity and antigenicity of the Acanthamoeba cyst. Mice were immunized intraperitoneally and serum anti-Acanthamoeba IgG was measured by ELISA. Lymphoproliferative assay and delayed type hypersensitivity (DTH) responses to Acanthamoeba castellanii cyst and trophozoite antigens were used to determine the cell mediated immune responses against Acanthamoeba cysts. A. castellanii cysts were both immunogenic and antigenic, producing anti-Acanthamoeba serum IgG, T lymphocyte proliferation, and delayed type hypersensitivity responses. These results indicate that Acanthamoeba cysts are recognized by the immune system. The persistence of the organism in the human cornea means that these adaptive immune responses fail to kill Acanthamoeba cysts.

Daytime presentations to a metropolitan ophthalmic emergency department

Background:  To determine the diagnoses causing patients to present to a dedicated ophthalmic emergency department. To detect associations with patient demographics.

Topical Non-Steroidal Anti-Inflammatory Drugs in Allergic Conjunctivitis: Meta-Analysis of Randomized Trial Data

Purpose: To assess the effect of topical Non-Steroidal Anti Inflammatory drugs in the treatment of allergic conjunctivitis. Method: Systematic Review. Data Sources and study selection: Reports of comparative randomized trials of topical NSAIDs and placebo identified by searches of Medline, Embase, the Cochrane Register of Controlled Trials. Data extraction and synthesis: Two reviewers assessed trials for eligibility and quality and extracted data independently. Data were synthesized (random effects model) and results expressed results for dichotomous outcomes as relative risk and continuous outcomes as weighted mean difference. Sensitivity analysis was used to examine potential heterogeneity by differences in study quality. Results: Eight studies incorporating 712 patients were included. The difference between the decrease in allergic sign and symptom score for NSAID treatment compared to placebo was between 4 and 19 percentage points. Topical NSAIDs produced significantly greater relief for conjunctival itching (cardinal symptom) than did placebo (combined standardized mean difference −0.54 (p < 0.001; 95% confidence interval −0.84 to −0.24). The results for the other allergic symptoms: ocular burning/pain, eyelid swelling, photophobia and foreign sensation were not significant. Topical NSAIDs produced significantly greater reduction of conjunctival injection than did placebo (combined standardized mean difference −0.51 (p = 0.03; 95% confidence interval −0.97 to −0.05). Topical NSAIDs did not reduce the allergic signs of conjunctival chemosis, conjunctival mucus, eyelid swelling and corneal disturbance. Topical NSAIDs had a significantly higher rate of burning/stinging on application of medication compared to placebo (P < 0.0001; odds ratio 3.97 (95% CI 2.67 t0 5.89). Conclusion: This meta-analysis confirms that topical NSAID are significantly more effective at relieving the cardinal symptom: conjunctival itching and improving the cardinal sign: conjunctival injection than placebo treatment. A systematic review comparing topical NSAIDs to topical antihistamines/mast cell stabilizers in treatment of allergic conjunctivitis is warranted as this will compare the topical NSAIDs to current therapeutic guidelines.

Contact lens-related acanthamoeba keratitis.

Acanthamoeba keratitis is a rare but severe disease, with more than 95% of cases occurring in contact lens wearers. With a worldwide resurgence of contact lens-related disease, this report illustrates the clinical characteristics and treatment challenges representative of this disease. This report describes Acanthamoeba keratitis in a 47-year-old female using extended wear silicone hydrogel contact lenses, with a history of swimming in a home pool and failure to subsequently disinfect the contact lenses. The diagnosis was based on clinical signs, disease course, and confocal microscopy results despite a negative result for corneal smear and culture. The corneal signs included an epithelial defect, epithelial irregularities, anterior stromal infiltrates, perineural infiltrates, an anterior stromal ring infiltrate, and hypopyon. The case was diagnosed as an infective keratitis and treated promptly using intensive topical administration of fortified gentamicin and cephalothin. The high likelihood Acanthamoeba prompted immediate use of polyhexamethylbiguanide and chlorhexidine, with propamide and adjunct treatment using atropine and oral diclofenac. Steroids were added on day 3, and the frequency of administration of antibacterial treatment was gradually reduced and ceased by day 10. The analgesia was stopped at 3 months. The frequency of administration of antiamoeba therapy and steroid treatment was slowly reduced and all treatment was ceased after 18 months. Despite considerable morbidity in terms of the treatment duration, hospitalization, outpatient appointments, and associated disease costs, the final visual outcome (6/6) was excellent.