Laboratory diagnosis of Acanthamoeba keratitis using buffered charcoal-yeast extract agar

Urgent unmet needs in the care of bacterial keratitis: An evidence-based synthesis

Bacterial corneal infections, or bacterial keratitis (BK), are ophthalmic emergencies that frequently lead to irreversible visual impairment. Though increasingly recognized as a major cause of global blindness, modern paradigms of evidence-based care in BK have remained at a diagnostic and therapeutic impasse for over half a century. Current standards of management - based on the collection of corneal cultures and the application of broad-spectrum topical antibiotics - are beset by important yet widely underrecognized limitations, including approximately 30% of all patients who will develop moderate to severe vision loss in the affected eye. Though recent advances have involved a more clearly defined role for adjunctive topical corticosteroids, and novel therapies such as corneal crosslinking, overall progress to improve patient and population-based outcomes remains incommensurate to the chronic morbidity caused by this disease. Recognizing that the care of BK is guided by the clinical axiom, "time equals vision", this chapter offers an evidence-based synthesis for the clinical management of these infections, underscoring critical unmet needs in disease prevention, diagnosis, and treatment.

The relative value of confocal microscopy and superficial corneal scrapings in the diagnosis of Acanthamoeba keratitis

PURPOSE

To compare the relative diagnostic value of confocal microscopy and superficial corneal cultures in the diagnosis of Acanthamoeba keratitis by using clinical and microbiologic definitions of disease.

METHODS

Results of confocal microscopy, superficial corneal smear, and superficial corneal culture were analyzed for validity against 2 different microbiologic and a clinical composite standard for Acanthamoeba keratitis.

RESULTS

In patients with both clinical characteristics and objective evidence of Acanthamoeba keratitis, confocal microscopy exhibited a sensitivity of 90.6% (95% confidence interval [CI]: 79.3%-96.9%) and a specificity of 100% (95% CI: 95.0%-100%). In patients with either positive culture or smear evidence of Acanthamoeba keratitis, confocal microscopy showed a sensitivity of 90.9% (95% CI: 78.3%-97.5%) and specificity of 90.1% (95% CI: 81.5%-95.6%). In strictly culture-positive patients, confocal microscopy showed a sensitivity of 92.9% (95% CI: 76.5%-99.1%) and a specificity of 77.3% (95% CI: 67.7%-85.2%). Of the 53 patients with Acanthamoeba keratitis, confocal microscopy was positive in 48 patients, whereas corneal smears and cultures were positive in 30 of 41 and 23 of 42 patients, respectively. Sensitivity of Acanthamoeba culture was 52.8% (95% CI: 38.6%-66.7%) in patients with a clinical diagnosis of Acanthamoeba keratitis. Simultaneous testing of smear and superficial corneal scraping resulted in a sensitivity of 83.0% (95% CI: 70.2%-91.9%), independent of the results of confocal microscopy.

CONCLUSIONS

As confocal microscopy comes into wider clinical use, it remains in need of clinical and pathologic correlation. When performed and interpreted by an experienced operator, confocal microscopy is both sensitive and specific in the diagnosis of Acanthamoeba keratitis. Contemporaneous corneal scrapings are independently sensitive in the detection of Acanthamoeba keratitis, and a combination of both diagnostic modalities offers the highest likelihood of rapidly and accurately diagnosing Acanthamoeba keratitis in patients with atypical keratitis.