Background Clinical outcomes in fungal keratitis vary between Fusarium and Aspergillus spp, therefore distinguishing between species using morphological features such as filament branching angles, sporulation along filaments (adventitious sporulation) or dichotomous branching may be useful. In this study, we assessed these three features within Heidelberg Retina Tomograph 3 in vivo confocal microscopy (IVCM) images from culture-positive Fusarium and Aspergillus spp keratitis participants.

Methods Prospective observational cohort study in Aravind Eye Hospital (February 2011–February 2012). Eligibility criteria: age ≥18 years, stromal infiltrate ≥3 mm diameter, Fusarium or Aspergillus spp culture-positive. Exclusion criteria: previous/current herpetic keratitis, visual acuity <6/60 in fellow eye, >80% corneal thinning. IVCM was performed and images analysed for branch angle, presence/absence of adventitious sporulation or dichotomous branching by a grader masked to the microbiological diagnosis.

Results 98 participants were included (106 eligible, 8 excluded as no measurable branch angles); 68 were positive for Fusarium spp, 30 for Aspergillus spp. Mean branch angle for Fusarium spp was 59.7° (95% CI 57.7° to 61.8°), and for Aspergillus spp was 63.3° (95% CI 60.8° to 65.8°), p=0.07. No adventitious sporulation was detected in Fusarium spp ulcers. Dichotomous branching was detected in 11 ulcers (7 Aspergillus spp, 4 Fusarium spp).

Conclusions There was very little difference in the branching angle of Fusarium and Aspergillus spp. Adventitious sporulation was not detected and dichotomous branching was infrequently seen. Although IVCM remains a valuable tool to detect fungal filaments in fungal keratitis, it cannot be used to distinguish Fusarium from Aspergillus spp and culture remains essential to determine fungal species.