Across various studies, smear results are reported to be significantly less sensitive than the culture; however, being a rapid procedure, it is considered useful [6]. The presence of uveal pigments (brown, oval or round) in the smears is one of the difficulties faced by the microbiologists during microscopy, especially in Gram and Giemsa stain where the round pigments may resemble staphylococci in shape and size and the oval pigments may resemble corynebacteria (Fig. 24.1). Giemsa stain helps determine the type of inflammatory response.

A correlation of type and quantity of cells and culture results made earlier did not show any significant difference in the culture-positive and culture-negative samples as well as between samples from patients with bacterial or fungal endophthalmitis [11]. A mononuclear cellular response may be indicative of a viral infection, and an eosinophilic response may suggest parasitic infection [6]. In phacolytic endophthalmitis, one may find macrophages laden with lens matter in the vitreous. Bacteria that can be discerned well in Gram stain of vitreous fluid include gram-positive cocci in pairs, short chains or groups (Fig. 24.2 top left) suggestive of staphylococci and in pairs and short chains with lanceolate shape and capsule suggestive of Streptococcus pneumoniae (Fig. 24.2 top right). Long and beaded gram-positive bacilli, often in chains, would suggest Bacillus group of bacteria (Fig. 24.2 middle left) and occurring in L- and V-shaped arrangements (Chinese letter pattern) would be Corynebacterium sp. (Fig. 24.2 middle right). Pseudomonas appears slender, often long, gram-negative bacilli (Fig. 24.2 bottom left), and stout gram-negative bacteria could be enterobacteria (Fig. 24.2 bottom right).