A wide variety of pathogens can infect the conjunctiva, including viruses, bacteria, atypical bacteria (eg, Chlamydiae), fungi, and parasites. Bacterial infection is more common in children (eg, Haemophilus influenzae, Streptococcus pneumoniae), whereas adenovirus and other viruses tend to be more common in adults. Infectious conjunctivitis may be diagnosed on the basis of clinical history and examination findings (typically sufficient for viral disease), or it may require laboratory studies such as biopsy with special stains (eg, Gram, Giemsa), culture, polymerase chain reaction analysis, or serology depending on the suspected organism. In cases of diagnostic uncertainty or nonresponsiveness to initial treatment, cytologic evaluation of the ocular surface epithelium (Fig 5-3) or tissue biopsy may help establish a definitive diagnosis.
Chlamydia, conjunctival scraping for cytologic examination for infectious conjunctivitis, Giemsa stain. The cytoplasmic inclusion body (asterisk), composed of chlamydial organisms, can be seen capping the epithelial cell nucleus (N). A distinct space separates the inclusion body from the nuclear chromatin. Since this finding is often difficult to identify in conjunctival samples, other methods such as polymerase chain reaction are usually used to identify chlamydial infection.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.