Collection of corneal impression cytology directly on a sterile glass slide for the detection of viral antigen: An inexpensive and simple technique for the diagnosis of HSV epithelial keratitis – A pilot study

BACKGROUND Herpes simplex keratitis (HSK) is a sight threatening ocular infection and occurs worldwide. A prompt laboratory diagnosis is often very useful. Conventional virology techniques are often expensive and time consuming. We describe here a highly economical, simple, rapid and sensitive technique for the collection of impression cytology, for the laboratory diagnosis of HSK. METHODS Fifteen patients with a clinical diagnosis of HSK (either dendritic or geographic ulcers) and five patients with other corneal infections (Mycotic keratitis, n = 3, Bacterial keratitis, n = 2) were included in the study. Corneal impression cytology specimens were collected using a sterile glass slide with polished edges instead of a membrane, by pressing the surface of one end of the slide firmly, but gently on the corneal lesion. Additionally, corneal scrapings were collected following the impression cytology procedure. Impression cytology and corneal scrapings were stained by an immunoperoxidase or immunofluorescence assay for the detection of HSV-1 antigen using a polyclonal antibody to HSV-1. Corneal scrapings were processed for viral cultures by employing a shell vial assay. RESULTS This simple technique allowed the collection of adequate corneal epithelial cells for the detection of HSV-1 antigen in a majority of the patients. HSV-1 antigen was detected in 12/15 (80%) cases while virus was isolated from 5/15 (33.3%) patients with HSK. All the patients with a clinical diagnosis of HSK (n = 15) were confirmed by virological investigations (viral antigen detection and/or viral cultures). HSV-1 antigen was detected in the impression cytology smears and corneal scrapings in 11/15 (73.3%) and 12/15 (80%) of the patients, respectively (P = 1.00). None of the patients in the control group were positive for viral antigen or virus isolation. Minimal background staining was seen in impression cytology smears, while there was some background staining in corneal scrapings stained by the immunoassays. CONCLUSIONS Collection of impression cytology on a sterile glass slide is a simple, rapid and inexpensive technique for the diagnosis of HSK. Immunological techniques applied on such smears provide virological results within 2-5 hours. This technique could be modified for use in the diagnosis of other external eye diseases, which needs further evaluation.