Impression Technique for Conjunctival Exfoliative Cytology in Healthy Horses

Conjunctival exfoliative cytology is a valuable tool in ophthalmology. Impression cytology (IC) and brush cytology (BC) are both described as methods of corneal and conjunctival cell collection. Few reports describe IC in the horse. To study conjunctivas of healthy horses by IC, to evaluate the normal cytological pattern and standardize the technique, and to compare feasibility and effectiveness of IC and BC. Conjunctival samples were taken from the eyes of 31 adult healthy horses using a Millipore filter for IC and a disposable brush for BC. The IC specimens were stained either with a modified haematoxylin and eosin protocol or Periodic Acid–Schiff (PAS) stains. The BC smears were stained with Diff-Quick. Cellularity was evaluated in IC smears. Cell distribution and integrity and technique feasibility were scored and compared between IC and BC samples. Both techniques allowed collection of an adequate quantity of well-preserved cells. Haematoxylin and eosin stain gave a better definition of cell morphology than PAS. Samples by BC had significantly better distribution than IC, whereas the cell damage was significantly lower in IC samples. The overall assessment of the IC smears was rated as insufficient in three samples. Feasibility was significantly better with BC. Impression cytology was confirmed to be a valuable complement for the evaluation of conjunctival surface. It may yield reliable information about conjunctival areas. Brush cytology, with its ease and safety of handling, is an effective tool for evaluating the conjunctival surface in clinical setting