Impression cytology as diagnostic tool in horses with and without ocular surface disease

Abstract

Summary Background Cytology plays a major role in the diagnosis of ocular surface diseases. Objective To compare 2 cytological sampling methods for obtaining corneal and conjunctival cell samples regarding irritation for the patient, invasiveness, sample quality and diagnostic equivalence. Study design Observational prospective study. Methods In 5 healthy horses, conjunctival and corneal samples were taken bilaterally by impression cytology sampling (ICS) and cytobrush sampling (CBS). Irritation and invasiveness were assessed with an eye irritation and an epithelial damaging score system, respectively. Sample quality was evaluated via morphometric analysis and graded by a board certified clinical pathologist. For the assessment of diagnostic equivalence, 15 eyes of 14 client owned horses with ocular surface anomalies were sampled by ICS and CBS. The methods were compared regarding the types of inflammatory cells and/or infectious agents detected and if the correct diagnosis could be achieved. Histopathology served as gold standard when available. Results ICS was significantly less invasive and less irritating for the horses. Both methods retrieved cells of overall high quality; the cell quantity was significantly higher in IC samples. ICS preserved the natural cellular layout. There was a fair, but no statistically significant agreement between the diagnostic outcomes between sampling methods although CBS resulted in a slightly greater variability of inflammatory cell types compared to ICS. Main limitations None. Conclusions Because of its low irritability and invasiveness ICS can be recommended for cell sampling in fragile corneas and for experimental studies. ICS is especially useful in cases where preservation of cellular layout is advantageous. CBS samples are easier to obtain because of the small equine palpebral fissure. Additionally, the identification of inflammatory cells within conjunctival cell samples is easier. Overall, CBS is still an appropriate method in clinical settings.

The effects of two different types of bandage contact lenses on the healthy canine eye

“…Cytology revealed a slight but overall insignificant increase in inflammatory cells in both types of lenses. Impression cytology has been recently established in cats and horses and proven to be less invasive than cytobrush sampling, so that it was chosen for the present study as an acceptable cellularity and easy identification of inflammatory cells was achieved in other species. As expected, there were no inflammatory cells present in conjunctival or corneal samples prior to the insertion of the lenses which is consistent with the unremarkable ocular examination findings.…”

“…Following the application of a local anesthetic (Oxybuprocain 0.4%; Novain ® , Agepha), a 0.4‐μm biopore membrane, mounted on a plastic tube (Millicell©, PICM 01250, Tulagreen, Ireland) was used to collect cells. Prior to usage, three preinstalled plastic ‘pegs’ were trimmed off the tube with scissors and the tear meniscus was gently absorbed with the help of a sterile cotton bud as described before . The membranes were fixated using a fixative spray (Merckofix, Merck Chemicals, Vienna, Austria).…”

“…For the cytologic evaluation, the membrane was removed from the plastic tube with scissors and stained using a Romanowsky‐type stain (Hemaquick; Biomed Labordiagnostik GmbH, Oberschleißheim, Germany) as described before . The membrane was then transferred to a glass slide (cells facing up) and covered with a coverslip.…”

“…Prior to usage, three preinstalled plastic 'pegs' were trimmed off the tube with scissors and the tear meniscus was gently absorbed with the help of a sterile cotton bud as described before. 9,10 The membranes were fixated using a fixative spray (Merckofix, Merck Chemicals, Vienna, Austria). Samples were stored until the end of the study at room temperature.…”

“…For the cytologic evaluation, the membrane was removed from the plastic tube with scissors and stained using a Romanowsky-type stain (Hemaquick; Biomed Labordiagnostik GmbH, Oberschleißheim, Germany) as described before. 10 The membrane was then transferred to a glass slide (cells facing up) and covered with a coverslip. The examiner, a board certified clinical pathologist (IS), who was blinded regarding the time of the sample taking, the type of lens used and the sampling site, evaluated the overall cellularity, the presence or absence of conjunctival and corneal epithelial cells, goblet cells, limbal cells, and inflammatory cells.…”