Equis ISSN 2398-2977

Cornea - conjunctiva: cytology

Contributor(s): Dennis E Brooks, Kathleen P Freeman, Graham Munroe

Overview

Sampling

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Tests

Methodologies

Slide preparation and staining
  • Microscopic slides with scrapings can be air dried and stained with Romanowsky stain or preferably fixed (95% ethanol) if other stains are to be used.
  • Suitable Romanowsky stains include Giemsa, Wright's or a quick (20 min) modified Wright-Giemsa (Diff-Quik): these provide excellent first staining for screen examination.
  • If bacteria are present in the cyology stain or infection is suspected then one slide should be stained with Gram stain.
  • Fungi are often identified on the above stains but detection is improved using silver stains such as Gomori methenamine silver or periodic acid-Schiff stains.
    Bacterial/fungal culture
  • Scrapings or swabs are inoculated on to fresh blood agar, bile lactose agar and Sabaroud's dextrose media.
  • The latter is particularly for fungal culture and can contain bacterial inhibitors to prevent bacterial overgrowth.
  • Sensitivity testing should be carried out on all significant cultured organisms including fungi.

Technique (intrinsic) limitations

  • Because of the horse's environment contaminants are widespread in the external eye and may be isolated.
  • Interpretation of culture results in the light of history/clinical signs, and particularly cytology, is essential.
  • The results of antimicrobial sensitivity testing are difficult to interpret because the regularly used techniques do not take into account the high conjunctival/corneal drug levels achieved by intensive topical administration.

Technician (extrinsic) limitations

  • Culture and sensitivity testing can take from 2-3 days for simple bacterial isolates and up to 2 weeks for fungi - results of gram stained smears may need to be used in the interim.

Result Data

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Further Reading

Publications

Refereed papers

  • Whitley R O & Moore C P (1984)Microbiology of the Equine eye in health and disease. Vet Clin N A Large Anim Pract6(3), 451-47 (Review).

Other sources of information

  • Brooks D E (1999)Equine Ophthalmology.In: Veterinary Ophthalmology.Ed: Gelatt K N. 3rd edn. pp 1053-1116.


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