Tear ferning in normal dogs and dogs with keratoconjunctivitis sicca

This study evaluates tear ferning as an ancillary technique for the evaluation of the canine tear film in normal eyes and eyes affected by keratoconjunctivitis sicca (KCS). Thirty dogs with KCS and 50 control dogs with normal tear film were evaluated with a full ophthalmoscopic examination and a Schirmer tear test type 1 (STT) determined before tear samples were obtained from the medial canthus with a microhaematocrit capillary tube. 10ul of tear was placed on a microscope slide and the time to first formation of a fern of crystallised tear solute was determined. The appearance of the ferning pattern was graded and correlated with the STT value. All eyes with KCS had abnormal ferning patterns while 39 out of the 50 normal dogs (78%) had so-called 'normal' ferning patterns. The mean STT for dogs showing 'normal' ferning patterns was 20.6mm/min for the left eye and 21.3mm/min for the right eye. STT values for eyes with 'abnormal' ferning patterns were 10.9mm/min and 12.4mm/min, these differing from the normal eyes with STT above 15mm/min significantly. These findings suggest that tear ferning could be a valuable technique for assessment of the tear film in dogs with KCS.