Correlation between corneal sensitivity and quantity of reflex tearing in cows, horses, goats, sheep, dogs, cats, rabbits, and guinea pigs.
OBJECTIVE
Guinea pigs have a very low threshold of corneal sensitivity and at the same time nearly no reflex tearing compared to dogs, cats, and horses. The question arose whether there is a general correlation between corneal sensitivity and the quantity of reflex tearing.


METHODS
Totally 160 animals of 8 different species (20 animals per species) were investigated.


METHODS
The corneal touch threshold (CTT) was measured with a Cochet-Bonnet esthesiometer. The palpebral fissure length (PFL) was measured with a calliper ruler. The Schirmer tear test (STT) was modified by adapting the width of the STT strip to the PFL of every species. For the STT II, 0.4% oxybuprocaine was applied.


RESULTS
Corneal touch threshold: Cows (1.67 g/mm(2)), horses (1.23 g/mm(2)), sheep (1.13 g/mm(2)), goats (1.44 g/mm(2)), dogs (2.16 g/mm(2)), and cats (1.33 g/mm(2)) show similar CTT values. In contrast, rabbits (6.21 g/mm(2)) and guinea pigs (7.75 g/mm(2)) show a significantly lower CTT. Tear Production Difference STT I - STT II: Rabbits have the greatest decline in tear production with 38.4%, followed by sheep (33.3%), dogs (31.1%), cats (24.7%), cows (23.7%), horses (18.0%), and goats (14.0%). Guinea pigs have no decline, but a slight increase of -16.0%. Correlation CTT and STT II - STT I Difference: Pearson's correlation coefficient shows a small, but significant correlation. The coefficient of determination can only forecast a value with 7.1% certainty.


CONCLUSIONS
The high variance and low reproducibility of results suggest that the measuring devices are inappropriate to assess the evaluated parameters. Therefore, no assured correlation between the corneal sensitivity and the quantity of reflex tearing could be found.
Department for Small Animals and Horses, Clinic for Surgery and Ophthalmology, University of Veterinary Medicine Vienna, Rautenkranzgasse 36/11, Vienna 1210, Austria. barbarawieser@gmx.at
Barbara
B
Wieser
Alexander
A
Tichy
Barbara
B
Nell
D000818:Animals; D000829:Animals, Domestic / Q000502:physiology*; D002415:Cats / Q000502:physiology; D002417:Cattle / Q000502:physiology; D003315:Cornea / Q000502:physiology*; D004285:Dogs / Q000502:physiology; D005260:Female; D006041:Goats / Q000502:physiology; D006168:Guinea Pigs / Q000502:physiology; D006736:Horses / Q000502:physiology; D006813:Humidity; D008297:Male; D011817:Rabbits / Q000502:physiology; D012756:Sheep / Q000502:physiology; D013666:Tears / Q000502:physiology*; D013696:Temperature