Measuring tear production

We may need to look again at how we treat eye infections in the light of research that found that horses produce more tears than previously thought.

Tears protect the eye by keeping the cornea moist. The tear film also carries nutrients to the cornea, which has no blood supply of its own.

The same route is also used to deliver medication to the cornea.

How many tears does a healthy horse produce? How quickly is the tear film replaced? There have been few studies into this, yet it is important to know, as it will affect the concentration of drugs applied to the eye - and so may affect their efficacy.

Dr Thomas Chen and Dr Daniel A. Ward examined the rate of production of tears in normal horses' eyes, in a study carried out at the College of Veterinary Medicine, University of Tennessee, Knoxville. They instilled fluorescein dye onto the eye and then collected small samples of the tear film, measured the fluorescein concentration, and noted how it changed with time.

They used two mathematical approaches to analyse the results. One method, which was considered the more accurate, suggested that the rate of tear production was 33.6mL /min. The mean tear film volume was estimated to be 233.74 mL.

The results showed that the tear film was likely to be completely replaced within a matter of 7 minutes. This suggests that current treatment protocols may not be adequate, and that drugs may need to be administered more frequently.

Read more at  the Equine Science Update website