A recent study was performed that measured the levels of cortisol in the tear production of horses with cushing's disease and levels of cortisol in the tears of horses with cushing's was found to be higher than normal horses. To explain why this is important, i need to give you a little background about Cushing's disease and to start by saying it has been shown to be in up to 30 percent of the horses over the age of 20. Cushing's disease is correctly called pituitary pars intermedia dysfunction and the acronym is PPID. In Cushing's, the pituitary gland produces increased hormone, which causes the adrenal gland to produce more cortisol and cortisol has multiple effects on the horse's body with the most serious one being susceptibility to laminitis and founder.
However, multiple other problems can occur including increased sweating, long hair that does not shed, increased thirst and susceptibility to infection. And the increased susceptibility of infection is where the increased cortisol in the tears can have a serious effect. Horse's eyes are very sensitive and develop infections easily after a simple scratch. Most horses eyes respond to treatment but if a horse develops an eye problem and the tears contain increased cortisol, healing may be delayed. Horses can develop severe infections that can cause them to lose sight in just a few hours and in Texas, horses can develop fungal ulcers that are extremely difficult to treat successfully. So the important thing to remember is that if you have any horse with an eye problem, your vet needs to see it immediately; if the horse is older and could have Cushing's,treatment must be very aggressive to prevent loss of the eye.