I have done pretty much every job there can be in ophthalmology that isnt done by a surgeon, anesthesiologist/anesthetist, from visual acuity tests, refractions, tonometry both with a "pen" type and the one of the scope (I never used the puff of air type though) to work ups for cataracts, I also used to see the Day 1 post ops and checked implant placement and for corneal edema or any complications. I have scrubbed in for surgery, been a circulator, I have done Pre-op helping the anesthesiologist and the post op sending patients home. I have helped with cataract surgeries, glaucoma surgeries, corneal transplants, retinal surgeries of various kinds, RK and LASIK refractive surgeries as well, so I had a pretty well rounded tour as an ophthalmic nurse.
Hi: This is heart breaking indeed. So, the bad news is that cataracts have begun to form, especially in one eye. The good news is that your horse still has sight out of one good eye and some sight out of the eye with the cataract. Research on Can-C reports that application of the Can-C eye drops as directed results in about 95% improvement in the subjects that were studied. Subjects have been dogs and humans – not horses – but researchers concluded that the Can-C helps reverse cataracts in all mammals including horses in, again, 95% of the cases. So, it is certainly worth a try, especially to insure that the good eye remains clear of a cataract.
Corticosteroids have been used as drug treatment for some time. Lewis Sarett of Merck & Co. was the first to synthesize cortisone, using a complicated 36-step process that started with deoxycholic acid, which was extracted from ox bile .  The low efficiency of converting deoxycholic acid into cortisone led to a cost of US $200 per gram. Russell Marker , at Syntex , discovered a much cheaper and more convenient starting material, diosgenin from wild Mexican yams . His conversion of diosgenin into progesterone by a four-step process now known as Marker degradation was an important step in mass production of all steroidal hormones, including cortisone and chemicals used in hormonal contraception .  In 1952, . Peterson and . Murray of Upjohn developed a process that used Rhizopus mold to oxidize progesterone into a compound that was readily converted to cortisone.  The ability to cheaply synthesize large quantities of cortisone from the diosgenin in yams resulted in a rapid drop in price to US $6 per gram, falling to $ per gram by 1980. Percy Julian's research also aided progress in the field.  The exact nature of cortisone's anti-inflammatory action remained a mystery for years after, however, until the leukocyte adhesion cascade and the role of phospholipase A2 in the production of prostaglandins and leukotrienes was fully understood in the early 1980s.