Thought you may find this interesting as well as informative....I would again consult the Vet, may save secondary issues as well as time and money.
Ironically for horse owners, onchocerca can sometimes first be identified by the onset of symptoms following worming with ivermectin. This is one drug that will effectively kill off the young microfilariae, but at the same time by doing its job it can initiate uveitis if a large quantity of the microfilariae are in the eye at the time of worming. After uveitis has started, some owners find that administering bute or banamine several days before and after worming can control the inflammation so that the uveitis does not flare up every time the horse is wormed. This also might indicate that in dealing with abandoned or abused horses who may not have been wormed on a regular basis, consulting a veterinarian regarding the possibility of onchocerca microfilariae in the eye before worming may prevent uveitis in addition to its other problems. A conjunctival biopsy can be used to identify onchocerca microfilariae in the eye, but it does involve using auriculopalpebral nerve block and topical anesthesia. Once the inflammation has quieted, treatment can commence. Diethylcarbamazine and ivermectin are two drugs that are used (Cook, 1983)." Equine Recurrent Uveitis
You will see a constant water stream out of the eye or eyes. There may be a white or yellow mucous in the eye on a regular basis. Many times vets will think this is a blocked tear duct. Again, there may be hair loss around the face and eye area. Ivermectin is the conventional treatment, but it did not really work for our horses. My vet of 24 years, was an incredible vet. She had a diagnostic sense unlike any that I have ever seen. Unfortunately, she is not in private practice any more. We surely miss her. She had a way of thinking outside the box. We had Wedgewood Pharmacy compound a pill for our horses that has worked really well after the Ivermectin did not. It is called Diethylcarbamazine Citrate. The capsules are each 400 mg. It is basically heart worm medicine compounded into capsule form. We open two capsules, once a week, and place the powder in a cup of sweet feed and the horse eats it. No problem! Spring time is when the Onchocera becomes most active. This has worked for both horses. You can discuss this with your vet. If not managed, complications can be blindness if in the eyes, and if left untreated, adult worms can travel into the ligaments and tendons of the horse. The horse may eventually fall and stumble. They can cause swelling and bumps because of the hardening of dead worms.