By Jackie Brown

From drugs to surgical techniques to new treatment protocols, the field of veterinary ophthalmology is ever evolving, bringing better care and more promising prognoses to patients.

"There is a constant influx of new and exciting research being performed," said Heather L. Chandler, Ph.D., associate professor at Ohio State University's College of Veterinary Medicine and chairwoman of the ACVO Vision for Animals Foundation Grant Committee.

"Research topics vary from improving corneal wound healing with new proteins to gene delivery targeting retinal disease," she said. "As one example, the ACVO [foundation] recently funded a proposal to examine the effect of immune-mediated damage in dogs affected with sudden acquired retinal degeneration syndrome."

Dissolve Cataracts?

Pursuing a pharmaceutical cure for cataracts, researchers continuously investigate medications. A report published a year ago in the journal Nature evaluated a steroidal type of drug that seemingly reversed cataracts.¹ However, Rachel Allbaugh, DVM, MS, Dipl. ACVO, assistant professor of ophthalmology at Iowa State University's College of Veterinary Medicine, believes more research is needed.

"Unfortunately, I don't think that article had good research design in terms of the animal lens evaluations," Dr. Allbaugh said. "It got a lot people excited about this cataract-reversing eye drop that frankly I don't believe has the scientific research solid [enough] to prove that it is of benefit.

"There's no current medication that's proven to reverse cataracts in an animal," she added. "I'm hoping there will be future developments that can achieve that, but people get excited about these things and owners find a paper or report that comes out and they think, 'Oh, this is available now,' and it's actually not."

FHV-1 Treatment

Exciting developments have occurred over the past five to 10 years in the treatment of feline herpesvirus-1, a common cause of conjunctivitis and keratitis, said Sara M. Thomasy, DVM, Ph.D., Dipl. ACVO, an associate researcher at the University of California, Davis, School of Veterinary Medicine.

"Cidofovir is a topical antiviral that can be administered twice daily, which contrasts with all other available topical anti-virals that need to be administered four to six times daily," she said. "In addition, a well-conducted study was published from Colorado State University in 2008 which showed that cidofovir was efficacious and well-tolerated in cats experimentally infected with FHV-1."²

Topical cidofovir is not available commercially but may be obtained from a compounding pharmacy. Another drug, the antiviral oral medication famciclovir, is helpful in treating ocular manifestations of FHV-1 and is used to manage herpetic rhinitis and dermatitis. Dr. Thomasy led a team of UC Davis and international veterinarians who studied the pharmacokinetics, safety and efficacy of famciclovir in cats.

"In 2011 we published a study³ demonstrating that famciclovir administered at 90 mg/kg orally three times daily was efficacious and without side effects in cats experimentally infected with FHV-1," Thomasy said. "We recently completed a retrospective study of 59 cats treated with famciclovir at UC Davis that will soon be published in the Journal of the American Veterinary Medical Association."

UC Davis veterinary resident Lionel Sebbag, Dr. Med Vet, conducted a large pharmacokinetic study of famciclovir. The study, which examined different doses and dose frequencies in healthy cats, is set to be published in the American Journal of Veterinary Research. "The results of both of these new studies, in combination with previous work performed at UC Davis, suggests that 90 mg/kg of famciclovir administered twice daily will be efficacious and safe for treating cats with FHV-1," Thomasy said.

Eosinophilic Keratitis

Sometimes a new formulation, rather than a new drug, presents novel treatment options. A pilot study examining the use of a new compounded ophthalmic formulation of megesterol acetate for treating cats with eosinophilic keratitis showed the drug effectively treated the disease.⁴

"The original results were quite promising," Allbaugh said. "The nice thing is that even though there is a medical treatment for this particular disease in cats, there are contraindications to that classic medical treatment and sometimes patients don't respond. The ophthalmic formulation of this compounded drug has been useful and is something that we've tried in some of our clinical patients."

Corneal Ulceration

Corneal collagen cross-linking is a newly reported therapy to treat melting keratitis in cats and dogs.^5,6

"The process uses corneal cross-linking therapy to reverse the devastating process that occurs when dogs and cats get infected corneal ulcers," said Eric J. Miller, DVM, MS, Dipl. ACVO, an assistant professor of clinical comparative ophthalmology at Ohio State. "This process uses a topical medication and a specialized laser to cross-link the corneal collagen to prevent its degradation."

Although not yet widely used, the treatment has promising potential, Dr. Miller said.

Strides in Equine Genetics

Thanks to rapid discoveries being made in animal genetics, and the increasing availability of new genetic tests, veterinary researchers can identify genes that cause many heritable eye diseases, and breeders are able to avoid producing animals that carry those genes.

UC Davis researchers studying the genetics of corneal disease are trying to understand two vision- threatening conditions in horses: limbal squamous cell carcinoma in Haflinger horses and corneal dystrophy in Friesian horses.

In one study, Haflinger horses were identified as an "at risk" breed for limbal squamous cell carcinoma, or SCC.⁷

"A mutation has been identified as a potential link between ultraviolet damage and the genetic risk for limbal SCC in Haflinger horses," said Mary Lassaline, DVM, Ph.D., Dipl. ACVO, a staff veterinarian at UC Davis who led the study. "Continued research is investigating the association between SCC and other horse breeds and for SCC at ocular locations other than the limbus."

Another study led by Dr. Lassaline investigated corneal dystrophy in Friesian horses, characterized by bilateral symmetric stromal loss, which can affect both eyes and lead to the loss of affected eyes. The disease, which is seemingly progressive but responds well to surgical repair, occurs more frequently in males.

"Current research is directed at identifying a genetic link to try to identify at-risk horses early in the disease process so as to minimize removal of affected eyes, and to help make optimal breeding decisions to reduce the risk of passing on a mutation that may be involved in the development of this disease," Lassaline said.

Solving Blockage Problems

The University of California, Davis, is conducting a clinical trial to evaluate a new method for treating nasolacrimal apparatus blockage in multiple species.

"When structures of the NLA [nasolacrimal apparatus] become blocked, infections can occur, leading to discomfort, tear staining and discharge from the eye, with subsequent skin inflammation," said David J. Maggs, BVSc, Dipl. ACVO, professor of veterinary ophthalmology at Davis' School of Veterinary Medicine. "Using cameras small enough to fit into the tiny drainage ducts, clinicians utilize endoscopy in combination with computed tomography and fluoroscopy to identify and bypass or remove these NLA obstructions.

"Whether the obstructions are caused by a partially scarred duct or a foreign body, such as a foxtail, stents can be placed in the duct from the eye to the nose."

As of late June, UC Davis clinicians had treated 15 dogs, two cats and one horse using this new, minimally invasive procedure.

For information about referring a patient to the clinical trial, contact ophthalmology service coordinator Pam McInnis at 530-752-3937.

Additionally, UC Davis is conducting 11 other clinical trials in veterinary ophthalmology. To learn more, visit the UC Davis website.

References

1. Ling Zhao, Xiang-Jun Chen, Jie Zhu, Yi-Bo Xi, Xu Yang, Li-Dan Hu, et al. "Lanosterol Reverses Protein Aggregation in Cataracts." Nature. July 30, 2015. 523, 607–611.
2. Fontenelle JP, Powell CC, Veir JK, Radecki SV, Lappin MR. "Effect of Topical Ophthalmic Application of Cidofovir on Experimentally Induced Primary Ocular Feline Herpesvirus-1 Infection in Cats." Am J Vet Res. 2008 Feb;69(2):289-93. doi: 10.2460/ ajvr.69.2.289.
3. Thomasy SM, Lim CC, Reilly CM, Kass PH, Lappin MR, Maggs DJ. "Evaluation of Orally Administered Famciclovir in Cats Experimentally Infected With Feline Herpesvirus Type-1." Am J Vet Res. 2011 Jan;72(1):85-95. doi: 10.2460/ ajvr.72.1.85.
4. Stiles J, Coster M. "Use of an Ophthalmic Formulation of Megestrol Acetate for the Treatment of Eosinophilic Keratitis in Cats." Veterinary Ophthalmology. 2016.
5. Spiess, BM, Pot, SA, Florin, M and Hafezi, F. "Corneal Collagen Cross- Linking (CXL) for the Treatment of Melting Keratitis in Cats and Dogs: A Pilot Study." Veterinary Ophthalmology, 2014. 17:1–11.
6. Famose,F. "Evaluation of Accelerated Collagen Cross-Linking for the Treatment of Melting Keratitis in Eight Dogs." Veterinary Ophthalmology, 2014. 17:358–367.
7. Lassaline M, Cranford TL, Latimer CA, Bellone RR. "Limbal Squamous Cell Carcinoma in Haflinger Horses." Vet Ophthalmol, September 2015. 18(5):404-8.