Equine GlaucomaT.J. JenningsPharmD CandidateUNC Eshelman School of PharmacyMarch 7, 2017

Brewdog.com

Objectives• Describe the pathophysiology of equine glaucoma• Outline a typical equine glaucoma patient• Identify key risks for equine glaucoma• Recommend drug therapy for an equine glaucoma patient• Explain non-pharmacologic procedures for equine glaucoma

Pathophysiology 1-3

• Congenital Glaucoma• Primary Glaucoma

• Usually genetic• Very rare; few if any reports exist

• Secondary Glaucoma• More common• Secondary to trauma & disease

• Inflammation (ERU)• Synechiae• Lens luxation

http://www.thehorse.com/articles/12395/eye-anatomy-and-physiology

• Increased intra-ocular pressure (IOP)• Increase in volume of aqueous humor

• Decrease in outflow due to obstruction• Overproduction of aqueous humor

• Resultant increase in pressure damages retina and optic nerve.

• Open Angle• Closed Angle

Signalment 4-6

• Breeds• Appaloosa (26%)• Thoroughbred (22%)• Paso Fino• Warmblood

• Age• >15 years (65%)

• Gender• Non-specific

Vesokone.ru

Horsebreedsinfo.com

Risk identification algorithm

Is the patient a horse?

No

Equine glaucoma risk is

0%

Other glaucomas may

be possible

Yes The patient is at risk!

Epidemiology3,5

• 1:1000 horses

• Complications• Blindness• Enucleation

• Curative…in a way

• Comorbidities/Risk Factors• Equine recurrent uveitis (ERU)• Intraocular neoplasia• Corneal ulcerations

http://www.horseadvice.com/horse/messages/4/352251.jpg

Signs & Symptoms4

• Buphthalmos

http://equinevetblog.blogspot.com

• Corneal Edema

• Dyscoria• Haab’s striae• Mydriasis or Miosis• Discharge and erythema around the globe• Blepharospasm/squinting• Decreased visual acuity

Vetbook.org

• Detachment of Descemet’s membrane

Diagnosis7-9

• History & clinical signs• Applantation tonometry (Tonopen)

• Normal IOP = 15-30 mmHg• Infrequently diagnosed

• Tonometer availability• IOP fluctuations

DE Brooks, DVM, PhD

University of Florida

Consistency is key!

Prognosis4

•Blindness• But usually only one eye!

• Enucleation

https://www.burwashequine.ca

www.jantoo.com

Pharmacotherapy10-13

TOIPICAL CARBONIC ANHYDRASE INHIBITORS

• Brinzolamide 1% (Azopt, Simbrinza): 2 drops in affected eye(s) QD• Dorzolamide 2% (Trusopt, Cosopt): 1 drop in affected eye(s) q8-12h

• MOA: CO2 + H2O carbonic anhydraseHCO3- + H+

• Inhibits carbonic anhydrase in the ciliary body• Bicarbonate is involved with aqueous humor production

• AE: stinging, burning, irritation• Cautions: Sulfa allergies• Dose Form: Topical ophthalmic suspension (brinzolamide); solution (dorzolamide)

MEAN IOP REDUCTION: ~3-5 mmHg ± 1.5 mmHg

Pharmacotherapy13,14

ORAL CARBONIC ANHYDRASE INHIBITORS

• Acetazolamide (Diamox, Dazamide): 2-3 mg/kg PO q8-12h• ADME: PK not studied in domestic animals

• Onset of Action: 30 min; Peak Effect: 2-4h; Duration of Action in 4-6h in small animals.

• Humans: highest levels found in the kidneys, plasma and erythrocytes

• 90% excreted unchanged in urine

• AE: GI disturbances, CNS depression, bone marrow suppression• DDI: insulin, potassium wasting drugs, ASA, cyclosporine• Cautions: hepatic disease, renal insufficiency

Pharmacotherapy15

Beta Blockers

• Timolol (Timoptic, Cosopt): 1 drop in affected eye(s) BID

• MOA: not well known• Blockade of sympathetic stimulation on the ciliary epithelium• Decreased cAMP activation• Inhibition of NaK ATPase activity

• AE: stinging, burning, irritation; slight miosis • Cautions: Heart block, asthma, bradycardia, chronic bronchitis, diabetes• Dose Form: Topical ophthalmic solution

• Not often seen alone. Usually seen in combo with a carbonic anhydrase inhibitor. • Clinical significance is doubtful (2 mmHg decrease in IOP)

Pharmacotherapy16,17

PROSTAGLANDIN ANALOGUE

• Latanoprost (Xalatan): 1 drop in affected eye BID

• MOA: increases uveoscleral outflow rate

• AE: burning, stinging, irritation, increased pigmentation of the iris, increased eyelash growth, may worsen inflammation

• Caution: Don’t use in presence of ocular inflammation

• Dose Form: Topical ophthalmic solution

Data is equivocal on safety/efficacy in the equine population (1-3mmHg). Tofflemire et al. suggest 0.1% diclofenac 1 drop 10 minutes prior to latanoprost

Counseling10, 11,14,15,17

• Shake brinzolamide before using

• Protect drops from light. Store unopened bottles at 2-8°C (36-46°F); do not freeze. Once a bottle is opened for use, it may be stored at room temperature up to 25°C (77°F) for 6 weeks. Do not use if the color changes, it becomes cloudy, or if particles are seen in solutions.

• Wait 5 min between ophthalmic medications

• Do not touch the dropper tip to the eye surface

• Dorzolamide may cause stinging

• If the horse squints or has eye discharge, call the vet

• Consider formulation of the drops as a gel

Counseling18

A subpalpebral lavage (SPL) catheter makes giving topical ophthalmics easier.• Subcutaneous catheter placed beneath eyelid

• Put medication (0.1 – 0.2 mL) in the catheter• Push it through with air• Equine tear film is only 230 μL. Don’t waste drug!

Non-pharmacologic Treatment19

• Transscleral cyclophotocoagulation• Use of neodymium: yttrium-aluminum garnet

(Nd:YAG) laser to ablate the ciliary body• OSU study found an IOP decrease from 37.17 ±

13.48 mmHg to 19.36 ± 12.04 mmHg postop (“p<0.05”)

• Hyphema (11%)was the only complication

https://www.researchgate.net

Non-pharmacologic Treatment20

• Gonioimplantation• Fibrosis can develop around implants• AE’s included corneal ulcers, neovascularization &

neutrophilic keratitis• Purdue study: IOP decreased from 20.7 ± 3.0 mmHg

to 12.6 ± 2.4 mmHg (p=0.048) in 7 normal horses

All images: http://www.newworldmedical.com/product-fp7

Monitoring/Follow-up4

• Serial Tonometry

• Pupillary Dilation

• Horses should be stall-rested until condition is controlled

• Diet consistent with training level of the horse

• Hard- or soft-cup hoods to avoid self trauma

• Observe horse’s behavior

Caregiver Concerns & Zoonotic Potential4

• No zoonotic potential!• Equine glaucoma is not transmissable

• Decreased riding safety

http://www.horse-riding-accidents.co.uk/

Summary & Clinical Pearls

• Encourage routine use of tonometry, especially with ERU• Set realistic expectations for the owner• Understand that there are no FDA-approved drugs for glaucoma in horses• Regular screenings for ERU, especially Appaloosas.• Prevention and vigilance are the best treatment• Publish case studies of your glaucomatous patients!• Glaucoma may be a contraindication for atropine

References1. Gelatt KN. Glaucoma. Merck Veterinary Manual. Kenilworth, NJ: Merck & Co: 2016.

http://www.merckvetmanual.com/eye-and-ear/ophthalmology/glaucoma. Accessed January 25, 2017.

2. Kornatowski A, Kornatowski M. Equine Glaucoma. Twin Pines Equine Veterinary Serivce. http://twinpinesequine.com/blog/equine-glaucoma. Accessed January 25, 2017

3. Meyer G. Equine Glaucmoa. University of Minnesota Extension. http://www.extension.umn.edu/agriculture/horse/health/equine-glaucoma/index.html. Accessed January 25, 2017

4. Lavoie, J. Glaucoma. Blackwell’s Five-Minute Veterinary Consult: Equine. Danvers, MA: Wiley-Blackwell; 2009.

5. Gerding JC, Gilger BC. Prognosis and impact of equine recurrent uveitis. Equine Veterinary Journal. 2016; 48(3)290-8.

6. Curto EM, Gemensky-Metzler AJ, Chandler HL, Wilkie DA. Equine glaucoma: a histopathologic retrospective study (1999-2012). Vet Ophthalmol. 2014;17(5)334-42.

7. Henriksen ML et. al. Glaucoma with Descemet’s membrane detachment in five horses. Vet Ophthalmol. 2016 May 18. doi: 10.1111/vop.12388. [Epub ahead of print].

8. Equine Glaucoma. [PowerPoint]. Gainesville, FL: Uinversity of Florida Equine Ophthalmology Service. http://largeanimal.vethospitals.ufl.edu/files/2012/01/Equine-Glaucoma.pdf. Accessed January 27, 2017.

9. Komaromy AM, Garg CD, Ying GS, Liu C. Effect of head position on intraocular pressure in horses. Am J Vet Res. 2006;67(7):1232-5.

References10. Brinzolamide. Plumb’s Veterinary Drugs.

https://www.plumbsveterinarydrugs.com/#!/monograph/5BrzW5tNXK. Updated Sep 2014. Accessed Jan 20, 2017.

11. Dorzolamide. Plumb’s Veterinary Drugs. https://www.plumbsveterinarydrugs.com/#!/monograph/9c28SHJYMk. Updated Sep 2014. Accessed Jan 20, 2017.

12. Willis AM, Diehl KA, Robbin TE. Advances in topical glaucoma therapy. Vet Ophtalmol. 2002; 5(1):9-17.

13. Germann SE, Matheis FL, Rampazzo A, Burger D, Roos M, Spiess BM. Effects of topical administration of 1% brinzolamide on intraocular pressure in clinically normal horses. Equine Vet J. 2008; 40(7):662-5.

14. Acetazolamide. Plumb’s Veterinary Drugs. https://www.plumbsveterinarydrugs.com/#!/monograph/dErOnUrxGQ/. Updated Aug 2013. Accessed Jan 21, 2017.

15. Timolol Maleate Ophthalmic. Plumb’s Veterinary Drugs. https://www.plumbsveterinarydrugs.com/#!/monograph/Sr83aJT23X/. Updated Sep 2014. Accessed Jan 21, 2017.

16. Tofflemire K, Whitley EM, Allbaugh R, Ben-Shlomo G, Griggs A, Strong T, Whitley R. Effect of topical ophthalmic latanoprost 0.005% solution alone and in combination with diclofenac 0.1% solution in healthy horses: a pilot study. Vet Ophthalmol. 2016 Oct 28. doi: 10.1111/vop.12439. [Epub ahead of print]

.

References17. Latanoprost Ophthalmic. Plumb’s Veterinary Drugs.

https://www.plumbsveterinarydrugs.com/#!/monograph/ot2VDb5ShK/. Updated Sep 2014. Accessed Jan 22, 2017.

18. Cole C, Bentz B, Maxwell L. Equine Pharmacology. Ames, IA: John Wiley & Sons; 2015.

19. Annear MJ, Wilkie DA, Gemensky-Metzler AJ. Semiconductor diode laser transsclearl cyclophotocoagulation for the treatment of glaucoma in horses: a restrospective study of 42 eyes. Vet Ophthalmol. 2010; 13(3): 204-9.

20. Townsend WM, Langhor IM, Mouney MC, Moore GE. Feasibility of aqueous shunts for reduction of intraocular pressure in horses. Equine Vet J. 2014; 46(2):239-43.

The End

Questions?“Eye” hope this has been enlightening.

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