Ad­vances in Equine Eye Health

Univer­sity re­searchers high­light four in­no­va­tions that are help­ing horses main­tain healthy eyes and sharp vi­sion.

Practical Horseman - - Special Dressage Issue - By Sushil Du­lai Wen­holz

Re­searchers from around the coun­try share new de­vel­op­ments in treat­ing and car­ing for equine eyes in or­der to main­tain their health and vi­sion.

We’ve all heard the say­ing, “No hoof, no horse.” But a horse’s eye­sight is just as im­por­tant as those four feet. In the wild, poor vi­sion could mean the dif­fer­ence be­tween life and death if a horse couldn’t spot preda­tors in time to avoid dan­ger. Even a mod­ern, do­mes­ti­cated horse can have his per­for­mance life dras­ti­cally al­tered or cut short if eye trou­ble leads to blind­ness or dis­torted vi­sion. And some eye trou­bles, such as can­cer, can lead to is­sues af­fect­ing the horse’s over­all health.

No won­der we get ex­cited when sci­ence pushes for­ward our abil­ity to di­ag­nose and treat dis­or­ders of the equine eye. Here, re­searchers from uni­ver­si­ties across the coun­try share some of their lat­est ad­vance­ments to help our horses main­tain healthy eyes and good vi­sion.

Imag­ing and Di­ag­nos­tics: Corneal In Vivo Con­fo­cal Mi­croscopy

For any type of health prob­lem, a cor­rect di­ag­no­sis is es­sen­tial to treat­ment, and var­i­ous forms of imag­ing play an im­por­tant role.

Equine eye is­sues are no dif­fer­ent, and one of the newer tech­niques giv­ing vet­eri­nar­i­ans bet­ter in­sights is corneal in vivo con­fo­cal mi­croscopy, ac­cord­ing to Eric C. Led­bet­ter, DVM, DACVO, an as­so­ciate pro­fes­sor of oph­thal­mol­ogy and oph­thal­mol­ogy sec­tion chief at Cornell Univer­sity’s Hos­pi­tal for An­i­mals.

This imag­ing tech­nique cen­ters around a con­fo­cal mi­cro­scope, which uses a nar­row beam of light to take mul­ti­ple two-di­men­sional im­ages of the eye at dif­fer­ent depths. The im­ages are au­to­mat­i­cally re­con­structed into a three­d­i­men­sional view. In use, the con­fo­cal mi­cro­scope is at­tached to an ad­justable ta­ble mounted on a mo­bile desk, says Dr. Led­bet­ter. It’s run by a com­puter with a stan­dard mon­i­tor for view­ing.

The exam is of­ten per­formed at a vet­eri­nary hos­pi­tal uti­liz­ing stand­ing se­da­tion and top­i­cal anes­thetic.

Us­ing this pro­ce­dure, vet­eri­nar­i­ans can eval­u­ate all lay­ers of the horse’s cornea (see side­bar, page 48), in­clud­ing deep corneal le­sions that are oth­er­wise not ac­ces­si­ble for di­ag­nos­tic eval­u­a­tion, says Dr. Led­bet­ter. It’s also use­ful for di­ag­nos­ing other corneal is­sues, in­clud­ing in­fec­tions, var­i­ous au­toim­mune con­di­tions, tu­mors, for­eign bod­ies and more.

Dr. Led­bet­ter and his Cornell col­leagues were the first to re­port the use of this imag­ing tech­nique in horses and are the only group to have pub­lished de­scrip­tions of its use in horses. (The tech­nique has shown prom­ise in other species, in­clud­ing dogs.)

“This is a non­in­va­sive imag­ing tech­nique that al­lows the cornea to be eval­u­ated in real time with mag­ni­fi­ca­tion and res­o­lu­tion sim­i­lar to his­tol­ogy of a stan­dard biopsy but with­out any cut­ting or other dam­age to the horse’s tis­sues,” says Dr. Led­bet­ter. “I of­ten ex­plain it as a vir­tual biopsy.”

Also, a small cam­era can project the im­ages im­me­di­ately for the vet­eri­nar­ian to in­ter­pret. For­tu­nately, this means the horse owner doesn’t have to wait days to hear back on re­sults from a biopsy.

The equip­ment re­quired for the tech­nique is ex­pen­sive—typ­i­cally cost­ing more than $50,000 for a unit, ac­cord­ing to Dr. Led­bet­ter. The cost to per­form an ex­am­i­na­tion varies by fa­cil­ity, but Dr. Led­bet­ter notes that it is rel­a­tively low and can pre­vent the need for other forms of di­ag­nos­tic test­ing. In ad­di­tion, the pro­ce­dure can po­ten­tially re­duce treat­ment costs while im­prov­ing out­comes by pro­vid­ing a spe­cific di­ag­no­sis early in the course of the dis­ease.

Corneal in vivo con­fo­cal mi­croscopy is avail­able only in a limited num­ber of lo­ca­tions world­wide. How­ever, its avail­abil­ity is spread­ing, says Dr. Led­bet­ter, who notes the tech­nol­ogy has been used at Cornell for sev­eral years to eval­u­ate equine eyes.

Treat­ment De­liv­ery Method: Di­rect Med­i­ca­tion In­jec­tion

Giv­ing eye drops is a com­mon method for med­i­cat­ing the equine eye. How­ever, it can be time-con­sum­ing for the owner to ad­min­is­ter, and over time the horse can be­come dif­fi­cult to treat as he tries to avoid the drops. In ad­di­tion, drops can be an in­ef­fi­cient way to ad­min­is­ter med­i­ca­tion, par­tic­u­larly to the cornea, says Brian Gil­ger, DVM, MS, DACVO, DABT, pro­fes­sor of oph­thal­mol­ogy at the North Carolina State Univer­sity Col­lege of Vet­eri­nary Medicine.

“The cornea is nor­mally about 1 mm thick,” he ex­plains. “When it be­comes

dis­eased, it be­comes much thicker. Us­ing stan­dard eye drops, it’s very dif­fi­cult to get med­i­ca­tion down deep enough.” That can mean that the horse faces surgery and the pos­si­bil­ity of a corneal trans­plant.

Now, says Dr. Gil­ger, a new type of nee­dle makes it very sim­ple to in­ject med­i­ca­tion ex­actly where it’s needed. “It’s a com­pletely new in­jec­tion de­vice,” he says. “It pre­cisely in­jects where you want the drug to go and does not rely on treat­ing the en­tire ocu­lar sur­face.”

With the horse stand­ing but tran­quil­ized—and typ­i­cally at a vet­eri­nary clinic—the vet­eri­nar­ian ad­min­is­ters a lo­cal top­i­cal anes­thetic, then uses im­agery (via high-fre­quency ul­tra­sound) to guide the in­jec­tion and de­liver med­i­ca­tion di­rectly into the af­fected area of the cornea.

Dr. Gil­ger adds, “The goal is to pro­vide treat­ment about ev­ery three days in­stead of ev­ery two to four hours with eye drops.”

Dr. Gil­ger says the pro­ce­dure can ef­fec­tively heal fun­gal ker­ati­tis (in­flam­ma­tion of the cornea caused by fun­gal in­fec­tion) and other dis­eases where the en­tire eye doesn’t need to be treated. As a bonus, the treat­ment can cost just $200 to $300 ver­sus, for ex­am­ple, stan­dard fun­gal ker­ati­tis treat­ments, which can run $1,000 to $2,000.

“This type of treat­ment will prob­a­bly com­pletely re­place eye drops in the next few years,” Dr. Gil­ger pre­dicts.

Treat­ment Pro­ce­dure: Corneal Cross-Link­ing

The horse’s cornea is a com­mon place for in­juries or ul­cers, which may stem from var­i­ous causes, in­clud­ing trauma, fun­gus or bac­te­ria. Corneal is­sues can cause se­ri­ous prob­lems, in­clud­ing scar­ring and loss of sight. In some cases, corneal ul­cers open the door to bac­te­rial or fun­gal in­fec­tion. This can ac­cel­er­ate the ul­cer­a­tion and lead to a jelly-like or liq­ue­fied ap­pear­ance of the eye, of­ten re­ferred to as “corneal melt­ing.” If med­i­cal treat­ment isn’t ef­fec­tive for corneal is­sues, the horse may re­quire surgery, which could in­clude insert­ing a catheter to pro­vide con­tin­u­ous med­i­ca­tion to the eye.

A new tech­nique called corneal crosslink­ing has the po­ten­tial to fix the prob­lem through a non­sur­gi­cal, in-pa­tient pro­ce­dure, ac­cord­ing to Dr. Gil­ger.

With corneal cross-link­ing, the vet­eri­nar­ian ap­plies ri­boflavin (vi­ta­min B ) eye drops to the sur­face of the cornea. (Dr. Gil­ger notes that im­proved tech­niques for ap­plica-

tion are be­ing de­vel­oped, such as lo­cal in­jec­tion.) The vet­eri­nar­ian then shines a UV light onto the eye, which ac­ti­vates the ri­boflavin, cre­at­ing bonds be­tween the col­la­gen fibers in the eye. This sta­bi­lizes and strength­ens the cornea to pre­vent melt­ing and also kills the in­fec­tion, says Dr. Gil­ger.

The pro­ce­dure it­self can cost around $500 and is widely used in Europe and be­gin­ning to see more use in the U.S. One draw­back, says Dr. Gil­ger, is that it is cur­rently a lengthy pro­ce­dure. It takes 30 min­utes or more to ad­min­is­ter the eye drops and an­other 30 min­utes for the UV light ap­pli­ca­tion, he ex­plains. Ad­di­tional re­search is now fo­cused on test­ing dif­fer­ent tech­niques to speed up the process.

Treat­ment Pro­ce­dure: Stem-Cell Ther­apy

Im­mune-me­di­ated ker­ati­tis is a com­mon equine eye con­di­tion, says Dr. Gil­ger. With IMMK, the horse’s own im­mune sys­tem es­sen­tially at­tacks cells in the cornea. It can lead to in­flam­ma­tion, cloudi­ness of the eye and blood ves­sels grow­ing into the cornea. It is con­sid­ered a chronic dis­ease that can wax and wane for years and ul­ti­mately lead to blind­ness, says Dr. Gil­ger.

Treat­ment typ­i­cally in­volves daily ap­pli­ca­tion of steroids. How­ever, the med­i­ca­tion can have long-term side ef­fects. “Top­i­cal use of steroids puts the horse at risk for de­vel­op­ing corneal in­fec­tions, such as fun­gal ker­ati­tis, and can re­sult in corneal de­gen­er­a­tion when used for a long pe­riod of time,” says Dr. Gil­ger. “Fur­ther­more, if the eye is in­jured when top­i­cal steroids are be­ing used, then the eye heals much slower than nor­mal.” Yet if treat­ment is stopped, the prob­lem can come back.

Dr. Gil­ger has been work­ing on a stem-cell-based so­lu­tion with his NCSU col­league Lau­ren Schn­abel, DVM, PhD, DACVS, DACVSMR, an as­sis­tant pro­fes­sor of equine or­tho­pe­dic surgery and stem-cell re­searcher, along with oph­thal­mol­ogy res­i­dent Amanda Davis.

“We can now safely har­vest stem cells from [the IMMK pa­tient’s] bone mar­row, grow [more cells] in the lab, in­ject them back into the horse’s eye and stop the im­mune re­sponse plus aid with heal­ing,” says Dr. Schn­abel.

Har­vest­ing the cells costs about $1,800 and in­volves us­ing a nee­dle in­serted into a bone (of­ten the horse’s ster­num) to re­move stem cells. Dur­ing the pro­ce­dure, the horse is se­dated, and a lo­cal anes­thetic is used to numb the site. Stem cells not used for the ini­tial treat­ment are frozen for fu­ture use, and any re­peat injections run about $500, says Dr. Gil­ger.

While the treat­ment takes a cou­ple of weeks to de­velop—time for the stem cells to grow in the lab—since IMMK is a chronic con­di­tion, wait­ing a lit­tle longer for a treat­ment won’t make much dif­fer­ence to the horse, says Dr. Schn­abel.

Dur­ing re­search on the pro­ce­dure, the stem-cell ther­apy cleared the dis­ease in a few pa­tients—some of whom needed no ad­di­tional treat­ment. Other horses showed a lesser re­sponse but still im­proved. This dif­fer­ence is an in­her­ent chal­lenge when stem cells are taken from the pa­tient, says Dr. Schn­abel.

“There is vari­a­tion in the qual­ity of stem cells from pa­tient to pa­tient,” she ex­plains. “What you get from a 3-year-old horse is dif­fer­ent [than] what you get from a 20-year-old horse or a horse that might have other is­sues.”

That’s why fu­ture re­search may in­clude us­ing cells from a horse other than the pa­tient—a horse with more op­ti­mal stem cells—to re­move some of that vari­abil­ity in re­sults. Re­searchers will also be work­ing to de­ter­mine the best de­liv­ery method for the treat­ment—one that will en­sure the best dis­tri­bu­tion and work most ef­fec­tively over the long term, says Dr. Schn­abel.

More to Come

These are just a few of the promis­ing ad­vance­ments in equine eye care now avail­able to vet­eri­nar­i­ans. More re­search is con­stantly in the works. There’s lit­tle doubt that own­ers can ex­pect more in­no­va­tion soon to help keep their horses’ eyes healthy and vi­sion crys­tal clear. For more in­for­ma­tion on ad­vance­ments in equine eye care, go to www.Prac­ti­cal Horse­manMag.com.

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