Final Exam - Equine Glaucoma & Lens

Question 1

what is normal equine vision?

Answer 1

large visual field with monocular & binocular vision

great at detecting motion - adapted to dim & bright light

dichromatic

Question 2

what are your treatment options for a blind horse? what should be prioritized above everything?

Answer 2

euthanasia, pasture pet, limited capacity use of the horse

prioritize the security/welfare of the horse & safety of handlers!!!

Question 3

what considerations should you think about when taking on management of a blind horse?

Answer 3

horse’s temperament, adaptation to vision loss, training, safety, economics, owner’s dedication, & presence of a safe & predictable environment

Question 4

T/F: horses have better vision than most domestic animals

Answer 4

true

Question 5

what is nuclear sclerosis?

Answer 5

age related change seen in animals 15-20 years old

nucleus & lens becoming more dense with the tapetal reflection still visible

Question 6

what is the most common glaucoma type in horses?

Answer 6

secondary more common than primary

Question 7

when is tonometry contraindicated for horses?

Answer 7

in horses with deep corneal ulcers & lacerations/perforations

Question 8

when is tonometry performed in your ophthalmic exam?

Answer 8

done before pupil dilation & after the auriculopalpebral nerve block

with head above the heart - IV sedation may decrease pressures

Question 9

what tonometry readings indicate glaucoma?

Answer 9

pressures > 30 mmHg with clinical signs/vision loss

Question 10

what are normal tonometry readings for horses?

Answer 10

10-25 mmHg is normal, under 30 mmHg

Question 11

what acute clinical signs are associated with glaucoma? what about chronic signs?

Answer 11

acute (<48-72 hours) - blepharospasm, epiphora, episcleral injection, transient corneal edema, & mydriasis

chronic - permanent corneal edema, haab’s stria, lens luxation, optic nerve atrophy, blindness, uveitis, buphthalmos, & narrowed/compressed ICA

Question 12

what is primary glaucoma?

Answer 12

abnormality of aqueous humor outflow & absence of concurrent ocular disease - rare in horses

Question 13

what is secondary glaucoma? what are some examples of causes?

Answer 13

obstruction caused by concurrent ocular disease

ERU, neoplasia, trauma, lens luxation, & after cataract surgery

Question 14

when considering therapy options for a horse with glaucoma, what must you consider?

Answer 14

think about their vision, ocular disease, age/purpose of the horse, economics, & ease of treatment

Question 15

what topical medication is most effective in reducing intraocular pressures in horses?

Answer 15

dorzolamine/timolol

DON’T USE LATANOPROST

Question 16

when is surgery indicated for a horse with glaucoma?

Answer 16

when medical therapy is not effective

Question 17

how is laser cyclophotocoagulation used for treating glaucoma?

Answer 17

surgery that destroys the ciliary body epithelium to reduce aqueous humor production

Question 18

how are gonioimplants used for treating glaucoma? what complications are associated with it? what’s the prognosis?

Answer 18

aqueous humor shunted to the subconjunctival space

risks - corneal edema, worsening uveitis, corneal ulceration, fibrosis around the implant, & uncontrolled glaucoma

prognosis is guarded for long-term maintenance of vision

Question 19

when are salvage procedures indicated for equine glaucoma?

Answer 19

medical therapy is inadequate & the horse has blind, painful eyes

Question 20

what is chemical ciliary body ablation? what complications are associated with this procedure?

Answer 20

gentamicin destroys the ciliary body epithelium

worsening uveitis, hyphema, & uncontrolled IOP

phthisis bulbi is expected!!!

Question 21

how is enucleation used as a salvage procedure for equine glaucoma?

Answer 21

fast recovery & a very low complication rate - also allows for histopathology

intraorbital silicone implant minimizes the sunken appearance of skin & is purely cosmetic

Question 22

what are cataracts?

Answer 22

true opacity of the lens classified by age, location, maturation, & etiology

Question 23

what are the different ages of onset that are seen with equine cataracts?

Answer 23

congenital, juvenile, adult, & senile/geriatric

Question 24

what horses are predisposed to congenital cataracts?

Answer 24

thoroughbreds, quarter horses, morgans, & rocky mountain horse

usually present with other anomalies

Question 25

what is the importance of location of cataracts in the equine eye?

Answer 25

need to specify where in the lens the opacity is for classification purposes!!!

Question 26

what are the 4 maturation categories for equine cataracts?

Answer 26

incipient - small opacity & <15% of the lens affected immature/incomplete - not 100% affected, still visual mature/complete - 100% of the lens is affected, the horse has a negative menace, no tapetal reflection hypermature/resorbing - lens cortex liquifies, lens shrinks, tapetal reflection can return, vision may return, & uveitis is present

Question 27

what is brunescence?

Answer 27

yellow lens - normal aging & seen with some cataracts!

Question 28

what is the most frequent cause of cataracts in horses? what are some other causes?

Answer 28

chronic uveitis!!!!!! inflammatory, inherited, metabolic, trauma, nutritional, toxic, etc

Question 29

what are the sequelae associated with cataracts?

Answer 29

visual impairment, lens-induced uveitis, lens luxation, glaucoma, & retinal detachment

Question 30

what topical drug is required for life for horses with cataracts?

Answer 30

topical NSAIDS to control uveitis

Question 31

what is phacoemulsification? what complications are associated with this procedure?

Answer 31

surgical procedure done to restore vision in horses with cataracts - high frequency vibrations emulsify cataract & it is then removed by aspiration through a small corneal incision poor success rate in horses!!!! corneal ulceration, uveitis, endophthalmitis, glaucoma, & retinal detachment

Question 32

why are horses not great candidates for phacoemulsification?

Answer 32

there is a poor success rate - ERU horses are not good candidates for this!!! extensive post-op care is required! vision after surgery is still compromised!!! may not be a safe animal!!!

Question 33

what horses may be a good candidate for phacoemulsification?

Answer 33

foals with congenital cataracts

Question 34

what horses do you especially need to do tonometry on?

Answer 34

horses with: corneal edema, red/painful eye, orbital/blunt ocular trauma, exophthalmos, buphthalmos, history of glaucoma in other eye, lens luxation/subluxation

Question 35

what lesion is shown here? what condition is it associated with?

Answer 35

haab's stria (striate keratopathy) chronic glaucoma

Question 36

what lesion is shown here? what condition is it associated with?

Answer 36

buphthalmos (visible enlargement of the eyeball) chronic glaucoma

Question 37

which photo of the iridocorneal angle is normal?

Answer 37

left photo is normal right is narrow & compressed

Question 38

which optic nerve is abnormal? how do you know?

Answer 38

optic nerve on the right is atrophied & abnormal! loss of myelin reveals reticulated lines of lamina cribosa

Question 39

what lesion is shown here? what does it mean?

Answer 39

phthisis bulbi - end stage ocular disease shrunken eye

Question 40

this foal has congenital glaucoma - what causes it?

Answer 40

developmental abnormality of the anterior segment

Question 41

what is your target IOP for a horse with high IOP?

Answer 41

wat it < 20 mmHg

Question 42

what horses are surgical candidates for glaucoma?

Answer 42

horses that have glaucoma but still have visual eyes!!!! still must control inflammation, IOP, & prevent infections after surgery

Question 43

in this photo, do you see nuclear sclerosis or cataracts? how do you know?

Answer 43

nuclear sclerosis - tapetal reflection remains intact, no affect on vision, & nucleus of the lens becomes more dense/apparent

Question 44

does age of onset = etiology for cataracts in horses?

Answer 44

nope

Question 45

what type of cataract is shown here? how do you know?

Answer 45

incipient cataract - small opacity with <15% of the lens affected still visual & you can see the tapetal reflection

Question 46

what type of cataract is shown here? how do you know?

Answer 46

immature cataract - larger than incipient, but smaller than mature! tapetal reflection is variable, but horse is menace positive

Question 47

what type of cataract is shown here? how do you know?

Answer 47

mature - 100% of the lens is affected, tapetal reflection isn't visible, & animal has lost its menace

Question 48

what type of cataract is shown here? how do you know?

Answer 48

hypermature - lens cortex liquifies, lens shrinks (wrinkles, deep anterior chamber) tapetal reflection may return, vision may return, & uveitis is often present

Question 49

what is this?

Answer 49

brunescence - increased yellow discoloration of the lens that occurs as a normal part of aging can also be seen in some equine cataracts

Question 50

what is the pathophysiology of chronic uveitis causing cataracts in horses?

Answer 50

mediators of inflammation diffuses into the eye & alters the lens structure/metabolism changes in aqueous humor production & synechiae

Question 51

what kind of cataracts are these?

Answer 51

mature cataracts from ERU