Ocular Diseases of Companion Animals

Animal Technology VT-116Adapted from Dr. Kristek

The Eyelids• Serve to protect, clean, and keep the globe

hydrated• Common diseases:

– Entropion• Hair chronically touches cornea• Shar Pei, Chow, Bulldog, Golden Retriever, Persian cats,

also seen in lambs and kids• Can be hereditary or acquired: spastic entropion

secondary to pain– Ectropion

• Exposure of conjunctiva leads to inflammation and higher risk of infection

• St. Bernards, spaniels, hounds

The Eyelids• Entropion • Ectropion

The Eyelids• Meibomian Glands

– aka Tarsal Glands– Produce meibum, a

lipid-heavy secretion that slows down tear evaporation and increases surface tension, holding tears in-between eyelids and surface of eyeball

Lacrimation

The Eyelids• Meibomian Gland Adenoma

– Most common form of neoplasia in the eyelid in dogs

– Nearly always benign– Most common in dogs > 8 years old

• Other eyelid tumors– Melanoma, basal cell carcinoma, squamous cell

carcinoma (SCC), adenomas, papillomas

“Cherry Eye”

Conjunctiva• Conjunctivitis – inflammation of the

conjunctiva– Most common eye disease in domestic

animals– Can be due to infection, trauma, or allergic

response– Common signs:

• Erythema• Discharge• Inflammation• Discomfort (demonstrated by repeated blinking,

squinting, or abnormal head position)

Feline Herpesvirus

The Cornea• Corneal ulcer – a break or erosion in the layers

that form the cornea

The Cornea• Corneal ulcer

– Can be the result of trauma, infection, or of idiopathic causes

– Can affect one or more of the five layers of the cornea:

1. Epithelium2. Bowman’s Layer/Bowman’s Membrane3. Stroma4. Descemet’s membrane5. Endothelium

The Cornea• Corneal ulcer

–Not usually visible to the naked eye• Fluorescein eye stain test

–Two categories:• Simple ulcers

• Deep Ulcers

– http://www.youtube.com/watch?v=3dr1FQB6Va8

The Cornea• Keratoplasty

– A graft of conjunctiva or flap of donor corneal tissue is placed over the site of the descemetocele.

– The graft provides immediate blood supply to damaged or abnormal cornea to speed healing and increase the amount of medications reaching the area

The Cornea• Corneal Debridement

– Debridement of the ulcer promotes healing by removing the outer non-adhering layer of the cornea with a cotton swab.

The Cornea• Grid Keratectomy

– The tissue under the diseased outer surface of the cornea is altered by making tiny scratches on the surface with a fine gauge hypodermic needle.

The Cornea• Superficial Keratectomy

– The outer or superficial layer of the affected cornea is surgically removed by careful dissection, using an operating microscope.

The Cornea• Pannus

Fluorescein Dye TestPROCEDURE:• Take out the Fluorescein dye strip, being

careful to handle the non-dye end• Apply a drop of eye wash or saline to the

orange end of the strip, and touch the strip to the animal’s eye– If only one eye appears infected, touch the normal

eye first, then the infected eye• Allow the animal to blink

Fluorescein Dye TestPROCEDURE cont’d:• Rinse the eyes will with eye wash• Use a wood’s lamp, an ophthalmoscope with

blue light, or even a simple pen light to examine the surface of the cornea for any retention of stain. It may be very subtle, or very obvious – so take your time examining– May wish to darken room to better visualize the

stain

Fluorescein Dye Test

The Uvea• Uveitis

–MANY causes, may be multifactorial• Infection• Immune-mediated reaction• Metabolic• Parasitic• Traumatic• Neoplastic

Uveitis

KCS

Schirmer Tear Test (STT)• Requires the use of a special tear test strip

which looks like a small piece of filter paper, sometimes with a scale in millimeters printed on it

• The end of the strip is bent and then carefully placed under patient’s lower eyelid

• Leave the strip in this position for 60 seconds• As the tear film travels up the strip, it creates a

line that can be measured on the mm scale

Schirmer Tear Test

Schirmer Tear Test• Normal tear production in the dog is 14-24

mm/minute

• A KCS diagnosis will be made with less than 10mm/min results AND clinical signs of KCS

• One low measurement of tear production without clinical signs is not diagnostic of KCS

Infectious Bovine Keratoconjunctivitis“Pink Eye” in cattle• Highly Infectious, highly contagious

– Pathogen is the bacteria Moraxella bovis– UV exposure and dust irritants can lead to infection – Transmitted by face flies

• Tx: antibiotics, fly control, reduce dust–Nictitating membrane or eyelids may be

temporarily sewn over the eye in cases of severe corneal ulceration

Infectious Bovine Keratoconjunctivitis

The Lens• Classification of cataracts:

–Congenital – present at birth–Juvenile – occurs in young dogs. Usually

hereditary–Diabetic – related to abnormal glucose

metabolism–Senile – due to aging–Secondary to PRA, diabetes, or uveitis–Traumatic – secondary to injury

• http://www.youtube.com/watch?v=yypMG4kB8zc

The Lens

The Lens• Luxated Lens

– The suspensory ligaments that attach lens to the ciliary break free

The Retina and Optic Nerve• Retinal Hemorrage

Open-Angle Glaucoma• In open-angle glaucoma,

the drainage canals themselves are blocked, but the space between the iris and the canals are open

Closed-Angle Glaucoma• In closed-angle glaucoma,

the opening to the drainage canals are blocked by another structure, the angle between iris and cornea is closed

Tonometry• Procedure:

– Apply topical anesthetic to eye, one drop per eye, repeat 2 to 3 times in 3-5 minute intervals

– Calibrate your tonometer– Elevate patient’s head vertically– Rest the base of the tonometer on the center of the

eye and let it bear the full weight on the cornea– Take a reading off the scale, then remove the

tonometer– Take 3 to 5 readings from an eye, and average your

readings

Tonometry• For the Schiotz tonometer, the relationship

between the IOP and the reading is inverse: the lower the reading, the higher the pressure

• Normal is 3.5 to 6.5 (using the standard 5.5g weight)

• If the reading is below 3.5, then additional weight is needed

• Actual (converted) IOP normals:– Dog: 12.2 – 25 mmHg– Cat: 10 – 25 mmHg