Common eye conditions in dogs
1) Conjunctivitis or ‘pink eye’
The conjunctiva is a mucous membrane that lines and protects the white of the eye and the eyelids. Dogs also have a ‘third’ eyelid or nictitating membrane which is also covered in conjunctiva. The third eyelid produces tear fluid and sits under the lower eyelid medially, moving across the surface of the eye to lubricate it.
Conjunctivitis is inflammation of part or all of this protective layer of the eye.
- Hyperaemia (inflammation) of the conjunctiva resulting in a reddened, hypervascular, injected conjunctiva.
- Chemosis or swelling of the conjunctiva and surrounding eyelids
- Epiphora or discharging eyes with excessive tear fluid production. The inflamed eye responds by producing tear fluid to aid healing.
- Mucoid green discharge around the eyelid margins.
- Blepharospasm or squinting/blinking eye closure from irritation
- Dog pawing at face or wiping head against surfaces.
- Infectious – bacterial, viral, mycoplasma, fungal and parasitic causes.
- Environmental irritants and allergens causing reactions
- Mechanical factors – foreign bodies like sand/grit, inverted eyelashes/eyelids, eyelid growths, ulceration of cornea, a dry eye can all lead to secondary conjunctivitis.
Treatment with topical eye drops should clear the inflammation within a week.
2) Corneal Ulceration
The cornea is the transparent membrane on the front of the eye that allows light to pass through while providing protection to the inner eye. The cornea is less than 1mm thick made up of layered transparent cells. This tissue is very sensitive and can become ulcerated easily.
Certain breeds with exophthalmos (bug-eyes) are more prone to corneal damage due to excessive exposure.
- Moderate to severe irritation with blepharospasm and severe squinting.
- Secondary conjunctivitis and epiphora or weeping eyes.
- Direct trauma to the eye
- Foreign bodies such as grit or sand stuck under eyelids
- Entropion, inverted eyelids, with trauma from the eyelash
- Distichia, an eyelash growing from abnormal location on the eyelid and causing topical irritation
- Eyelid growths can scratch the cornea, the same as a pebble in a windscreen wiper.
- Chemical irritation, commonly Stink Bug spray directly on the eye will cause ulceration
Under examination sometimes we can grossly see an ulcer of the cornea. This is usually a deep or larger ulcer. Milder ulcers require Fluorescein staining. This stain will colour the eye green and if there is an imperfection of the cornea the deeper cell layers uptake the stain in a fluorescent manner. We can then measure and assess the highlighted green ulcers.
Treatment depends on the severity. Milder ulcers will heal within 7 days with eye drops alone. More severe cases may require surgical intervention to clean the ulcerated area and promote successful healing. More aggressive surgery may be required if the ulcer is not healing or becomes a deep ‘indolent’ ulcer. These ulcers must be managed carefully, if they reach full depth and cause corneal rupture enucleation (eye removal) may be necessary.
3) Entropion and Ectropion
Entropion is an inversion of part or all of the upper/lower eyelids. This is a common inheritable defect which can affect any breed but more commonly sporting breeds, bulldog and wrinkly faced breeds such as Shar-Peis.
Puppies must be thoroughly examined to monitor for eyelid abnormalities and breeders should take action to prevent passing on this genetic defect.
Clinical signs are primarily eye irritation with secondary conjunctivitis and discharge.
Treatment requires structural correction. We must wait until maturity for surgical intervention. Puppies can have eyelids sutured or stapled into position while waiting for surgery. Surgery entails removing excess skin and pulling eyelids externally into a correct position.
Ectropion is slack, everted eyelid margin often bilateral affecting larger saggy faced breeds such as Great Danes, St. Bernard and Basset Hounds. These breeds often can have entropion and ectropion affecting the same eye in different eyelid areas, forming a diamond eyelid shape vrs oval.
Prolonged conjunctival exposure leads to recurrent conjunctivitis. Mild cases can be managed with eye drops and regular lavaging however severe cases benefit from surgical correction to shorten the eyelid margin.
The lens focuses light onto the retina where vision is perceived. Cataracts are opacities of the lens which block light reaching the retina and cause visual deficits and blindness. They must not be confused with the normal increase in lens nuclear density, ‘nuclear sclerosis’, which we see in ageing animals with pale blue lenses and does not affect vision.
The most common cataracts in dogs are congenital cataracts, diabetes mellitus secondary cataracts and spontaneous cataracts.
Congenital cataracts are seen once the puppies’ eyes open. Vision deficits are also noted.
Diabetic cataracts are caused by glucose saturation of the lens leading to a different metabolite sorbitol forming which is not readily diffused in the lens and leads to clouding and eventual loss of vision.
Surgical correction involving replacement of the lens is up to 95% successful. Results are best if the lens is replaced before full cataract maturity.
5) Dry eye – Keratoconjunctivitis Sicca (KCS)
KCS means inflammation of the cornea and surrounding conjunctiva due to a chronic dry environment, or ‘dry eye’.
- Unilateral or bilateral
- dry eye with secondary conjunctivitis and green mucoid discharge
- Irritation with blepharospasm
It’s due to insufficient production of the aqueous tear film from the tear glands. The tear glands are made up of lacrimal glands above the eye, tarsal glands along the eyelid and the nictitating membrane or ‘3rd eyelid’ below the eye. Autoimmune destruction of the glands lead to a dry, harsh environment.
We perform a Schirmer Tear Test (STT) on both eyes to measure the volume of tear fluid production in 60 seconds with a wicking paper placed under the eyelid. A healthy eye will produce >15mm in 60 seconds, levels below this are suspicious with levels <5mm severely dry.
A fluorescein stain test may be done to rule out secondary corneal ulceration from dryness.
The aim of treatment is to stimulate lacrimal gland tear fluid production. We have two drugs that we commonly use for this, Optimmune and Tacrolimus. It can take a number of weeks for gland function return, in that time we might need to supplement the eye with lubricant eye drops. This condition will require long term management to maintain optimal ocular hydration and health.
6) Prolapsed Nictitating Membrane or ‘Cherry Eye’
Swelling, inflammation and prolapse of the nictitating membrane or 3rd eyelid is common in juvenile dogs. It can occur in any breed but more commonly brachycephalic breeds such as bulldogs and pugs. The 3rd eyelid is a vital structure for tear fluid production and maintaining optimal ocular hydration.
Patients present with a prolapsed ‘cherry eye’ on the medial aspect of the eye. With prolonged exposure it can become dry and irritated. Both eyes can be affected.
On the first presentation for prolapse the gland can often be gently replaced. If repeat prolapse occurs surgical replacement of the gland to its correct position is recommended to allow normal tear production. To read up more about Cherry eye, check out our blog here.