Resources

What is a cataract and what is the cause?
A cataract is an opacity of the normally transparent lens of the eye. It can range from a small opacity not significantly affecting vision to a complete opacity blocking out all vision in the eye. Cataracts generally lead to a cloudy or opaque appearance to the eye, but since other eye diseases can lead to similar changes, a ‘suspected cataract’ may be something different. Cataracts are commonly hereditary in origin, but can be secondary to other diseases such as diabetes, ocular inflammation and/or trauma, retinal disease and sometimes just old-age.

What is the treatment ?
Cataracts are either surgically removed or not treated. No medical treatment is effective in clearing them but if they are associated with inflammation of the eye anti-inflammatory drops are needed to keep the eye comfortable.

When should a cataract NOT be removed ?
All cataracts and suspected cataracts in animals require a thorough assessment by a veterinary eye specialist if the owner is considering cataract surgery. After examining an animal’s eyes and finding cataracts, I recommend against cataract surgery in the following instances:

• Insufficient visual impairment to mean that surgery will significantly improve vision and quality of life (very small or early cata-racts).
• Other ocular problems such as retinal disease which may mean that even when a cataract is removed, vision will still be poor.
• Animal is a high anaesthetic risk or has a low life expectancy, for example animals with major health problems or very old animals.
• Owner cannot afford the surgery – generally animals are not in pain with cataracts and while their quality of life is greatly improved if vision is restored, they can still be reasonably happy without surgery.

What does cataract surgery involve ?
Cataracts in animals are removed under general anaesthesia (humans are usually done conscious) through a small corneal incision using a probe inside the eye via a process of fragmentation, irrigation and aspiration called phacoemulsification. An artificial intraocular lens implant can be inserted in the eye after the original lens (which has become a cataract) is removed. This adds to the cost of surgery, but lens implants improve close vision after surgery and are standard in human cataract surgery. Artificial lens implantation is strongly recommended but it is not feasible in all animal eyes and the final decision to place a lens implant is based on the suitability of the individual eye at the time of surgery. Following surgery, your pet will usually go home later the same day and return for its first post-operative check between 1 and 5 days later. A number of further post-operative checks will be required over the next few months. Medications start with eye drops 4 times daily and gradually taper off over around 3 months, although some animals need to stay on once daily drops longer term.

What is the success rate of cataract surgery ?
Around 95% of cataract extraction surgeries in animals result in good, useful vision long-term. That also means that around 5% of operated eyes will have some sort of unpredicted complication meaning that useful vision is not restored. As with all surgical procedures, there can never be a guarantee of a successful outcome. More common complications include self-trauma related inflammation, retinal detachments and glaucoma. Occasionally due to the development of scar tissue or regenerative lens material, an eye has to undergo a minor follow-up ‘clean-up’ surgical procedure a few months after the initial surgery.

Cataract surgery in humans has a slightly higher success rate as it is a simpler, quicker, more routine and more controlled procedure. Cataract surgery in animals is a more involved and subject to a wider variety of complications than in humans for the following reasons:

• Animal lenses are much larger, meaning a more time consuming procedure to remove them.
• Animal cataracts are generally much denser, also increasing the time and effort involved with surgery.
• A greater inflammatory reaction by animal eyes to intraocular surgery prolongs post-operative medication periods.
• Animals are less easily controlled after surgery and more prone to self injury.

What is entropion ?
Entropion is a rolling in of the eyelid margin leading to rubbing, irritation and sometimes ulceration of the eye by eyelid hairs. It is painful and can lead to serious eye damage.

What is the cause ?
Most cases of entropion are due to breed-related eyelid anatomical problems such as over-long eye-lids or excess skin around the eyes and as such usually occur during development. Classic breeds include Sharpeis, Rottweilers, Mastiffs, Bulldogs, Spaniels, Retrievers and Persian cats. Occasion-ally it is secondary to another painful eye condition where spasm of the eyelid occurs.

What is the treatment ?
Entropion generally requires surgery to correct the underlying eyelid problem or pain and eye dam-age will continue.

What does entropion surgery involve ?
Entropion surgery is performed under general anaesthesia as day surgery. Excision of extra skin is performed with the aid of magnification. Most animals are fitted with an Elizabethan collar after surgery to minimize the chance of any rubbing of eyelid sutures. Twice daily antibiotic eye ointment is used post-operatively and sutures are removed after 14 days. Puppies less than 12 weeks of age with entropion usually undergo a minor procedure under very light anesthesia called eyelid ‘tacking’ to temporarily turn out the eyelids and prevent ongoing damage, but definitive surgery is often still required later in life if eyelid anatomical problems persist.

What is the success rate of entropion surgery ?
Very high in specialist hands, but we cannot give a lifetime ‘guarantee’ on surgery as eyelid conformation can change with time and age. However, in the unlikely event of further corrective surgery being needed within three months of the initial surgery we will re-operate at no charge. Re-operating does not of course include those cases where self trauma arising from failure to follow post-operative instructions leads to wound breakdown. Any re-suturing costs need to be recovered in such cases. Scarring is generally minimal and undetectable following surgery.

What is a corneal ulcer ?
A corneal ulcer is where the external surface of the cornea (the clear front of the eye) has been damaged. The initial cause is usually some form of trauma to the eye, but other factors can then come into play. Corneal ulcers can be shallow or deep, small or extensive, infected or non-infected, healing or non-healing. All ulcers are painful and all have the potential to become very deep, leading to rupture and loss of the eye. Quite often both eyes will be affected during a pets lifetime and occasionally they will be affected simultaneously.

Why do some corneal ulcers not heal ?
Shallow, broad, non-infected non-healing corneal ulcers (sometimes known as indolent ulcers) are particularly common in dogs and cats. The inability of some ulcers to heal appears to be due to defects in the healing mechanism relating often to genetics (certain breeds) and age (older animals are more prone). Classic canine breeds for non-healing ulcers include Boxers, Corgis and Staffordshire Bull Terriers, while Persian, Exotic Short-Hair and Burmese cats are also often affected.

What are the treatment options for non-healing ulcers ?
The healing process has to be stimulated into action. This can sometimes be achieved by corneal diamond burr debridement under sedation and local anaesthesia, followed by placement of a bandage contact lens. Larger and more long-standing non healing ulcers are best treated with superficial keratectomy surgery under general anaesthesia to remove the unhealthy surface layer of the cornea (performed at high magnification with the aid of an operating microscope), with the eye being temporarily covered by a third eyelid flap (nictitans flap) for 2-3 weeks to promote rapid, uninterrupted healing and adhesion of the new surface layer. Operated eyes are frequently initially slightly cloudy following surgery and further eye drops may then be required to settle down any residual corneal inflammation causing this cloudiness. Long-term scarring is usually minimal following surgery providing eyes have not been left for too long prior to surgery and typically any such scarring does not interfere significantly with vision.

What are the success rates of burring versus keratectomy?
Corneal diamond burr debridement has a 50-80% success rate depending on ulcer size and duration.
Superficial keratectomy in specialist hands has a success rate approaching 100% in dogs, although occasionally a second procedure is required in cats.

What is ‘cherry eye’ ?
‘Cherry eye’ refers to a prolapse of the gland of the third eyelid. The third eyelid in animals is not really an eyelid, but rather a fold of conjunctival tissue (the same tissue that lines the inner surfaces of the upper and lower true eyelids and covers the white of the eye). The gland of the third eyelid is important in tear production, along with another tear producing gland under the upper eyelid. Technically the third eyelid is called the nictitating membrane or nictitans, so the correct name for cherry eye is nictitans gland prolapse. It leads to irritation of the eye and degeneration of the gland.

What is the cause ?
Most cases of cherry eye are due to what is thought to be breed-related poor development of a ligament which should hold the third eyelid gland tucked away out of sight in the base of the third eyelid. Prolapse of the gland usually occurs as a sudden onset event during development and both eyes can be affected. Classic breeds include Shih Tzus, Lhasa Apsos, Maltese Terriers, Sharpeis, Beagles, Bulldogs, Cavalier King Charles Spaniels, terrier and ‘squashed face’ breeds. Occasionally some larger breeds such as Newfoundlands, St Bernards, Great Danes and Neapolitan Mastiffs develop cherry eye, but it is usually complicated by other problems involving the third eyelid cartilage.

What is the treatment ?
Cherry eye generally requires surgery to reposition the gland back into its original location or irritation and gland degeneration will continue. Simple excision of the gland should be avoided as it can lead to the development of dry eye problems which can be difficult and expensive to treat.

What does cherry eye surgery involve ?
Cherry eye surgery is performed under general anaesthesia as day surgery. A pocket surgical imbrication or ‘pocket’ technique is usually used to tuck the gland back into position and retain it there. Twice daily antibiotic eye ointment is used post-operatively and an external suture is removed after 10 days.

What is the success rate of cherry eye surgery ?
Approaching 100% in specialist hands in small and medium breeds, but the longer the gland has been prolapsed the more likely complications are to arise. A more involved initial procedure and/or second procedure may be required in large/giant breeds due to the severity or complexity often associated with this problem in these particular breeds.

What causes viral eye infections in cats ?
Viral eye infections in cats are part of the ‘cat flu’ complex of diseases. The specific cause of eye infection cat flu cases is Feline Herpes Virus (FHV). This virus is very common in the domestic cat population and many cats are carriers. Even cats fully vaccinated for cat flu can acquire the infection as this particular vaccine often only stops more severe or classical diseases from occurring, whereas less typical forms such as chronic eye infections will still occur. Once an infection has become established it will often become life-long although the severity of signs may wax and wane, often becoming worse during times of ‘stress’. This virus is NOT transmissible to humans.

What are the signs of FHV infection ?
Apart from sneezing and snuffling associated with upper respiratory tract infections with FHV, the virus may target the eyes, most commonly causing redness and discharge (conjunctivitis) and sometimes other problems such as corneal ulceration and sequestration (layer of dead black tissue on the cornea) and sometimes a more unusual disease called eosinophilic keratitis. Kittens are more susceptible to severe disease, while adults often show milder but more persistent signs. Typically purebred cats such as Persians, Burmese and Siamese are more prone to infection than ‘moggies’.

What is the treatment ?
There is no cure for FHV infections in cats. The severity and duration of signs can be reduced in some cases with eye drops or tablets, but these generally only slow viral replication or treat secondary problems rather than truly eliminate infection. Corneal problems will often require surgery for resolution.

What is PRA ?
PRA stands for progressive retinal atrophy and refers to a slow, progressive dying off of the retina. The retina is located at the back of the eye and is a bit like a film in a camera. It is responsible for absorbing light and images and converting them into a signal for the brain to interpret. Slow dying off of the retina leads to blindness over a period of months to years, with night vision generally being lost first followed by day vision. Sometimes cataracts will develop as a secondary event, probably due to release of toxic agents from the degenerating retina.

What is the cause ?
PRA results from a hereditary genetic defect which leads to the early degeneration of retinal tissues. A variety of types of PRA exist, differing in breeds affected, age of onset and rate of progression. Age of onset varies from a few months old to a few years old, the latter being more common. Most forms of PRA are recessive, so the parents of an affected individual may not have the disease. Commonly affected canine breeds include Miniature and Toy Poodles, English and American Cocker Spaniels, Labrador Retrievers, Australian Cattle Dogs, Lhasa Apsos and puppy farm bred ‘pet shop crossbreeds’. PRA is sometimes also seen in cats, particularly Siamese and occasional ‘moggies’.

How is it detected ?
Specialist eye and retina examination is the usual form of detection, but other tests such as an Electroretinogram (ERG) or DNA test can be used for earlier detection in selected breeds (see prevention below).

What is the treatment ?
There is no effective treatment for PRA. The younger the age of onset, the faster the progression (and vice versa).

How can it be prevented ?
Eye screening by a veterinary eye specialist is currently a practical and reliable technique to detect PRA in breeding animals and thereby prevent breeding from affected individuals. At risk breeds need to be checked annually until they are well beyond the usual age of onset. However, eye screening will not detect carriers or disease in animals prior to the age of onset (which can be as late as 5 or more years old in some breeds).
Breeding outcomes should be remembered with recessive hereditary conditions to avoid a mating which could produce affected offspring:

• Normal x normal parents = 100% normal offspring
• Normal x carrier parents = average 50% normal offspring, 50% carrier offspring
• Carrier x carrier parents = average 25% affected, 50% carrier, 25% normal offspring
• Normal x affected parents = 100 % carrier offspring
• Affected x affected parents = 100% affected offspring
• Carrier x affected parents = average 50% carrier, 50% affected offspring

DNA tests are now becoming available and they have the great advantage of being able to detect both affected animals, prior to onset of problems, and carriers. In fact they can be performed on a simple cheek swab. More information is available from a company called Genetic Science Services: www.geneticscienceservices.com or 03 84127077.

What is dry eye ?
‘Dry eye’ or keratoconjunctivitis sicca (KCS) is the condition where the tear glands of the eye are producing insufficient tears to keep the eye lubricated, washed, healthy and comfortable. This manifests as persistent thick sticky discharge from the eye or eyes, redness, cloudiness and vision threatening damage due to the eye drying out.

What is the cause ?
The vast majority of cases are due to the animal’s own immune system mistakenly attacking the tear gland or glands (immune-mediated inflammation) during middle age. Other rarer causes include a lack of proper tear gland development from birth, trauma and drug reactions. Classic breeds include Cavalier King Charles Spaniels, Cocker Spaniels, West Highland White Terriers, Staffordshire and English Bull terriers, Bulldogs, Mastiffs, Shih Tzus, Lhasa Apsos, Pugs and terrier breeds in general.

What is the treatment ?
Immune-mediated dry eye is treated medically with ointment or drops which control the inflammation that has caused poor tear production, allowing tear secretion to recover. If this condition is not treated your pet will go blind, but unfortunately treatment is usually lifelong as immune-mediated inflammation tends to recur if medication is stopped. In other words dry eye is controlled not cured. If there is a poor response to this type of medication, artificial tear preparations can be used to help make the eye(s) more comfortable. Finally surgery to move a salivary gland duct to the eye can be performed so that the animal salivates into the eye to keep it moist, but this can be associated with problems due to excessive facial wetting, mineral deposits on or around the eye and irritation from the saliva.

What is the success rate of dry eye therapy ?
The great majority of immune-mediated dry eye cases can be well controlled with medical therapy, but this requires diligence and persistence on the part of the owner!