Cataracts are opacities within the lens that may affect a small portion of the lens or the entire lens. These opacities vary from an incipient form (barely discernible ie retina easily seen), to a mature (retina not seen) to a hypermature or Morganian cataract (parts of retina seen as lens cortex or the “egg-white clears”). Most cataracts develop as a result of abnormalities in metabolic pathways but the precise mechanisms are poorly understood and still the subject of a lot of investigation. I make the analogy when explaining to clients, that the lens is becoming more hard-boiled as the cataract develops.

What is not cataract

The most common change in the lens which is mistaken for cataract is nuclear sclerosis. All dogs from eight years of age onwards undergo a process whereby the lens nucleus becomes more-dense. This gives the pupillary area a greyish appearance but the retina can be easily examined using an ophthalmoscope. It is possible to have nuclear sclerosis and cataract coexisting, in which case retinal detail will gradually be lost.

Why did my dog develop cataract ?

Heredity, metabolic diseases, senile changes, trauma, nutritional deficiencies, toxins, drugs, radiation therapy and inflammation will cause cataracts in dogs. The major causes in NZ are:

• Heredity — inherited cataracts affect a large number of breeds in New Zealand. Most cataracts are recessively inherited and many will progress to complete blindness in the affected individual. In a breed such as the Bichon Frise, the development may not be bilateral and cataract development in one eye can precede the development in the other by several months or a year. Breeds such as the miniature schnauzer, Boston terrier and Staffordshire Bull terrier will develop cataract as early as three months of age and be totally blind by 2-3 years. Some breeds such as the Labrador retriever, Golden retriever and standard poodle have an inherited cataract form which in most cases does not progress to blindness but nevertheless is not desirable in breeding programmes.
• Metabolic Disease — the most common seen by myself is diabetes mellitus. Up to 60 or 70% of diabetic dogs will develop cataract which is usually of sudden onset (dogs can go from being visual to completely blind within 3-5 days). These animals are usually middle-aged to older and represent a large portion of the cataract patients we see. There are some special considerations both surgically and post operatively with regard to anti-inflammatory treatment one must consider in these cases, but overall the results are extremely gratifying.
• Senile — these can be amenable to surgery but it is essential there is early referral for retinal assessment (Generalised Progressive Retinal Atrophy needs to be ruled out as well as any other coexisting retinal diseases). The situation can then be monitored until the optimum time for surgery is assessed.
• Trauma and inflammation — some of these cases are not amenable to surgical intervention because of intraocular changes such as adhesions and pigment deposition which detracts from an overall successful result. The exception in my experience can be the acute cat-scratch injury in young pups which causes lens damage and secondary cataract. If recognised early, cataract surgery can save an eye and give good useful vision

Diabetic cataract- 6yo crossbred Terrier

How are cataracts treated

It may be argued that an older sedentary dog with cataract and no vision has a good quality of life. This may be so but many of our cataract patients are young to middle-aged dogs and the vast majority of the owners of older dogs, would like to give their aging companion the chance of sight if the choice is available. At this time surgery is the only viable alternative as there is no available product on the market which will remove cataract. Drug therapy in the form of atropine which dilates the pupil can sometimes be used in situations where nuclear (“yolk” or central area) cataract is causing the major visual disturbance, but the cortex (“white” or outer) is relatively clear. From my perspective, I will give you an assessment where the cataract surgery is a viable option or not. I do not question the wisdom or otherwise of cataract surgery in older animals as this is really a decision for the owner — the judgement that “the animal is too old for surgery,” can be offensive to many owners!

What sort of visual function and does the animal have post surgically

• After cataract extraction animals do not require a focusing lens. They do not have the same degree of visual acuity as man and do not require it in their daily lives as they utilise other senses such as hearing and smell.
• The surgery aims to give a blind animal vision and allow it to live a relatively normal life.
• Adequate vision can be achieved without a lens because:

(a) Accommodation in the normal animal is poorly developed and the absence of lens has little effect.

(b) Lens represents only 10-20% of the total optical power of the eye – the cornea is more important for the visual focusing function.

• It will be found that the dog may have some trouble focusing on near objects at first, but will get better at this with time. Far vision will be good. The ability of an animal to approach the normal optical state is more likely to occur the younger the surgery is done!

The visual improvement in a 12-year-old diabetic dog is noticeable within hours of surgery!

How is cataract diagnosed

In many instances an observant owner will notice a difference in the look of an eye(s). The pupil will appear more cloudy rather than dark and there will be subtle changes in the animals ability to see eg walking into objects, inability or clumsiness when fetching. Many cases get referred because a veterinarian may notice a change during routine health examination. Many breeds have a greater propensity to develop cataracts so there is a greater awareness by breeders and owners of these breeds.

What will happen if cataracts are not removed

The longer a cataract remains in a dogs’ eye the more likely cataract associated pathology which can cause severe pain or permanent blindness will be seen. In most cases these cataract-related disorders could be avoided by early surgical cataract removal. These disorders are:

• The leading one is Lens Induced Uveitis.(LIU)–this is an autoimmune disorder in which the immune system launches an inflammatory response within the eye, when lens protein materials leaks out of the lens through the lens capsule. We are suspicious this is happening when one is presented with an eye with a mature cataract and a ‘red eye’. LIU can result in glaucoma, adhesions within the eye, pigment deposition and dislocation (luxation) of the lens.
• Dislocation or Luxation of the Lens — the longer a cataract remains in an eye the thicker and more contracted the anterior and posterior capsules become. This contraction process tears the supporting zonular ligaments leading to subluxation and eventual luxation.
• Posterior Capsular Opacities — these are more likely to form in mature cataracts and will cloud vision when the lens is removed (the posterior capsule is always left intact in cataract surgery to prevent vitreous prolapse). The longer a cataract is left in place the greater the chance of these forming.
• Pigment Deposition — this may follow cataract surgery if there has been a prolonged bout of LIU prior to surgery and effectively cause the same problems as capsular opacities.
• Glaucoma — prolonged LIU can cause adhesions which disturbs the flow of aqueous through the pupil or out the angle of filtration, thus producing a secondary glaucoma.
• Retinal Detachment — in the Bichon Frise there appears to be a high correlation between mature cataract and retinal detachment which results in permanent blindness. Early removal will greatly reduce the risk and the chance of retinal detachment.

Lens induced uveitis –note the red eye and inflamed iris with a very mature cataract

Glaucoma in a young doberman

When is the best time to remove cataracts

In the situation where it is evident that there is progression of the cataract(s) and the animals vision is becoming compromised, early referral is advised so that a full ophthalmic examination can be done with particular reference to the state of the retina. Some cataracts can form secondary to retinal disease e.g. I would always be suspicious of retinal disease if a five to six-year-old English Cocker or Labrador retriever developed cataract. At this point it may be advisable, depending on the rate of progression and the maturity of the cataract, to either monitor the situation or go to surgery.

In the case of an acute onset cataract e.g. diabetes, bearing in mind what may happen if the cataract is not removed, then early surgical intervention is best advised. If surgery is not contemplated or has to be postponed, then the eyes must be monitored for LIU and a start made on prophylactic topical anti-inflammatories if needed e.g. Predforte one drop one to two times daily.

Why is cataract surgery so expensive

Currently the cost of cataract surgery in our clinic is in the region of $1700-1900 for one eye to $2700-2900 for both. The equipment used for this procedure expensive with phacoemulsification units currently costing $50-$80000 and the consumables such as sutures and instruments are costly. This cost structure will also include several post-operative checks in Palmerston North or in any of the other clinics I visit in New Zealand.

What if cataracts are secondary to retinal disease

In a situation where a retinal disease is either suspected or known, and cataract progression has been mainly responsible for the sudden progression of the visual difficulties the dog is having, surgery will allow the utilisation of what retinal function the dog has left. It is important to warn the owner that the surgery will not halt the progression of the retinal disease. I have seen cases where there has been noticeable benefits for the animal in this situation.

What are the risks involved with cataract surgery

Cataract surgery is a highly successful procedure but there are risks. The chances of having improved vision after surgery are high (80 to 90%) but 5 to 10% of dogs may suffer complications.

• Scar tissue — all dogs develop some intraocular scar tissue. Excessive scar tissue will limit vision.
• Glaucoma — occurs in some dogs that have cataract surgery. There is a breed predisposition to this problem so that good presurgical assessment is necessary to minimise this complication.
• Retinal Detachment — certainly a factor in the Bichon if cataracts are left in too long.
• Intraocular Infection — while this is rare it can cause loss of the eye.
• General Anaesthesia — these days with Isofluorane anaesthesia, fluid support and close monitoring with pulse-oximeter, maintenance and recovery from anaesthesia poses few problems with all cases going home the day of surgery.

Why do clients ask for cataract surgery

Cataracts are the most common cause of treatable visual deficits and blindness in dogs. The overriding feeling amongst most of the owners I see who present their animals for assessment, is the emotional upset of seeing their companion trying to cope with blindness. My job is to assess the advisability or not of surgery strictly on the basis of whether a good surgical result can be achieved. Once some clarity is obtained in this area then the final decision is left to the owner. I am no longer surprised at the commitment many owners have for their animals and take great delight in restoring very useful vision to most of the cases I see.

What is the owners’ input

The owners major input is in transport, paying the bill for the surgery (and hoping for an improvement in relations with the dog if there was a problem prior to surgery-payback time!),instilling drops into the eye pre and post-operatively for up to 6-8 weeks and returning after the surgery for post-operative checks. The administration of drops is most frequent in the first week after surgery then tapers off considerably.

6yo Bichon –before and after cataract surgery-note bubble of air to reinflate eye!

The operation

This involves -

• General anaesthesia – The anaesthesia involves induction with an intravenous drug but maintenance for the duration of the surgery is oxygen and an anaesthetic gas (Isofluorane).

This ensures – (a) A smooth and quick post operative recovery.

(b) Minimal risk for older patients (a lot of our cataract patients are dogs over 10 years of age).

(c) A respiratory monitor is used in the anaesthetic system to warn of any problems during the surgery.

• Opening the cornea 180 degrees or if phacoemulsification is utilised, then a 3mm incision at 12 o’clock is used. Phaco is used on dogs up to 6 years of age. After this the lens becomes hard and the eye will have to be opened more

in order to extract the large lens.

• Removal of the lens material inside the capsule of the lens i.e. making the analogy between the lens and an egg – we remove the end of the egg shell and remove the contents leaving the residual egg shell to hold the eye contents in place.
• During the surgery these lens contents are released into the eye will cause an intense inflammatory reaction. The frequent drug therapy before and after surgery is designed to suppress this reaction but treatment may be necessary for several months afterward.
• The cornea is stitched back in place and the eye is reinflated with air and saline.

Pre and post-operative medications-what they achieve

• 1% Atropine – this keeps the pupil dilated to allow vision and reduce the possibility of adhesions of iris to residual lens capsule, reduces the pain from iris spasm in the eye and reduces the release of debris into the eye which can cause adhesions.

• Cortisone (steroid) eye drops eg. Predforte, – suppresses the inflammation within the eye. These drops:

(a) Will be used for a minimum of 4-6 weeks after surgery and maybe longer(months or indefinitely at a v low dose).

(b) Shake the bottle before use (esp. Predforte).

(c) If while using these drops the eye becomes ‘sore’ ie the eye blinks more than normal and is kept tightly closed, there is excessive production of tears, cornea goes blue with discomfort and the blueness is over most of the cornea or the animal suddenly starts rubbing the eye, stop the drops contact me or your own vet. I do not mind phone calls to my clinic or after hours to home or my mobile if you are concerned.

• Prednisone tablets – have the same effect as 2. A side effect of these tablets on the initial high dosage (we reduce the dose over a 4 week period) is that they:

(a) Increase your pets’ appetite – do not feed any more than necessary as they will put on weight.

(b) Increase the thirst and frequency of urination. Ensure there is plenty of fresh water available and let outside frequently!!!

(c) Cause your pet to be less active and pant a little more than normal. If you feel any of these side effects are excessive, please contact me.

• Rimadyl/Norocarp (20mg or 50 mg tablets) – has a similar effect to Prednisone but will not be used together. This drug is best given with food and has very good anti-inflammatory and pain relieving properties. We will often use these for the first 14-21 days after surgery then change onto Prednisone tablets if needed.

• Antibiotics – used immediately after surgery but will only be used as a course of treatment in diabetic animals because of their greater risk of infection.

The stitches in the cornea will dissolve in 6-8 weeks and they may cause a mild reaction in the cornea so that a low dose of eye drops may be needed.

The assessment of whether vision has been returned is best left for at least 2 weeks to allow debris within the eye to clear, although some vision may be attained within hours to several days. Creating an obstacle course, letting cotton wool balls fall in front of the eye or general behaviour around the house can be some guide. An examination by myself would allow more accurate assessment. The fact that the pupil is dilated with Atropine will reduce good optical function but this will improve when the pupil starts moving again (takes 5-7 days after the drops stop for this to occur)

It should be stressed that not every cataract operation is successful in restoring vision. Rarely is the eye ever lost or ends up looking a lot different to an observer but there are a variety of problems which can occur either during surgery or at varying periods afterwards, over which we have little or no control. These have already been mentioned.

These problems can be minimised by meticulous surgical technique, attendance to medicating the eye post operatively but even when everything seems right technically, restoration of vision may not eventuate. The success rate in my hands is high as we have the equipment and the experience to do this type of surgery.

My policy is not to charge for the first post operative visit as I would like to check on the progress of the eye for several months even years post operatively. The only future costs would be for any medication prescribed and a fee to cover rental costs at the clinics I use outside of Palmerston North.

Regards

Craig Irving -Specialist Veterinary Ophthalmologist

Ps –you have in the handouts relating to this ophthalmic service, my after-hours phone numbers and email address craigeyet@clear.net.nz which is probably the best means of contact unless the situation is urgent. I am very happy for you to ring if you have any problems or are unsure of what may be happening and cannot contact me at the clinic -a lot of time, effort and expense has gone into this surgery so I want to ensure its success. For peace of mind there may be a requirement for an earlier post-operative check than previously planned.

It has become possible to distinguish two essential subdivisions of the PRA complex, namely developmental and degenerative. According to whether the photo-receptor disease (i.e. elements in the retina which convert the light energy into electrical energy and give the so called vision in the brain) commences before or after maturation of the retina. As a generalisation it has been noted that in the developmental diseases eg Collie, onset of night blindness tends to occur before the occurrence of obvious changes in the retina when viewed by an ophthalmoscope, while in the degenerative condition eg Labrador, a degree of retinal change is usually present at the time of night blindness onset.

In the Irish Setter and the Collie there is an arrested development of the photo-receptors in the early post natal period, so that clinical and behavioural signs of blindness may be obvious by six months of age or earlier. With both these breeds research has shown there to be an obvious bio-chemical deficiency in the function of the retina.

The age at which PRA symptoms start in various breeds is:

3 months – 2 years: *Miniature Long-Haired Dachsund, Cardigan *Welsh Corgi, Cairn Terrier, *Irish Setter, Rough Collie, Smooth Collie

1 – 1 1/2 years: Norwegian Elkhound.

1 – 2 1/2 years: *English Springer Spaniel, Tibetian Terrier, Tibetian Spaniel, Miniature Schnauzer

3 – 5 years: * English Cocker Spaniel,*Labrador Retriever.

4 – 6 years: *Toy Poodle, *Miniature Poodle.

( * – seen by the author in New Zealand.)

Some of the more specific clinical features which we find with Generalised PRA are:

1. The condition is bilateral and symmetrical, i.e. both eyes are affected equally although there may be a small lag interval between the two.

2. You may notice that the dog in the early stages of blindness has good day vision but deficient night vision. In order to be able to display night blindness the dog of course has to be walked at night preferably without a lead so that it can display its visual deficiency. This may be seen as bumping into objects such as trees or even walking over the edge of swimming pools and falling into the water and trouble negotiating stairs (this is often reported by owners). Ultimately there is a point at which the dog is totally blind both night and day.

3. Far vision is better than near vision with a reduced ability to see stationary objects. Also there develops a degree of tunnel vision – the dog sees things immediately in front of it but not peripherally.

4. Dilated pupils are frequently observed by the owner. This is due to the reduced nerve impulse to the brain because the retina is dying, and as a consequence the feed-back to the iris is less so that the iris, instead of constricting in bright light, tends to be more relaxed and thus we get a dilated pupil. Also it will be noted that the eyes glow and look more yellow or green than previously. This is due to the dilated nature of the pupils and the increased reflectivity of the retina-it reflects light more than absorbing it because the retina is becoming thinner.

5. PRA is an inherited condition, which in those breeds examined (some 14 now) is the classic recessive type which everyone who did biology in school will remember as the first part of Mendelism. Very simply, a dog having both genes for PRA will develop the disease; if it doesn’t have the gene will never have it; or carries one gene and because its’ dominant associated gene prevents the recessive genes expression, the dog will appear outwardly completely normal, remaining fully sighted all its life but it is a true example of the ‘carrier state’.

Left -6mo Irish setter-normal retina Right-6mo Irish setter –littermate –serious blindness-note the smaller blood vessels, grainy area around optic disc and pale optic nerve

Any carrier has a statistical chance of passing on the same carrier status to 50% of his or her progeny who are themselves out of the ‘clear’ mate. These carriers remain hidden within the breed population until one day two carriers are bred together. Then, statistically 25% of the resultant progeny may inherit the gene to be affected by PRA and may go blind in early, or later, adulthood. Some of the littermates will carry the gene hidden in their genetic make-up, to possibly hand it on to the next generation. So here are the results of five possible matings with a recessive mode of inheritance:

1. Both parents affected
all progeny affected.
2. One parent affected – one carrier parent
50% progeny affected – 50% progeny carriers.
3. One parent affected – one parent free
all progeny carriers.
4. Both parents carriers
50% progeny carriers – 25% progeny free – 25% progeny affected.
5. One parent free – one carrier parent
50% progeny carriers – 50% progeny free.

From this it follows that both parents – sire and dam – and all progeny of an affected animal, must be at least carriers. A 2% incidence of the disease in the population means 24% of that population will be carriers. If the incidence is 10% then the carrier state is 45%!
No affected dog should be used for breeding or if the DNA status is known, then carriers can be bred to others of known status and offspring DNA tested. This way breeds can still be salvaged where there may be a high incidence of the carrier or affected state. The ideal, which is now available, is a blood test which can be done on all present breeding stock, to determine whether they are carrying either none, one (carrier) or both (affected) genes for PRA or any other genetic disorder (e.g. cataract). New-born pups could also be tested so that one could get an early insight into whether they may have a vision problem later in life (they could be euthanased or sterilised if they were only carriers).
This DNA test is now available in NZ with the DNA collected from an individual by a check swab or blood with the tests done in Australia.

At the moment all we can:

• Routinely examine all breeding stock and offspring for those problems that DNA testing doesn’t uncover –eg cataract.
• Test mating is no longer needed because of the availability of the DNA test.
• A national recording scheme of all pedigree stock is essential in order that the disease be eradicated in some of the worst affected breeds.
• Cataract development may follow in the latter stages of the retinal disease. The development of cataract will of course further impede the affected animal’s vision, but of course cataract surgery is not going to give any real benefit to the animal unless it is obvious that the onset of cataract produces a sudden change in vision and blindness. Surgery in selected cases can be of benefit and allow some use of the remaining retinal function but remember the retina is gradually degenerating.
• With the development of cataract it is possible that an inflammatory reaction may occur within the eye due to material leaking out of the lens into the eye. The eye reacts against this foreign protein. If this occurs the eye may show signs of redness and there will be some discomfort to your pet. Eye drops should be given for this and may involve long term treatment to control the problem. No treatment can result in continuing pain and the possibility of glaucoma developing in the eye.

• There is no known treatment for this problem as yet with total blindness the end result. The rate of progression can be different from one individual to another with the development of cataract variable as well.

There are other disease conditions which affect both cats and dogs where the final stages of the retinal disease can mimic the appearance of Generalised PRA (so called pheno-copies). It is very important from a breeder’s viewpoint that some distinction is made between the genetic and the non-genetic causes of vision loss in an animal. With this in mind it is most important before one hangs the label of blindness caused by a genetic disease i.e. Generalised PRA on an animal, that one consider the history, the breed, the age of onset of the disease and factors such as the appearance of the retinal disease (e.g. it is unlikely to be a genetic disease if only one eye is affected or there is an obvious difference between the two eyes).

Any disease which causes blindness in an animal is distressing probably more to the owner than to the animal. One of the advantages of Generalised PRA is that the onset of blindness is gradual thus giving the animal time to accommodate to its disability and better utilize its other senses such as hearing and smelling. Completely blind animals can have an excellent quality of life and one should not consider, unless in extreme situations, euthanasia.

New Zealand breed clubs are working to eliminate genetic disease from those breeds at risk. This involves yearly testing of pedigree animals and the interchange of information between breed members of the genetic status on dogs being used as studs (although this certainly could be improved further). The development of a national eye scheme is underway with the possible collation of all eye certificate examination results being logged into a national database.

Craig Irving
EYEVET SERVICES
Craig Irving – Registered Specialist Veterinary Ophthalmologist
84 Pitt Street
Palmerston North Ph 06-3575887 Fax 06-3575863
craigeyevet@clear.net.nz

DNA test providers for Inherited Canine diseases

• Genetic Science Services- Australia-www.geneticscienceservices.com
• America- www.optigen.com
• Both these sites offer a range of DNA tests for ophthalmic problems in dogs as well as other inherited diseases.