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!