However,declining vision is not necessarily a major handicap for dogs, as they rely much more heavily on their sense of smell than of sight.
Even a puppy will tend instinctively to search for a titbit dropped on the ground using its nose rather than its eyes.
DEAFNESS: A dog may also be afflicted by deafness as a result of advancing years.
This is difficult to recognize with certainty, although you are likely to find that you dog does not respond in certain situations-perhaps when you call it from some distance away-whereas in the past it would have shown some recognition of your call.
Cases of deafness increase dramatically from the age of about ten years onwards, when perhaps one in ten dogs suffers from the condition; the figure rises six-fold in dogs of fourteen years old and above.
Your vet will be able to carry out certain hearing tests on you dog, but little can be done to treat deafness at present.
MENTAL PROBLEMS: There is now growing recognition among vets and canine experts of declining mental faculties in old dogs, even to the extent of identifying a canine equivalent of Alzheimer's syndrome.
Like their owners, dogs are now tending to live longer than in the past, and so such ailments are becoming more commonplace.
One of the most frequently seen problems in older dogs has been dubbed "geriatric separation anxiety", signs of which usually become apparent at night when the household is asleep.
The dog wakes up, and feels disoriented.
It starts barking and panting, showing signs of obvious distress;in an extreme case, it may even soil its surroundings.
If this happens with your dog, you must give reassurance rather than reacting angrily least so that everyone can go back to sleep.
You should then arrange a veterinary check-up as a matter of rgency, in case there is an underlying medical reason-such as a tumour-for your dog's behaviour.
TUMOURS: Advances in veterinary care are now helping to treat a number of the ailments of old age.
For example, instead of having to rely largely on surgery to treat tumours in dogs, a vet may be able to use chemotherapy or radiotherapy.
Cryosurgery can also be useful in situations in which conventional surgery could be dangerous because of the blood flow to an area, or because of an underlying risk of infection.
This technique uses a special probe to apply freezing liquid nitrogen to a tumour, to mask it off from the surrounding healthy tissue.
There is no need for a scalpel.
By freezing the cells comprising the tumour, the liquid nitrogen should kill them so that in due course they slough away, hopefully to be replaced by healthy cells.