Findings of Ophthalmic Visit to Iceland
Lorna Newman Cert VOphthal BVM&S MCVS
I visited Iceland 12-14 November 2010 at the invitation of Soffia Kwaszenko on behalf of the Shih Tzu Breeders Club to look at their dogs and for any other dog owners who may also wish to have an eye examination.
The eye examinations were carried out under the standard protocol of the KC/BVA/ISDS Kennel club scheme. A standard letter detailing this scheme is enclosed.
I have been a standing member of the BVA Eye Panel scheme for the last 15 years. All examinations included a full examination of the eye and adnexa with direct and indirect ophthalmoscopy and slit lamp biomioscopy following dilation of the pupil with tropicamide drops. Examination of 73 dogs was carried out over two consecutive days.
The results of individual dogs have been submitted to you. The main area of concern was the possible presence of a retinal atrophy condition in the Shih Tzu breed, which had been diagnosed during previous examinations.
From my examinations, four Shih Tzus were found to have abnormalities present which could represent a retinal degeneration type condition. The condition present matches closely the one recently described in Japan (Vet Ophthal (210) 13 ,5 ,289-293 Investigation of fellow eye of unilateral retinal detachment in Shih Tzu Yoshiki Itoh et al ) where not only retinal atrophy but cataract, vitreal degeneration and retinal detachments were present. Two of the affected are littermates and one is an offspring of one of the affected animals. It should be noted that the last affected animal is not related suggesting that this may be a widespread problem in differing breed lines
The ages of the dogs we found to be affected ranged from four onwards. One individual has early retinal atrophy and the others have retinal atrophy with a combination of vitreal degeneration and cataract also. In addition two other dogs were found to have vitreal degeneration alone. As there were no other findings in these dogs at present they could not be classed as affected but monitoring the condition is advised..
DNA samples of these dogs and related individuals were taken for the purpose of DNA analysis and the possible eventual isolation of a gene mutation responsible for the condition. These samples were submitted to the Animal Health Trust Genetics Department at Newmarket.
I was asked to give some advice on breeding and have consulted the chief panellist in the UK before doing so.
In short, it is not possible to give certain advice on a condition that seems to be an atypical PRA and where the genetics of the condition are not certain.
Affected animals should be withdrawn from the breeding population. Removing all of the offspring at this stage however may well be excluding normal animals from within a restricted breeding population-many inherited conditions are recessive, so that the presence of one normal gene from either parent gives a carrier status ( a normal appearing animal carrying one hidden affected gene). When two carriers (appearing normal) animals are bred together they should statistically produce affected to carrier to clear animals in the ratio of 1: 2: 1.
In view of the fact that there is no certainty that any animals brought in from abroad will be genetically clear and breeding strategy is very difficult.
This situation requires more information gathering and more investigation. It would be a disincentive breeders to impose breeding sanctions at this stage and probably not justified unless there is clear science to back these up. It is clear however that related animals in particular should be eye screened regularly before any breeding is considered. In the UK there are two schedules of conditions on the scheme Schedule A where the inheritance is known and animals are certified clinically free of these conditions on examination and Schedule B which is for condition we feel may be emerging in breeds and where investigation data gathering is required. The latter schedule would now be appropriate for the Shih Tzu if we find similar problems in UK lines
I am hoping that breeders in the UK will follow the example of Iceland and start eye testing Shih Tzus before breeding. This is a late onset condition, which may be why it is not being picked up in the pet population with owner accepting blindness and eye problems in older animals.
I very much enjoyed my visit to Iceland where I was made very welcome and hope my comments have been helpful.