Aetiopathological aspects of inherited lens dislocation in the Tibetan Terrier

Four litters of Tibetan Terriers were bred in order to study the ocular pathology of primary lens luxation, which in this breed is due to an autosomal recessive gene. Scanning and transmission electron microscopy were carried out on ocular tissues of 5 dogs from 2 homozygous litters killed at various ages up to the time of onset of clinical subluxation. All eyes showed zonular abnormality, in particular a bizarre arrangement of fibrillar material associated with the ciliary processes and relating to the system of zonular fibres inserting posteriorly at the lens equator. A further litter, the result of an affected X carrier mating and killed at 20 months of age, included 2 affected and 2 unaffected dogs. The pathological changes noted in affected eyes are reconciled with the clinical signs observed in 4 homozygous dogs developing lens luxation.