PULVERULENT NUCLEAR CATARACT

IN THE NORWEGIAN BUHUND

By:  E Bjerkas and M B Haaland  

Department of Small Animal Clinical Sciences, Norwegian College of Veterinary Medicine, PO Box 8146 Dep, N-0033 Oslo, Norway and Tu Small Animal Clinic N-4340 Bryne, Norway.

Journal of Small Animal Practice (1995) 36, 471-474

ABSTRACT 

Pulverulent cataracts were diagnosed in 52 of 102 Norwegian Buhunds, with both sexes being equally affected.  All the dogs were otherwise considered clinically healthy.  Initial lens changes were visible from six and a half weeks of age as small dots paralleled to the suture lines behind the nucleus.  Gradually, the opacities along the suture lines became more opaque until, by the age of four to five and a half years, they had progressed to involve the fetal nucleus which then resembled a ball of candy floss.  The outer part, the adult nucleus, usually remained clear, and the cortex was not involved.  The ages of the dogs in the present study ranged from 3.5 weeks to 12 years at first examination.  An out-cross of an affected bitch to a mixed-breed dog resulted in 3 puppies, of which 2 were affected.  The retinas could be evaluated in all the examined dogs, and revealed no abnormalities except for 1 case of focal retinopathy.  In addition to the pulverulent cataracts, 10 cases of cortical cataracts were diagnosed, 3 of which also had pulverulent cataracts.  Based on the pedigrees, an autosomal dominant mode of inheritance with a high degree of penetrance is suggested for pulverulent cataract.

INTRODUCTION

Cataracts involving the lens nucleus, which may be both congenital or acquired, have been described in many breeds of dogs (Koch 1972, Barnett 1985a.b. 1988, Monaco and others 1975, Collins and others 1992).  These nuclear changes may be associated with other malformations of the eye, or may occur without other eye abnormalities.  Primary nuclear cataract without other ocular changes has been shown to be inherited in many breeds of dogs, as well as in other animal species (Kincaid 1989, Zigler 1990).  However, non-genetic causal factors such as nutritional deficiencies (Glaze and Blanchard 1982) toxic agents (Martin and others 1972) infections and metabolic diseases (Gelatt 1991) are not uncommon. 

Inherited cataract in the Norwegian Buhund, involving mainly the cortex, has been described by Barnett (1988).  The cataract changes were diagnosed at an early age and rapidly progressed to affect vision.  Lens-induced uveitis developed in certain cases and spontaneous regression of the cataract occasionally occurred. 

The lens opacities described in the present study were of a different type.  A preliminary report on the condition was given by Haaland (1991).  Initial changes were seen in the young dog as small opacities along the suture lines posterior to the nucleus.  With increasing age, the nucleus became involved gradually covering the suture line opacities.  However, the nucleus never became totally dense and apparently did not affect the dog’s vision.  The changes might be comparable to inherited pulverulent types of cataract described in humans (Marner and others 1989, Scott and others 1994). 

Pulverulent cataracts are occasionally seen in other breeds of dogs, mainly the German Shepherd Dog, the Leonberger and the Flat Coated Retriever, but to the author’s knowledge, the progression and inheritance have not been thoroughly studied.  The present study presents the progression and the mode of inheritance of the pulverulent cataract in the Norwegian Buhund. 

MATERIALS AND METHODS

102 Norwegian Buhunds were examined between 1987 and 1994 by the authors.  The dogs were brought in by the breeders for examination after the finding of nuclear changes in some dogs of the breed.  The majority of the examined dogs were related, and were from a line within the breed that could be traced back to the same ancestors.  However, export of a few Norwegian Buhunds about 15 years earlier resulted in the forming of another line of dogs.  82 of the examined dogs were from the Norwegian line, whereas 8 were from the foreign line and 12 were offspring after the mating of dogs from each line. 

All the dogs were considered healthy without any history of systemic disease.  49 males and 53 females were examined.  The ages at first examination ranged from 3.5 weeks to 12 years, with 74 dogs less than 4 years old at the first examination.  Of these, 13 were puppies between 2 and 5 months of age.  4 puppies examined at the age of 3.5 weeks, and 6 five week old were re-examined at 6.5 weeks of age, to evaluate the age of appearance of initial lens changes.  In addition to the examined Norwegian Buhunds, the 3 offspring of a mating of an affected Norwegian Buhund bitch to a mixed breed male were examined.  13 affected dogs, the first time examined at 1 to 4 years of age, under-went 1 to 5 re-examinations.  Pedigrees were obtained for all the examined dogs. 

Examinations were performed in a darkened room following instillation of 0.5 percent tropicamide (Mydriacyl Alcon).  Complete mydriasis was sometimes difficult to obtain in the youngest puppies, but the centre of the lenses could still be examined.  The lenses were examined both in retro-illumination and with a Kowa SL5 slit lamp biomicroscope x 10 magnification.  Retinas were evaluated by the use of an indirect ophthalmoscope. 

RESULTS 

Pulverulent cataracts were diagnosed in 52 of 102 dogs – 26 males and 26 females.  Except for 2 cases, 5 and 8 years of age, the changes were bilateral, affecting both lenses to the same degree.  Based on the clinical finding related to age, the progression of the lens changes is as illustrated in Fig.1.  The earliest changes, diagnosed for 6.5 weeks of age, were seen as small sparkling opacities more or less parallel to the posterior suture lines, just behind the nucleus.  Opacities along the anterior suture lines were not  diagnosed in any of the dogs. 

FIG 1.  Progression of lens changes related to age in the Norwegian Buhund.
<<note, the images did NOT come through>>

With increasing age, the opacities became denser and could easily be seen with retro-illumination.  At 4 to 5.5 years of age, progressive changes in the nucleus became visible, gradually covering the opacities along the suture lines.  The nuclear changes had a powdery, candy floss-like appearance and involved mainly the fetal nucleus around the opacity.  The nuclear changes became denser with increasing age, but the lenses never became totally opaque.  In all the examined dogs, despite the lens changes, the retinas could be examined by indirect ophthalmoscopy.  All the affected dogs fitted into the described pattern with relation of age.  The nuclear changes are illustrated in Figs 2 and 3. 

The study of pedigrees showed that a combination of two normal parents produced only normal offspring.  Matings of one affected and one unaffected dog resulted in both affected and un-affected offspring, as did mating of two affected dogs.  A mating of an affected bitch to a mixed-breed male resulted in 3 offspring, of which two were affected.  In dogs from the foreign line, no cases of cataract were found, but matings to affected dogs from the Norwegian line produced affected offspring.  The pedigree from a group of the Norwegian dogs is shown in Fig.4. 

In addition, cortical cataracts, mostly in connection with the suture lines, were diagnosed in 10 dogs.  3 of these also showed the described nuclear changes, the other 7 showed only cortical changes.  The cortical changes were uni or bilateral slowly progressing upon re-examination, and did not affect vision severely.  Apart from two 6 month old puppies, the cortical changes were diagnosed in dogs between 1.5 and 10 years of age.  Clearly demarcated suture lines in the posterior cortex were seen in 12 dogs of all ages, ranging from narrow lines to broad, well demarcated, feather-like lines.  Arrowhead tips of the suture lines were seen in 6 of the youngest puppies however, these were not observed on re-examination. 

DISCUSSION 

The Pulverulent cataracts diagnosed in the present study resemble the pulverulent cataracts described in humans (Scott and others 1994).  Prevalent cataracts in humans appear at an early age and, although progressive rarely disturb vision severely.  Lens changes in humans typically are bilateral and symmetric in the two eyes.  However, while pulverulent cataract in humans may be associated with mild micro-cornea this was not observed in any of the affected dogs.  Pulverulent cataract in hums is inherited in an autosomal dominant fashion with a high degree of penetrance.  A systemic metabolic defect has not been shown. 

In the affected dogs in the present study, the eyes were considered normal, except for the cataract changes, and one case had focal retinopathy.  The affected dogs were clinically healthy with a normal life span and litter sizes were normal.  Initial Pulverulent lens changes along the posterior suture lines were present from 6.5 weeks of age and the nuclear changes appeared after four years of age.  All the affected dogs showed the same type of pulverulent lens changes with the same rate of progression. 

Males and females were equally affected and about half the examined dogs showed cataract changed.  Matings of two normal dogs had not produced affected offspring.  Both matings of normal dogs to affected, as well as mating of two affected dogs, resulted in both affected and normal offspring.  The outcross of an affected bitch to a mixed-breed resulted in two affected puppies in a litter of three.  Although it cannot be excluded that the mixed-breed was a part Norwegian Buhund, this information, as well as study of the pedigree, suggest an autosomal dominant inheritance with a high degree of penetrance. 

Cortical cataracts diagnosed in three dogs with Pulverulent cataract and seven other dogs most probably represent a type of cataract with a different aetiology, as do the strongly demarcated suture lines found in the posterior cortex in a number of the dogs.  Feather-like opacities along the suture lines have been found in toxic cataracts (Martin and others 972), however, a toxic agent was considered unlikely in the present cases.  The cortical changes appeared in related dogs, which might indicate an inherited condition, but the number of dogs in the present material is too small to allow any conclusions to be drawn.  The Pulverulent cataract differs from the cortical cataracts described in the breed by Barnett (1988), both in localization, age of appearance and rate of progression.  The cortical changes found in 10 dogs were of a slowly progressing type that did not severely disturb vision.  The changes were diagnosed in dogs of all ages, in contrast to the cataracts described by Barnett (1988) and therefore probably represent a different from of cataract. 

The clinical significance of the pulverulent cataract may be questioned.  None of the older affected dogs showed sights of reduced eye-sight, although minor changes in vision may be difficult to evaluate.  A metabolic defect as a cause of cataract is known in humans (Yanoff and Fine 1992), and there is a possibility that the lens opacities in the Norwegian Buhund swerve as an indicator of a metabolic disturbance not yet diagnosed.