Other Ocular (Eye) Disorders

 Presumed to be inherited in purebred dogs

2010 Genetics Committee of the American College of Veterinary Ophthalmologists

 

How do we identify an inherited eye disease?

Although there are noteworthy exceptions, most of the ocular diseases of dogs which are presumed to be hereditary have not been adequately documented. Genetic studies require examination of large numbers of related animals in order to characterize the disorder (age of onset, characteristic appearance, rate of progression) and to define the mode of inheritance (recessive, dominant). In a clinical situation, related animals are frequently not available for examination once a disorder suspected to be inherited is identified in an individual dog. Maintaining a number of dogs for controlled breeding trials through several generations is a long and costly process. Both of these obstacles are compounded by the fact that many ocular conditions do not develop until later in life. Until the genetic basis of an ocular disorder is defined in a published report, we rely on what statistical information is available from registry organizations, informed opinions and consensus from ACVO diplomates, and must satisfy ourselves with terms like "presumed inherited" and "suspected to be inherited". Several companies provide information on genetic testing greatly assist in providing more information and data to aid in defining the canine genetics of ocular diseases.

What can be detected during a CERF examination?

A routine CERF screening examination includes indirect ophthalmoscopy and slit lamp biomicroscopy following pharmacological dilation of the pupils. Gonioscopy, tonometry, Schirmer tear test, electroretinography, and ultrasonography are not routinely performed; thus, dogs with goniodysgenesis, glaucoma, keratoconjunctivitis sicca, early lens luxation/subluxation or some early cases of progressive retinal atrophy might not be detected without further testing. The diagnoses obtained during an ophthalmic CERF examination refer only to the phenotype (clinical appearance) of an animal. Thus it is possible for a clinically normal animal to be a carrier (abnormal genotype) of genetic abnormalities.

For each breed, specific ocular disorders have been listed which are known or suspected to be inherited based on one or more of the following criteria:

  1. There are published reports in the scientific literature regarding a condition in a particular breed with evidence of inheritance.

  2. The incidence of affected animals (from CERF reports) is greater than or equal to 1% of the examined population with a minimum of five affected animals per five year period. Regardless of the population of dogs examined, if 50 or more affected individuals are identified in a five year period, the entity will be listed for that breed.

  3. A specific request from a breed club that a condition be included for their breed may be considered at the ACVO annual meeting of the Genetics Committee if information is received by August 1. Such requests are reviewed critically and must include specific documentation as to the disorder in question and the numbers seen. Further information from the breed club may be requested. The request must receive agreement by a majority of the committee.

  4. There is overwhelming opinion by a majority of the Genetics Committee members that clinical experience by ACVO Diplomates would indicate a particular condition should be listed for a breed, in spite of the absence of direct evidence of affected animals on CERF reports.

  5. Results of genetic laboratory research and genetic testing.

 

CERF - FINNISH LAPPHUNDS

  • 1991 - 1999 TOTAL NUMBER OF FINNISH LAPPHUND EXAMINED 29

  • 2000 - 2008 TOTAL NUMBER OF FINNISH LAPPHUND EXAMINED 196

 

The following specific ocular disorders have been listed which are known or suspected to be inherited in the Finnish Lapphund:

 

Persistent pupillary membranes (PPM)

Persistent pupillary membranes (PPM) Persistent blood vessel remnants in the anterior chamber of the eye which fail to regress normally during the first three months of life. These strands may bridge from iris to iris, iris to cornea, iris to lens, or form sheets of tissue in the anterior chamber. The last three forms pose the greatest threat to vision and when severe, vision impairment or blindness may occur.

Retinal atrophy-generalized

A degenerative disease of the retinal visual cells which progresses to blindness. This abnormality, also known as progressive retinal atrophy or PRA, may be detected by electroretinogram (not part of a routine eye screening examination) before it is apparent clinically. PRA is inherited as an autosomal recessive trait in most breeds.

Brief Glossary of Terms

Bilateral - both eyes.

Cataract - partial or complete opacity of the lens and/or its capsule. In cases where cataracts are complete and affect both eyes, blindness results. The prudent approach is to assume cataracts to be hereditary except in cases known to be associated with trauma, other causes of ocular inflammation, specific metabolic diseases, persistent pupillary membrane, persistent hyaloid or nutritional deficiencies. Cataracts may involve the lens completely (diffuse) or in a localized region.

Electroretinogram (ERG) - a test of retinal function; a graphic record of the electrical response that follows stimulation of the retina by light. Note that the ERG test is not part of a routine eye screening examination.

Genotype - refers to the allele(s) present at one or more genetic loci. Most commonly refers to the pair of alleles (either identical or different) present at a single chromosome locus; distinct from phenotype.

Glaucoma - Glaucoma is characterized by an elevation of intraocular pressure (IOP) which causes intraocular damage resulting in blindness. The elevated intraocular pressure occurs because the fluid cannot leave through the iridocorneal angle. Diagnosis and classification of glaucoma requires measurement of the IOP (tonometry) and examination of the iridocorneal angle (gonioscopy). Neither of these tests is part of a routine screening exam for certification.

Gonioscopy - a specialized procedure which uses a contact lens to examine the drainage angle. Note that this test is not part of a routine eye screening examination.

Hereditary - genetically transmitted or transmissible as a physical characteristic from parent to offspring.

Intraocular pressure (IOP) - the pressure formed by a balance between intraocular fluid production and outflow.

Keratoconjunctivitis sicca (KCS) -an abnormality of the tear film with a deficiency of the aqueous portion of the tears. Progressive KCS may result in ocular irritation and/or vision impairment. Also called dry eye. The test for this condition is the Schirmer Tear Test, which is not part of a routine eye screening examination.

Persistent pupillary membranes (PPM) - persistent blood vessel remnants in the anterior chamber of the eye which fail to regress normally during the first three months of life. These strands may bridge from iris to iris, iris to cornea, iris to lens, or form sheets of tissue in the anterior chamber. The last three forms pose the greatest potential threat to vision.

Phenotype - physical appearance. Distinct from genotype.

Retinal atrophy, generalized - a degenerative disease of the retinal visual cells which progresses to blindness. This abnormality is also known as progressive retinal atrophy or PRA, and may be detected by electroretinogram (not part of a routine eye screening examination) before there are detectable funduscopic changes seen by ophthalmoscopy. There are multiple genetic types of PRA including the rod cone dysplasias described elsewhere. Tests are available to identify the genetic mutation in some breeds.

Retinal dysplasia - abnormal development of the retina present at birth; typically nonprogressive and generally recognized to have three forms: folds, geographic, and detached. Retinal dysplasia is known to be inherited in many breeds. The genetic relationship between the three forms of the disease is not known for all breeds.

Retinal dysplasia - folds - seen ophthalmoscopically as linear, triangular, curved or curvilinear foci of retinal folding that may be single or multiple. In some puppies this condition may partially or completely resolve with maturity. Its significance to vision is unknown. There are two other forms of retinal dysplasia (geographic, detached) which are known to be inherited in some breeds and, in their most severe form, cause blindness. The genetic relationship between folds and more severe forms of retinal dysplasia is undetermined.

Retinal dysplasia - geographic - any irregularly shaped area of abnormal retinal development containing both areas of thinning and areas of elevation representing folds and areas of retinal disorganization. This form may be associated with vision impairment.

Retinal dysplasia - detached - severe retinal disorganization associated with separation (detachment) of the retina. The geographic and detached forms of retinal dysplasia are associated with partial or complete vision impairment or blindness.

Schirmer tear test - a test to measure tear production; this test is not part of the routine screening examination.

Tonometry - measurement of the intraocular pressure. Note that this is not part of a routine eye screening examination. There are currently ten disorders for which there is an unequivocal recommendation against breeding in all breeds:

These are conditions which frequently result in blindness and for which there is definite evidence of heritability in one or more breeds. However, these disorders will not be listed on the individual breed page for a given breed, unless they also meet the criteria described above. *Note: The prudent approach of these disorders is to assume they are hereditary except in cases specifically known to be associated with trauma, other causes of ocular inflammation, specific metabolic diseases or nutritional deficiencies.

  1. Keratoconjunctivitis sicca (KCS) - Breeding is not recommended for any animal demonstrating keratitis consistent with KCS. The prudent approach is to assume KCS to be hereditary except in cases suspected to be non-genetic in origin. See above *note.

  2. Cataract Breeding is not recommended for any animal demonstrating partial or complete opacity of the lens or its capsule unless the examiner has also checked the space for "significance of above cataract unknown" or unless specified otherwise for the particular breed. See above *note.

  3. Lens luxation or subluxation. See above *note.

  4. Glaucoma. See above *note.

  5. Persistent hyperplastic primary vitreous.

  6. Retinal detachment. See above *note.

  7. Retinal dysplasia - geographic or detached forms. See above *note.

  8. Optic nerve coloboma.

  9. Optic nerve hypoplasia.

  10. Progressive Retinal Atrophy (PRA) - Breeding is not advised for any animal demonstrating bilaterally symmetric retinal degeneration (considered to be PRA unless proven otherwise).

In breeds recognized with Persistent Pupillary Membrane (PPM) as an inherited problem there is an unequivocal recommendation against breeding when there is PPM iris to lens, or PPM iris to cornea, or iris sheets. Breeding advice is ‘NO’.