Understanding Eye & Ear Screening
For some health issues that are thought or known to have a strong genetic component but do not have DNA testing available, physical exams can instead provide the information that we seek. In some cases, such as Choroidal Hypoplasia/Collie Eye Anomaly (CH/CEA), DNA testing is available and if a result is returned showing a dog is affected, physical testing can be used to confirm the status of the disease.
Eye assessments are carried out by registered veterinary eye specialists, and the breed scheme for Border Collies includes Collie Eye Anomaly, Glaucoma, Primary Lens Luxation and Retinal Pigment Epithelial Dystrophy (formerly Central Progressive Retinal Atrophy), with results from ANKC registered dogs entered into ORCHID (Officially Registered Canine Health Information Database) under the Australian Canine Eye Scheme (ACES). Only those diseases affecting the eyeball are recorded however the screening also checks the eyelids, tear ducts and surrounding structures.
Choroidal Hypoplasia is considered the mild form of Collie Eye Anomaly and does not cause visual defects or blindness. The choroid is a layer of tissue in the eye responsible for supplying blood and nutrients to the retina, and hypoplasia indicates that there is a lesion on the back of the eye where the choroid did not develop properly and is thinner than usual. CH can only be seen ophthalmoscopically and is generally considered present from birth.
Collie Eye Anomaly is a more severe lesion and as the name would suggest, it affects a number of breeds in the Collie family. All dogs with CEA by definition have CH, and more severely affected dogs may have pits (colobomas) affecting the retina and nearby tissues, or in the most severely affected eyes, retinal bleeding and detachments can occur resulting in blindness. This is not a progressive disease however and most affected dogs may only have mildly impaired vision. CEA can be detected in a physical eye examination performed by a veterinary ophthalmologist between 5 - 12 weeks of age (preferably by 8 weeks old), after which retina pigmentation can often mask changes. DNA testing will then confirm a dog's clear/carrier/affected status.
Eye assessments are carried out by registered veterinary eye specialists, and the breed scheme for Border Collies includes Collie Eye Anomaly, Glaucoma, Primary Lens Luxation and Retinal Pigment Epithelial Dystrophy (formerly Central Progressive Retinal Atrophy), with results from ANKC registered dogs entered into ORCHID (Officially Registered Canine Health Information Database) under the Australian Canine Eye Scheme (ACES). Only those diseases affecting the eyeball are recorded however the screening also checks the eyelids, tear ducts and surrounding structures.
Choroidal Hypoplasia is considered the mild form of Collie Eye Anomaly and does not cause visual defects or blindness. The choroid is a layer of tissue in the eye responsible for supplying blood and nutrients to the retina, and hypoplasia indicates that there is a lesion on the back of the eye where the choroid did not develop properly and is thinner than usual. CH can only be seen ophthalmoscopically and is generally considered present from birth.
Collie Eye Anomaly is a more severe lesion and as the name would suggest, it affects a number of breeds in the Collie family. All dogs with CEA by definition have CH, and more severely affected dogs may have pits (colobomas) affecting the retina and nearby tissues, or in the most severely affected eyes, retinal bleeding and detachments can occur resulting in blindness. This is not a progressive disease however and most affected dogs may only have mildly impaired vision. CEA can be detected in a physical eye examination performed by a veterinary ophthalmologist between 5 - 12 weeks of age (preferably by 8 weeks old), after which retina pigmentation can often mask changes. DNA testing will then confirm a dog's clear/carrier/affected status.
Goniodysgenesis/Glaucoma is the name used to describe a sustained increase in the fluid pressure within the eye. It has a number of possible causes - primary (inherited) regarding the angles within the eye structure, and secondary (non-inherited) such as infections, PLL (primary lens luxation), trauma and neoplasia (tumours). There is no DNA test available, however screening of parents prior to breeding can identify the likely hereditary risk.
Primary Lens Luxation is an inherited defect of a ligament in the lens leading to partial or complete dislocation of the lens from its normal position. Signs are usually observed between 3 and 7 years of age, and PLL is a leading secondary cause of Glaucoma, causing pain and vision loss. There is DNA testing available for PLL in a number of breeds, however the gene mutation in this test is not the mutation that causes PLL in Border Collies, so can not be relied upon for an accurate result in our breed.
Retinal Pigment Epithelial Dystrophy formerly known as Central Progressive Retinal Atrophy is a disease of the outermost layer of the retina, the retinal pigment epithelium. Caused by the inability of the RPE cells to degrade used photoreceptor material used in the sight process (the ability of the eye to pick up light - an integral aspect of vision). This will initially show in working dogs as an inability to work in bright light whilst dim light appears unaffected until the disease progresses. This is different to Progressive Retinal Atrophy seen in other breeds, where night vision is often the first affected and blindness is common - RPED rarely causes blindness however it does cause a loss of the central field of vision and whilst some peripheral vision can be retained, this disease can severely impact the abilities of a working dog.
Primary Lens Luxation is an inherited defect of a ligament in the lens leading to partial or complete dislocation of the lens from its normal position. Signs are usually observed between 3 and 7 years of age, and PLL is a leading secondary cause of Glaucoma, causing pain and vision loss. There is DNA testing available for PLL in a number of breeds, however the gene mutation in this test is not the mutation that causes PLL in Border Collies, so can not be relied upon for an accurate result in our breed.
Retinal Pigment Epithelial Dystrophy formerly known as Central Progressive Retinal Atrophy is a disease of the outermost layer of the retina, the retinal pigment epithelium. Caused by the inability of the RPE cells to degrade used photoreceptor material used in the sight process (the ability of the eye to pick up light - an integral aspect of vision). This will initially show in working dogs as an inability to work in bright light whilst dim light appears unaffected until the disease progresses. This is different to Progressive Retinal Atrophy seen in other breeds, where night vision is often the first affected and blindness is common - RPED rarely causes blindness however it does cause a loss of the central field of vision and whilst some peripheral vision can be retained, this disease can severely impact the abilities of a working dog.
Example: An ACES Certificate following an eye screening by one of the panel ophthalmologists. The structure of the eye is examined and conditions in the breed schedule are diagnosed affected or unaffected. Breeding dogs should be screened at 12 months old and annually thereafter. They are not required to undergo sedation or anaesthesia.
Breeds that carry the piebald or merle gene (Border Collies carry both) are at risk of deafness, due to the impact that a lack of melanin (pigment) can have on the hairs inside the ear that are vital for hearing, and the way that merle and piebald can increase the amount of white on the dog - see Coat Colour Genetics for more information on this.
Brainstem Auditory Evoked Response (BAER) Testing is an electrodiagnostic test used to evaluate hearing. It is a non-invasive test that takes 5 - 15 minutes to perform, and tests the ear canal, middle ear cavities, cranial nerve and certain areas of the brain stem. It can be used to diagnose congenital sensorineural hearing loss and assess brain stem function. Testing is able to be performed on puppies from 7 weeks of age, and as hearing can be lost up to 16 weeks of age retesting is often done prior to breeding or if the owner notices any problems. Congenital (from birth) deafness can not be restored and no mode of inheritance is currently known however there are strong links to parent hearing status so hearing tests should be performed prior to breeding and when litters are around 7 weeks old, particularly within lines that carry merle/piebald.
Early Adult Onset Deafness is currently being researched to identify the causal gene mutation and whilst it is included in some DNA testing panels, this is a linkage marker test only and BAER testing is required to check hearing loss. It usually presents between 5 - 7 years of age but may be noticed as early as 18 - 24 months old or as late as 8 - 10 years. Hearing loss in dogs older than this would usually be considered more normal and age related. Due to the fact that EAOD tends to begin in only one ear, often dogs are nearly completely deaf before the issue is identified.
Brainstem Auditory Evoked Response (BAER) Testing is an electrodiagnostic test used to evaluate hearing. It is a non-invasive test that takes 5 - 15 minutes to perform, and tests the ear canal, middle ear cavities, cranial nerve and certain areas of the brain stem. It can be used to diagnose congenital sensorineural hearing loss and assess brain stem function. Testing is able to be performed on puppies from 7 weeks of age, and as hearing can be lost up to 16 weeks of age retesting is often done prior to breeding or if the owner notices any problems. Congenital (from birth) deafness can not be restored and no mode of inheritance is currently known however there are strong links to parent hearing status so hearing tests should be performed prior to breeding and when litters are around 7 weeks old, particularly within lines that carry merle/piebald.
Early Adult Onset Deafness is currently being researched to identify the causal gene mutation and whilst it is included in some DNA testing panels, this is a linkage marker test only and BAER testing is required to check hearing loss. It usually presents between 5 - 7 years of age but may be noticed as early as 18 - 24 months old or as late as 8 - 10 years. Hearing loss in dogs older than this would usually be considered more normal and age related. Due to the fact that EAOD tends to begin in only one ear, often dogs are nearly completely deaf before the issue is identified.