TRD
Total Retinal Dysplasia
Testing method
Ophthalmoscopic examination. The classic presentation is leukocoria, a white pupillary reflex, with the detached retina visible posterior to the lens. The pupillary light response is sluggish or absent. In the Labrador Retriever, the condition may be associated with skeletal abnormalities (short-limbed dwarfism) in the oculoskeletal dysplasia form. Litter screening is the primary testing route given the congenital nature of the condition.
What is total retinal dysplasia?
Total retinal dysplasia (TRD) is the most severe form of inherited retinal dysplasia, in which the retina fails to develop normally and becomes completely detached from the retinal pigment epithelium at birth or in the first weeks of life. Unlike multifocal retinal dysplasia — where only areas of the retina are affected and vision is usually retained — total retinal dysplasia results in complete or near-complete blindness from birth.
The classic clinical presentation is leukocoria — a white or grey pupillary reflex visible when a light is shone into the eye — caused by the detached retina lying immediately behind the lens. The pupillary light response is sluggish or absent and affected animals are congenitally blind or become blind very early in life. Associated abnormalities including microphthalmos (abnormally small eyes) and nystagmus (involuntary eye movements) are commonly seen.
Breeds affected and breed-specific features
TRD is certified under the BVA scheme in the Bedlington Terrier, Labrador Retriever, Samoyed, and Sealyham Terrier.
In the Bedlington Terrier, most affected dogs have an infundibular retinal detachment with deficiency of the secondary vitreous — a presentation sometimes described as vitreoretinal dysplasia. Puppies are blind from birth and rotary nystagmus is usually present. Posterior suture line subcapsular cataracts are not uncommon, and retinal neovascularisation may lead to recurrent intraocular haemorrhage.
In the Sealyham Terrier, the presentation is similar to the Bedlington Terrier, with total retinal detachment, possible secondary vitreous deficiency, and microphthalmos.
In the Labrador Retriever, the situation is more complex. Total retinal dysplasia may occur as an isolated ocular condition or as part of oculoskeletal dysplasia (OSD), in which retinal abnormalities are associated with short-limbed dwarfism. Homozygous affected dogs have the most severe ocular and skeletal manifestations. Heterozygous dogs have only focal or multifocal retinal lesions. The genetic defect for OSD has been identified in both the Labrador Retriever and the Samoyed, though the two breeds have different underlying mutations.
What the examination involves
TRD is a congenital condition and litter screening between 5 and 12 weeks of age is the primary testing route. The examination is performed following pupil dilation using indirect ophthalmoscopy. The characteristic leukocoria and retinal detachment are usually immediately apparent on examination of an affected puppy.
Given the severity of the condition, any puppy suspected of being affected should be referred promptly for specialist ophthalmological assessment. Affected dogs should not be used for breeding.