Macular Corneal Dystrophy (MCD)
A novel diagnosis in Labrador Retrievers
This 9-year old female Labrador presented to me in 2014 due to unusual changes to both corneas. She had been rescued a few months earlier. Her eyes were not painful, but had multifocal white stromal opacities with long branching vascularisation and generalised haze.
Close up of the two eyes in March 2014
Due to the neovascularisation and apparent inflammatory component of the corneal changes, she was put on cyclosporine and dexamethasone/neomycin/polymixin B ointments. The owner reported an improvement in vision and confidence and this was her 3 weeks later
3 weeks later
Close up 3 weeks later
The changes were hard to quantify, but she genuinely appeared to have some improved clarity. This was a presentation that Ida had not come across before, but we were lucky enough to have a diagnosis within a few months, after a DNA test was performed on a blood sample. In fact Veterinary Ophthalmologists at the Animal Health Trust (AHT) were the first to describe this disease in dogs only in 2013 and only about 10 dogs had been seen in the UK and Europe.
Middle-aged Labradors develop cloudy corneas due to an abnormal accumulation of carbohydrates (glycosaminoglycans) in the stroma. Both eyes will be affected and the condition is slowly progressive with neovascularisation, but is not a painful condition. The vision is reasonably well retained initially, but will reduce over time and detailed vision will be lost, with the condition eventually leading to severe visual impairment.
The genetic mutation causing MCD has been identified by the genetics team at the AHT and it is inherited in an autosomally recessive fashion. This means that both parents will need to be carriers for the offspring to develop the dystrophy. The DNA test for this dog showed that she had two copies of the associated MCD mutation, explaining her clinical presentation. This case will be included in a scientific paper, which is due to be published shortly hopefully. The genetic test became available commercially this year (2015). Dogs can be diagnosed through a simple cheek swab test or a blood sample at any age. Treatment options are limited, so hopefully this condition can rapidly be eliminated from the breed through selective breeding.
BVSc CertVOphthal MRCVS
RCVS Advanced Practitioner in Veterinary Ophthalmology
Head of Ophthalmology Referral Service