youtube/watch?v=OQxBqF7xJBIBlinded By the Light BLINDED BY THE LIGHT You might think that day vision and night vision are one and the same process, but if you ask a person with achromatopsia, they would set you straight. Achromatopsia is a rare inherited eye disease which is characterised by very poor colour vision, blindness in bright daylight but near normal vision in dim light. Affecting about 1 human in 33,000, it also has been recorded in other species, in particular dogs and sheep. The mechanism is a dysfunction of the cone cells in the retina , which are present but which do not send their electrical signals to the brain. Day blind dogs are presented to vets because their owners notice that they collide with objects in daylight but have no problems in dim light or at night. It has been recorded in Alaskan Malamutes, Shi-Tzus, Cattle Dogs, Chihuahuas and several other breeds. I have never seen a case but recently was shown video of two setter litter mates negotiating an obstacle course. In the dark, both dogs weaved through with no problems, whereas in bright light it was carnage. Think of The Stig versus Mr Magoo. Sheep can be similarly affected. A few years ago Veterinary Opthalmologist, Dr Ron Ofri, got a call from an Israeli shepherd who noticed that sporadically lambs would be born which showed strange behaviour. They would stand stock still during the day instead of moving with the flock, but move normally at night. Dr Ofri examined the sheep with an obstacle maze and then by tissue analysis, and confirmed a type of congenital a chromatopsia or cone dysfunction. These sheep might prove to be a useful model for the human disease. With a team of researchers, he developed a gene therapy by injecting a harmless carrier virus programmed with a gene to switch on the missing protein in the retina at the back of the eye of day blind sheep. (This is a delicate procedure, don’t try this at home). The results were a dramatic improvement on the obstacle course, with Mr Magoo Sheep transformed into Stig sheep, slipping through the chicane at normal speed. These formerly day blind sheep had normal day vision nearly two years after a single treatment. How do you get a sheep to walk through an obstacle course? Put the rest of the flock at the other end!
Posted on: Wed, 24 Sep 2014 03:44:32 +0000
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