Abstract
In this report, we provide clinical information on the diagnosis of postretinal blindness in veterinary ophthalmology. We have diagnosed three dogs with postretinal blindness (bilateral in one case and in the left eye in two cases). The electroretinogram results were normal and the optic axis was relatively clear in all cases. Our findings indicate that the reason for the blindness in these dogs was an intracranial lesion. Fundus photography did not reveal any significant changes, except in the optic disc. A normal optic disc, an optic disc that appeared to be smaller than that in the other eye, and a severely hyperemic and edematous optic disc were seen in cases 1, 2, and 3, respectively. On magnetic resonance imaging, two dogs had optic chiasm lesions (one a tumor, one inflammation) and the remaining dog had inflammation in the right optic tract and occipital lobe even though bright flash electroretinograms were normal. Magnetic resonance imaging and electroretinography can be used as diagnostic tools for detection and localization of central nervous system lesions in the visual pathways.
Highlights
There are four main locations and causes of blindness: lesions that produce opacification of the ocular media, lesions that cause failure of the retina to process images, lesions that interrupt transmission of the message along the visual pathways, and lesions that cause failure of final processing of the image on the visual cortex [1,2]
When there is no abnormality in the eye and the ERG is normal, it is possible that blindness originates somewhere along the afferent visual pathway
Visual evoked potentials (VEPs) are used to evaluate the visual pathway from the retina to the visual cortex [3] and can detect brain wave signals from the visual cortex induced by a light stimulus
Summary
There are four main locations and causes of blindness: lesions that produce opacification of the ocular media, lesions that cause failure of the retina to process images, lesions that interrupt transmission of the message along the visual pathways, and lesions that cause failure of final processing of the image on the visual cortex [1,2]. When there is no abnormality in the eye and the ERG is normal, it is possible that blindness originates somewhere along the afferent visual pathway. In cases where systematic diagnostic tests, including full ophthalmic and ERG examinations, do not reveal a significant lesion as a cause for blindness, intracranial MRI examination would be strongly recommended.
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