![]() Pupillary testing: a relative afferent pupillary defect (RAPD) is the only objective test of optic nerve dysfunction. Patients with unilateral optic nerve impairment have great difficulty identifying colours between eyes (dyschromatopsia), and this is more affected than visual acuity. Optic nerve damage may result in central visual loss.Ĭolour vision: this can be assessed with a series of colour plates. ![]() Cranial nerve assessment: a concise guide to clinical examination. Visual acuity: this can be tested using a Snellen chart. To define the degree of optic nerve dysfunction, the following tests are frequently performed. 2009 29:29-35.Ī detailed description of visual dysfunction is essential and can narrow the differential. Symptoms of optic nerve damage can represent changes in visual acuity, contrast, brightness, or colour. The potential causes of optic neuropathy are diverse and include vascular, toxic, metabolic, traumatic, compressive, infectious, inflammatory, and idiopathic aetiologies. Optic nerve lesions typically produce monocular visual loss, which can be sudden or gradual, and may or may not be associated with pain. Vision is critical for human function and, therefore, optic nerve pathology can severely affect quality of life. Topography of ganglion cells in human retina. The optic nerve carries millions of fibres from the retina into the central nervous system (CNS). Humans have a highly developed visual system, which transmits information from the environment. The central retinal artery and vein course through the middle of the nerve. The intra-orbital portion is surrounded by the subarachnoid space and dura that extends from the intracranial cavity. 2009 29:29-35.Īction potentials are then carried to the lateral geniculate body. The nerve continues to course upwards and inwards until it meets with the contralateral nerve to form the optic chiasm superior to the sella and pituitary gland. In the orbital apex, the nerve passes through the muscle origins and enters the optic canal. At this point, they form the optic nerve. These axons run towards the lamina cribrosa and merge in the optic papilla. Olfactory evoked potentials are available in specialist centres.Īxons making up the optic nerve arise from retinal ganglion cells. Psychophysical tests are useful to validate and classify olfactory dysfunction, but establishing the cause of olfactory loss relies heavily on the history. These may be useful to confirm olfactory dysfunction. Development of the University of Pennsylvania Smell Identification Test: a standardized microencapsulated test of olfactory function. ![]() Commercial odour identification tests are available, which require patients to identify several pre-defined smells. The diagnosis can usually be made clinically. Infrequently, olfactory dysfunction can be the presenting sign/symptom of neurodegenerative disorders (such as idiopathic Parkinson’s disease), or an intracranial mass lesion. Disorders can manifest as a total loss of smell (anosmia), partial loss of smell (hyposmia), distortions (dysosmias), or spontaneous olfactory hallucinations (phantosmias). Olfaction is critically important for safety, nutritional status, and quality of life. Patients may notice altered taste, rather than a loss of sense of smell. 2002 22:10819-10828.Ĭhanges in olfactory function frequently go unnoticed and often do not present to a clinician. Functional heterogeneity in human olfactory cortex: an event-related functional magnetic resonance imaging study. Gottfried JA, Deichmann R, Winston JS, et al. These areas encode characteristics of odour quality, identity, familiarity, and emotion. The second-order neurons leave the olfactory bulb to synapse on the primary olfactory cortex. The paired olfactory bulbs are located at the base of the frontal lobe overlying the cribriform plate. The receptor cell axons project through the cribriform plate of the ethmoid bone and synapse within the glomerular layer of the olfactory bulb. The fine structure of the olfactory mucosa in man. Moran DT, Rowley JC 3rd, Jafek BW, et al. Action potentials are induced in these cells, which synapse with olfactory bulb glomeruli. These odorants diffuse or are transported to bipolar receptor cells located in the olfactory neuroepithelium in the roof of the nasal chamber. Olfaction begins with transduction of odorants from the air into the nasal mucosa. The signs and symptoms of a cranial nerve mononeuropathy vary depending on which nerve is affected. The effects of a mononeuropathy depend on where in its pathway the nerve is affected and the aetiology. They serve a variety of functions and predominantly provide the motor and sensory innervation to the head. There are 12 paired cranial nerves, named and numbered according to the rostral-caudal order of attachment to the brain.
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