|Year : 2011 | Volume
| Issue : 2 | Page : 51-53
Cervico-ocular reflex in cervical vertigo
Editor, IJO, Delhi, India
|Date of Web Publication||20-Dec-2011|
M K Taneja
Editor, IJO, Delhi
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Taneja M K. Cervico-ocular reflex in cervical vertigo. Indian J Otol 2011;17:51-3
The term "Vertigo" is derived from the Latin word "Verto" which means spinning or whirling movement. It gives an illusionary sense that either the environment or one's own body is moving. In dizziness, there is a feeling of unsteadiness, falling tendency, faintness, and transient blackout, and in the majority of patients, it improves by rest or lying down. Dizziness is seen in one in three elderly patients and one in five people of working age. , To distinguish true vertigo from other commonly mistaken conditions like light headedness, imbalance, oscillopsia, vertigo of psychiatric origin, a three-pronged approach is crucial to a neurootologist. It includes detailed history taking, thorough clinical neurootological examination, and then ordering a set of relevant investigations.
Patients generally complain of dizziness or vertigo by certain neck postures which are aggravated by movement of the head relative to the body. This complaint should alarm the physician about the possibility of cervical vertigo. Cervical vertigo results from paravertebral stretch receptors in the neck. Physiologically, there are various causes of cervical vertigo, the most important cause being vascular compression of the vertebral artery. Vertebral artery, which arises from the first branch of the subclavian artery, is closely associated in the neck in its cervical course as it passes through the foramina in the transverse canal of all cervical vertebrae except seventh. Transverse process of the seventh cervical vertebrae lies posterior to it above, it is medial to rectus capitis lateralis, and covered by semispinalis capitis in the suboccipital triangle, hence involvement of muscles and ligaments may also result in vascular compression. Another important cause is dissection of the vertebral artery which can be damaged at points where it is anchored in the neck.
Conditions like pain, whiplash injury, anxiety, or ergonomics may produce hyperlordosis in lower cervical spine and kyphosis in upper cervical spine, resulting in overactivity of the extensor group of the muscles and underactivity of the flexor group of muscles of neck. Neck trauma, even minor, neck manipulation, or spontaneous cervical spondylosis may result in transient ischemia by reduced flow via vertebral artery, basilar artery, and finally posterior inferior cerebellar artery supplying the dorsolateral medulla, inferior cerebellar peduncle, and posterior inferior cerebellar peduncle of ipsilateral side.
Though cervical spondylosis is the predominant etiological factor, associated conditions like atherosclerosis, embolism or vascular occlusion, hyperviscosity syndrome, and hypercoagulation disorder can precipitate or aggravate the vertigo.
There is no need to emphasize that proprioception has its own place in balance. In cervical region, short muscles of neck are rich in spindle, specifically rectus capitis lateralis and semispinalis capitis. Proprioception is also maintained by the pacini receptors and golgi tendon organ of periarticular tissue of cervical vertebrae.
During head movements, it is the ocular stabilization reflex which serves to stabilize the visual image on the retina. Three important reflexes in this context are the vestibulo-ocular reflex (VOR), optokinetic reflex (OKR), and finally cervico-ocular reflex (COR). For example, when the head is turned to right on fixed body, brain differentiates the movements of head by vestibular and visual cues, but body remaining in the same position is differentiated by proprioceptive system. The COR works in conjunction with VOR and OKR to prevent visual slip over the retina during head movement.  Hence, COR induces eye movement in response to afferent proprioceptive signals from the neck which shows significantly lower equilibrium scores in the patients with vertigo than in controls and much more lower scales in particular position to provoke unsteadiness. 
The COR which is mediated by medial and descending vestibular nuclei alone has got submissive role and usually does not generate a severe vertigo which may amount for medical emergency. The stabilization reflexes mentioned above work in conjunction at all head velocities to optimize the ocular response. The problem with this synergy of the reflexes arises in old age when the VOR and OKR decrease. Studies have demonstrated that COR gain increases with age and there is a significant covariation between the VOR and COR gains.  Thus, the importance of COR arises in old age and in cases of vestibular loss where the COR maintains an important role in maintaining body balance.
Cervical vertigo is associated with neck tenderness and limitation of movement which is attributed to inflammatory mediator of sensitive muscle spindle and myofascial trigger points. This may result in mismatch between vestibular and proprioceptive system input, hence resulting in cervical vertigo.
The ocular stabilization reflexes serve to stabilize the visual image on the retina during head movements. Several sensory systems contribute to this process. The VOR moves the eyes on the basis of vestibular information opposite to the direction of head movement. It is mainly responsive to head movements with a high frequency.  The OKR responds to visual motion stimulation. It directs the eyes in the same direction as the visual slip on the retina. The COR is a reflexive eye response that is elicited by rotation of the neck. The proprioception of muscles and the facet joints of the cervical spine form the receptor part of this reflex.  In contrast to the VOR, both the OKR and COR respond optimally to head movements with a low velocity. ,
In an optimal situation, these stabilization reflexes work in conjunction at all head velocities to optimize the ocular response.
For a diagnosis of cervical vertigo, it is essential to exclude other causes of vertigo. Generally, the patient has no hearing complaints and characteristically the symptoms are elicited by neck massage or neck vibration which is a technique adopted by chiropractics for neck pain. On examination, the patient has positional nystagmus that changes direction according to the direction of the head on neck, and if positive, generally there is a disk herniating at C5-C6. 
Various investigations can be used to diagnose cervical vertigo like Videonystagmography (VNG), Vestibular evoked myogenic potentials (VEMP), Otoacoustic emissions (OAE), flexion-extension neck X-rays, posturography, CT, MRI and transcranial Doppler ultrasonography of vertebral artery (which may be used as a screening test before proceeding to angiography). The "gold standard test" for the diagnosis of cervical vertigo due to vertebral artery occlusion is selective vertebral artery angiography with the head turned to either side, but this may itself precipitate a stroke, so is less commonly resorted to.
Another test is dynamic posturography in which vibratory stimulus is applied to muscles as input and the body sway thus induced is recorded as output. Three parameters - swiftness, stiffness, and damping - are studied. The patients of cervical vertigo show differences, hence may serve as a future tool for differentiating vertigo. 
To conclude, the cervical vertigo is usually characterized by ataxia, unsteadiness and sense of floating during walking and not by rotational or linear vertigo. Neurological, vestibular, and psychosomatic disorder must first be excluded with the available investigations before the dizziness of unsteadiness in cervical pain syndrome can be attributed as cervical vertigo. 
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