Generally, a person has a good ability to perceive verticality which depends on the input from visual, vestibular and somatosensory systems. The Otolithic organs, utricle & saccule both are responsible for maintaining verticality. Any disorder or injury to the otoliths organs or to the nerve that is responsible for sending signals from the inner ear to the brain hampers the judgment of vertical which is responsible for tilting vision abnormally.
The inner ear sends confusing signals that indicate the head is tilted while the eyes and somatosensory systems indicate it’s not. It denotes a sensory conflict that results in making a person experience bouts of dizziness thereby tilting vision. If you are experiencing any vestibular disorder it may result in the deviation in perceiving the vertical line. The person may not be able to see the vertical line as vertical.
Effect on vision affects the verticality which can be measured by putting a frame. Alterations of the angle made by frame sometimes affect the verticality.
What is subjective visual vertical?
Subjective Visual Vertical (SVV) is a test that helps in examining the abnormal subjective tilt. SVV test is an inner ear test to diagnose the patient’s perception of verticality. The abnormal vertical tilt can be one such major cause of vertigo or lead to bouts of dizziness, which makes the general life of a person quite difficult. The subjective visual vertical test helps in identifying whether any underlying signs of abnormal tilt exist in the patient or not.
Subjective Visual Vertical test helps in identifying the function of the utricle which is located in the inner ear. It helps in examining the perception of verticality. If any vertical tilt is found in the inner ear, its an indicator of Subjective Visual Vertical diagnosis in a patient.
SVV test is not capable enough to diagnose Meniere’s disease, vestibular migraine, vestibular neuritis, etc. due to its subjective nature.
Subjective Visual Vertical diagnosis range from inexpensive tests to expensive clinical tests for severe conditions.
If you are experiencing any symptoms like chronic dizziness, otolithic disorders, etc it indicates the onset of static or dynamic subjective visual vertical. Consulting an expert neurologist is recommended for Subjective Visual Vertical diagnosis. Your doctor may ask you to undergo various tests to examine the accurate cause of subjective visual vertical.
Static SVV, head vertical, head inclined at 30 degrees, dynamic moving background, head vertical, etc. are some of the common SVV tests. Subjective vertical is widely categorized into three parts: let’s have a look at them.
Types of subjective vertical
Subjective vertical is divided into three components. Subjective visual vertical, Subjective postural vertical and Subjective haptic vertical.
- Subjective visual vertical
Subjective visual vertical refers to where a subject adjusts to a visible Luminus line in complete darkness. The subjective visual vertical test is effective for all age groups whether we talk about children or adults. A person who is suffering from a vestibular disorder may experience the bar tilted at 10 degrees.
Patients suffering from cerebellar lesions are generally diagnosed with subjective vertical whereas brainstem patients show profound deviations frequently.
- Subjective postural vertical
If we talk about Subjective postural vertical, it refers to the position of the head or body with respect to true vertical. Cerebral lesions may be one such cause that is responsible for the disturbance of the subjective postural vertical (SPV). A person may experience Subjective postural vertical (SPV) along with Subjective visual vertical. A person who is reported with tilts of SPV along with SVV may even experience contraversive pushing as they lean on the side of hemiparesis to compensate for the tilt caused due to Subjective postural vertical.
- Subjective haptic vertical
If we talk about Subjective haptic vertical it remains unaffected by a vestibular disorder that is responsible for disrupting subjective visual vertical. It can be diagnosed by manipulating the rod in a vertical position in front of the eyes.
Let’s have a look at some of the subjective visual vertical test for SVV diagnosis
A brief look on some tests that are used for SVV diagnosis in a patient:
- Bucket Test
One of the SVV tests is known as a Buket test. It is one of the most conventional and inexpensive SVV vertigo tests for diagnosing the inner ear. In the bucket test, a bucket is placed over the head of the patient which consists of a line or rectangular object. The bucket is revolved around the head of the patient until he believes in the fact that the line is vertical. Your doctor will examine the angle of deviation from the back of the bucket. Bucket test is a static test as the patient is not in motion.
- OVAR Rotational Chair test
OVAR Rotational Chair test is another type of SVV test that can diagnose subjective visual vertical by using a rotational chair along with complete darkness. The rotational chair can rotate up to 300°/sec during the SVV diagnosis test.
As the chair rotates, the patient is asked to look at a laser line on the wall until they see it as a vertical line. OVAR Rotational Chair test gives accurate results in diagnosing subjective visual vertical (SVV). This SVV test is controlled by the software throughout the process.
- Virtual SVV Goggle
With the advancement in medical technology, more portable and less expensive devices for Subjective Visual Vertical diagnoses are found. Virtual SVV Goggle is counted as the latest technology for diagnosing SVV in patients. Virtual SVV Goggle is built to monitor the head movements and target that adjusts for verticality. This test can be carried out in children quite easily as it allows the patient to simply move in the direction of the target inside the goggles.