Gaze test or Horizontal Gaze Nystagmus Test - (HGN test) is one of the 3 Standardized Field Sobriety Tests (SFST) conducted by the police to check if the person is driving under the influence of alcohol. Nystagmus refers to involuntary rapid movements of the eyes that are caused by abnormal function in the areas of the brain that control eye movements. Nystagmus is caused by various conditions, one of which is alcohol consumption. Gaze test is a useful indicator of alcohol intoxication.
During the Gaze test, the police officer will hold a stimulus such as a flashlight or pen or even his finger in front of the driver's face and moves it sideways. The officer then observes the eyes of the driver as he follows the moving object horizontally with his eyes. The suspect's eyes may bounce or involuntarily jerk (nystagmus) if he is impaired due to alcohol consumption. The higher a person's blood alcohol content level, the more pronounced the nystagmus becomes.
As the subject's eyes follow the object, police will look for the following three indicators:
1. Whether the suspect was able to follow the object smoothly. Normal and sober person follows the stimulus whereas person under the influence of alcohol may have difficulty following the object.
2. The extent of stability of the eye at maximum deviation.
3. The angle at which the jerking begins. Jerking movements in the eye before the gaze reaches a 45-degree angle is indicative of a higher blood alcohol content level.
Gaze test is the most accurate test of all the sobriety tests and does not require any special equipment to conduct it. However gaze test requires a well trained police officer to read the eye movements.
Diplopia is one of the serious disorders of the eyes, which is associated with vision impairment. In common terms it is referred to as double vision. The occurrence of diplopia is closely associated with the cranial nerves. The effects caused by this optical disorder restrict normal activities of a person such as reading, walking and driving. The causes associated with diplopia when closely examined are myogenic and neurogenic in origin leading to an optical disruption both of vision and movement of the eyes.
Clinical manifestations and classification
Diplopia can be monocular or binocular in origin. Monocular Diplopia has preexisting-associated conditions such as cataracts, luxation of the lens and keratoconus, which results in light refraction within the eye. Macular degeneration and vitreous damage also causes light refraction retention inside eye causing blurred vision.
Binocular diplopia is caused by neurogenic impairments related to Oculomotor nerve damage, which is an important nerve in facilitating the movement of eye. The muscles associated with the respective functionality are also damaged in this condition. In most cases binocular diplopia is caused because of head injuries leading to cranial damage or traumas caused to the eyes. In some cases aniseikonia (condition which results in difference in the size of images as seen by the person) is also a predominant factor leading to binocular diplopia.
Diplopia occurrence and its respective effects can be further classified as sustained and short-lived forms. Intermittent or short-lived forms are usually a postoperative sequel especially in the case of cataract surgeries. However, diplopia of both continued and short-lived forms predominantly depend upon the thyroid hormone levels and underlying medical conditions such as myasthenia gravis.
Diagnosis of diplopia is a chronological aspect consisting of various factors. A patient complaining of blurred vision has to undergo series of medical and diagnostic investigations to rule out false positive findings. Since diplopia is associated with cranial nerves predominantly the oculomotor nerve, a gaze test is administered by the optometrist to estimate the functionality of nine cardinal vision factors.
This is prior to examining the patient history thoroughly in checking for conditions such as diabetes and hyperthyroidism. Important optometric examinations such as prism test, Bilshowsky test, Stereo acuity test and visual field testing are done to evaluate the impairments existing in the muscles associated with the eye. These tests are carried out after general examinations such as tonometry, fundoscopy and slit lamp examinations.
Corrective measures are incorporated to treat the movements of the eye, which is affected drastically in this condition. Refraction errors are analyzed and corrected in order to rectify the blurred vision. Patients are given eye exercises to facilitate proper oculomotor nerve functionalities and also to prevent squint occurrence.
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Bibliography / Reference
Collection of Pages - Last revised Date: December 9, 2019