Horizontal Gaze Nystagmus (HGN)

The Horizontal Gaze Nystagmus (HGN) test may include noting the angle of onset of the nystagmus as an indication of degree of intoxication. This test has not had adequate validation. The threshold of angle of onset with respect to the degree of intoxication is in dispute by researchers and the studies have unacceptably high error rates.

The methodology used for this test does not include electronystagmography and has also not been adequately studied. The test is not generally acceptable for these reasons as well as the poor sensitivity and specificity associated with the test. In regards to this poor sensitivity and specificity, it is well recognized that there are a significant number of other causes of nystagmus.

Many factors can cause nystagmus. These factors vary from atmospheric conditions to changes in biorhythms. Normal medical conditions as well as pathological medical conditions and medications can cause nystagmus.

Climate changes such as changes atmospheric pressure including barometric pressure as well as temperature and other weather changes can result in nystagmus. For example, irrigation of the ears with water of varying temperatures is utilized as a diagnostic test by a neurologist.

Biorhythms such as the circadian rhythm can be associated with nystagmus. Pathological conditions including infections, both bacterial such as streptococcus, or viral, such as measles, influenza, the common cold. Other infections, such as syphilis, can also cause nystagmus. This is primarily due to their effect on the labyrinth associated in the inner ear.

Vitamin deficiency such as Thiamine or vitamin B1 causes what is known as Wernicke’s encephalopathy or Wernicke-Korsakoff syndrome which can include nystagmus.

Neurologic disorders such as multiple sclerosis and epilepsy as well as psychogenetic factors are associated with nystagmus.
Endocrine conditions like thyroid disease and diabetes mellitus can present with nystagmus.

Cardiovascular diseases such as arteriosclerotic cardiovascular disease (ASCVD) and associated hypertension, arrhythmias and cerebral vascular accidents (CVA) or strokes.

Other pathological conditions including sunstroke, motion sickness, eye strain, Glaucoma, and exposure to relatively innocuous substances, such as caffeine, nicotine and aspirin. Of course, various eye conditions including strabismus and amblyopia severely and negatively impact upon this test.

All of these conditions and many others can result in HGN which is indistinguishable from that caused by the consumption of alcohol.

Therefore, the appreciation of nystagmus in an individual is not a very specific test. There are a lot of false positives when searching for alcohol intoxication with this test. The test for nystagmus is too non-specific, producing a very high error rate when used for the purpose of determining alcohol intoxication, let alone the degree of alcohol intoxication.

It is impossible to develop a methodology to reliably ascertain nystagmus short of electronystagmography and even with that, it is not possible to determine the etiology without more information. With the additional information the error rate still makes the test much too unreliable to provide a specific diagnosis of alcohol intoxication. It is readily apparent why HGN is not generally an accepted test, it is not conclusive, it is not specific, it is insensitive and the methodology that is commonly used has not been systematically validated.

In addition, without recorded electronystagmography, the test itself and its interpretation can be “fudged,” that is, it is subject to fraud.

{Observations/Psychophysical tests}