HGN (Eye Test)

HGN (Eye Test) in Ohio OVI Cases

The eye test, formally known as the Horizontal Gaze Nystagmus test, is often treated as the most technical field sobriety test. Officers frequently describe it as objective or scientific.

That confidence is misplaced.

The HGN test is not a medical exam. It is a roadside observation exercise that depends heavily on how it is performed, what the officer is trained to look for, and how the results are later described. Small deviations matter here more than almost anywhere else in an OVI investigation.

What the HGN Test Is Supposed to Do

The purpose of the HGN test is to observe involuntary eye movement as a person follows a stimulus from side to side. Under specific conditions, certain types of eye movement may correlate with alcohol consumption.

That is the theory.

In practice, the test requires precise positioning, timing, lighting, distance, and observation. When those requirements are not followed carefully, the conclusions drawn from the test become unreliable very quickly.

This is not a test that tolerates shortcuts.

Why the HGN Test Is Often Overstated

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Officers are trained that the HGN test can produce multiple “clues.” Those clues are often presented later as strong indicators of impairment.

What is rarely discussed is how easy it is to misinterpret what the officer believes they are seeing.

Eye movement can be affected by medical conditions, prescription medications, fatigue, head injuries, lighting conditions, distractions, and improper stimulus movement. Even minor errors in how the test is administered can change the outcome.

The more confidence an officer expresses about this test, the more important it becomes to examine how it was actually conducted.

How the HGN Test Fits with Other Field Sobriety Tests

The eye test is typically administered alongside balance-based tests like the walk-and-turn and the one-leg stand. Together, these tests are used to build a narrative of impairment.

But they do not measure the same things.

Unlike balance tests, the HGN test relies almost entirely on officer observation and interpretation. There is no video replay of eye movement that captures what the officer claims to have seen. That makes accuracy, training, and consistency especially important.

When the HGN test is relied on heavily, it deserves careful scrutiny.

How the HGN Test Is Evaluated Later

The HGN test is not evaluated in isolation.

Courts look at body camera footage, dash camera footage, officer reports, training records, and testimony. What matters is not just that the test was performed, but whether it was performed correctly and whether the conclusions drawn are supported by the evidence.

Details that seem minor at the roadside often become central issues later.

Why This Test Matters in an OVI Case

The HGN test is frequently used to justify an arrest or to support the decision to request a chemical test. When it is administered improperly or described inaccurately, it can distort how an entire case is viewed.

A careful review looks at what was done, how it was done, and whether the officer’s conclusions are actually supported by the facts.

That review often changes the posture of a case.

How This Fits Into the Bigger Picture

The HGN test is one piece of the field sobriety testing process. It is not proof on its own.

Understanding how it works, and where it commonly breaks down, makes it easier to evaluate the role it played in your case and how much weight it should really carry.

For a broader discussion of how field sobriety tests are used and evaluated, see our Field Sobriety Overview. For discussion of balance-based tests, see the Walk-and-Turn and One-Leg Stand pages.

Talking Through What Happened

Many people are told they “failed” the eye test without any explanation of what that actually means or how the test is supposed to work.

A conversation allows us to walk through what happened, explain how the HGN test is intended to be administered, and talk honestly about how it may be viewed in your case.

Clear explanations make it easier to understand where you stand and what actually matters going forward.

Talk to an OVI attorney.

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