Lack of Convergence in NC DWI and DRE Cases: The Eye Test Most Drivers Never Heard Of

Drugged driving · Eye tests · DRE

Lack of convergence is the eye check most drivers have never heard of. The officer moves a pen or fingertip in toward the bridge of your nose and watches whether your eyes cross together to follow it. In NHTSA and IACP drug-impairment training, eyes that fail to converge are treated as a possible sign of four drug categories, including cannabis. But the check has no validated clues, it can be thrown off by ordinary eye conditions and fatigue, and in North Carolina its courtroom value depends on who performed it and under which part of Evidence Rule 702. This guide explains how the test works, what it is supposed to show, and where its limits are.

What is convergence?

Convergence is the inward turning of both eyes so they stay locked on an object as it comes closer. It is what lets you read a phone or a dashboard with single, clear vision. The National Eye Institute describes convergence problems as a condition that “affects how your eyes work together when you look at nearby objects.”

Police training uses the same idea. The NHTSA/IACP Advanced Roadside Impaired Driving Enforcement (ARIDE) participant guide defines convergence as the “crossing” of the eyes that occurs when a person can focus on a stimulus “as it is pushed slowly toward the bridge of their nose.” Lack of convergence (LOC) is the opposite: “the inability of a person’s eyes to converge, or ‘cross'” while trying to follow the stimulus in.

Unlike nystagmus, which is a jerking of the eyes, lack of convergence is about alignment. One eye or both may stop short, drift outward, or bounce away instead of crossing. The training says drug impairment, including from alcohol, can cause LOC and with it double vision at near distances, or when a driver looks back and forth between the road and the dashboard.

How officers test for lack of convergence

Lack of convergence is not one of NHTSA’s three standardized field sobriety tests (HGN, walk and turn, and one-leg stand). It is taught in drug-impairment courses: ARIDE, which many patrol officers take, and the Drug Recognition Expert (DRE) school. The ARIDE participant guide (revised February 2023, Session 5) lays out the procedure this way:

1. Give the instructions

   Tell the person to keep the head steady and “try to cross the eyes” to keep them focused on the stimulus as it moves toward the nose, and that the officer will not actually touch the nose.

2. Start 12 to 15 inches out

   Hold the stimulus (a pen, penlight or fingertip) 12 to 15 inches from the nose and move it slowly in a circle, confirming the person is tracking it.

3. Stop above eye level

   End the circular motion with the stimulus above eye level.

4. Bring it in to about two inches

   Move the stimulus to within approximately two inches of the bridge of the nose and hold it there for approximately one second.

5. Watch both eyes

   Observe whether both eyes converge on the stimulus and stay converged.

6. Repeat

   The guide recommends checking at least two times; if the results differ, a third check is permissible. No delay between checks is required.

Interpretation is simple on paper. If the eyes cross when the stimulus is about two inches from the bridge of the nose and stay converged for one second, LOC is “none.” If they do not come together, or do not stay converged for one second, LOC is “present.” The guide’s examples include one eye that starts to converge and then “bounced down and back out,” and both eyes stopping “before the convergence was completed.”

Which drugs DRE materials associate with lack of convergence

DREs sort impairing drugs into seven categories: CNS depressants, CNS stimulants, hallucinogens, dissociative anesthetics, narcotic analgesics, inhalants and cannabis. The ARIDE guide says LOC may be caused by four of them, CNS depressants, inhalants, dissociative anesthetics and cannabis, which it calls the “DIDC” drugs. The North Carolina Drug Category Matrix (revised 03/2019) lists LOC as “present” for those same four categories and “none” for the other three.

Cannabis stands out. In the North Carolina matrix, it is the only category with LOC present but no horizontal or vertical gaze nystagmus. That means a convergence finding can carry a lot of weight in a suspected marijuana case, because it is often the only eye-movement sign the officer can point to. The chart and table below show how the three eye-movement signs line up across all seven categories.

Where convergence fits in the DRE 12-step evaluation

A Drug Recognition Expert evaluation is a standardized, 12-step protocol, normally done after an arrest. The International Association of Chiefs of Police lists the 12 steps as: (1) breath alcohol test, (2) interview of the arresting officer, (3) preliminary examination and first pulse, (4) eye examination, (5) divided attention tests, (6) vital signs and second pulse, (7) dark room examinations, (8) muscle tone, (9) injection sites and third pulse, (10) the subject’s statements and other observations, (11) the evaluator’s analysis and opinion, and (12) toxicological examination.

Lack of convergence belongs to step 4. In the IACP’s words, “The DRE examines the subject for HGN, vertical gaze Nystagmus (VGN), and a lack of convergence.” The DRE then combines those eye findings with balance and coordination tests, pulse, blood pressure, temperature, pupil size under different lighting conditions in a dark room, and muscle tone to reach an opinion about whether you were impaired and, if so, by which category. Step 12, the lab test, comes last and is meant to corroborate the opinion.

So a single LOC finding is never supposed to stand alone. Its proper role is as one piece of a pattern: for example, LOC plus elevated pulse and dilated pupils, with no nystagmus, is the profile a DRE would associate with cannabis. If the rest of the evaluation does not fit the pattern, the convergence finding loses much of its meaning.

Limits and alternative causes

Many people who have taken no drugs at all cannot converge well. Some of the most common explanations:

• Convergence insufficiency. The National Eye Institute says this condition “usually starts in childhood, but it can happen in people of all ages after a brain injury,” and that “you can have perfect vision and still have convergence insufficiency,” so a routine eye exam may not catch it. Symptoms include tired eyes, blurry or double vision and headaches.
• Head injury. NEI notes convergence problems are common after a brain injury or concussion. A driver in a crash may have both a head injury and a DWI charge.
• Fatigue. The ARIDE guide lists “extreme fatigue” among conditions that may mimic drug impairment, along with very recent head injuries, diabetic reactions, low blood pressure, inner ear disorders and severe depression. Late-night stops are when people are most tired.
• Long-standing eye conditions. The ARIDE guide recognizes that people with a long-standing eye-movement abnormality “often learn to compensate.” An eye that has always turned out, or a history of eye surgery or patching, is not a sign of recent drug use.
• Glasses and contacts. Removing corrective lenses for the test can make it harder to focus on a near target.
• Administration problems. Stimulus too fast, too close or not held long enough; head movement; glare from emergency lights; a single check instead of two.

There is also a research gap. NHTSA’s validation work on field sobriety tests concerns HGN, walk and turn and one-leg stand. We have not found a NHTSA validation study establishing how accurately lack of convergence alone identifies drug impairment, and the training’s own statement that there are no validated clues points the same way. Broader reviews of the DRE program, such as the February 2019 AAA Foundation for Traffic Safety review by Douglas Beirness and Amy Porath, describe “mixed evidence” on the program’s accuracy, with laboratory studies giving only weak support for officers’ ability to name the specific drug category.

How lack of convergence is used in NC drugged-driving cases

North Carolina’s DWI statute reaches far beyond alcohol, which is why eye signs associated with drugs matter. Under G.S. 20-138.1(a)(1), a person commits impaired driving by driving “while under the influence of an impairing substance.” G.S. 20-4.01(14a) defines an impairing substance to include alcohol, Chapter 90 controlled substances, “any other drug or psychoactive substance capable of impairing a person’s physical or mental faculties,” or any combination, and subdivision (48b) defines being under the influence as having physical or mental faculties “appreciably impaired.”

That Schedule I prong matters less in a suspected marijuana case than many people assume. North Carolina lists marijuana and tetrahydrocannabinols in Schedule VI, under G.S. 90-94, not Schedule I. So a blood result showing THC does not by itself prove the offense; the State must prove appreciable impairment under (a)(1). That is exactly why the officer’s observations, including any lack-of-convergence finding, carry so much weight in cannabis cases, and why they deserve close scrutiny. Our marijuana DWI guide covers the exceptions, such as synthetic cannabinoids, which are Schedule I.

In practice, LOC shows up in two ways. First, as one observation an officer cites for probable cause to arrest when the breath result is low or zero. Second, as part of a DRE’s basis for naming a drug category at trial. In both settings, the lab result often matters more: toxicology from a blood sample analyzed under G.S. 20-139.1 can confirm or contradict the category the DRE named. Blood is usually obtained through the implied-consent procedure in G.S. 20-16.2, with the driver’s actual consent, or with a search warrant; Missouri v. McNeely (2013) held that the natural dissipation of alcohol does not automatically justify a warrantless blood draw. And if a warrant is later found defective, State v. Rogers (N.C. Oct. 17, 2025) now recognizes a good-faith exception under the North Carolina Constitution, overruling State v. Carter.

Admissibility: Rule 702 and DRE testimony

Notice what the rule names and what it does not. Subdivision (a1)(1) covers only HGN. Lack of convergence is not mentioned anywhere in Rule 702. A certified DRE may rely on LOC as part of an opinion on impairment and drug category under (a1)(2). For any other witness, such as a patrol officer with ARIDE training but no DRE certification, testimony that LOC indicates a drug category falls outside (a1) and must satisfy Rule 702(a): the testimony must be “based upon sufficient facts or data,” be “the product of reliable principles and methods,” and the witness must have “applied the principles and methods reliably to the facts of the case.”

The North Carolina cases draw these lines. In State v. Fincher (2018), the Court of Appeals held that a certified DRE could testify that the driver was impaired by a CNS depressant without a separate showing that the DRE protocol is reliable, because the General Assembly authorized that testimony. In State v. Moore (2025), the court held that Rule 702(a)(3) still applies: a DRE opinion built from records and trial testimony rather than an actual evaluation should have been excluded, although the error was not prejudicial there. In the unpublished State v. Lewis (2022), an officer who was not a certified DRE should not have been allowed to testify that the defendant was impaired by a category of impairing substance, or by a specific drug. We have not found a North Carolina appellate decision that rules specifically on lack-of-convergence testimony.

Find more decisions in our North Carolina DWI case law library, especially the drug and impairing substance cases, expert testimony cases and field sobriety test cases. Our case note on State v. Godwin covers the HGN rule in depth.

Questions a defense lawyer asks about an LOC finding

1. Who did the check, and with what training?

   A certified DRE testifies under Rule 702(a1)(2). An officer with only SFST or ARIDE training does not, and an opinion tying LOC to a drug category must meet Rule 702(a).

2. Was it done to the training standard?

   Start 12 to 15 inches out, circle, stop above eye level, bring in to about two inches, hold about one second, at least two checks. Time it on body-cam or dash-cam video.

3. What does the rest of the evaluation show?

   LOC is supposed to fit a pattern with pupils, pulse, blood pressure and muscle tone. Signs that point to different categories weaken the opinion.

4. What is the medical history?

   Convergence insufficiency, prior concussion, crash injuries, eye surgery, lazy eye, glasses, fatigue and diabetes. Bring records to your lawyer.

5. Does the lab agree?

   Compare the DRE’s category with the toxicology. A positive test for a drug’s presence is not, by itself, proof of impairment. The exception is the Schedule I theory in G.S. 20-138.1(a)(3), which does not reach marijuana or THC because North Carolina lists them in Schedule VI.

6. Object specifically and on time

   Object to LOC testimony separately, and file suppression motions before trial in district court under G.S. 20-38.6.

For the wider context, see our guides to the HGN eye test, the standardized field sobriety tests, marijuana and THC DWI, prescription drug DWI, blood and toxicology evidence and how to review DWI evidence.

Quiz: how well do you know the convergence check?

Two inches from the nose, one second, no validated clues. A convergence finding should never carry more weight than the training, the video and the driver’s own eyesight can support.Adkins & Purkey

Related guides

Top 10 FAQs: Lack of Convergence

General North Carolina legal information as of November 2026, not legal advice for any specific case. Reading this article does not create an attorney-client relationship. Attorney advertising. Training procedures described here come from the NHTSA/IACP ARIDE Participant Guide (rev. 2/2023) as published by the Washington State Patrol, the IACP’s description of the DRE 12-step process, and the North Carolina Drug Category Matrix (rev. 03/2019).