Yes. Alcohol can degrade aspects of vision that a conventional eye-chart test does not adequately describe. Controlled human studies have reported reductions in contrast sensitivity, changes in retinal straylight, impaired stereopsis (depth perception), and poorer simulated driving performance after drinking. These outcomes are not interchangeable, however: no single vision test reconstructs a blood alcohol concentration (BAC), diagnoses impairment in every task, or establishes why an individual collision occurred.
The distinction matters in forensic toxicology and DUI evidence review. Visual acuity measures the recognition of high-contrast detail; contrast sensitivity concerns the detection of differences between light and dark; retinal straylight relates to light scattered within the eye; and stereopsis concerns binocular depth perception. Each addresses a different physiological or performance question.
In a 2020 study of 40 healthy volunteers, Casares-López and colleagues measured visual function and driving-simulator performance at baseline and after 300 mL and 450 mL of red wine. Mean breath alcohol concentrations (BrAC) were approximately 0.18 and 0.30 mg/L after the two doses. Contrast sensitivity worsened, retinal straylight increased, and simulator performance deteriorated, particularly at the higher exposure. The investigators also reported associations between visual measures and driving-simulator outcomes.
These results do not mean that a straylight measurement independently predicts a real-world crash or can identify the cause of a particular driving error. The study was experimental and used a simulator rather than observing actual traffic crashes.
A 2021 study by Martino and colleagues examined 30 healthy licensed drivers before and after alcohol consumption at a mean BrAC of 0.40 mg/L. Distance and near stereoacuity, several measures of binocular coordination, and simulated driving performance worsened. Mean simulated dual-carriageway speed increased from 116.9 to 129.4 km/h, while the standard deviation of lateral position increased from 0.54 to 0.75 m in the same road scenario.
The researchers noted that mean binocular visual acuity remained above the study’s referenced visual-acuity threshold despite other deficits. Passing a high-contrast acuity threshold therefore did not rule out poorer depth perception or other task-relevant visual changes in that experiment. It also did not establish how any specific driver would perform on a real road.
In 2023, Martino and colleagues studied 26 healthy young adults using vision-degrading filters and a baseline-versus-alcohol comparison at 0.40 mg/L BrAC. Both alcohol and the filters degraded measured monocular and binocular visual performance, including stereopsis. The important distinction: induced interocular differences and reduced binocular summation were primarily associated with filter conditions, not caused to the same extent by alcohol itself.
This matters when a reviewer is tempted to attribute every abnormal binocular finding to ethanol. The 2023 findings show why baseline vision, between-eye differences, correction, experimental conditions, and other ocular factors must be considered before assigning a cause.
| Measure | What it describes | What it does not establish alone |
|---|---|---|
| High-contrast visual acuity | Recognition of fine detail on an eye chart | Normal contrast sensitivity, stereopsis, or safe driving |
| Contrast sensitivity | Ability to distinguish targets from backgrounds with limited contrast | A person’s BAC or legal impairment status |
| Retinal straylight | Forward-scattered light contributing to veiling glare | The precise reason for an individual roadway event |
| Stereopsis | Depth perception from coordinated binocular viewing | A diagnosis that alcohol, rather than an ocular condition, caused an abnormal finding |
| Simulator lane-position variation | Variation in vehicle lateral position during a controlled task | The probability or cause of an actual collision |
Across these studies, sample sizes were modest (26–40), participants were generally healthy, and controlled simulator or laboratory measurements served as outcomes. Beverage dose and achieved BrAC differed between experiments; the studies were not designed to validate a universal impairment cutoff or to estimate BAC from an eye examination. Associations between measured vision and simulator behavior do not, by themselves, prove that visual changes mediated every performance deficit.
When assessing an individual case, identify the actual visual task, measurement method, time relative to alcohol consumption, vision history, corrective lenses, alternative explanations, and objective testing records. Distinguish an observed sign from a physiological mechanism, a measured concentration, and a causal opinion.
Yes. In controlled research, visual acuity could remain above a referenced threshold while stereoacuity, binocular coordination, and simulator performance worsened. An eye chart does not measure every visual function.
No. Binocular visual performance can also be affected by differences between the eyes and other ocular factors. An abnormal result is not a chemical identification test.
No. The cited studies chiefly measured optical quality, visual acuity, contrast, stereopsis, and simulated driving; they did not validate these measurements as replacements for an HGN examination. For vestibular-ocular physiology, see alcohol and the vestibulo-ocular reflex.
No. Visual-function results do not provide a validated backward BAC calculation. See the separate discussion of blood alcohol versus brain alcohol for another limit of concentration-based inference.