Binocular vision and vergence in athletes: what 33 studies measure

In brief. In a Portuguese study, more than one professional soccer player in three has a binocular anomaly, and closing one eye lowers success at the free throw or in archery. According to 33 studies, experts do not always see depth better, and none of the eight training trials measures the match. Updated on November 3, 2026.

Hello to you, the movement professional,

In Braga, Jorge's optometry team put 107 professional soccer players through a full assessment of two-eyed vision: 36.4% had at least one binocular vision difficulty, the most frequent linked to esophoria, a latent tendency of the eyes to drift inward (Jorge et al., 2022).

Imagine your midfielder who cushions a long ball then looks for a teammate thirty meters away: his two eyes converge, diverge and refocus. If he belongs to that third, perhaps nobody knows it, and the convergence exercises seen on video seem to be the answer. The 33 studies gathered here raise a prior question: who measures, and who decides?

Binocular vision in athletes: what a vergence, phoria and stereopsis assessment measures

Binocular vision is the ability of the two eyes to aim at the same point and fuse their images into one. Ocular convergence turns them inward for a near target, and ocular accommodation adjusts focus at the same time. Cover one eye and it drifts slightly from its position: that is phoria, inward (esophoria) or outward (exophoria).

The assessment quantifies the margin of each function: fusional vergences in prism diopters, vergence facility in cycles per minute, and the near point of convergence, the distance at which fusion breaks when a target approaches the nose. Stereopsis, the depth drawn from the slight offset between the two images, is expressed in arcseconds: the lower the number, the finer the depth perception. These functions occupy the top of the binocular vision pyramid, and the Brock string, a cord with colored beads, is used by the vision professional to read them. Their role in standing balance is covered in our article on ocular convergence and posture.

How many athletes have a binocular vision difficulty

The Braga figure includes notably 13.0% of anomalies linked to esophoria, 10.3% of convergence insufficiency and 6.5% of reduced accommodative facility. Surveyed online, 6.3% of professional soccer players from four countries exceeded the threshold of a visual symptoms questionnaire, a score only weakly related to their self-rated performance (rho = -0.215; Jorge et al., 2023).

Follow-up is often missing: 70% of 95 Nepalese national players had never had a full eye examination (Sapkota et al., 2006). Among 59 cricket and rugby league players, 27% had a visual problem on the field, most often an uncorrected refractive error (Barrett et al., 2017).

In 28 shooters, the longer the shooting experience, the poorer the binocular balance and the more near convergence deteriorates (r = 0.335), which the authors attribute, as a hypothesis, to years spent closing one eye to aim (Garaszczuk et al., 2025). A binocular anomaly can therefore easily go unnoticed in a high-performing athlete, and only an assessment spots it.

Do athletes have better vergence? Results that contradict each other

Semi-professional basketball players converge from closer and fuse faster than sedentary individuals (Vera et al., 2020), convergence starts earlier in baseball players (Yoshimura et al., 2021), and table tennis champions have better accommodative facility (Jafarzadehpur and Yarigholi, 2004). The Braga professionals exceed published reference values, without a control group (Jorge and Diaz-Rey, 2022).

The largest matched comparison blurs this picture: among 214 teenagers, athletes and non-athletes each come out ahead on some measures, and the authors judge the whole inconclusive (Omar et al., 2017). In 218 elite soccer players, no correlation between binocular vision and visuo-cognitive tasks exceeds 0.35 in absolute value (Jorge et al., 2026). All these studies are cross-sectional: they don't say whether sport shapes vergence or whether it retains those who already have it.

Stereopsis: does the expert see depth better?

Professional (Laby et al., 1996) or youth (Boden et al., 2009) baseball players, professional table tennis players (Zhu et al., 2019) and jumpers under 18 (Salcman et al., 2021) see depth more finely than their comparison groups (non-players, general population or swimmers of the same age). Soccer players (Paulus et al., 2014) and basketball, futsal, hockey and roller derby players (Nascimento et al., 2025) do no better than non-athletes.

The link with performance changes depending on how it is measured. In 23 university baseball players, stereopsis is related to no game statistic (Molia et al., 1998). In 24 infielders, depth perception is the measure most related to catching rate in the laboratory (R = -0.844), and the authors recall that its causal role remains to be established (Long et al., 2026). In 59 elite soccer referees, stereoacuity and visual memory together explain 22% of the differences in federation ranking (Baptista et al., 2021).

Closing one eye: what binocular vision brings to the movement

Removing binocular vision gives clearer results. In 23 basketball players, covering the dominant eye lowers free-throw success by about 8%, whereas a blur placed over both eyes, which keeps binocular vision, changes nothing (Vera et al., 2020). At 30 meters, 14 archers place 11.85 arrows out of 36 in the 9-point zone with two eyes, against 9.36 with one eye (Hirota et al., 2023).

In the gymnastics vault, removing binocular vision alters the movement of novices and leaves that of experts intact (Heinen and Vinken, 2011). Learning depends on it too. In two weeks, poor catchers with good stereopsis go from 18% to 59% of catches, those with weak stereopsis from 10% to 31%, a non-significant improvement (Mazyn et al., 2007). These experiments compare the same athlete with and without both eyes, and their scope stops at the movement tested.

Training vergence and stereopsis: eight trials, no match measured

The most cited trial is that of Zwierko et al. (2015): 24 female students in soccer, basketball and handball, 12 of them randomly assigned to eight weeks of orthoptic-inspired eye work. Three of the six measures improved, mainly near phoria and fusional convergence, and the gain held four weeks after stopping.

The seven others, detailed in the table, last from a single session to six weeks, and only three compare with a control group. The only one that measures a sport movement, the target-zone hitting of Chiang et al. (2026), is also the one where binocular function does not move, so the origin of the gain remains to be explained. This trial and the one-session pilot by Shyu et al. (2025) come from the same Taiwanese team, very probably involve the same group of 26 badminton players, and one of the co-authors of both articles is the inventor of the patented prism device they test. In double-blind conditions, three weeks of digital procedures do no better than a placebo in 32 baseball and softball players, while 15 of the 16 athletes in the placebo group believed they were following the real program (Shekar et al., 2021).

In the systematic review by Rawstron et al. (2005), of 43 publications on eye exercises, only convergence insufficiency rests on small controlled trials, less solid evidence points toward a refinement of depth perception, and no clear evidence supports these exercises for sport performance.

Links between the studies

Braga, Taiwan and Erlangen weigh heavily in this corpus, and concordant results from a single team are not worth independent replications.

What an athlete's vergence doesn't yet tell us about their game

Established, on small samples: depriving an athlete of binocular vision degrades certain precision movements, and a notable share of high-level athletes show a binocular anomaly when you look for it. Debated: the binocular superiority of experts, which matched comparisons refute, and the link between depth perception and performance. Extrapolation: that training the vergence of an athlete with no identified difficulty improves their game. No trial has shown it, and nobody can promise it to you.

A single season would be enough to test the idea that vergence weighs on play: if, among professional soccer players measured at the start of the season, those with an anomaly do not differ in any way from the others on match measures linked to gaze, such as controls of long balls, this idea loses its main support at that level.

Double vision, blur, headaches: the referral chain before any binocular work

If your athlete reports double vision, persistent blur, headaches during effort or dizziness, visual training waits. They first consult an ophthalmologist, then an orthoptist in France, or an optometrist in Switzerland or the United States. LabO RNP is neither medical nor paramedical, and comes as a complement to a care pathway, never in its place.

The ophthalmologist, the eye physician, checks that nothing else explains the signal; the orthoptist or optometrist then carries out the binocular assessment and decides whether there is work to be done. Your role is to listen to what the athlete reports, including fatigue after video sessions that they don't connect to their eyes, then to wait for their green light before any vergence or fusion exercise. A test found online is enough for neither you nor the athlete to conclude, and the only indication backed by controlled trials, convergence insufficiency, falls precisely within these professionals' remit.

Tell them what the sport imposes, such as a shooter who has closed one eye for years, or a player who does not wear in matches the correction that was prescribed, a case that Barrett et al. (2017) note in cricket and rugby league players. LabO RNP works with optometrists; the curriculum was built with them.

Two eyes, one movement: binocular vision in the sensorimotor loop

The eyes are an entry point. What LabO RNP teaches is the whole sensorimotor loop: how what the athlete perceives organizes what they do. The distance at which we fixate also takes part in postural control, to a degree still debated. The oculomotor exercises in the warm-up keep vergence and fusion for a dedicated session, and the map of the evidence in sports vision places this work among the others. Depth perception comes back in our articles on oculomotor function in table tennis, vision in badminton and how to follow the ball with your eyes.

Convergence, depth, Brock string: what trainers ask

What is binocular vision in an athlete?

It is the ability of the two eyes to aim at the same point and fuse their images, which gives depth. An assessment measures it through phoria, fusional vergences, the near point of convergence and stereoacuity. In athletes, it mainly serves to spot an anomaly, because experts don't always have better values (Omar et al., 2017).

How many athletes have a binocular vision difficulty?

Among 107 professional soccer players, 36.4% had at least one binocular anomaly according to the authors' criteria, mostly linked to esophoria or convergence insufficiency (Jorge et al., 2022). Among 95 Nepalese national players, 70% had never had a full eye examination (Sapkota et al., 2006).

Do top athletes see depth better?

Sometimes. Baseball and table tennis players have better stereoacuity than their controls (Boden et al., 2009; Zhu et al., 2019), soccer and team-sport players do not (Paulus et al., 2014; Nascimento et al., 2025). And in 23 university baseball players, depth perception is related to no game statistic (Molia et al., 1998).

Does the Brock string improve sport performance?

No trial shows it. The only study in athletes that makes it the core of a session involves 27 children, without a control group, and measures balance and throws right afterward (Tekin et al., 2026). The Brock string remains a tool for reading and working in the hands of the vision professional.

Who should you consult if an athlete sees double or blurry?

The ophthalmologist first, the eye physician. Then, depending on the country, the orthoptist in France or the optometrist in Switzerland and the United States for the binocular assessment. Visual training waits for their green light. LabO RNP is neither medical nor paramedical, and comes as a complement to a care pathway, never in its place.

Before training two eyes to work together, you check that they are capable of it, and that check belongs to the vision professional.

👉 I want to understand where binocular vision fits into my athlete's movement.

By the LabO RNP team

Method. LabO RNP inventory of 1,275 studies on athletes' vision (PubMed and our reading notes), consolidated on November 3, 2026. 83 deal primarily with vergence, accommodation or fusion, 14 of them on concussion, set aside. Of the remaining 69, 36 are excluded (25 where the binocular measure is secondary or redundant, 4 on eye dominance, 6 without original data or narrative reviews, 1 without a verifiable identifier) and 33 publications are analyzed, two of which very probably concern the same group of players. Each PMID was checked against its PubMed record on November 3, 2026, and each figure comes from the PubMed abstract, from our notes or, for the age of the badminton players in Shyu et al. (2025), from the full text.

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