Several investigative efforts have been made to profile the visual makeup of baseball players1-3 with the goal of discovering a link between certain visual skills and success in baseball performance,4-8 and whether or not performance improves by changing the visual aspects of the game or player,9-13 or simply what occurs physiologically when a batter is facing a ball they want to hit.14-17
When one stops to consider the visual demands placed on a batter, it is easy to conclude that hitting a baseball is a unique and challenging task requiring the evaluation, correction, and training of the visual system.
Batters are given less than a second to view and analyze facets of the pitcher’s delivery (arm slot, speed, grip on the ball, etc.) and the ball itself (spin pattern, trajectory, speed). Correct analysis can help the batter identify the type of pitch thrown, predict the ball’s approach, and anticipate the time at which it will enter the contact zone.
In addition, batters are doing this across different, dynamic environments. Noise levels rise and fall, teams travel to different stadiums, pitchers are rotated out, and lighting levels range from high noon, through dusk, and into the artificially lit environment of night games.
The intersection of sports vision and primary care optometry
There is increased clinical and scholarly interest in vision and sports currently. Analytics and the “Moneyball” revolution have introduced behavioral and biomechanics studies as well as evidence-based decision-making by players, coaches, and teams.
As athletes and their industry wish to become more informed on the nuances of their performance, eyecare providers will find themselves answering questions about how improved visual abilities and talents will translate to elevated performance levels.
The role of visual acuity in sports vision
Among the elements of vision, visual acuity is often determined to be the most fundamental, even in sports vision.18 General population studies show that 53.9% of the US adult population has 20/20 binocular, uncorrected vision or better and 30.3% have 20/15 or better visual acuity. When corrected, 72.9% obtain 20/20 visual acuity, and 40.0% reach 20/15 or better.19
These distributions aren’t observed in a specialized sample such as in professional baseball players. According to one study, in a sample of 387 major league ball players, Laby et al. found that 81% of right eyes measured had 20/15 vision or better.1
Other studies investigating visual acuity (combined with other visual facets) found a favorable effect in a batter’s plate discipline (whether to swing or not),20 and have confirmed better visual acuity for interceptive tasks at higher levels of expertise.6
The benefits of contrast sensitivity
The ability to distinguish the borders or margins of an object from its background is a typical definition of contrast sensitivity. When one limits their view to contrast in this way it may be difficult to see how contrast sensitivity is able to help a player hit a baseball. However, if contrast sensitivity is viewed as the ability to harvest recognizable and useful visual information from a degraded image, it becomes easier.
Studies show that the majority of Major League Baseball (MLB) players have above-average sensitivity to contrast,1 and that this when paired with visual acuity and image presentation time, is correlated with their discipline at the plate.20 It is difficult to separate the benefits of contrast sensitivity from visual acuity as they function simultaneously and dependently.
Clinically speaking, the best way to improve contrast is to improve visual acuity. Research demonstrates that contrast may be improved through the use of lutein supplementation.21,22 Supplementation of this kind may also help eyes recover better from photostress23 and have a faster visual processing speed.21
Overview of ocular dominance
Often in baseball, the concept of ocular dominance is brought forward. This is commonly done when determining if the batter’s lead eye—the eye closest to the pitcher—is the dominant eye.
Although logical, clinically this may lead the provider down a fruitless path. Studies in ocular dominance and baseball have shown that cross dominance (right-handed-left-eye dominant), is not related to performance at the plate.2
However, it has been shown that the Pulfrich phenomenon has a greater effect on batting performance when a neutral density filter is placed over the dominant eye.24 It might, therefore, be important to identify the dominant eye and ensure that it is seeing optimally.
Targeting in sports vision: Where to look
A 95-mph fastball takes 0.434 seconds to arrive at the plate from the pitcher’s hand. This is near the time it takes to blink an eye. It is worth noting that players eagerly look for useful information ascertainable before the pitch is released. They look for clues indicating the location or speed of the ball from the pitcher and the pitcher’s delivery.
Studies have shown that experienced ball players are more consistent in where they look to first pick up the ball,25 as well as at identifying the pitching method by assessing the grip used by the pitcher.5 Research also indicates that even novices are able to identify a pitch rotation pattern (spin).16 It also is very sensible to assume that batters will attempt to gather as much information as possible from their environment to gain an advantage.
At all levels, players may assess the glove hand prior to the wind-up, to assess if a pitcher is tipping, or revealing, their pitches. Both young and old pitchers can have a “tell,” (equivalent to what might be found at a poker table) since a curveball requires a different grip on the ball.
Competitive baseball players’ eyes likely move to the location of the first appearance of the ball as it comes from behind the pitcher’s body and is raised (or lowered in the case of underhand pitchers) to come forward.25,26 It is at this time that batters may be able to identify a grip, or a different arm slot, that may foretell the pending pitch.
In some studies, the ability to predict the pitch has been correlated with on-field performance.5 It is possible that this skill and its correlation to performance is limited to the stimulus, as other studies have found that a mere measure of quickly interpreting visual information (letters and numbers) is not correlated with performance.27
The ocular impact of concussions
Mild traumatic brain injuries (mTBI) have been linked to cognitive, emotional, and mental health issues, but also leave many individuals with ocular symptoms.28 This includes issues with the very important vestibulo-ocular reflex.29 In order to optimize vision, players need not only good resolution, contrast, and targeting skills, but also healthy, reliable neural pathways.
Studies have shown the impact that concussions have on eye movements—which is an essential skill that baseball players rely on to perform the task of tracking then hitting a baseball.30
It is imperative therefore that the health of these pathways be assessed by the clinician during annual exams using tools that currently exist,31 with greater sensitivity towards those athletes participating in high-contact sports.32
Redefining sports vision
Sports vision is being redefined as an umbrella term covering the examination, care, and treatment of all an athlete’s vision and ocular health demands. This new emphasis embraces both ends of the visual management spectrum, from rehabilitation to high-level performance, much of which can be managed through informed and careful primary care efforts.
Optometrists are distinctively qualified to meet this range of unique visual needs among this highly specific patient population.
Table 1 outlines helpful primary care tests for athletes and sports vision patients.
| Category | Test |
|---|---|
| History | Ask about hobbies: Almost all patients are athletes in some capacity. Ask about concussions/head injuries: This is particularly important with multi-sport athletes and baseball catches |
| Entrance Testing | Visual acuity: Check and target for 20/15. Contrast sensitivity (CS): 1.9% or 1.72 log CS is a good norm for performance. Near point convergence (NPC): Reduced with concussion and can improve with healing. King-Devick/Developmental eye movement (DEM): Measure baseline performance, often reduced with a mTBI. Ocular dominance: Measure it and ensure it's clear. |
| Education | School/vision screenings: “Screenings catch big ocular and visual deficits but can't ensure your child is seeing well enough for baseball at high levels. That's just not what screenings are designed to do.” |
Table 1: Courtesy of Adam Blacker, OD, MS, MBA.
Conclusion
Through the advent of technology, the coordination of athletes and teams as well as the analytical revolution sweeping through baseball currently, more performance-enhancing discoveries will be made, behaviors will be revealed, and further understanding will be gained.
Through this rigorous effort, evidence-based examinations, treatments, and training will take leaps forward in assisting the athletes to achieve the careers of their dreams.
