The effect of laser refractive surgery on the on-field performance of professional baseball players

Article Outline

• Abstract
• Materials and Methods
• Results
• Discussion
• References
• Copyright

Background

The aim of this study was to determine the effect of laser refractive surgery on the offensive performance of professional baseball players.

Methods

Extensive search of the public media was conducted to determine which major league baseball players had undergone laser refractive surgery and when the procedure was performed. Baseball performance data were then used to determine presurgery and postsurgery baseball performance averages. A total of 17 position players were identified; however, 5 of these players were not considered in the analysis owing to insufficient playing experience either before or after the laser procedure.

Results

No statistically significant or practically significant difference was found between the presurgery and postsurgery means on either on-base percentage (P = 0.31), batting average (P = 0.39), slugging percentage (P = 0.66) or on-base plus slugging (OPS; P = 0.997) of major league baseball players.

Conclusions

These preliminary findings suggest that professional baseball players should not expect a laser refractive surgical procedure to significantly improve their offensive baseball performance, despite the elimination of glasses or contact lens wear.

Key Words:  Batting , LASIK , refractive surgery , sports performance , sports vision

Recently, there has been great public interest in the various laser refractive surgical procedures. Refractive surgery has enabled myopes and astigmats to achieve “normal” visual acuity without the use of glasses or contact lenses. Initially, laser refractive surgery consisted of the photorefractive keratectomy (PRK) technique. In 1991, the laser in situ keratomileusis (LASIK) technique was developed, with a significant improvement in postoperative visual function. Specifically, LASIK decreased the incidence of postoperative haze, which was thought to interfere with a subject’s visual function (acuity, contrast sensitivity, and nighttime glare). Coincident with the general public’s interest in the procedure, many professional athletes have undergone LASIK in an effort to eliminate their dependence on refractive devices.¹, ² Additionally, several professional athletes have publicly advocated the merits of the procedure in commercial publications. In an effort to determine whether the laser refractive surgical procedure enhanced or detracted from offensive baseball performance, we analyzed the playing statistics of all major league baseball position players who have publicly reported having undergone a laser refractive surgical procedure.

Back to Article Outline

Materials and Methods 

Although athletes from many sports have undergone laser refractive surgical procedures, we elected to study solely major league professional baseball players. This study group was chosen because of the unusually high level of visual function required to play at the major league level. Our previous research has found that professional baseball players, and position players (all players except pitchers) in particular, have visual acuity, stereo vision, and contrast sensitivity that are significantly better than that of the general population.³ In addition, position players as a group have better visual function than pitchers.³ By studying the effect of the laser refractive surgical procedure on this elite population, we hope to detect the smallest effects of vision (either positive or negative) on baseball performance. In addition, professional baseball players constitute perhaps the largest group of professional athletes who have publicly reported having a laser refractive surgical procedure.

Because of privacy concerns, no private medical records could be used in this analysis. To identify players who had undergone a laser refractive surgical procedure, an exhaustive search of the public media was performed that identified 17 major league position players. Sources included a review of commercial Web sites containing information regarding a specific player, a review of the baseball-specific print media, as well as communication with journalists in the field, in an effort to identify as many professional baseball players as possible who had been publicly identified as having undergone a laser refractive surgical procedure. At a minimum, the source was required to identify both the player’s name as well as the approximate date of the procedure.

In an effort to minimize the natural short-term fluctuations in a player’s baseball performance not necessarily related to the effect of the laser procedure, we removed from the analysis any player who had not had at least 2 seasons (with a minimum of 100 major league at bats per season) of baseball offensive experience both before and after the laser surgical procedure. Baseball performance data through the 2004 season were included. Thus, a total of 12 major league position players met these criteria and were included in the analysis.

Although the offensive baseball indices used to measure the effect of the laser refractive surgical procedure are well established, a brief review of their origins is in order. Each of the 4 measures evaluates a slightly different type of offensive ability. Batting average (AVG), perhaps the most commonly discussed measure, is determined by totaling the number of hits a player has achieved divided by the total number of opportunities to achieve a hit (known as an “at bat”—without including walks or sacrifice hits). Slugging percentage (SLG), a measure of how “potent” a player is, is calculated by adding together the total number of bases achieved by the player (singles plus twice the number of doubles plus 3 times the number of triples plus 4 times the number of home runs) divided by the number of at bats. On-base percentage (OBP) measures a player’s ability to get on base, either by achieving a hit, achieving a walk, or being hit by a pitch, divided by the total number of opportunities (at bats plus walks plus hit by pitch plus sacrifice flies). Finally, on-base plus slugging (OPS) is simply the sum of OBP and SLG. This measure attempts to combine a player’s ability to get on base and his ability to achieve an extra base hit. Although the first 3 measures are well established baseball indices, OPS is a newer measure gaining importance in the age of critical statistical analysis of a player’s abilities.⁴

Yearly performance data for each of the players in the study were obtained from standard baseball performance data available to the public (through the internet address www.espn.com and www.si.com). The date of the laser refractive procedure, the average number of at bats, and the averages for each of the performance indices were calculated for the 2 seasons before and the 2 seasons after the laser refractive surgical procedure for each player (see Table 1). A paired, 2-tailed Student’s t test was used to test the hypothesis that there is no difference in the mean values before and after the laser refractive surgical procedure. In addition, the Bonferroni correction was used to protect against the effect of multiple tests.

Table 1. Hitting indices before and after the laser refractive surgical procedure

AB, Average number of at bats per season.

Note: Dates are indicated as month and year or as occurring between 2 consecutive seasons. Results include data through 2004 season.

Back to Article Outline

Results 

Table 2 summarizes the results of our analysis. The mean performance data for each index by player are presented as well as the results of the paired t tests. A total of 6 players had a higher AVG presurgery compared with postsurgery, and 8 players had a higher SLG before surgery compared with post surgery. OBP and OPS were more evenly divided with 5 and 6 players, respectively, each having better offensive performance pre-operatively compared with postoperatively. As a group (see Table 2), the mean number of at bats before surgery was 422 per season compared with 410 after surgery. Except for SLG, each of the mean offensive measures was lower after the surgical procedure compared with the same measure before the laser refractive surgical procedure.

Table 2. Mean values for baseball performance data with statistical analysis

AB, Average number of at bats before the refractive surgical procedure.

AB^a, Average number of at bats after refractive surgical procedure.

For each measure, a preliminary Anderson-Darling test was conducted to test the hypothesis that the change in performance from before to after the laser surgery followed a normal distribution. In each case the result was not significant (P > 0.14) implying that normality could be assumed. Each of the 4 paired sample t tests failed to give significance at the 0.05 level. Hence, this statistical analysis showed that there was no statistically significant difference on the average between players’ offensive abilities after the laser refractive surgical procedure when compared with preprocedure offensive performances.

Identifying players through the public media who have not had a laser refractive surgical procedure is problematic, so a control group is difficult to form. However, to provide a context for these results, 275 major league players were identified who had at least 200 official at bats during both the 2003 and 2004 seasons. The mean and SD for the distributions of change in performance for these players on the AVG, OBP, SLG, and OPS from 2003 to 2004 are provided in Table 3. For each measure this table also provides the proportion of the sample in this study in which changes in performance were less than one half SD of the sample of the 275, less than 1 SD, and less than 2 SDs. For all 4 measures, at least 75% (9 of 12) of the study sample was within 1 SD of the large sample and at least 92% (11 of 12) were within 2 SDs. That is, assuming that the changes in performance from the 2003 season to the 2004 season are typical of major league players, the changes in performance of the players in this study are quite typical fluctuations. Not only are the mean changes in this study not statistically significant, they are also not of practical significance. A parallel analysis using data that span across each player’s major league career provided very similar results.

Table 3. Comparison of performance change to all players with at least 200 at bats in the 2003 and 2004 seasons

Mean Change, the average change in performance for the 275 players; SD of Change, standard deviation of the change in performance; Within 0.5 SD, the percentage of the 12 players in this study whose change in performance is less than one-half SD of the changes; Within 1 SD, the percentage of the 12 players in this study whose change in performance is less than one SD of the changes; Within 2 SD, the percentage of the 12 players in this study whose change in performance is less than two SD’s of the changes.

Back to Article Outline

Discussion 

Laser refractive surgical procedures have been increasing in popularity, with estimates of nearly 1 million procedures performed each year. Players of several different professional sports have undergone the procedure (e.g., football, golf, basketball, soccer) in an effort to eliminate their dependence on refractive devices. Because of the above average visual performance of professional baseball players on various vision tests,³ we theorized that this group would be most sensitive to any decrease or increase in visual performance afforded by the laser refractive surgical procedure. Several players have anecdotally noted an increase in visual function as well as baseball performance¹, ²; however, this was not confirmed by statistical evidence. All of the professional baseball players reported being pleased with the procedure, and none were reported to have regretted their decision.

In an effort to evaluate the true benefit of laser refractive surgery in this population as well as evaluate the benefit in terms of the published risks concerning the procedure, we compared only the baseball performance of qualifying players (those having at least 2 seasons of offensive experience both before and after the refractive surgical procedure). Although the players’ final visual results are important, their on-field performance is of the utmost importance in deciding whether a surgical procedure would be beneficial to baseball players. Additionally, because the procedure carries associated risks to eye health and visual function, a player should consider the effect on offensive performance when weighing the risks and benefits of undergoing a laser refractive surgical procedure during his playing career.

Laser refractive surgical procedures are, for the most part, very safe and effective elective surgical procedures. In a recent 12-year followup study of the PRK procedure, Rajan et al.⁵ published their results concerning the original cohort of 120 subjects who participated in the United Kingdom excimer laser clinical trial. They found that the postoperative refractive results remained relatively stable over this period. Between 65% and 75% of the subjects with original refractive errors up to 3.00 diopters of myopia were found to be within 1 diopter of the intended target correction. Four percent of the subjects had residual corneal haze, and 12% had persistent nighttime halos at 12 years. Finally, 3% of the patients had dry eyes.

PRK has since been replaced by newer procedures, with LASIK being the most popular. Shorter-term reports of the LASIK procedure, with 6 years of followup, have suggested that the problem of corneal haze remains; 1 investigator noted an incidence of 75% of the subjects noting glare and halos at night.⁶ In an effort to reduce the nighttime glare symptoms encountered in prior procedures, the optical treatment zone has been changed. Also, newer lasers use a scanning spot or slit for some, or all, of the treatment. In addition, the newer LASIK procedure carries an additional risk factor owing to the use of the microkeratome to create a corneal flap. The same investigator noted 5 of 33 eyes suffered a microkeratome complication with 3 eyes having a reduction in best-corrected visual acuity.⁶ Although the use of a corneal flap in the LASIK procedure has reduced the incidence of corneal haze in short-term reports, a leading expert in contrast sensitivity reports a decrease in contrast sensitivity and visual function after the LASIK procedure.⁷

Our previous work³ described the level of function common to professional baseball players. We described the visual acuity, stereo acuity, and contrast sensitivity function for this elite visual population. In addition, we documented the difference between the general population, the minor league baseball players, and those at the higher functioning major league level. There was a statistically significant difference between the 3 groups, with major league hitters having the best visual function overall. Although perhaps intuitive, it is clear that vision is of critical importance in successfully hitting a baseball thrown at speeds approaching 100 mph. Thus, it is not surprising that the most successful group of hitters, the major league hitters, had the highest scores on visual function testing.

To remain successful, one would expect that a major league hitter would need to retain this “visual advantage.” In fact, in an effort to maintain this advantage, players routinely wear sunglasses to reduce glare during day games, and some wear different lens tints during daylight conditions in an effort to improve visual function. Also, nearly all professional baseball players are screened on a yearly basis, to ensure normal visual function as well as detect any pathologic process that could interfere with their health and hitting performance.

Care was taken to properly consider the relatively small sample size presented. To be certain that multiple tests are not causing a significant finding, the Bonferroni correction technique can be applied. This technique suggests that when 4 different indices are evaluated in the same population, the level of significance should be tightened. Therefore, although we tested our hypothesis at the 0.05 confidence level, with 4 performance variables, significance should be more correctly tested at the 0.0125 confidence level. Because our results do not show any statistically significant difference between the prerefractive and postrefractive surgery groups at the 0.05 level, they also do not show any significant difference at the 0.0125 confidence level. In addition, with a small sample size of 12, the ability of this series to show a difference between prerefractive and postrefractive surgery should be considered (power calculation). For example, statistical analysis shows that with a power of 80% (i.e., our analysis had an 80% chance of obtaining a significant difference) a change in perhaps the most important measure, batting average, of 0.023 in either direction could have produced a statistically significant difference between the before and after procedure means at the 0.05 confidence level. Similar findings were obtained for OBP, SLG, and OPS. Therefore, at the accepted power level of 80%, our sample was capable of statistically detecting a significant performance difference in means had there been one present.

Although studies have found refractive surgical procedures to be successful in reducing a subject’s reliance on refractive devices, with 75% of the subjects “satisfied” with their postoperative visual acuity,⁶ this report shows that a player considering surgery should not expect a resultant improvement in hitting performance. In addition, when one considers the increased risk of corneal haze, nighttime glare and halos, as well as a potential loss in best-corrected visual acuity, a player may prefer to wait until he retires from professional baseball to undergo this procedure. Specifically, we are not only concerned that a loss of best-corrected visual acuity could result in a loss of hitting performance, but the commonly noted corneal haze could interfere with contrast sensitivity critical to batting and also affect a player’s fielding ability. Significant corneal haze could certainly interfere with a player’s ability to follow and successfully catch a fly ball when viewed against the stadium lights at night or the sun during the day.

Our preliminary data do not show a loss in performance after the refractive surgical procedure, which some may interpret as an indication that the procedure can be performed during a player’s career. Although this is statistically correct, a review of the data indicates that most players studied had better offensive baseball indices before the procedure than after. Also, although the published studies describing the benefits of the refractive surgical procedures noted success when a subject is within a diopter or more of emmetropia, professional baseball players, with a mean visual acuity of 20/12.5³ cannot tolerate vision with a diopter or more of uncorrected ametropia. Thus, a refractive aid, albeit of lesser power, would still be needed after the refractive surgical procedure. The risk of a complication, although minimal, (e.g., postoperative glare, halos, loss of best-corrected visual acuity) with the potential to end a player’s career is real and likely not worth assuming without a scientifically documented on-field hitting benefit to undergoing the surgical procedure. The ultimate decision to undergo a refractive surgical procedure is a personal one, although this preliminary report suggests that there may not be statistical or practical evidence that supports the position that baseball performance will improve as a result of this procedure.

Back to Article Outline

References 

1. Berardino M . Seeing is believing . Sun-Sentinel . 1999; August 17.
   • View In Article
2. Hill T . They can see clearly now—Athletes opt for laser surgery to improve their vision and on-field performance . New York Daily News; 1999; April 4.
   • View In Article
3. Laby DM , Rosenbaum AL , Kirschen DG , et al.   The visual function of professional baseball players . Am J Ophthalmol . 1996;122(4):476–485
   • View In Article
   • MEDLINE
4. Lewis M . Moneyball . New York & London: WW Norton and Company; 2004; p. 80,128
   • View In Article
5. Rajan MS , Jaycock P , O’Brart D , et al.   A long-term study of photorefractive keratectomy; 12-year follow-up . Ophthalmology . 2004;111:1813–1824
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (318 KB)
   • CrossRef
6. Sekundo W , Bonicke K , Mattausch P , et al.   Six-year follow-up of laser in situ keratomileusis for moderate and extreme myopia using a first-generation excimer laser and microtome . J Cataract Refract Surg . 2003;29(6):1152–1158
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (259 KB)
   • CrossRef
7. Holladay JT , Dudeja DR , Chang J . Functional vision and corneal changes after laser in situ keratomileusis determined by contrast sensitivity, glare testing, and corneal topography . J Cataract and Refract Surg . 1999;25(5):663–669
   • View In Article