Epidemiology of United States tennis-related ocular injuries from 2000 to 2019

To characterize trends in ocular tennis injuries over the last 20 years. The National Electronic Injury Surveillance System was utilized to characterize tennis-related eye injuries in a nationally representative sample of emergency department visits. Data were divided into 5 age groups, and various demographic information was obtained. Approximately 16,000 tennis-related ocular injuries were identified with males being affected nearly 2:1 compared to females. The youngest age group (0–20) had the greatest proportion of injuries, with most injuries in boys 11–15 years old. Injuries occurred most often during the spring season. Most patients were treated and released from the ED. Of those patients who were hospitalized, one-third had an open globe injury. The overall number of injuries trended downward during the timespan of the study. Although most patients did not experience serious visual consequences, the greatest proportion of ocular tennis injuries occurred in the pediatric age group in whom the risk of amblyopia is high. Primary care providers and tennis regulatory bodies should consider recommending eye safety sports goggles in children to mitigate the potential for significant visual morbidity.


Introduction
Tennis is among the ten most popular sports in America in terms of television viewership [1]. Tennis participation overall is increasing; a 1% increase was seen from 2017 to 2018 totaling 17.84 million players, with a nearly 2% increase in youth tennis players during that time according to the Physical Activity Council. In addition, there are another 14 million who are considered intermittent players (those who have not been on the court in the past 2 years). The greatest proportion of tennis players are between the ages of 25-34 [2]. Tennis is a popular sport in both genders; in a 2018 survey, 55% of players were males and 70% White; Hispanics, African Americans and injuries with the ankle being the most common site of injury. More injuries occur during match play compared to practice. Data from the NCAA has shown an injury rate of 4.9 per 1000 athlete exposures (AE), with 8.9 per 1000 AE in men compared to 7.4 per 1000 AE in women during competitive play compared to 3.8 per 1000 AE and 4.3 per 1000 AE in men and women during practice, respectively [3].
While many tennis-related injuries have been described and studied there is limited information on tennis-related ocular injuries in the scientific literature. Since tennis has large domestic and international appeal, understanding the current epidemiology of ocular tennis injuries may help guide measures to prevent severe injury to players and spectators [4]. It also informs ophthalmologists of the prevalence of this injuries as a means to educated and warn patients of the potential hazard associated with the sport of tennis. Therefore, the goal of this study was to characterize the epidemiology of tennis-related ocular injury in the US from 2000 to 2019.

Study design
This retrospective epidemiologic study utilizes data sourced from the National Electronic Injury Surveillance System (NEISS); an injury surveillance system run by the Consumer Product Safety Commission primarily to gather data on consumer-product-related injuries. The NEISS database encompasses a representative sample of 100 US hospital Emergency Departments (EDs). A similar search methodology was used as previously described [5]. The NEISS query code 3284 (tennis) was used to gather cases related to ocular injuries caused by tennis activity or equipment. The NEISS query code 77 was used to identify injuries to the eyeball. Open globe injuries (OGIs) were identified by reviewing the narrative variable for each case for description of an OGI. The time period examined was between January 1, 2000 and December 31, 2019. Patients were divided into five age groups: 0-20, 21-40, 41-60, 61-80 and 80 + years. The youngest age group was further subdivided into 0-5, 6-10, 11-15, 16-20 years.

Statistical analysis
The data were analyzed using IBM SPSS version 23. Trendlines and line-of-best-fit regression coefficients were calculated using Microsoft Excel. The population estimates used as the denominator for annual injury rate calculations were obtained from the US Census Bureau population estimates from 2010 to 2019 [6]. The Tennis Industry Association's average estimates of tennis participation (individuals 6 years and older) from 2006 to 2017 were used to calculate annual injury rates for tennis players [2]. A t-test and a simple linear regression model was used for analysis of injury trends with an alpha of 0.05. Prior to analysis data weights were applied, by the NEISS database, to make estimates representative of the national population.

Results
An estimated 15,903 ED visits were included for tennis-related ocular injuries in the US between 2000 and 2019; demographic information is shown in Table 1. Males accounted for most injuries in all age groups with the highest in the 0-5 group (79.1%) (Fig. 1). About 1% of injuries resulted in either the patient being transferred or admitted. Of those transferred, 80.8% had an OGI. The majority (> 60%) of the patients hospitalized were under the age of 12, and over 1/3 of those admitted to the hospital had OGIs. Of the cases with known location, 72% occurred in places of sports/recreation (courts, stadiums, parks, amusement parks, beach, lake, mountain etc.). The greatest number of injuries occurred between April-July and the lowest in October (5.5%).
There was a decrease in the frequency of tennisrelated ocular injuries during the timeframe of the study (slope = − 20.2, p < 0.05; R 2 = 26.5%) as shown in Fig. 2. From 2000 to 2019, the annual ocular injury rate for the entire US population decreased from 3.8 per 1 million persons in 2000 to 1.4 per 1 million persons in 2019 (slope = − 0.08, p < 0.05; R 2 = 38%). The annual injury rate among tennis players showed a decreasing trend from 65.2 injuries per 1 million in 2006 to 36.5 per 1 million in 2019 (slope = − 1.4, p > 0.05; R 2 = 18.6%) as shown in Fig. 3.

Discussion
The findings in our study illustrate that the greatest number of tennis-related ocular injuries presenting to the ED were in the pediatric age (0-20) group, specifically ages 11-15 years. The Tennis Industry Association reported 7.08 million tennis players in the 6-24 age group and 8.89 million in the 25-54 group in 2018 [1], suggesting that the incidence of ocular trauma is much higher in young tennis players in the pediatric age group and in young adults compared to the older 25-54 group. Most injuries were in males, which may just reflect higher proportion of males playing the sport [2]. Most injuries were caused by the tennis ball, and typically players presented with an ocular contusion that did not require hospitalization. Injuries most often occurred during the spring season, which interestingly, coincides with boys' high school tennis season.
Our results show a decrease in both the frequency and rate of ocular injury per 1 million in the population between 2000 and 2019. This could be due to a greater emphasis on safety by regulatory bodies such as American Academy of Ophthalmology (AAO) and American Academy of Pediatrics (AAP) along with generalized trends across all sports focusing on safety of athletes. Certain injuries, especially in the pediatric population, occur from accidental trauma to the eye as seen from certain narrative descriptions such as "Pt playing tennis with mom and accidently struck in eye Table 1 Demographic data of tennis-related ocular injuries *Race/ethnicity data given as proportion of those with known racial information, 29.6% of patients did not have racial information included **Location of injury data also given as proportion of those with known locations of injury, 26.6% of patients did not have locations of injury reported  with ball, now with eye pain, pt had his glasses on; eye pain" or "Pt was playing tennis when another student accidently hit pt with ball. Dx: Left eye trauma". Furthermore, certain injuries occur where the student may not have been involved in the activity such as "14 yo hyphema to left eye after accidently getting hit with tennis racquet at school. Dx: Hyphema left eye". Though the latter may not be preventable, the former injuries would be prudent to continue to recommend eye protection for all children whether playing competitively or recreationally." Most ocular injuries seen in our study were treated in the ED with subsequent discharge. Although less than 1.5% of cases suffered an OGI, protective eyewear may help in reducing this severe injury that is generally associated with marked visual morbidity. A few sports have mandated the use of eye protection during active play such as squash since 2005, the National Hockey League (NHL) with the use of visors for rookie players since 2013 and women's high school lacrosse [7,8]. The widespread messaging about the use of protective eyewear in squash/racquetball in the 1980s showed a decreasing trend in the proportion of racquet sport ocular injuries in Canada from 73 to 23% compared to tennis/badminton sports which lacked the use of this eyewear during the same period and the proportion of ocular injuries related to tennis/badminton increased from 27 to 72% [11]. It has been previously shown that eye injuries were significantly more common among players who did not wear a visor [9]. In addition, during the 2014-2015 NHL season, players who did not wear a visor, had 3 times more penalty minutes for every 100 min played. This compounded with the finding that players that did utilize a visor had more goals and assists lends credence to the idea that eyewear protection does not necessarily hinder performance [10].
This study adds information regarding epidemiological trends in ocular injuries from tennis-related activity in the last two decades for which data is scarce in the literature. Gaw et al. report that head/ neck injuries constituted 20% (estimated 96,292) of all tennis injuries between 1990 and 2011, in the US, of which 22.5% (estimated 21,666) affected the eye [10]. In addition, a breakdown of all injuries associated with tennis (between 1966 and 2005) showed a preponderance of lower extremity injuries compared to upper extremity injuries [11] along with 29 cases of retinal detachments from tennis ball injury from July 2002 to Dec 2004 at an eye hospital in Pakistan [12]. Evaluations from similar sports such as lacrosse showed that head injuries and injury rates increased from 2002 to 2010 and decreased from 2010 to 2016 in high school players due to changes in play rules such as not allowing body checks to defenseless players and stricter enforcement of penalties for contact to head/neck [13]. Pickleball-related injuries from 2001 to 2017 showed that head/neck injuries accounted for 17% of all injuries [14].
The prevalence of these injuries has encouraged the use of eye protection in a variety of sports. One sport, female lacrosse, has implemented the use of mandatory eye protection which has been investigated [15,16]. One study collected injury data from 25 schools in Virginia and compared the rates and types of injuries that occurred before and after the implementation of eye protection: 2000-2003 versus 2004-2009. The eyewear mandate was put into place for the 2004 spring season. There was a statistically significant decrease in eye injuries and head/ face injuries excluding concussion following the implementation of protective eye equipment [16]. Similarly, a statement from the National Federation of State High School Associations mandated the use of protective eyewear in high school athletes for field hockey during the 2011 season. The mandate led to a reduced incidence of ocular/orbital injuries and fewer severe eye/orbital and head/face injuries [17]. This has prompted new developments in eyewear protection for increased safety in racquet sports from manufacturers and general recommendations for all sports [18].
The findings reported here can be utilized by tennis safety regulatory bodies such as the US Tennis Association to emphasize the use of eyewear protection in youths, as recommended by both the AAP and AAO [19,20]. Previous computational analysis has shown that the high-speed of a tennis ball can induce stress to the cornea and iris during impact [21]. The ball speed on serves can reach over 120 km/ hr (75 mph) even in the lowest ranked youth players. The relationship between increasing ball speed and skill level; however, may justify eye protection even more for experienced professional athletes where the ball speed reported is 260 km/hr (150 mph) according to the Association of Tennis Professionals [22]. Such high speed balls have also have potential to injure spectators and officials on the court. Recently, an innocuous gesture of hitting the ball in the stands by a professional tennis player hit the chair umpire by gaffe, causing an orbital floor fracture [23]. Safety goggles for officials and ball boys/girls on the court may also be a justifiable approach. Continued education to prevent such actions could help to continue the decreasing trend.
Our findings show that the greatest proportion of injuries occur in the pediatric age group which may suggest a greater risk in players at a beginner level. Use of eye protection in youth players may be beneficial due to long term adverse effects of impaired vision in children [24].Beyond the economic and psychosocial effects of trauma, amblyopia can ensue, causing permanent visual impairment in children < 10 years of age [25,26].
There are a few limitations to this study that need to be addressed. As NEISS provides information for ocular injuries presenting to the ED, it does not capture those injuries managed at home, in urgent care settings, and by community specialists and primary care physicians. Therefore, the total number of injuries is likely an underrepresentation of the true frequency of ocular injury. In addition, since visual acuity is not reported, severity of injury is difficult to discern other than a patient being treated and released directly from the ED rather than being admitted to the hospital. Finally, NEISS captures data associated with consumer-product injuries based on narratives written in the electronic health record. Vague descriptions not meeting inclusion criteria would not have been included in the database. Nonetheless, An average of 800 eye injuries results from tennis-related trauma every year. Most are minor ocular contusions, but OGIs are reported in 1.5% of the eyes and can lead to significant visual morbidity. Most eye injuries occur in the pediatric group under age 10 which suggests it is more commonly seen in beginner level children where the hand-eye coordination is still developing. The data outlined in this study can guide primary care providers' recommendations when completing sports physicals for participation in organized youth tennis as well as tennis regulatory bodies to mitigate risks of visual morbidity.
Author contributions NB, PP, and AU are responsible for study conception and design. Data collection and analysis were performed by PP and AU. Drafting of the manuscript was conducted by PP. Manuscript revision was conducted by PDL, MAZ, and MO. All authors approved of the final manuscript.
Funding No funding was used for this investigation.

Conflict of interest
The following authors state their respective competing interests: Marco A. Zarbin, MD, PhD is a consultant for Genentech/Roche, Novartis Pharma AG, Frequency Therapeutics, Iveric Bio, Ophthotech, Perfuse Therapeutics, Selphagy, Iduna, and Life Biosciences. He is a stockholder for Frequency Therapeutics, Iveric Bio, and NVasc. He is Co-Founder of NVasc. Paul D. Langer, MD is a consultant for Matrix Surgical, USA. None of the following authors have any proprietary interests or conflicts of interest related to this submission: Parth S Patel, Aditya Uppuluri, Marko Oydanich, Neelakshi Bhagat Ethical approval This is a retrospective observational study. The Rutgers Biomedical Health Sciences IRB has confirmed that no ethical approval is required as the data is sourced from a national de-identified database.