Ocular metrics in concussion: An analytical prospective cohort study to establish normative ocular metrics in a healthy sporting population

Abstract

Introduction: Concussion diagnosis is a clinical challenge for healthcare providers. Identification of concussion is presently aided by tools such as the Sport Concussion Assessment Tool (SCAT3); such tools remain largely subjective in nature. There is currently no objective gold standard for concussion diagnosis. The overall aim of this study was to investigate potential objective ocular bio-markers for the purpose of concussion diagnosis. The ocular tools employed in this study were the iCare Pro rebound tonomoter (RBT), which measures intraocular pressure (IOP), Topcon OCT-DRI triton plus, which measures thickness of various retinal layers, and the SCAT3. The research was split into 3 component, complimentary studies. 1. iCare pro rebound tonometer reliability study. 2. Effects of Exercise on ocular metrics. 3. The effects of concussion on ocular metrics. Methods: Intra-rater reliability of the RBT was established in a single session in a standing position in 31 male and female particpants. Mean IOP±SD(mmHg), standard error of the mean (SEM), minimum detectable change (MDC) and Intra-class correlation coefficients (ICC’s) were calculated for both left and right eyes. The effects of exercise on IOP and OCT values were established using a simulated team-sport running protocol in 11 male and female participants. Mean±SD values of IOP(mmHg) and OCT measures of RNFL, GCL++ and Choroidal thickness(μm) were established pre-exercise and follow up measures taken 2-minutes and 10-minutes following exercise. Normative values for SCAT3 measures and OCT measures of RNFL and GCL++ thickness(μm) were established for 151 male and female team sport athletes. The effects of concussive injury on these measures were established in 3 individual case studies. Results: Fair/Acceptable intra-rater reliability of the RBT was established (ICC’s 0.771 and 0.753 in left and right eyes respectively). There was a minimal thinning effect of exercise on RNFL, there was a thickening effect of exercise on GCL++, there was an initial thinning effect of exercise on the choroid, followed by a return toward baseline thickness. There was a similar response in IOP. IOP and choroidal responses to exercise were positively and strongly correlated (R = 0.948 and R = 0.786 in left and right eyes respectively). There were some gender differences with regard to the subjective SCAT3 elements. There were no significant differences in RNFL with regard to gender, sport or history of concussion. Males displayed a significantly thicker superior temporal GCL++ sector in the left (P = 0.012) and right eyes (P = 0.007). SCAT-3 symptom scores increased following concussive injury and improved in the days following injury. There were minimal OCT findings in the small number of case studies observed. Conclusion: A sports medicine professional with minimal ophthalmic training can obtain acceptable reliability with the RBT. Further research is needed to establish reliability over a number of days. This is the first study to establish the effects of exercise on ocular metrics in team sport athletes, further research is warranted with an increased sample size. Gender must be taken into account when interpreting SCAT-3 symptom scores. SCAT-3 scores of SAC and mBESS along with RNFL and GCL++ thickness are interchangeable within this cohort. The study was limited by the lack of follow-up data, future research is needed with an increased sample size.