Structural And Functional Integrity Of The Visual System Following A Collision-sport Season

Repetitive head impacts (RHIs) experienced during sport participation may cause structural and functional deficits to the visual system. Changes in retinal tissue thickness lead to functional decline, increasing risk of further injury. PURPOSE: To evaluate (1) structural changes including ganglion cell complex (GCC), retinal nerve fiber layer (RNFL), and retinal map thickness (RM), and (2) functional changes including contrast sensitivity (CS) and critical flicker fusion frequency (CFFF) from pre- to post-season among both collision (rugby) and non-collision (track and field, T&F) athletes. METHODS: 20 rugby (10 M/10F; 20 ± 2 yrs) and 18 (12 M/6F; 20 ± 2 yrs) T&F athletes completed pre- and post-season testing. Optical Coherence Tomography scans measured GCC, RNFL, and RM thickness. CS was measured via software and a densitometer was utilized to measure CFFF. RESULTS: Left eye (OS) GCC Superior region was thinner at post- vs pre-season for rugby (101.1 + 1.1 vs 102.1 + 1.2 μm, p = 0.03) but not T&F (99.8 + 1.2 vs 99.7 + 1.2 μm, p = 0.8). Similarly, the OS GCC Inferior region was thinner at post- vs pre-season for rugby (103.0 + 1.2 vs 103.9 + 1.2 μm, p = 0.047) but not T&F (100.4 + 1.3 vs 100.9 + 1.3 μm, p = 0.6). Right eye (OD) RNFL Inferior region was thicker post- vs pre-season for T&F (102.6 + 2.0 vs 99.3 + 2.0 μm, p = 0.02) but not rugby (103.9 + 1.9 vs 103.7 + 1.9 μm, p = 0.8). RM thickness was not different (all p > 0.05). CS trials were not different in all but one trial; mesopic 100 glare trial improved post- vs pre-season for T&F (6.3 + 1.0 vs 8.1 + 1.7%, p = 0.02) but not rugby (5.6 + 0.9 vs 6.3 + 1.5%, p = 0.4). CFFF was not different at post-season testing for rugby (27.0 + 0.4 vs 26.7 + 0.4 Hz, p = 0.4) or T&F (26.7 + 0.4 vs 26.2 + 0.4 Hz, p = 0.2). CONCLUSION: These data demonstrate GCC thinning in rugby players following a competitive season. There were no reductions in functional vision; however, GCC thinning following RHIs is argued to occur prior to RNFL thinning resulting in contrast sensitivity decline, with a loss of 25-35% before a deficit is noticed. Therefore, these data suggest rugby players may experience declines in structural integrity of the visual system following RHIs throughout a competitive season and possibly decreased functional integrity over a competitive career if continued thinning is experienced.