Effect of blast trauma and corneal foreign bodies on visual performance

Purpose. To evaluate the effect of non-penetrating corneal foreign bodies secondary to explosive blasts on the visual performance of soldiers. Methods. In a prospective, non-interventional study subjective visual performance and objective optical quality of 11 injured eyes with retained corneal foreign bodies were compared with that of 11 normal controls. Visual performance measures consisted of best spectacle-corrected high-contrast visual acuity (HCVA), low-contrast (5%) visual acuity (LCVA), and contrast sensitivity (CS). LCVA was evaluated in two luminance levels (photopic and mesopic) and two glare conditions (with and without glare). Acuity measurements were scored using logMAR notation. Objective optical quality was assessed comparing total root mean square wavefront error (WFE) and percent higher order aberrations. Modulation transfer functions calculated from the wavefront maps were used to predict the results of the psychophysical contrast testing. Results. HCVA of injured eyes (M = -0.03) did not differ significantly (t₍₂₀₎ = 1.56, p = 0.13) when compared with controls (M = -0.09). However, visual performance of injured eyes (M = 0.33) was significantly worse than control eyes (M = 0.11) on photopic LCVA (t₍₂₀₎ = 4.16, p < 0.001), mesopic LCVA(M = 0.44 vs. M = 0.21, t₍₂₀₎ = 3.85, p = 0.001), mesopic LCVA with glare (M = 0.49 vs. M = 0.21, t₍₂₀₎ = 3.66, p = 0.002), and small letter CS (M = 0.25 vs. M = 0.90, t₍₂₀₎ = -6.6, p < 0.001). For a 6-mm pupil, mean absolute WFE attributed to higher order aberrations for the injured eyes was 0.86 μm and 0.59 μm for the control eyes. This difference was significant (t₍₂₀₎ = -2.15, p = 0.044). Conclusions. Although HCVA was no different than the normal controls, visual performance of the injured eyes was significantly worse in terms of LCVA and CS. On average, visual performance can be broadly predicted by the modulation transfer function derived from the subjects' wavefront aberration map.