Prognosticators for Visual Outcome in Indirect Traumatic Optic Neuropathy: A Prospective Cohort Study

Abstract

Introduction Traumatic optic neuropathy (TON), with indirect TON as its more prevalent form, is a dreadful cause of severe visual dysfunctions. The condition is known to have a contentious treatment plan and poor visual sequelae; hence, the assessment of prognostic signs becomes valuable. Prospective studies evaluating important predictors of visual recovery after traumatic optic nerve injury can particularly be helpful in a longitudinal observation. The possible roles of clinical variables need to be assessed. Absent visual evoked potential (VEP) records as a crucial finding associated with TON has reportedly valuable prognostic significance. This also needs to be explored. Hence, the study sought to determine the role of prognosticators in the visual outcome of the patients, with a focus on evaluating the role of VEPs in the severity and prognosis of indirect TON. Methods A prospective observational study involving 40 patients with indirect TON was conducted. Ocular, neuro-ophthalmological, radiological, and neurophysiological variables, including flash VEP, were investigated at their initial visit and followed up until the end of six months. Final visual acuity was the primary outcome variable studied. Paired t-test was used to perform the comparison between the flash VEP variables for normal and affected eyes at the initial visit. Pearson correlation coefficient was computed for obtaining the association of initial visual acuity and flash VEP variables with the outcome variable. Relative risk was calculated and analysed for the prognosticators in univariate analysis. Statistical significance was defined as p < 0.05. Results Statistically significant variations in mean P100 latency, N75-P100, and P100-N145 amplitudes compared between normal and affected eyes in the patients at the initial visit were obtained (p < 0.0001; paired t-test). Pearson correlation coefficient for initial visual acuity and flash VEP variable as independent variables and final visual acuity as the dependent variable were statistically significant (p < 0.05). The relative risks for prognosticators with a statistically significant range of confidence intervals were poor initial visual acuity, greater relative afferent pupillary defect (RAPD) grades, deranged flash VEP variables (absent VEP, reduction in amplitude ratio (>50%), and increased interocular latency differences), loss of consciousness during injury, age greater than 40 years, and lack of improvement after 48 hours of steroid treatment. Conclusion The identified negative prognosticators may be helpful in deciding the kind of therapeutic approach and predicting the visual outcome in patients with indirect TON.

Keywords: amplitude; indirect traumatic optic neuropathy; latency; optic neuropathy; predictors; traumatic optic neuropathy; visual acuity; visual evoked potential.

Figure 1. Flash VEP record of a patient with indirect TON (with a history of assault on the head)

Diminished vision in the left eye, visual acuity in the right eye: 6/6 and left eye: HMFC. VEP findings demonstrate a 50% reduction in interocular amplitude ratio (left/right eye) with delayed P100 latency in the left eye (at the initial visit). VEP: visual evoked potential; TON: traumatic optic neuropathy; HMFC: hand movements close to the face.

Figure 2. Comparison of VEP variables (mean P100 latency (ms), N75-P100 amplitude (µv), and P100-N145 amplitude (µv)) between normal eyes and affected eyes in patients with indirect TON at the initial visit (n = 34; six patients with absent VEP response)

VEP: visual evoked potential; ms: milliseconds; µv: microvolts; TON: traumatic optic neuropathy.