Multifocal visual evoked potentials in amblyopia due to anisometropia

Evaluation of Pupillary Light Reflex in Amblyopic Eyes Using Dynamic Pupillometry

Objectives

To evaluate the pupillary light reflex responses in patients with unilateral strabismic and anisometropic amblyopia using dynamic pupillometry.

Materials and Methods

A total of 102 eyes of 51 patients with unilateral amblyopia were included in this cross-sectional study. Of the 51 patients, 37 (72.5%) had strabismic amblyopia and 14 (27.5%) had anisometropic amblyopia. All patients underwent complete ophthalmological examination, and pupillary light reflex responses were measured using a computerized dynamic pupillometry system (MonPack One; Metrovision, France). Initial pupil diameter; the amplitude, latency, duration, and velocity of pupil contraction; and the latency, duration, and velocity of pupil dilation were recorded. Results obtained from the patients’ amblyopic and normal fellow eyes were compared using paired-samples t-test and Wilcoxon signed rank test.

Results

The mean age of the patients was 11.9±6.0 years. Amblyopic eyes had longer contraction latency (p=0.009), shorter contraction duration (p=0.002), and higher dilation velocity (p=0.033) compared to fellow eyes, while other parameters did not show significant differences. In subgroup analysis, eyes with strabismic amblyopia had longer contraction latency (p=0.006) and shorter contraction duration (p=0.017), while eyes with anisometropic amblyopia had shorter contraction duration (p=0.030) when compared with fellow eyes.

Conclusion

In this study, the objective records obtained by dynamic pupillometry showed that pupillary light reflex responses are affected in amblyopic eyes. This finding may shed light on unclear aspects of the pathophysiology of amblyopia.

Comparison of the Wave Amplitude of Visually Evoked Potential in Amblyopic Eyes between Patients with Esotropia and Anisometropia and a Normal Group

BACKGROUND

We compared the wave amplitude of visually evoked potential (VEP) between patients with esotropic and anisometropic amblyopic eyes and a normal group.

METHODS

The wave amplitude of VEP was documented in 2 groups of persons with amblyopia (15 with esotropia and 28 with anisometropia) and 1 group of individuals with normal visual acuity (n, 15). The amplitude of P100 was recorded monocularly with different spatial frequencies.

RESULTS

Our statistical analysis revealed that the wave amplitude in the 2 groups with amblyopia was significantly decreased compared to that in the normal group (P<0.001). There was a significant difference regarding the amplitude in high spatial frequencies in both high- and low-contrast conditions between the groups with esotropia and anisometropia and the normal group (P<0.001). There were also significant differences in large check-size stimuli and low-contrast condition between the amblyopic groups with esotropia and anisometropia and the normal group (P=0.013 and P=0.044, respectively). In large check-size stimuli and high-contrast condition, a significant difference was indicated only in the comparison between the esotropic amblyopic eyes and the normal eyes (P=0.036).

CONCLUSION

The wave amplitude parameter of VEP was influenced by both types of amblyopia, but it seems that this parameter was more sensitive to esotropic amblyopia than anisometropic amblyopia. This outcome may reflect a non-parallel pattern of cortical responses in the comparison of the 2 types of amblyopia with each other and with the control group, which may be beneficial for the diagnosis and treatment of amblyopia.

Anodal Transcranial Direct Current Stimulation Transiently Improves Contrast Sensitivity and Normalizes Visual Cortex Activation in Individuals With Amblyopia

Background. Amblyopia is a neurodevelopmental disorder of vision that is associated with abnormal patterns of neural inhibition within the visual cortex. This disorder is often considered to be untreatable in adulthood because of insufficient visual cortex plasticity. There is increasing evidence that interventions that target inhibitory interactions within the visual cortex, including certain types of noninvasive brain stimulation, can improve visual function in adults with amblyopia. Objective. We tested the hypothesis that anodal transcranial direct current stimulation (a-tDCS) would improve visual function in adults with amblyopia by enhancing the neural response to inputs from the amblyopic eye. Methods. Thirteen adults with amblyopia participated and contrast sensitivity in the amblyopic and fellow fixing eye was assessed before, during and after a-tDCS or cathodal tDCS (c-tDCS). Five participants also completed a functional magnetic resonance imaging (fMRI) study designed to investigate the effect of a-tDCS on the blood oxygen level–dependent response within the visual cortex to inputs from the amblyopic versus the fellow fixing eye. Results. A subgroup of 8/13 participants showed a transient improvement in amblyopic eye contrast sensitivity for at least 30 minutes after a-tDCS. fMRI measurements indicated that the characteristic cortical response asymmetry in amblyopes, which favors the fellow eye, was reduced by a-tDCS. Conclusions. These preliminary results suggest that a-tDCS deserves further investigation as a potential tool to enhance amblyopia treatment outcomes in adults.