Amblyopic deficit beyond the fovea : delayed and variable single-trial ERP response latencies, but unaltered amplitudes

Purpose. Amblyopia was first described as a deficit of central vision. However, it has long been debated whether this dysfunction is limited to the fovea or whether extrafoveal vision is also affected, as studies concerning the latter are equivocal. The purpose of the study was to resolve this issue. Methods. We investigated the amblyopic effect on event-related potentials (ERPs) with foveal and perifoveal stimuli, either matched in size based on cortical magnification or presented as large annular stimuli. In two separate experiments we measured ERPs on amblyopic patients and control subjects using face images. Latency and amplitude of averaged ERPs and their single-trial distributions were analyzed. Results. When the fovea was stimulated, latency and amplitude of the early averaged ERP components increased and were reduced, respectively, in the amblyopic compared with the fellow eye. Importantly, perifoveal stimulation also elicited similar amblyopic deficits, which were clearly significant in the case of using cortical magnification scaled stimuli. However, single-trial peak analysis revealed that foveal and perifoveal effects differed in nature: Peak amplitudes were reduced only in foveal stimulation, while latencies were delayed and jittered at both the fovea and perifovea. Event-related potentials obtained from fellow eyes were not significantly different from those of normal observers. Conclusions. Our findings revealed the existence of amblyopic deficits at the perifovea when the stimulated cortical area was matched in size to that of foveal stimulation. These deficits manifested themselves only in the temporal structure of the responses, unlike foveal deficits, which affected both component amplitude and latency

How the Visual Cortex Handles Stimulus Noise: Insights from Amblyopia

<div><p>Adding noise to a visual image makes object recognition more effortful and has a widespread effect on human electrophysiological responses. However, visual cortical processes directly involved in handling the stimulus noise have yet to be identified and dissociated from the modulation of the neural responses due to the deteriorated structural information and increased stimulus uncertainty in the case of noisy images. Here we show that the impairment of face gender categorization performance in the case of noisy images in amblyopic patients correlates with amblyopic deficits measured in the noise-induced modulation of the P1/P2 components of single-trial event-related potentials (ERP). On the other hand, the N170 ERP component is similarly affected by the presence of noise in the two eyes and its modulation does not predict the behavioral deficit. These results have revealed that the efficient processing of noisy images depends on the engagement of additional processing resources both at the early, feature-specific as well as later, object-level stages of visual cortical processing reflected in the P1 and P2 ERP components, respectively. Our findings also suggest that noise-induced modulation of the N170 component might reflect diminished face-selective neuronal responses to face images with deteriorated structural information.</p></div

Results of the single-trial analysis.

<p>(A) Statistical analysis of the amplitude medians of components P1 (top panel), N170 (middle panel) and P2 (bottom panel). (B) Amplitude distributions collected from right side cluster electrodes in the case of P1 and N170 and left side cluster electrodes in the case of P2, as indicated by dashed circles in panel A. (C) Spearman correlations between the magnitude of the noise-induced amplitude median increase/decrease observed in the fellow and amblyopic eye for each component over the hemisphere indicated by dashed circles in panel A. The shaded area denotes bigger noise-induced change in the fellow eye relative to the amblyopic eye. FE: fellow eye, AE: amblyopic eye, PC: phase-coherent, N: noisy. Error bars indicate ±SEM (N = 18 unless indicated otherwise; **<i>p</i><.01, ***<i>p</i><.001).</p

Clinical details of amblyopic subjects.

<p>A: anisometropic, S: strabismic, SA: strabismic & anisometropic, RE: right eye, LE: left eye, VA: visual acuity, D: distant, N: near, ET: esotropia, XT: exotropia. Patients listed as strabismics and having no squint angle, have been operated on after developing amblyopia.</p

Noise effect on behavior and amplitude medians.

<p>(A) Spearman correlation between the noise-induced increase in P1 and P2 amplitude medians over the right and left hemisphere, respectively and the noise-induced decrease in performance of the amblyopic eye. Negative correlation indicates that the larger the P1/P2 amplitude increase in a subject, the smaller the performance decrement. (B) Same correlation as in panel A for amplitude median decrease of the N170 component. AE: amblyopic eye, PC: phase-coherent, N: noisy.</p

Grand-average event-related potentials (ERP) to faces from (A) the fellow and (B) the amblyopic eye.

<p>Trial-averaged waveforms are displayed as clusters averaged from electrodes marked with white dots on the topographical maps. Peak topographic maps are displayed at the time of their respective maxima/minima. P1 and N170 were analyzed over bilateral temporal clusters (L/R-Tmp) while P2 was analyzed over bilateral occipital clusters (L/R-Occ). Note, that cartoon heads are plotted with unrealistic head radius for better electrode visibility. FE: fellow eye, AE: amblyopic eye, PC: phase-coherent, N: noisy.</p

Visual cortical responses to the input from the amblyopic eye are suppressed during binocular viewing

Amblyopia is a visual disorder caused by an anomalous early visual experience. It has been suggested that suppression of the visual input from the weaker eye might be a primary underlying mechanism of the amblyopic syndrome. However, it is still an unresolved question to what extent neural responses to the visual information coming from the amblyopic eye are suppressed during binocular viewing. To address this question we measured event-related potentials (ERP) to foveal face stimuli in amblyopic patients, both in monocular and binocular viewing conditions. The results revealed no difference in the amplitude and latency of early components of the ERP responses between the binocular and fellow eye stimulation. On the other hand, early ERP components were reduced and delayed in the case of monocular stimulation of the amblyopic eye as compared to the fellow eye stimulation or to binocular viewing. The magnitude of the amblyopic effect measured on the ERP amplitudes was comparable to that found on the fMRI responses in the fusiform face area using the same face stimuli and task conditions. Our findings showing that the amblyopic effects present on the early ERP components in the case of monocular stimulation are not manifested in the ERP responses during binocular viewing suggest that input from the amblyopic eye is completely suppressed already at the earliest stages of visual cortical processing when stimuli are viewed by both eyes

Stimuli, experimental protocol and behavioral results.

<p>(A) Experimental protocol, which shows the general stimulus sequence (two trials). (B) Exemplar gender pair for the phase-coherent and the 50% phase noise stimulus condition. The subjects of the photographs have given written informed consent, as outlined in the PLOS consent form, to publication of their photograph. (C) Phase noise impaired accuracy in both eyes, but the impairment was significantly greater in the amblyopic eye. FE: fellow eye, AE: amblyopic eye. Error bars indicate ±SEM (N = 18, ** <i>p</i><0.01, *** <i>p</i><0.001).</p

Astigmatism and maternal myopia as important factors affecting success rate of DIMS lens treatment

Objective To assess the efficacy of myopia control spectacle lenses (defocus incorporated multiple segments/DIMS) in slowing myopia progression among a diverse Central European paediatric population and investigate the contribution of baseline parameters on treatment outcomes.Methods and analysis This retrospective observational study included 62 individuals aged 4–17 years (mean±SD: 10.21±2.70) with progressing myopia but without ocular pathology with a range of −0.88 to −8.25 D spherical equivalent refraction (SER) (−3.73±1.56), coupled with astigmatism up to −3.25 D cylindrical. All participants were prescribed DIMS (Hoya MiyoSmart) spectacles. Key outcome variables were cycloplegic SER, measured for all participants and axial length (AL), assessed in a subset of patients, recorded at baseline, 6 months and 12 months. Quality of life assessments were conducted at baseline, at 2 weeks, and 3, 6, 9 and 12 months. Additionally, parental myopic dioptre was recorded when applicable.Results At the 12-month mark, myopia progression in patients (mean±SE: −0.40±0.05) mirrored findings from prior European DIMS studies, but with 50% of patients showing no progression. A multivariate analysis of covariance model revealed that baseline astigmatism and younger age adversely affected therapy outcomes in both SER and AL, while severe maternal myopia led to greater SER progression. In contrast, only young age but not astigmatism was associated with AL increase in a comparable group of children with myopia, part of the LIFE Child Study, wearing single-vision spectacles. Patients reported consistent satisfaction with treatment, with minimal side effects, which diminished over the year.Conclusion In the European population, astigmatism, young age and severe maternal myopia are risk factors for suboptimal outcomes following DIMS therapy. Further research is necessary to elucidate the impact of astigmatism on myopic defocus therapy