Monocular Stimulation Research Articles

Application of the Virtual Reality-Pattern Visual Evoked Potential in Forensic Visual Acuity Evaluation

Objective To explore a kind of visual evoked potential test equipment and method that is more suitable for the application of forensic clinical visual acuity evaluation. Methods Thirty-four volunteers （68 eyes） were selected, including 15 males and 19 females, aged between 20 and 40 years. Test lenses were placed before the tested eyes of volunteers to induce refractive myopia with insert method, and the diopter lenses were adjusted so that the visual acuity level of one eye of volunteers was above 0.8, and the visual acuity of the other eye was at moderate damage level （<0.3 and ≥0.1）. The tests were carried out under the binocular simultaneous asynchronous stimulation mode （hereinafter referred to as "binocular mode"） and monocular separate stimulation mode （hereinafter referred to as "monocular mode"） of virtual reality-pattern visual evoked potential （VR-PVEP）, and the amplitude of PVEP of volunteers under the two modes was compared at four spatial frequencies of 8×8, 16×16, 24×24 and 32×32. Results The differences in the amplitude of P100 wave between monocular and binocular modes at 8×8 spatial frequency had no statistical significance and the differences in amplitude of P100 wave between monocular and binocular modes at 16×16, 24×24, and 32×32 spatial frequencies had statistical significance （P<0.05）. The amplitude of the same eye in monocular mode was higher than that in binocular mode. Through correlation analysis, it was found that the amplitude of P100 wave in monocular mode was moderately correlated with amplitude of P100 wave in binocular mode. Conclusion In forensic identification practice, VR-PVEP is helpful for overcoming the disturbance of poor fixation, and to increase the reliability of PVEP evaluation results. It can greatly shorten the detection time of PVEP and improve work efficiency.

Modulation of binocular rivalry with rapid monocular visual stimulation.

Rapid visual stimulation can increase synaptic efficacy by repeated synaptic activation. This long-term potentiation-like (LTP-like) effect can induce increased excitability in the human visual cortex. To examine the effect of rapid visual stimulation on perception, we tested the hypothesis that rapid monocular visual stimulation would increase the dominance of the stimulated eye in a binocular rivalry task. Participants (n=25) viewed orthogonal 0.5cpd gratings presented in a dichoptic anaglyph to induce binocular rivalry. Rivalry dynamics (alternation rate, dominance, and piecemeal durations) were recorded before and after 2min of rapid monocular stimulation (9Hz flicker of one grating) or a binocular control condition (9Hz alternation of the orthogonal gratings viewed binocularly). Rapid monocular stimulation did not affect alternation rates or piecemeal percept duration. Unexpectedly, the rivalry dominance of the stimulated eye was significantly reduced. A further experiment revealed that this effect could not be explained by monocular adaptation. Together, the results suggest that rapid monocular stimulation boosts dominance in the non-stimulated eye, possibly by activating homeostatic interocular gain control mechanisms.

Characterising the orientation-specific pattern-onset visual evoked potentials in children with bilateral refractive amblyopia and non-amblyopic controls.

An orientation-specific visual evoked potential (osVEP) protocol was developed to probe meridional anisotropies in children with refractive amblyopia. The aim was to characterise the osVEP response in children with bilateral refractive amblyopia, evaluate the intra-session repeatability of the main osVEP components (C1, C2 and C3), coefficient of repeatability (CoR) of the response to gratings in different meridians and determine if refractive amblyopes have poorer repeatability as compared with non-amblyopic controls. Children aged 4-7years with newly diagnosed and untreated bilateral refractive amblyopia and non-amblyopic controls were recruited. Orientation-specific pattern-onset VEPs were recorded in response to an achromatic sinewave grating stimulus of 4 cycles per degree under monocular and binocular stimulation. The grating lines used for monocular stimulation were parallel with the subjects' most positive and negative astigmatic meridians when considered in sphero-minus cylinder form (Meridians 1 and 2, respectively). In subjects without astigmatism, meridians 1 and 2 were designated horizontal and vertical gratings, respectively. Binocular stimuli were presented with grating lines parallel to meridians 45, 90, 135 and 180°. The repeatability of latencies of the main osVEP components (C1, C2 and C3) were investigated using two successive osVEPs recordings for each stimulus meridian and the CoR for each component's latencies were assessed. Seven amblyopic children (Visual acuity (VA) ranging from 0.08 to 0.40 LogMAR in the less amblyopic eye and 0.26-0.52 LogMAR in the more amblyopic eye) and 7 non-amblyopic controls (VA ranging from 0.00 to 0.02 LogMAR in either eye), with a median age of 4.6 and 7.0years, respectively, completed the study. C1 had the highest CoR for most conditions assessed. Ratio of CoRs C1:C2 was > 2 for all binocular meridians in controls and the 90 and 180 meridians in the amblyopes; C1:C3 was > 2 for the binocularly assessed 45, 90 and 135 meridians in the controls and the 90 and 180 meridians in the amblyopes; C2:C3 were all < 2 for all meridians assessed in both groups. The osVEP waveforms are reliable and useful for future investigations into the meridional anisotropies in children with refractive amblyopia, particularly the C3 component. Component C1 had the poorest repeatability, which consequentially affected C2 amplitude estimation. Only C3 amplitude and latency could be consistently estimated as C2 and C3 latencies were similarly repeatable. Coefficients of repeatability of osVEP latencies did not appear to systematically differ between non-amblyopic and amblyopic children.

Dichoptic Spatial Contrast Sensitivity Reflects Binocular Balance in Normal and Stereoanomalous Subjects.

PurposeTo study binocular balance by comparing dichoptic and standard monocular contrast sensitivity function (CSF) in stereonormal and stereoanomalous/stereoblind amblyopic subjects.MethodsSixteen amblyopes and 17 controls participated. Using the capability of the passive three-dimensional display, we measured their CSF both monocularly and dichoptically at spatial frequencies 0.5, 1, 2, 4, and 8 cpds using achromatic Gabor patches on a luminance noise background. During monocular stimulation, the untested eye was covered, while for the dichoptic stimulation the untested eye viewed background noise. Dichoptic CSF of both eyes was acquired within one block.ResultsIn patients with central fixation, dichoptic viewing had a large negative impact on the CSF of the amblyopic eye, although it hardly affected that of the dominant eye. In contrast, dichoptic viewing had a small but significant effect on both eyes for controls. In addition, all participants lay along a continuum in terms of how much their two eyes were affected by dichoptic stimulation: by using two predefined contrast sensitivity ratios, namely, amblyopic sensitivity decrement and dichoptic sensitivity decrement, not only did we find a significant correlation between these variables among all participants, but also the two groups were identified with minimum error using a cluster analysis.ConclusionsDichoptic CSF may be considered to measure visual performance in patients with altered binocular vision, because it better reflects the visual capacity of the amblyopic eye than the standard monocular examinations. It may also be a more reliable parameter to assess the efficacy of modern approaches to treat amblyopia.

Microsaccadic rate signatures correlate under monocular and binocular stimulation conditions.

Microsaccades are involuntary eye movements occurring naturally during fixation. In this study, microsaccades were investigated under monocularly and binocularly stimulated conditions with respect to their directional distribution and rate signature, that refers to a curve reporting the frequency modulation of microsaccades over time. For monocular stimulation the left eye was covered by an infrared filter. In both stimulation conditions, participants fixated a Gabor patch presented randomly in orientation of 45° or 135° over a wide range of spatial frequencies appearing in the center of a monitor. Considering the microsaccadic directions, this study showed microsaccades to be preferably horizontally oriented in their mean direction, regardless of the spatial characteristics of the grating. Furthermore, this outcome was found to be consistent between both stimulation conditions. Moreover, this study found that the microsaccadic rate signature curve correlates between both stimulation conditions, while the curve given for binocular stimulation was already proposed as a tool for estimation of visual performance in the past.Therefore, this study extends the applicability of microsaccades to clinical use, since parameters as contrast sensitivity, has been measured monocularly in the clinical attitude.

In vivo evaluation of retinal ganglion cells and optic nerve's integrity in large animals by multi-modality analysis

Large animal models of optic nerve injury are essential for translating novel findings into effective therapies due to their similarity to humans in many respects. However, most current tests evaluating the integrity of retinal ganglion cells (RGCs) and optic nerve (ON) are based on rodent animal models. We aimed to evaluate and optimize the in vivo methods to assess RGCs and ON's function and structure in large animals in terms of reproducibility, simplicity and sensitivity. Both goats and rhesus macaques were employed in this study. By using goats, we found anesthesia with isoflurane or xylazine resulted in different effects on reproducibility of flash visual evoked potential (FVEP) and pattern electroretinogram (PERG). FVEP with the large-Ganzfeld stimulator was significantly more stable than that with mini-Ganzfeld stimulator. PERG with simultaneous binocular stimulation, with superior simplicity over separate monocular stimulation, was appliable in goats due to undetectable interocular crosstalk of PERG signals. After ON crush in goats, some FVEP components, PERG, OCT and PLR demonstrated significant changes, in line with the histological study. By using rhesus macaque, we found the implicit time of PVEP, FVEP and PERG were significantly more reproducible than amplitudes, and OCT and PLR demonstrated small intersession variation. In summary, we established an optimized system to evaluate integrity of RGCs and ON in large animals in vivo, facilitating usage of large animal models of optic nerve diseases.

Pull-push neuromodulation of cortical plasticity enables rapid bi-directional shifts in ocular dominance.

Neuromodulatory systems are essential for remodeling glutamatergic connectivity during experience-dependent cortical plasticity. This permissive/enabling function of neuromodulators has been associated with their capacity to facilitate the induction of Hebbian forms of long-term potentiation (LTP) and depression (LTD) by affecting cellular and network excitability. In vitro studies indicate that neuromodulators also affect the expression of Hebbian plasticity in a pull-push manner: receptors coupled to the G-protein Gs promote the expression of LTP at the expense of LTD, and Gq-coupled receptors promote LTD at the expense of LTP. Here we show that pull-push mechanisms can be recruited in vivo by pairing brief monocular stimulation with pharmacological or chemogenetical activation of Gs- or Gq-coupled receptors to respectively enhance or reduce neuronal responses in primary visual cortex. These changes were stable, inducible in adults after the termination of the critical period for ocular dominance plasticity, and can rescue deficits induced by prolonged monocular deprivation.

Pupillary light responses in type 1 and type 2 diabetics with and without retinopathy.

We assessed the function of rod/cones and melanopsin in type 1 (T1DM) and type 2 diabetes mellitus (T2DM) with and without non-proliferative diabetic retinopathy (NPDR). We performed pupillometry on 22 healthy controls and four diabetic groups: 12 T1DM patients without NPDR and 12 with moderate NPDR, and 16 T2DM patients without NPDR and 12 with moderate NPDR. Monocular stimulations of 20seconds with red (λ=633nm) and blue light (λ=463nm) at ~15log quanta/cm2 /second were performed. The primary outcome was the melanopsin-mediated late redilation phase of postillumination pupillary light response (PIPRL ate ) to blue light. The secondary outcomes were the mixed rod/cone and melanopsin responses, that is maximal pupil constriction and the early redilation phase of PIPR (PIPRE arly ). Late redilation phase of PIPR (PIPRL ate ) to blue and red light stimuli was not significantly different between healthy control and the four diabetic groups (n.s.). The maximal pupil contractions to blue light stimulus were significantly reduced in T1DM patients as well as in T2DM patients with NPDR (p≤0.02), whereas for red light stimuli, the maximal pupil constriction was only reduced in T2DM with NPDR (p<0.01). Early redilation phase of PIPR (PIPRE arly ) to blue and red light stimuli was not significantly different between healthy controls and diabetic patients (n.s.). Neither the PIPRE arly nor the PIPRL ate was significantly reduced in diabetics with or without NPDR compared to healthy controls. The reduced maximal pupil constrictions in diabetics with NPDR indicate decreased mixed rod/cone and melanopsin responses.

Temporal dynamics of binocular integration in primary visual cortex.

Whenever we open our eyes, our brain quickly integrates the two eyes' perspectives into a combined view. This process of binocular integration happens so rapidly that even incompatible stimuli are briefly fused before one eye's view is suppressed in favor of the other (binocular rivalry). The neuronal basis for this brief period of fusion during incompatible binocular stimulation is unclear. Neuroanatomically, the eyes provide two largely separate streams of information that are integrated into a binocular response by the primary visual cortex (V1). However, the temporal dynamics underlying the formation of this binocular response are largely unknown. To address this question, we examined the temporal profile of binocular responses in V1 of fixating monkeys. We found that V1 processes binocular stimuli in a dynamic sequence that comprises at least two distinct temporal phases. An initial transient phase is characterized by enhanced spiking responses for both compatible and incompatible binocular stimuli compared to monocular stimulation. This transient is followed by a sustained response that differed markedly between congruent and incongruent binocular stimulation. Specifically, incompatible binocular stimulation resulted in overall response reduction relative to monocular stimulation (binocular suppression). In contrast, responses to compatible stimuli were either suppressed or enhanced (binocular facilitation) depending on the neurons' ocularity (selectivity for one eye over the other) and laminar location. These results suggest that binocular integration in V1 occurs in at least two sequential steps that comprise initial additive combination of the two eyes' signals followed by widespread differentiation between binocular concordance and discordance.

Selective processing of all rotational and translational optic flow directions in the zebrafish pretectum and tectum

BackgroundThe processing of optic flow in the pretectum/accessory optic system allows animals to stabilize retinal images by executing compensatory optokinetic and optomotor behavior. The success of this behavior depends on the integration of information from both eyes to unequivocally identify all possible translational or rotational directions of motion. However, it is still unknown whether the precise direction of ego-motion is already identified in the zebrafish pretectum or later in downstream premotor areas.ResultsHere, we show that the zebrafish pretectum and tectum each contain four populations of motion-sensitive direction-selective (DS) neurons, with each population encoding a different preferred direction upon monocular stimulation. In contrast, binocular stimulation revealed the existence of pretectal and tectal neurons that are specifically tuned to only one of the many possible combinations of monocular motion, suggesting that further downstream sensory processing might not be needed to instruct appropriate optokinetic and optomotor behavior.ConclusionOur results suggest that local, task-specific pretectal circuits process DS retinal inputs and carry out the binocular sensory computations necessary for optokinetic and optomotor behavior.

Changes in the Dendrite Morphology of Mauthner Neurons in Goldfish under the Conditions of Monocular Deprivation and Sensory Stimulation

Abstract—The effects of sensory stimulation on the model of paired Mauthner neurons of monocularly deprived goldfish have been studied by light- and electron microscopy. Three-dimensional reconstruction was performed using serial semi-thin sections in order to determine the volumes of soma and dendrites for the right and left Mauthner neurons. These data suggested that long-term stimulation of some fish caused a decrease in the volume of the lateral dendrites of neurons contralateral with respect to the side of the enucleated eye. As a result, the morphological homeostasis in the dendrites of Mauthner neurons, which was observed in the control fish, was disturbed after the effect of stimulation upon this group of fish. The main mechanism of this effect of stimulation, according to ultrastructural analysis, is the compaction of the cytoskeleton in the lateral dendrite of a neuron and a reduction in the number of synaptic vesicles in the region of afferent synapses. In contrast, stimulation of the remaining fish induced the resistance of the contralateral Mauthner neuron to prolonged stimulation, as well as the hypertrophy of its lateral and shortening of the ventral dendrites. These results suggest that the homeostasis of the dendrites of Mauthner neurons essentially depends on the state of the visual inputs, the load on which increased as a result of the doubled impact.

Visual evoked potentials are similar in polysomnographically defined quiet and active sleep in healthy newborns

Morphology and late components of evoked potentials change depending on wake-sleep stages in adults. Visual Evoked potentials (VEPs) have been frequently studied in newborns to identify abnormal development of visual pathways; however, large variability has been reported and there is uncertainty as to the effect of sleep stages on VEPs in neonates. ObjectiveTo describe the characteristics of VEPs in one month old, healthy full-term newborns during active sleep (AS) and quiet sleep (QS), defined by simultaneous polysomnography (PSG). MethodsVEPs were obtained by monocular LEDs stimulation of each eye during AS and QS, in 20 healthy full-term newborns (gestational age 37–40 weeks) with normal birth weights and normal prenatal Doppler ultrasound indices. Latencies and amplitudes of N2, P2 and N3 components in AS and QS were compared, and their association with absolute power of EEG frequency bands, assessed. ResultsThere were no significant differences in VEP morphology, latencies and amplitudes between sleep states. Typical wave forms were obtained in all newborns in AS; however, no VEPs could be identified clearly in 3 newborns in QS; QS VEPs were less reliable than in AS: more averaging was required; correlation was significantly lower between the VEP averages; and a larger number of babies needed more than two averages to obtain replicable responses needed for clinical purposes. ConclusionsThese results indicate that changes in amplitude and latency of some VEP components observed in NREM and REM sleep in adults are not yet present in one month old newborns probably due to immaturity of cortical and sleep mechanisms. VEPs are more reliable during AS than QS in newborns. Systematic VEP recording during AS, and polysomnographic control to identify this stage, are highly recommended as methods that can increase there liability of neonatal VEPs.

Dynamics of Stability of Orientation Maps Recorded with Optical Imaging

Orientation selectivity is an important feature of visual cortical neurons. Optical imaging of the visual cortex allows for the generation of maps of orientation selectivity that reflect the activity of large populations of neurons. To estimate the statistical significance of effects of experimental manipulations, evaluation of the stability of cortical maps over time is required. Here, we performed optical imaging recordings of the visual cortex of anesthetized adult cats. Monocular stimulation with moving clockwise square-wave gratings that continuously changed orientation and direction was used as the mapping stimulus. Recordings were repeated at various time intervals, from 15 min to 16 h. Quantification of map stability was performed on a pixel-by-pixel basis using several techniques. Map reproducibility showed clear dynamics over time. The highest degree of stability was seen in maps recorded 15–45 min apart. Averaging across all time intervals and all stimulus orientations revealed a mean shift of 2.2 ± 0.1°. There was a significant tendency for larger shifts to occur at longer time intervals. Shifts between 2.8° (mean ± 2SD) and 5° were observed more frequently at oblique orientations, while shifts greater than 5° appeared more frequently at cardinal orientations. Shifts greater than 5° occurred rarely overall (5.4% of cases) and never exceeded 11°. Shifts of 10–10.6° (0.7%) were seen occasionally at time intervals of more than 4 h. Our findings should be considered when evaluating the potential effect of experimental manipulations on orientation selectivity mapping studies.

Response Properties of Pulvinar Neurons Studied with Single-Unit Electrophysiological Recordings.

In this chapter, we discuss the types of visual receptive fields revealed by single-unit electrophysiological recordings in the pulvinar. Nearly all neurons with identifiable receptive fields responded to visual stimulation presented on the contralateral hemifield, within 25° of the fovea. The majority of the visual neurons responded to some form of moving stimulus, and some additionally exhibited direction or orientation selectivity. Most units could be driven by monocular stimulation and showed receptive fields of at least 100 square degrees in area. Finally, most of the units recorded exhibited continuous peripheral receptive fields, even though a few of them could be bilaterally activated.

VEP-based acuity assessment in low vision

Objective assessment of visual acuity (VA) is possible with VEP methodology, but established with sufficient precision only for vision better than about 1.0 logMAR. We here explore whether this can be extended down to 2.0 logMAR, highly desirable for low-vision evaluations. Based on the stepwise sweep algorithm (Bach et al. in Br J Ophthalmol 92:396-403, 2008) VEPs to monocular steady-state brief onset pattern stimulation (7.5-Hz checkerboards, 40% contrast, 40ms on, 93ms off) were recorded for eight different check sizes, from 0.5° to 9.0°, for two runs with three occipital electrodes in a Laplace-approximating montage. We examined 22 visually normal participants where acuity was reduced to ≈ 2.0 logMAR with frosted transparencies. With the established heuristic algorithm the "VEP acuity" was extracted and compared to psychophysical VA, both obtained at 57cm distance. In 20 of the 22 participants with artificially reduced acuity the automatic analysis indicated a valid result (1.80 logMAR on average) in at least one of the two runs. 95% test-retest limits of agreement on average were ±0.09 logMAR for psychophysical, and ±0.21 logMAR for VEP-derived acuity. For 15 participants we obtained results in both runs and averaged them. In 12 of these 15 the low-acuity results stayed within the 95% confidence interval (±0.3 logMAR) as established by Bach et al. (2008). The fully automated analysis yielded good agreement of psychophysical and electrophysiological VAs in 12 of 15 cases (80%) in the low-vision range down to 2.0 logMAR. This encourages us to further pursue this methodology and assess its value in patients.

Analysis of the Relationship Between Training Experience and Visual Sensory Functions in Athletes from Different Sports

Abstract Introduction. Gaining insight into the mechanisms and scope of possible adaptations of visual functions to the conditions determined by the demands imposed by sports training seems to be very interesting not only from a cognitive point of view, but also with respect to the practical applications of the findings of such investigations in the training process. The aim of the study was to assess the function of early visual processing in athletes representing different sports disciplines with varying training experience. Material and methods. The study involved 95 athletes practising football (n = 24), volleyball (n = 22), boxing (n = 26), and rowing (n = 23). The bioelectric function of the visual pathway was assessed based on recordings of visual evoked potentials (VEPs). The regions which were stimulated were the peripheral and central areas of the retina. During the test, we recorded the amplitude (μV) and latency (ms) of the P100 component of the VEP waveform for both monocular stimulation (for the dominant and non-dominant eye) and binocular stimulation. Results. Lower VEP P100 amplitude values were found for the peripheral and central locations for monocular and binocular viewing in more experienced volleyball players and rowers (p &lt; 0.05). In the case of boxers with greater training experience, a significantly lower (p &lt; 0.05) amplitude of the VEP P100 wave was observed in the central location in the dominant eye. However, we did not find significant differences (p &gt; 0.05) in intragroup variability in VEP P100 latency in relation to training experience in any of the sports disciplines examined. Conclusions. Training experience has an influence on the early stage of sensory processing with respect to neural activity. Training experience has been found to differentiate athletes in terms of the temporal parameters of the visual evoked potentials recorded in the current study only to a limited extent.

Seeing is believing: a demonstration of critical fusion frequency and its multidimensional nature.

critical fusion frequency (CFF), or the flicker fusion threshold, is defined as the critical frequency above which a flickering light source appears steady to the observer (see [Fig. 1][1]). It is known to depend on a number of parameters, namely, intensity of the light source ([5][2], [15][3]),

Gender-based normative values for pattern-reversal and flash visually evoked potentials under binocular and monocular stimulation in healthy adults.

To determine gender-based normative values for pattern-reversal (PR) and flash (F) visually evoked potentials (VEP) under binocular and monocular stimulation in healthy adults. Healthy adults (age ≥18years) were recruited among university employees and students. Inclusion criteria were absence of abnormalities in fundoscopy, tracking ability, stereopsis and pupillary reflexes; best-corrected visual acuity ≤.00 logMAR; and refractive error (spherical equivalent) from -6.00 to +6.00. Exclusion criteria were previous intraocular surgery, systemic and/or neurological disorders. Binocular and monocular tests were performed according to International Society for Clinical Electrophysiology of Vision standards for PRVEP (reversal rate=1.9Hz, checkerboard stimuli 15' and 60' at 100% contrast) and FVEP (3cds/m2, rate=1Hz). VEP parameters of amplitude (µV) and peak times (ms) were measured. Inter-ocular differences, inter-peak intervals (N135-N75) and binocular summation were determined. Fifty-four subjects (28 females; mean age=40.4±13.7years; median=40.0years) were included. Mean P100 latencies for 15' and 60' stimuli were, respectively, 94.6±4.7ms and 96.1±4.2 for women. Mean values of P100 latency for men were 97.4±4.9 for 15' and 97.7±4.2 for 60' stimuli. Larger mean P100 for 15' checks was observed in women (12.8±5.7µV) than men (8.6±2.5µV) in PRVEP. Similar results were found for FVEP N2-P2 amplitudes (mean=14.6±4.9 for women and 9.8±4.0 for men). Gender-based normative values for PRVEP and FVEP were determined, with women disclosing higher responses than men for smaller stimuli in the visual pathway. The use of gender-based normative values in the analysis of clinical VEP data for diagnostic and therapeutic purposes is recommendable. Additional analysis including inter-peak intervals and binocular summation ratio might improve the diagnostic power of VEP.

Recherche d’indices électrophysiologiques de confort visuel après correction de la presbytie par lentilles de contact

Starting at 40years of age, prespyopia affects a quarter of the world population. Many techniques of presbyopia surgery have emerged in recent years. The purpose of this study was to compare monovision and multifocality and to identify clinical and electrophysiological predictive markers of visual comfort for each correction available in clinical practice. Ten presbyopic patients participated in this study. Patients received monovision and multifocal correction using contact lenses for three weeks each in a random order. A clinical evaluation (visual acuity, TNO test, binocular contrast sensitivity and quality of vision questionnaires) and an electrophysiological evaluation (monocular and binocular pattern VEP with multiple spatial frequencies: 60, 30and 15') were performed before and after each correction modality. The P100was significantly wider and slightly earlier after binocular compared to monocular stimulation at T0. The TNO stereopsis score decreased significantly after correction. No other significant differences, either on clinical or electrophysiological criteria, were found between the two modes of correction. Several significant correlations were found between the stereoacuity difference depending upon correction and evoked potentials by binocular pattern at T0. The larger the stereoacuity difference (better stereoacuity with multifocal compensation), the longer the latency of the P100using 60' checks (R=0.82; P=0.004) and the greater the amplitude of the N75using 30' (R=0.652; P=0.04). Our study found no differences between the 2types of correction, but it highlights a benefit of VEP used in current practice and measurement of the P100wave, the best indicator of stereopsis and the most consistent, to predict visual comfort after compensation presbyopia.

Influence of refractive error on pupillary dynamics in the normal and mild traumatic brain injury (mTBI) populations

PurposeThere have been several studies investigating static, baseline pupil diameter in visually-normal individuals across refractive error. However, none have assessed the dynamic pupillary light reflex (PLR). In the present study, both static and dynamic pupillary parameters of the PLR were assessed in both the visually-normal (VN) and the mild traumatic brain injury (mTBI) populations and compared as a function of refractive error. MethodsThe VN population comprised 40 adults (22–56 years of age), while the mTBI population comprised 32 adults (21–60 years of age) over a range of refractive errors (−9.00D to +1.25D). Seven pupillary parameters (baseline static diameter, latency, amplitude, and peak and average constriction and dilation velocities) were assessed and compared under four white-light stimulus conditions (dim pulse, dim step, bright pulse, and bright step). The Neuroptics, infrared, DP-2000 binocular pupillometer (30Hz sampling rate; 0.05mm resolution) was used in the monocular (right eye) stimulation mode. ResultsFor the majority of pupillary parameters and stimulus conditions, a Gaussian distribution best fit the data, with the apex centered in the low myopic range (−2.3 to −4.9D). Responsivity was reduced to either side of the apex. ConclusionsOver a range of dynamic and static pupillary parameters, the PLR was influenced by refractive error in both populations. In cases of high refractive error, the PLR parameters may need to be compensated for this factor for proper categorization and diagnosis.