Effect Of Pupil Size Research Articles

Investigating causal effects of pupil size on visual discrimination and visually evoked potentials in an optotype discrimination task.

Pupil size primarily changes to regulate the amount of light entering the retina, optimizing the balance between visual acuity and sensitivity for effective visual processing. However, research directly examining the relationship between pupil size and visual processing has been limited. While a few studies have recorded pupil size and EEG signals to investigate the role of pupil size in visual processing, these studies have predominantly focused on the domain of visual sensitivity. Causal effects of pupil size on visual acuity, therefore, remain poorly understood. By manipulating peripheral background luminance levels and target stimulus contrast while simultaneously recording pupillometry and EEG signals, we examined how absolute pupil size affects visual discrimination and visually evoked potentials (VEP) in a task using optotype mimicking the Snellen eye chart, the most common assessment of visual acuity. Our findings indicate that both higher background luminance levels and higher target contrast were associated with improved target discrimination and faster correct reaction times. Moreover, while higher contrast visual stimuli evoked larger VEPs, the effects of pupil size on VEPs were not significant. Additionally, we did not observe inter-individual correlations between absolute pupil size and discrimination performance or VEP amplitude. Together, our results demonstrate that absolute pupil size, regulated by global luminance level, played a functional role in enhancing visual discrimination performance in an optotype discrimination task. The differential VEP effects of pupil size compared to those of stimulus contrast further suggested distinct neural mechanisms involved in facilitating visual acuity under small pupils.

Effects of Pupil Size as Manipulated through ipRGC Activation on Visual Processing

Effects of Pupil Size as Manipulated through ipRGC Activation on Visual Processing

The effect of pupil size on near-threshold detection is not mediated by alpha, beta, or theta power

The effect of pupil size on near-threshold detection is not mediated by alpha, beta, or theta power

Modulation transfer function of implantable phakic intraocular contact lens (IPCL) for myopia and presbyopia.

This study aimed to assess the optical quality of myopic and presbyopic IPCLs with different additional powers, and to investigate the effects of pupil size on the optical quality of these IPCLs using an in-vitro modulation transfer function (MTF) measurement system. Linear scatter functions (LSFs) were recorded using the OPAL Vector system and an eye phantom consisting of wet cells filled with a balanced salt solution. A myopic IPCL or a presbyopic IPCL was placed in the posterior chamber of this model. The MTF was calculated from the LSF using the fast Fourier transform techniques. The effective apertures were set at 2.0 to 5.0mm in 1.0mm steps. The in-focus MTF values of the myopic IPCL and presbyopic IPCL with additional powers of + 2.0 and + 4.0 diopters at 100 cycles/mm for an effective aperture of 3.0mm were 43%, 27%, and 24%, respectively. The in-focus MTF value of both myopic and presbyopic IPCLs was the highest when the effective aperture was set at 3.0mm, and it gradually worsened when the effective aperture became larger than 3.0mm at 20, 60, and 100 cycles/mm. Both myopic and presbyopic IPCLs provided excellent MTF values, but the additional power profile can deteriorate optical performance in presbyopic IPCL-implanted eyes, even with a low additional power. Pupil size can influence visual quality in IPCL-implanted eyes for both myopia and presbyopia.

Effects of pupil size as manipulated through ipRGC activation on visual processing

The size of the eyes’ pupils determines how much light enters the eye and also how well this light is focused. Through this route, pupil size shapes the earliest stages of visual processing. Yet causal effects of pupil size on vision are poorly understood and rarely studied. Here we introduce a new way to manipulate pupil size, which relies on activation of intrinsically photosensitive retinal ganglion cells (ipRGCs) to induce sustained pupil constriction. We report the effects of both experimentally induced and spontaneous changes in pupil size on visual processing as measured through EEG. We compare these to the effects of stimulus intensity and covert visual attention, because previous studies have shown that these factors all have comparable effects on some common measures of early visual processing, such as detection performance and steady-state visual evoked potentials; yet it is still unclear whether these are superficial similarities, or rather whether they reflect similar underlying processes. Using a mix of neural-network decoding, ERP analyses, and time-frequency analyses, we find that induced pupil size, spontaneous pupil size, stimulus intensity, and covert visual attention all affect EEG responses, mainly over occipital and parietal electrodes, but—crucially—that they do so in qualitatively different ways. Induced and spontaneous pupil-size changes mainly modulate activity patterns (but not overall power or intertrial coherence) in the high-frequency beta range; this may reflect an effect of pupil size on oculomotor activity and/ or visual processing. In addition, spontaneous (but not induced) pupil size tends to correlate positively with intertrial coherence in the alpha band; this may reflect a non-causal relationship, mediated by arousal. Taken together, our findings suggest that pupil size has qualitatively different effects on visual processing from stimulus intensity and covert visual attention. This shows that pupil size as manipulated through ipRGC activation strongly affects visual processing, and provides concrete starting points for further study of this important yet understudied earliest stage of visual processing.

The effect of pupil size on the measurement of corneal birefringence properties: preliminary study

We used a partial Mueller matrix polarimeter to measure the corneal anisotropic properties at three pupil sizes (dilated, natural, and constricted). The geometrical parameters of first order isochromes were described by quadrilaterals. These parameters are statistically significantly different between the three pupil sizes. The pupillary size changes do not influence the azimuth angle distribution α. The retardation R and birefringence distributions show asymmetry in the nasal–temporal cross-section. There are differences between pupil sizes for both nasal and temporal parts of the cornea for these distributions. Iridial light scattering and diffraction might be the reason for these differences.

Effects of pupil size in video head-impulse tests.

The results of video head impulse tests (video-HITs) may be confounded by data artifacts of various origins, including pupil size and eyelid obstruction of the pupil. This study aimed to determine the effect of these factors on the results of video-HITs. We simulated ptosis by adopting pharmacological dilatation of the pupil in 21 healthy participants (11 women; age 24-58years). Each participant underwent video-HITs before and after pupillary dilatation using 0.5% tropicamide. We assessed the changes in the vestibulo-ocular reflex (VOR) gain, corrective saccade amplitude, and frequency of eyelid flicks. After pupillary dilatation, the VOR gain decreased for both right (RAC; 1.12 [Formula: see text] 0.12 vs. 1.01 [Formula: see text] 0.16, p = 0.011) and left anterior canals (LACs; 1.15 [Formula: see text] 0.13 vs. 0.96 [Formula: see text] 0.14, p < 0.001), and right posterior canal (RPC, 1.10 [Formula: see text] 0.13 vs. 0.98 [Formula: see text] 0.09, p = 0.001). The corrective saccade amplitudes also decreased significantly for all four vertical canals. The frequency of eyelid flicks, however, did not change. The changes of VOR gain were positively correlated with the lid excursion in RPC (r = 0.629, p = 0.002) and LPC (r = 0.549, p = 0.010). Our study indicates that eyelid position and pupil size should be considered when interpreting the results of video-HITs, especially for the vertical canals. Pupils should be shrunk in a very well-lit room, and artifacts should be prevented by taping or lifting the eyelids as required during video-HITs.

Cone-isolation contrast sensitivity – do pupil and stimulus sizes matter?

ABSTRACT Clinical relevance Computer-based colour perception tests permit clinical assessment of cone-specific pathways, proving valuable for both identifying type and severity of hereditary colour vision deficiency and enhanced detection and monitoring of acquired colour deficiency from disease. Understanding the parameters that affect computer-based colour perception tests may enhance their veracity and clinical utility. Background Testing contrast sensitivity separately for the three cone systems enables a quantification of colour perception that can be clinically useful. This study evaluated the effects of pupil diameter and stimulus size on cone contrast sensitivity (CCS) assessed with the ColorDx (Konan Medical, Incorporated). Methods Forty subjects, aged 21–31 years, who met the inclusion criteria participated. The tested eye was randomised. Two Landolt C sizes (2.68 degrees, 6/194, “small”; 8.58 degrees, 6/619, “large”) were used, with one size and three chromaticities presented per block of trials. Stimulus presentation used the adaptive screening mode, sequentially determining contrast sensitivity for long-, medium-, and short-wavelength stimuli. Subjects were tested with their natural pupil size (range 4–5 mm diameter), then while viewing through a 2.5-mm artificial pupil. Parametric statistical tests were used for comparisons of performance across pupil size and stimulus size. Results Two-way within-subjects ANOVA indicates no interaction between pupil size and stimulus size for any of the three stimulus chromaticities. The main effect of stimulus size was significant for M-cone (F = 6.506, 2-tailed P = .015) and S-cone (F = 67.728, 2-tailed P < .001) stimuli. The main effect of pupil size was significant for all three stimulus chromaticities (L-cone: F = 227.161, M-cone: F = 249.979, S-cone: F = 89.371, 2-tailed P < .001 for all). Conclusion Although CCS was reduced for all three chromaticities and both stimulus sizes with lower retinal illuminance, only S-wavelength cone contrast sensitivity was significantly different for the small versus large stimuli under the 2.5-mm pupil condition in this cohort. Whether CCS in older patients with naturally small pupils changes with an enlarged stimulus or dilated pupils remains to be explored.

Optical bench evaluation of the effect of pupil size in new generation monofocal intraocular lenses

BackgroundA new generation of enhanced monofocal IOLs has been introduced to slightly increase the depth of focus as compared to standard monofocal IOLs. The purpose of this study is to evaluate the effect of pupil size on the through-focus optical performance of three new enhanced monofocal IOLs, designed to improve the range of vision as compared to standard monofocal IOLs.MethodsOptical bench testing in white light was performed for different pupils, using an average cornea eye. Distance image quality was evaluated using Modulation Transfer Function (MTF) measurements. Through-focus Visual Acuity (VA) was simulated from these measurements (sVA). Three enhanced monofocal IOLs (ICB00, ISOPure, and RayOne-EMV) and three standard monofocal IOLs: two aspheric (ZCB00 and SN60WF) and one spherical (AAB00) were included.ResultsThe enhanced monofocal IOLs provided an improvement in the intermediate sVA as compared to standard monofocal IOLs. For ICB00, the improvement was independent of the pupil size, while for the ISOPure and RayOne-EMV, the intermediate sVA improved with increased pupil size. Similar to the spherical monofocal IOL, the ISOPure and RayOne-EMV showed a strong correlation between improvement in intermediate sVA and reduction of distance sVA and MTF, and increasing pupil size. ICB00 provided the same distance sVA as the aspheric monofocal IOLs and the lowest variability in MTF with pupil size.ConclusionOptical bench results showed that the ISOPure and RayOne-EMV provide similar performance to a spherical monofocal IOL, with a strong pupil dependency for distance and intermediate vision. The other enhanced monofocal IOL, ICB00, provided a sustained improvement in simulated intermediate VA and maintained distance image quality comparable to that of the standard aspheric monofocal IOLs, even for larger pupils.

Humanity at first sight: Exploring the relationship between others' pupil size and ascriptions of humanity

Social targets' eyes are a rich source of information: partners with dilated and constricted pupils are perceived positively and negatively, respectively. Here, we tested whether observed pupil size influences the ascription of humanity. In Study 1 (n = 198) participants were asked to attribute positive uniquely human and non-uniquely human traits to ingroup (i.e., university students), derogated (i.e., homeless people) and non-derogated (i.e., Dutch) targets whose pupils varied in size. Results showed higher attribution of uniquely human traits to targets with dilated (vs. constricted) pupils, whereas no difference based on pupil size emerged on the attribution of non-uniquely human traits. The effect was stronger for non-derogated (vs. derogated and ingroup) targets. In Study 2 (n = 117) participants were asked to attribute positive uniquely human and non-uniquely human traits and emotions. Results replicated the effect of pupil size on trait attribution, especially for outgroup (vs. ingroup) members. The effect of pupil size was not qualified by emotions type (uniquely human vs. non uniquely human). Taken together, our findings show that pupil size is interpreted as a cue to attribute humanity to social targets.

Pupil size effect on binocular summation for visual acuity and light disturbance.

Smaller pupil size under binocular conditions could justify partially the improvement of visual performance when compared to monocular conditions. The purpose of this study was to assess the binocular summation for increasing levels of spherical and cylindrical defocus when the pupil size factor is ruled out as a confounding factor. Fifteen young subjects were recruited in this crossover study. Light disturbance index (LDI) was evaluated with the light disturbance analyzer and low (LCDVA) and high (HCDVA) contrast visual acuity with the ETDRS test. Two positive spherical and cylindrical defocus levels (+ 1.5 and + 3.0 D) were used to induce a controlled degradation of the retinal image for two pupil sizes (3 and 5mm). Our results showed poorer visual performance in monocular than the binocular condition. An increasing deterioration was observed with the level of spherical defocus. Positive binocular summation for visual acuity was found in all the parameters studied and was stronger under larger pupil size and for higher levels of spherical defocus. It was observed a positive binocular summation for the LDI under all the conditions studied. Strong and significant correlations were found between LDI and LCDVA and between LDI and HCDVA for all the conditions. Higher correlations were obtained between disturbance index and visual acuity for spherical defocus compared to cylindrical. Binocular summation was observed under different conditions of spherical and cylindrical optical degradation of the image quality when the pupil size was fully controlled. This suggests that a neural factor is involved.

Attention Towards Pupil Size in Humans and Bonobos (Pan paniscus)

Previous work has established that humans have an attentional bias towards emotional signals, and there is some evidence that this phenomenon is shared with bonobos, our closest relatives. Although many emotional signals are explicit and overt, implicit cues such as pupil size also contain emotional information for observers. Pupil size can impact social judgment and foster trust and social support, and is automatically mimicked, suggesting a communicative role. While an attentional bias towards more obvious emotional expressions has been shown, it is unclear whether this also extends to a more subtle implicit cue, like changes in pupil size. Therefore, the current study investigated whether attention is biased towards pupils of differing sizes in humans and bonobos. A total of 150 human participants (141 female), with a mean age of 19.13 (ranging from 18 to 32 years old), completed an online dot-probe task. Four female bonobos (6 to 17 years old) completed the dot-probe task presented via a touch screen. We used linear mixed multilevel models to examine the effect of pupil size on reaction times. In humans, our analysis showed a small but significant attentional bias towards dilated pupils compared to intermediate-sized pupils and intermediate-sized pupils when compared to small pupils. Our analysis did not show a significant effect in bonobos. These results suggest that the attentional bias towards emotions in humans can be extended to a subtle unconsciously produced signal, namely changes in pupil size. Due to methodological differences between the two experiments, more research is needed before drawing a conclusion regarding bonobos.

Motion adaptation improves acuity (but perceived size doesn't matter).

Recognition acuity—the minimum size of a high-contrast object that allows us to recognize it—is limited by optical and neural elements of the eye and by processing within the visual cortex. The perceived size of objects can be changed by motion-adaptation. Viewing receding or looming motion makes subsequently viewed stimuli appear to grow or shrink, respectively. It has been reported that resulting changes in perceived size impact recognition acuity. We set out to determine if such acuity changes are reliable and what drives this phenomenon. We measured the effect of adaptation to receding and looming motion on acuity for crowded tumbling-T stimuli (). We quantified the role of crowding, individuals’ susceptibility to motion-adaptation, and potentially confounding effects of pupil size and eye movements. Adaptation to receding motion made targets appear larger and improved acuity (–0.037 logMAR). Although adaptation to looming motion made targets appear smaller, it induced not the expected decrease in acuity but a modest acuity improvement (–0.018 logMAR). Further, each observer's magnitude of acuity change was not correlated with their individual perceived-size change following adaptation. Finally, we found no evidence that adaptation-induced acuity gains were related to crowding, fixation stability, or pupil size. Adaptation to motion modestly enhances visual acuity, but unintuitively, this is dissociated from perceived size. Ruling out fixation and pupillary behavior, we suggest that motion adaptation may improve acuity via incidental effects on sensitivity—akin to those arising from blur adaptation—which shift sensitivity to higher spatial frequency-tuned channels.

Small Pupils Lead to Lower Judgements of a Person’s Characteristics for Exaggerated, but Not for Realistic Pupils

Our eyes convey information about a person. The pupils may provide information regarding our emotional states when presented along with different emotional expressions. We examined the effects of pupil size and vergence on inferring other people’s characteristics in neutral expression eyes. Pupil sizes were manipulated by overlaying black disks onto the pupils of the original eye images. The disk area was then changed to create small, medium, and large pupils. Vergence was simulated by shifting the medium-sized disks nasally in one eye. Pupil sizes were exaggerated for Experiment 1 and followed values from the literature for Experiment 2. The first Purkinje image from the eye photos in Experiment 2 was kept to preserve image realism. The characteristics measured were sex, age, attractiveness, trustworthiness, intelligence, valence, and arousal. Participants completed one of two online experiments and rated eight eye pictures with differently sized pupils and with vergence eyes. Both experiments were identical except for the stimuli designs. Results from Experiment 1 revealed rating differences between pupil sizes for all characteristics except sex, age, and arousal. Specifically, eyes with extremely small pupil sizes and artificial vergence received the lowest ratings compared to medium and large pupil sizes. Results from Experiment 2 only indicated weak effects of pupil size and vergence, particularly for intelligence ratings. We conclude that the pupils can influence how characteristics of another person are perceived and may be regarded as important social signals in subconscious social interaction processes. However, the effects may be rather small for neutral expressions.

Irissometry: Effects of Pupil Size on Iris Elasticity Measured With Video-Based Feature Tracking.

PurposeIt is unclear how the iris deforms during changes in pupil size. Here, we report an application of a multi-feature iris tracking method, which we call irissometry, to investigate how the iris deforms and affects the eye position signal as a function of pupil size.MethodsTo evoke pupillary responses, we repeatedly presented visual and auditory stimuli to healthy participants while we additionally recorded their right eye with a macro lens–equipped camera. We tracked changes in iris surface structure between the pupil and sclera border (limbus) by calculating local densities (distance between feature points) across evenly spaced annular iris regions.ResultsThe time analysis of densities showed that the inner regions of the iris stretched more strongly as compared with the outer regions of the iris during pupil constrictions. The pattern of iris densities across eccentricities and pupil size showed highly similar patterns across participants, highlighting the robustness of this elastic property. Importantly, iris-based eye position detection led to more stable signals than pupil-based detection.ConclusionsThe iris regions near the pupil appear to be more elastic than the outer regions near the sclera. This elastic property explains the instability of the pupil border and the related position errors induced by eye movement and pupil size in pupil-based eye-tracking. Tracking features in the iris produce more robust eye position signals. We expect that irissometry may pave the way to novel eye trackers and diagnostic tools in ophthalmology.

It Is Written in the Eyes: Inferences From Pupil Size and Gaze Orientation Shape Interpersonal Liking

Research has shown that pupil size shapes interpersonal impressions: Individuals with dilated pupils tend to be perceived more positively than those with constricted pupils. Untested so far is the role of cognitive processes in shaping the effects of pupil size. Two preregistered studies investigated whether the effect of pupil size was qualified by partner's attention allocation inferred from gaze orientation. In Experiment 1 (N = 50) partners with dilated pupils were more liked when gazing toward the participant, but less liked when gazing toward a disliked other. Experiment 2 (N = 50) unveiled the underlying mechanism of the pupil-gaze interplay. Pupillary changes led to inferences about the feelings held by the partner toward the gazed target: Larger pupils signaled positive feelings. Crucially, target identity moderated the response of the participants (i.e., liking toward the partner). This work shows the importance of considering the interplay of affective and cognitive eye-signals when studying person perception.

Effect of pupil size on posterior chamber phakic intraocular lens vault measurements.

Purpose:The aim of this study was to measure the implantable collamer lens (ICL) vault changes with anterior segment optical coherence tomography (AS-OCT) after the implantation of the Visian posterior chamber phakic ICL with a central hole (V4c) in relation to the pupil size.Methods:This retrospective observational pilot study included 32 eyes of 16 patients, who underwent V4c ICL implantation. ICL vault was measured with AS-OCT in undilated and fully dilate state of the pupil. Primary outcome measure was the change in the vault of V4c ICL at the maximum and minimum pupil size.Results:Median (IQR) undilated and post-dilated vault measurement was 393.00 (335.50–493.50) microns and 421.00 (338.50–503.75) microns, respectively, which was not statistically significant (P = 0.44).Conclusion:No statistically significant difference was observed between the undilated and post-dilated ICL vault measurements. Hence, the postoperative vault can be measured either in resting, undilated state or fully dilated state of the pupil and would be similar irrespective of the pupil size.

Dissociation of task engagement and arousal effects in auditory cortex and midbrain.

Both generalized arousal and engagement in a specific task influence sensory neural processing. To isolate effects of these state variables in the auditory system, we recorded single-unit activity from primary auditory cortex (A1) and inferior colliculus (IC) of ferrets during a tone detection task, while monitoring arousal via changes in pupil size. We used a generalized linear model to assess the influence of task engagement and pupil size on sound-evoked activity. In both areas, these two variables affected independent neural populations. Pupil size effects were more prominent in IC, while pupil and task engagement effects were equally likely in A1. Task engagement was correlated with larger pupil; thus, some apparent effects of task engagement should in fact be attributed to fluctuations in pupil size. These results indicate a hierarchy of auditory processing, where generalized arousal enhances activity in midbrain, and effects specific to task engagement become more prominent in cortex.

Humans’ pupillary contagion extends to cats and dogs

When viewing pupil sizes change, our own pupil sizes change, a phenomenon known as pupillary contagion. This involuntary response is reliable between humans but can be affected by familiarity and empathy. We investigated whether the pupillary contagion response occurs for humans viewing familiar species—cats and dogs—and whether it is modulated by preferences for particular species. Pupil sizes were measured while viewing cat, dog and human images with small, medium and large pupils. Trait empathy, cat and dog affiliation and experience were subsequently measured. There was an image pupil size effect, but this did not vary by species. There was greater pupil size change to cats and dogs than to humans, but this might have been due to the varying size and appearance of the cats and dogs. Greater dog affiliation was also associated with smaller overall pupil size change to dogs and larger change to humans, but this did not interact with image pupil size. Dog affiliation might be associated with less arousal to dog images. In sum, pupillary contagion responses indicate a spontaneous transfer of information about internal states and the findings suggest that humans are sensitive to this across species, regardless of individual preference.

Рhotopic Negative Response for Testing the Function of Inner Retina: Registration Requirements and Comparison in the Eyes with Natural Pupil Width and in Conditions of Drug Mydriasis

Purpose: To evaluate the possibility of registration of the photopic negative response (PhNR) without pupil dilatation in healthy individuals to determine the dysfunction of neurons of the inner retina.Methods: 12 healthy persons (23 eyes) aged 24 to 40 years were examined. Refraction anomalies did not exceed 0.5 diopters. A PhNR was evaluated in photopic ERGs recorded on a blue background with red flashes of four intensities (0.375, 0.75, 1.5, 3.0 cd·s/m2) using the RETIport/scan21 (Roland Consult). First, ERG was recorded with the natural pupil (3.5 ± 0.2 mm). Then, the recording was repeated after drug mydriasis (average pupil size 8.7 ± 0.1 mm).Results. In eyes with natural pupil width, in comparison with drug mydriasis, PhNR amplitudes in responses to weakest stimuli (0.375 cd·s/m2) were significantly reduced. The effect of pupil size on the PhNR amplitude from a baseline was virtually absent in responses to higher strength flashes. This phenomenon can be associated with an irregular distribution of light over the retina with small pupil size, the effect of which is maximal in responses to weak flashes. For the maximal brightness stimuli (3.0 cd·s/m2), differences were found between groups of non-dilated and dilated pupils in the amplitudes of the b-wave and PhNR from the b-peak, which may reflect a decrease in the number of stimulated photoreceptors during ganzfeld stimulation when the pupil is not dilated.Conclusion. The effect of pupil size on the parameters of the PhNR was most significant in the ERG with minimal flash strength and it decreases in responses to flashes of higher brightness. If it is necessary to record the ERG without drug mydriasis, especially in screening studies, it is recommended to limit the protocol to estimate the PhNR from a baseline in responses to maximal flashes, and use the relative parameter — the amplitude ratio of PhNR/b. Keywords: photopic negative response, electroretinography, pupil width