Visual field inhomogeneous in brain-computer interfaces based on rapid serial visual presentation

Objective. Visual attention is not homogeneous across the visual field, while how to mine the effective EEG characteristics that are sensitive to the inhomogeneous of visual attention and further explore applications such as the performance of brain-computer interface (BCI) are still distressing explorative scientists. Approach. Images were encoded into a rapid serial visual presentation (RSVP) paradigm, and were presented in three visuospatial patterns (central, left/right, upper/lower) at the stimulation frequencies of 10Hz, 15Hz and 20Hz. The comparisons among different visual fields were conducted in the dimensions of subjective behavioral and EEG characteristics. Furthermore, the effective features (e.g. SSVEP, N2pc and P300) that sensitive to visual-field asymmetry were also explored. Results. The visual fields had significant influences on the performance of RSVP target detection, in which the performance of central was better than that of peripheral visual field, the performance of horizontal meridian was better than that of vertical meridian, the performance of left visual field was better than that of right visual field, and the performance of upper visual field was better than that of lower visual field. Furthermore, stimuli of different visual fields had significant effects on the spatial distributions of EEG, in which N2pc and P300 showed left-right asymmetry in occipital and frontal regions, respectively. In addition, the evidences of SSVEP characteristics indicated that there was obvious overlap of visual fields on the horizontal meridian, but not on the vertical meridian. Significance. The conclusions of this study provide insights into the relationship between visual field inhomogeneous and EEG characteristics. In addition, this study has the potential to achieve precise positioning of the target's spatial orientation in RSVP-BCIs.

Dissociation between red and white stimulus perception: A perimetric quantification of protanopic color vision deficiencies

Significance Horizontal visual field extension was assessed for red and white stimuli in subjects with protanopia using semi-automated kinetic perimetry. In contrast to a conventional anomaloscope, the “red/white dissociation ratio” (RWR) allows to describe protanopia numerically. For the majority of subjects with protanopia a restriction for faint red stimuli was found. Purpose Comparing the horizontal visual field extensions for red and white stimuli in subjects with protanopia and those with normal trichromacy and assessing the related intra-subject intra-session repeatability. Methods The subjects were divided into groups with protanopia and with normal trichromacy, based on color vision testing (HMC anomaloscope, Oculus, Wetzlar/FRG). Two stimulus characteristics, III4e and III1e, according to the Goldmann-classification, were presented with semi-automated kinetic perimetry (Octopus 900 perimeter, Haag-Streit, Köniz/CH). They moved along the horizontal meridian, with an angular velocity of 3°/s towards the visual field center, starting from either the temporal or nasal periphery. If necessary, a 20° nasal fixation point offset was chosen to capture the temporal periphery of the visual field. For each condition the red/white dissociation ratio (RWR); Pat Appl. DPMA DRN 43200082D) between the extent of the isopter for red (RG610, Schott, Mainz/ FRG) and white stimuli along the horizontal meridian was determined. Results All data are listed as median/interquartile range: Five males with protanopia (age 22.1/4.5 years) and six males with normal trichromacy (control group, age 30.5/15.2 years) were enrolled. The RWR is listed for the right eye, as no clinically relevant difference between right and left eye occurred. Protanopes’ RWR for mark III4e (in brackets: control group) was 0.941/0.013 (0.977/0.019) and for mark III1e 0.496/0.062 (0.805/0.051), respectively. Conclusions In this exploratory “proof-of-concept study” red/white dissociation ratio perimetry is introduced as a novel technique aiming at assessing and quantifying the severity of protanopia. Further effort is needed to understand the magnitude of the observed red-/white dissociation and to extend this methodology to a wider age range of the sample and to anomalous trichromacies (protanomalia) with varying magnitude.

The Role of Transient Attention in the Radial-tangential Anisotropy of Crowding

Crowding refers to the failure to identify a peripheral object due to its proximity to other objects (flankers). This phenomenon can lead to reading and object recognition impairments, and is associated with macular degeneration, amblyopia, and dyslexia. Crucially, the minimal target-flanker spacing required for the crowding interference (critical spacing) increases with eccentricity. This spacing is also larger when target and flankers appear along the horizontal meridian (radial arrangement) than when the flankers appear above and below the target (tangential arrangement). This phenomenon is known as radial–tangential anisotropy. Previous studies have demonstrated that transient attention can reduce crowding interference. However, it is still unclear whether and how attention interacts with the radial–tangential anisotropy. To address this issue, we manipulated transient attention by using a cue either at the target (valid) or fixation (neutral) location, in both radial and tangential target-flanker arrangements. Results showed that critical spacing was larger in the radial than in the tangential arrangement, and that cueing the target location improved performance and reduced the critical spacing for both radial and tangential arrangements, to the same extent. Together, our findings suggest that transient spatial attention plays an essential role in crowding but not in the radial-tangential anisotropy.

The Correlations between Horizontal and Vertical Peripheral Refractions and Human Eye Shape Using Magnetic Resonance Imaging in Highly Myopic Eyes

The aim of this study was to determine the relationship between relative peripheral refraction and retinal shape by 2-D magnetic resonance imaging in high myopes. Thirty-five young adults aged 20 to 30 years participated in this study with 16 high myopes (spherical equivalent < −6.00 D) and 19 emmetropes (+0.50 to −0.50 D). An open field autorefractor was used to measure refractions from the center out to 60° in the horizontal meridian and out to around 20° in the vertical meridian, with a step of 3 degrees. Axial length was measured by using A-scan ultrasonography. In addition, images of axial, sagittal, and tangential sections were obtained using 2-D magnetic resonance imaging. The highly myopic group had a significantly relative peripheral hyperopic refraction and showed a prolate ocular shape compared to the emmetropic group. The highly myopic group had relative peripheral hyperopic refraction and showed a prolate ocular form. Significant differences in the ratios of height/axial (1.01 ± 0.02 vs. 0.94 ± 0.03) and width/axial (0.99 ± 0.17 vs. 0.93 ± 0.04) were found from the MRI images between the emmetropic and the highly myopic eyes (p < 0.001). There was a negative correlation between the retina’s curvature and relative peripheral refraction for both temporal (Pearson r = −0.459; p < 0.01) and nasal (Pearson r = −0.277; p = 0.011) retina. For the highly myopic eyes, the amount of peripheral hyperopic defocus is correlated to its ocular shape deformation. This could be the first study investigating the relationship between peripheral refraction and ocular dimension in high myopes, and it is hoped to provide useful knowledge of how the development of myopia changes human eye shape.

Manual Segmentation of 12 Layers of the Retina and Choroid through SD-OCT in Intermediate AMD: Repeatability and Reproducibility

Purpose: To evaluate the repeatability and reproducibility of the segmentation of 12 layers of the retina and the choroid, performed manually by SD-OCT, along the horizontal meridian at three different temporal moments, and to evaluate its concordance with the same measurements performed by two other operators in intermediate AMD. Methods: A cross-sectional study of 40 eyes from 40 subjects with intermediate AMD was conducted. The segmentation was performed manually, using SD-OCT. The 169 measurements per eye were repeated at three time points to study the intra-operator variability. The same process was repeated a single time by two different trained operators for the inter-operator variability. Results: Forty participants (28 women and 12 men) were enrolled in this study, with an average age of 76.4 ± 8.2 (range, 55–92 years). Overall, the maximum values of the various structures were found in the 3 mm of the macula. Intra-operator variability: the highest ICC values turned out to be discovered in thicker locations. Inter-operator variability: except correlation values of 0.826 (0.727; 0.898) obtained in the OPL (T2.5) and 0.634 (0.469; 0.771) obtained in the IPL (N2), all other correlation values were >0.92, in most cases approaching higher values like 0.98. Conclusion: The measurements of several layers of the retina and the choroid achieved at 13 locations presented a good repeatability and reproducibility. Manual quantification is still an alternative for the weaknesses of automatic segmentation. Locations of greatest concordance should be those used for the clinical control and monitoring.

Repeatability and Reproducibility of Macular Hole Size Measurements Using Optical Coherence Tomography

The purpose of this study was to assess the repeatability and reproducibility of measuring the minimum linear diameter (MLD) of macular holes (MHs) using horizontal linear and radial scan modes in optical coherence tomography (OCT). Patients with concurrent sets of radial and horizontal linear OCT volume scans were included. The MLD was measured twice in both scan modes by six raters of three different experience levels (groups). Outcome measures were the reliability and repeatability of MLD measurements. Fifty patients were included. Mean MLD was 317.21(±170.63) µm in horizontal linear and 364.52 (±161.71) µm in radial mode, a difference of 47.31 (±26.48) µm (p < 0.001). In the radial scan mode, MLD was identified within 15° of the horizontal meridian in 27% and within 15° of the vertical meridian in 26.7%, with the remainder (46.3%) in oblique meridians. The intra-group coefficients of repeatability (CR) for horizontal linear mode were 23 µm, 33 µm and 45 µm, and for radial mode 25 µm, 44 µm and 57 µm for groups 1, 2 and 3, respectively. The inter-group CR, taking group 1 as reference standard for groups 2 and 3, were 74 µm and 71 µm for the linear mode, and 62 µm and 78 µm for radial mode. The radial mode provides good repeatability and reliability for measurement of MLD. In a majority of cases the MLD does not lie in the horizontal meridian and would be underestimated using a horizontal OCT mode.

Features of meridional separable visual acuity changes in amblyopia treatment by accommodation training method in patients with astigmatism

Objective. To investigate the influence of the optic-reflex method of accommodation training on the indices of the meridional separable visual acuity in the treatment of children with amblyopia and astigmatism. Material and methods. 24 children aged 5 to 12 years with refractive amblyopia and direct hyperopic astigmatism were examined. Accommodation training was performed by defocusing the image with optical glasses of variable optical power. The course of treatment lasted 10 days. Results. In the group with meridional amblyopia, 2 different clusters were identified: in one of them, the indicators of separable visual acuity were higher in the horizontal meridian and in the other - in the vertical. After treatment, the number of eyes with the same meridional visual acuity increased. Simultaneously with the elimination of the meridional asymmetry of visual acuity, the number of eyes in the category of patients with visual acuity of 0.75-0.8 according to the Sivtsev table increased by 8.52%. Conclusion. In the standard of assessment of visual functions in patients with astigmatism and amblyopia, it is necessary to introduce methods for determining the meridional visual acuity. Evaluation of the effectiveness of treatment of meridional amblyopia should be carried out in homogeneous clusters, which take into account the coincidence or discrepancy of the directions of meridional asymmetries of visual acuity with refractive. Preliminary data on the effectiveness of treatment of amblyopia by the method of accommodation training allows us to consider it as a method of treatment of meridional amblyopia.

Three-Random-Point Marking Method for Toric Intraocular Lens Alignment Using the iTrace Aberrometer

Purpose. To evaluate the clinical outcome of the three-random-point (TRP) marking method for toric intraocular lens (IOL) alignment using the iTrace aberrometer (Tracey Technologies Corp., Houston, TX). Setting. Department of Ophthalmology, Guangdong Eye Institute, Guangdong Academy of Medical Sciences, Guangdong Provincial People’s Hospital, Guangzhou, China. Design. Prospective, randomized comparative trial. Method. Thirty eyes of 30 patients undergoing cataract surgery with coexisting corneal astigmatism of over 1.0 D were included in this study. All patients were prospectively randomized into the TRP marking group or slit-lamp horizontal meridian (SHM) marking group. TRP marking involved marking three points randomly in the corneal limbus of the patients and accurately marking the horizontal meridian was not required. The follow-up duration was 3 months after cataract surgery. Results. Fifteen eyes of 15 patients were in the TRP marking group and 15 eyes of 15 patients in the SHM marking group. There was no statistically significant difference in BCVA, UDVA, preexisting corneal astigmatism, or residual astigmatism between the groups before or after surgery P > 0.05 . The mean toric IOL misalignment was lesser but without significance in the TRP marking group than in the SHM marking group after 3 postoperative months (2.66° ± 1.42° versus 3.29° ± 1.67°; P = 0.295 ). Conclusion. The TRP marking method using the iTrace aberrometer is simple and accurate for preoperative marking of toric IOLs. It can eliminate the potential systematic errors resulting from varying head positions during the preoperative keratometry measurement and from manual marking.

Optical Coherence Tomography Biomarkers of Photoreceptor Degeneration in Retinitis Pigmentosa

Purpose: Several parameters on optical coherence tomography (OCT) have been suggested as biomarkers for photoreceptor degeneration in retinitis pigmentosa (RP). This study is to investigate which OCT parameters can serve as the earliest biomarkers in RP.Methods: OCT line scans of the horizontal meridian were conducted in 22 eyes of 22 RP patients and 30 eyes of 30 healthy controls. Longitudinal reflectance profiles were obtained using ImageJ at every 5 pixels. The following parameters on OCT were quantitatively measured: 1) relative optical intensity (ROI) of ellipsoid zone (EZ) and interdigitation zone (IZ); 2) thickness of outer nuclear layer (ONLT), photoreceptor (PRT), inner segment (IST) and outer segment (OST). The variations of these parameters across different regions were analyzed. Results: From fovea to peripheral retina, all the OCT biomarkers declined before disappeared, except IST and IZ-ROI. There was no identifiable declining zone for the IST and IZ-ROI between the normal and disappeared zones. The earliest biomarker was the shortening of OST and reduced IZ-ROI, followed by the shortening of PRT, EZ-ROI, then IST, and finally, ONLT. All these biomarkers had significant correlations with best-corrected visual acuity, except ONLT.Conclusion: In retinitis pigmentosa, EZ-ROI, IZ-ROI, PRT, OST, IST and ONLT are valuable biomarkers of photoreceptor degeneration. OST and IZ-ROI may serve as the earliest biomarkers.