Presbyopia and myopia research shows a growing interest in ciliary muscle biometry using optical coherence tomography (OCT). Until now, segmentation of the ciliary muscle is often performed manually ...using either custom-developed programs or image processing software. Here we present a novel software for semi-automatic segmentation of the ciliary muscle. It provides direct import of OCT images in DICOM format, a standardized procedure for segmentation, image distortion correction, the export of anatomical ciliary muscle landmarks, like ciliary muscle apex and scleral spur, as well as a continuous thickness profile of the ciliary muscle as a novel way of analysis. All processing steps are stored as XML files, fostering documentation and reproducibility of research through the possibility of replicating the analysis. Additionally, CilOCT supports batch processing for the automated analysis of large numbers of images and the respective data export to tabulated text files based on the stored XML files. CilOCT was successfully applied in several studies and their results will be summarized in this paper.
Environmental factors favoring myopia development are still being studied and there is accumulating evidence for a significant role of nearwork. Recently, reading standard black-on-white text was ...found to activate the retinal OFF pathway and induce choroidal thinning, which is associated with myopia onset. Contrarily, reading white-on-black text led to thicker choroids, being protective against myopia. Respective effects on retinal processing are yet unknown. Here, we exploratively assessed the impact of contrast polarity on the retinal activity and possible interactions with eccentricity and refractive error. We recorded pattern electroretinograms in myopic and emmetropic adults while presenting a dead leaves stimulus (DLS), overlaid by masks of different size in ring or circle shape, either filled with uniform gray or text of inverted or standard contrast. In myopes, retinal responses for DLS with standard and inverted contrast were larger when the perifovea was stimulated (6-12 deg), however, including the fovea resulted in smaller amplitudes for inverted contrast than in emmetropes. The retina of emmetropes was more sensitive to inverted contrast than to standard and gray within 12 deg, but most sensitive for gray in the perifovea. This demonstrates that the refractive error influences the sensitivity to text contrast polarity, with a special role of the peripheral retina, which is in line with previous studies about blur sensitivity. Defining whether the differences derive from retinal processing or anatomical features of a myopic eye requires further investigation. Our approach might be a first step to explain how nearwork promotes the eye's elongation.
Anterior segment optical coherence tomography (AS-OCT), being non-invasive and well-tolerated, is the method of choice for an in vivo investigation of ciliary muscle morphology and function. The ...analysis requires the segmentation of the ciliary muscle, which is, when performed manually, both time-consuming and prone to examiner bias. Here, we present a convolutional neural network trained for the automatic segmentation of the ciliary muscle in AS-OCT images.
is based on the Freiburg U-net and was trained and validated using 1244 manually segmented OCT images from two previous studies. An accuracy of 97.5% for the validation dataset was achieved.
performance was evaluated by replicating the findings of a third study with 180 images as the test data. The replication demonstrated that
performed on par with two experienced examiners. The intersection-over-union index (0.84) of the ciliary muscle thickness profiles between
and an experienced examiner was the same as between the two examiners. The mean absolute error between the ciliary muscle thickness profiles of
and the two examiners (35.16 µm and 45.86 µm) was comparable to the one between the examiners (34.99 µm). A statistically significant effect of the segmentation type on the derived biometric parameters was found for the ciliary muscle area but not for the selective thickness reading ("perpendicular axis"). Both the inter-rater and the intra-rater reliability of
were good to excellent.
avoids time-consuming manual segmentation, thus enabling the analysis of large numbers of images of ample study cohorts while avoiding possible examiner biases.
is available as open-source.
To evaluate the PandAcuity test for visual function testing in a paediatric cohort and to examine its agreement with conventional visual acuity (VA) testing.
PandAcuity scores were determined in 152 ...children (77 males) aged between 3 and 15 years after VA testing (LEA
-test, E-chart, Landolt-C-rings or numbers). The PandAcuity test consisted of illusions made up from silhouettes of animals 'hidden' within zig-zag-patterns of decreasing spatial frequencies. Correlation analyses between PandAcuity score and VA were performed.
150 children completed the test in at least one eye, 148 in both eyes. The PandAcuity test demonstrated good test-retest reliability (intraclass correlation coefficient=0.89) between two runs. VA and PandAcuity score showed a medium to large correlation (Spearman's ρ=0.52, p<0.0001). 93% of the children's visual impairment was classified in the same range by both test types. Receiver operating characteristic analysis of predicted visual impairment showed an excellent agreement with the classification based on VA testing (AUC=0.84).
The PandAcuity test is rapid, simple and well accepted, rendering it a suitable supplement for the clinical assessment of VA in children. Because of its counterintuitive application (a higher number of correctly identified images means worse VA), it can be used to cross-validate conventional acuity tests to assure children's compliance.
To call attention to the danger of extinction of the panda bear, the Lithuanian artist Ilja Klemencov created the artwork "They can disappear". The illustration is composed of black-and-white ...zigzagged lines, which form the famous panda logo of the World Wild Fund For Nature (WWF) when seen from a distance. If one is too close to the artwork, it is difficult to spot the bear, however, if one steps back or takes off one's glasses the panda suddenly appears. This led us to ask if the ability to see the panda is related to the visual acuity of the observer and if therefore, the panda illusion can be used to assess the spatial resolution of the eye. Here we present the results of the comparison between visual acuity determined using the Landolt C and that predicted from the panda illusion in 23 healthy volunteers with artificially reduced visual acuity. Furthermore, we demonstrate that the panda illusion is based on a 2D pulse-width modulation, explain its technical history, and provide the equations required to create the illusion. Finally, we explain why the illusion indeed can be used to predict visual acuity and discuss the neural causes of its perception with best-corrected visual acuity.
There is evidence for a possible link between myopia development and near vision. We investigated the effect of prolonged nearwork on ciliary muscle (CM) morphology and accommodation in 18 myopic and ...17 emmetropic subjects (age 19 to 25). The CM was imaged during far (0.25 D) and near vision (4 D) using optical coherence tomography (OCT), and accommodation to a step pulse (0.25 D - 4 D - 0.25 D, 15 s each) was assessed by eccentric infrared photorefraction before and after a 30-min reading task at 25 cm. OCT images were analyzed using a custom-developed semi-automatic segmentation algorithm to determine CM thickness (CMT) profiles and selective CMT readings. Accommodation was assessed using a non-linear model. On average, the CM got thinner after nearwork, predominantly at 0.0–1.4 mm posterior to the scleral spur in emmetropes, and at 1.0–1.9 mm in myopes. Selective CMT readings confirmed a significant thinning after nearwork (univariate ANOVA F1,66 = 26.313, p < 0.001), without any influence of the subjects’ refractive state (F1,66 = 1.887, p = 0.174) or the target distance (F1,66 = 0.014, p = 0.907). The mean accommodation response for targets at infinity was significantly increased after nearwork (F1,32 = 7.775, p = 0.009), with a larger myopic shift in myopes (F1,32 = 11.310, p = 0.002). No change in velocity of accommodation was found. Sharing properties of striated muscles, the CM was expected to increase its thickness, but the opposite was found. Previous studies suggesting sustained nearwork to result in a CM spasm cannot be confirmed by the data presented here. Further research exploring the possible impact of sympathetic innervation is necessary as it is activated during intense nearwork.
•Combined AS-OCT and photorefraction were used to monitor ciliary muscle morphology.•Ciliary muscle unexpectedly thins during 30 min of continuous close reading (25 cm).•Muscle thins in emmetropes and myopes but latter show sustained lens power increase.•Currently no explanation for ciliary muscle thinning despite its sustained activity.
The aim of this study was to investigate the use of inexpensive and easy-to-use hydrogel "marble" electrodes for the recording of electrical potentials of the human visual cortex using visual evoked ...potentials (VEPs) as example. Top hat-shaped holders for the marble electrodes were developed with an electrode cap to acquire the signals. In 12 healthy volunteers, we compared the VEPs obtained with conventional gold-cup electrodes to those obtained with marble electrodes. Checkerboards of two check sizes-0.8° and 0.25°-were presented. Despite the higher impedance of the marble electrodes, the line noise could be completely removed by averaging 64 single traces, and VEPs could be recorded. Linear mixed-effect models using electrode type, stimulus, and recording duration revealed a statistically significant effect of the electrode type on only VEP N75 peak latency (mean ± SEM: 1.0 ± 1.2 ms) and amplitude (mean ± SEM: 0.8 ± 0.9 µV) The mean amplitudes of the delta, theta, alpha, beta, and gamma frequency bands of marble electrodes were statistically significantly different and, on average, 25% higher than those of gold-cup electrodes. However, the mean amplitudes showed a statistically significant strong correlation (Pearson's
= 0.8). We therefore demonstrate the potential of the inexpensive and efficient hydrogel electrode to replace conventional gold-cup electrodes for the recording of VEPs and possibly other recordings from the human cortex.
Purpose
To investigate the applicability of liquid crystal displays (LCD) as suitable replacement for cathode ray tube monitors (CRT) as stimulator for the sweep VEP for estimating visual acuity.
...Methods
In a first experiment, sweep VEPs were recorded in 13 healthy volunteers with best-corrected visual acuity with an LCD and a CRT monitor, respectively. Time-to-peak after stimulus and peak-to-trough amplitudes as well as the visual acuity, estimated using a second-order polynomial and the modified Ricker model, were compared between both monitor types. In a second experiment, sweep VEPs were recorded in six healthy volunteers with two levels of stimulus contrast using artificially reduced visual acuities as well as best-corrected with the same monitors as in the first experiment and additionally, a modern LCD gaming monitor with a response time of 1 ms. Time-to-peak after stimulus and peak-to-trough amplitudes were compared between the different combinations of monitors and contrasts. Finally, visual acuities estimated using the modified Ricker model were compared to subjective visual acuities determined using the Freiburg Visual Acuity and Contrast Test (FrACT).
Results
In the first experiment, the time-to-peak after stimulus presentation was statistically significantly delayed for LCD displays (mean difference confidence interval: 60.0 54.0, 65.9 ms;
t
(516) = 19.7096,
p
< 0.0001). Likewise, peak-to-trough amplitudes were statistically significantly smaller for the LCD stimulator, however, not clinically relevant (mean difference confidence interval: − 0.89 – 1.59, − 0.20 µV;
t
(516) = − 2.5351,
p
= 0.0115). No statistically significant effect of the monitor type on the estimated visual acuity was found for neither method, second-order polynomial, nor the modified Ricker model. In the second experiment, statistically significant delays of the time-to-peak after stimulus onset were found for all combinations of monitor and contrast compared to the CRT monitor. A statistically significant, but not clinically relevant, difference of the peak-to-trough amplitudes was only found between the CRT monitor and the LCD gaming monitor (mean difference confidence interval: 2.6 1.2, 4.0 µV;
t
(814) = 4.66,
p
< 0.0001). Visual acuities estimated from LCD stimulation significantly underestimated the subjective visual acuity up to 0.2 logMAR using the conversion formula of the first experiment. No statistically significant difference was found when using conversion formulas adjusted for each combination of monitor and contrast.
Conclusions
Based on the results of this study, LCD monitors may substitute CRT monitors for presenting the stimuli for the sweep VEP to objectively estimate visual acuity. Nevertheless, it is advisable to perform a calibration and to collect normative data of healthy volunteers using best-corrected and artificially reduced visual acuity for establishing a conversion formula between sweep VEP outcome and the subjective visual acuity before replacing a CRT with an LCD stimulator.
Standards in Pupillography Kelbsch, Carina; Strasser, Torsten; Chen, Yanjun ...
Frontiers in neurology,
02/2019, Letnik:
10
Journal Article
Recenzirano
Odprti dostop
The number of research groups studying the pupil is increasing, as is the number of publications. Consequently, new standards in pupillography are needed to formalize the methodology including ...recording conditions, stimulus characteristics, as well as suitable parameters of evaluation. Since the description of intrinsically photosensitive retinal ganglion cells (ipRGCs) there has been an increased interest and broader application of pupillography in ophthalmology as well as other fields including psychology and chronobiology. Color pupillography plays an important role not only in research but also in clinical observational and therapy studies like gene therapy of hereditary retinal degenerations and psychopathology. Stimuli can vary in size, brightness, duration, and wavelength. Stimulus paradigms determine whether rhodopsin-driven rod responses, opsin-driven cone responses, or melanopsin-driven ipRGC responses are primarily elicited. Background illumination, adaptation state, and instruction for the participants will furthermore influence the results. This standard recommends a minimum set of variables to be used for pupillography and specified in the publication methodologies. Initiated at the 32nd International Pupil Colloquium 2017 in Morges, Switzerland, the aim of this manuscript is to outline standards in pupillography based on current knowledge and experience of pupil experts in order to achieve greater comparability of pupillographic studies. Such standards will particularly facilitate the proper application of pupillography by researchers new to the field. First we describe general standards, followed by specific suggestions concerning the demands of different targets of pupil research: the afferent and efferent reflex arc, pharmacology, psychology, sleepiness-related research and animal studies.
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