Analysis of Experimental IOP-Induced Scleral Deformations at the Sub-Micrometer Scale Using Electronic Speckle Interferometry

2011 ◽  
Author(s):  
Massimo A. Fazio ◽  
Luigi Bruno ◽  
Rafael Grytz ◽  
J. Crawford Downs
Keyword(s):  
Visual Information ◽  
Computational Models ◽  
Speckle Interferometry ◽  
Posterior Pole ◽  
Retinal Ganglion ◽  
Electronic Speckle Interferometry ◽  
Ocular Biomechanics ◽  
Pass Through ◽  
Scleral Shell ◽  
Micrometer Scale

The retinal ganglion cell axons carry visual information, and pass through the optic nerve head (ONH) as they traverse from inside the eye to the brain. The ONH is the site of axonal damage in glaucoma, the second leading cause of blindness in the world, and ONH biomechanics is hypothesized to play a crucial role in the development and progression of the disease. The load bearing tissues of the ONH insert into the surrounding sclera, which provides the boundary conditions for this important structure. It is therefore important to develop accurate experimental techniques to measure scleral shell deformations under intraocular pressure (IOP) loading that can be used to drive constitutive and computational models of scleral biomechanics. The overall goal of this project is to better understand the role of ocular biomechanics in the development of glaucoma by constructing eye-specific finite element models of the posterior pole and ONH.

Biomechanics of the Posterior Pole During the Remodeling Progression From Normal to Early Experimental Glaucoma

2009 ◽  
Author(s):  
Ian A. Sigal ◽  
Hongli Yang ◽  
Michael D. Roberts ◽  
Claude F. Burgoyne ◽  
J. Crawford Downs
Keyword(s):  
Visual Information ◽  
Lamina Cribrosa ◽  
Posterior Pole ◽  
Glaucomatous Optic Neuropathy ◽  
Retinal Ganglion ◽  
Experimental Glaucoma ◽  
Pass Through ◽  
Mechanical Insult ◽  
The Brain ◽  
Connective Tissue Structure

Glaucoma is one of the leading causes of blindness worldwide. The loss of vision associated with glaucoma is due to damage to the retinal ganglion cell axons, which transmit visual information to the brain. Damage to these axons is believed to occur as the axons pass through the lamina cribrosa (LC), a connective tissue structure in the optic nerve head at the back of the eye. Elevated intraocular pressure (IOP) has been identified as the main risk factor for the development of the neuropathy, but the mechanism(s) by which a mechanical insult (elevated IOP) is translated into a biological effect (glaucomatous optic neuropathy) is not well understood.

scholarly journals Linkage between retinal ganglion cell density and the nonuniform spatial integration across the visual field

2019 ◽  
Vol 116 (9) ◽  
pp. 3827-3836 ◽  
Author(s):  
MiYoung Kwon ◽  
Rong Liu
Keyword(s):  
Object Recognition ◽  
Visual Field ◽  
Ganglion Cell ◽  
Cell Density ◽  
Visual Information ◽  
Computational Models ◽  
Target Location ◽  
Fixed Number ◽  
Retinal Ganglion ◽  
Spatial Integration

The ability to integrate visual information over space is a fundamental component of human pattern vision. Regardless of whether it is for detecting luminance contrast or for recognizing objects in a cluttered scene, the position of the target in the visual field governs the size of a window within which visual information is integrated. Here we analyze the relationship between the topographic distribution of ganglion cell density and the nonuniform spatial integration across the visual field. The extent of spatial integration for luminance detection (Ricco’s area) and object recognition (crowding zone) are measured at various target locations. The number of retinal ganglion cells (RGCs) underlying Ricco’s area or crowding zone is estimated by computing the product of Ricco’s area (or crowding zone) and RGC density for a given target location. We find a quantitative agreement between the behavioral data and the RGC density: The variation in the sampling density of RGCs across the human retina is closely matched to the variation in the extent of spatial integration required for either luminance detection or object recognition. Our empirical data combined with the simulation results of computational models suggest that a fixed number of RGCs subserves spatial integration of visual input, independent of the visual-field location.

Microstructure Motivated Growth and Remodeling of the Lamina Cribrosa in Early Glaucoma

2011 ◽  
Author(s):  
Rafael Grytz ◽  
Ian A. Sigal ◽  
Jeffrey W. Ruberti ◽  
J. Crawford Downs
Keyword(s):  
Connective Tissue ◽  
Structural Changes ◽  
Lamina Cribrosa ◽  
Posterior Pole ◽  
Retinal Ganglion ◽  
Experimental Glaucoma ◽  
Relevant Risk Factor ◽  
Orbital Space ◽  
Iop Elevation ◽  
Pass Through

Glaucoma is a leading cause of blindness in the world and is due to the loss of retinal ganglion cell axons. These axons deteriorate in a region in the posterior pole of the eye known as the optic nerve head (ONH). The axons pass through the lamina cribrosa (LC) as they exit the eye at the ONH. The LC is characterized by a porous, connective tissue structure composed of laminar beams. The function of the LC is unclear, but is believed to include providing mechanical support to the axons as they transition from inside the pressurized globe to the lower pressure orbital space. Early experimental glaucoma studies have shown that the LC remodels into a thicker, more posterior structure which incorporates more connective tissue after chronic IOP elevation [1,2]. The process by which this occurs is unknown. These structural changes are assumed to play an important role in the pathophysiology of the ocular disease glaucoma, where elevated IOP is known to be the most relevant risk factor.

Determining Heterogeneity in the Scleral Shell Using an Inverse Mechanics Approach

2013 ◽  
Author(s):  
Avinash Ayyalasomayajula ◽  
Jonathan Vande Geest
Keyword(s):  
Race And Ethnicity ◽  
Visual Information ◽  
Primary Open Angle Glaucoma ◽  
Ganglion Cells ◽  
Open Angle Glaucoma ◽  
Retinal Ganglion ◽  
Ocular Tissues ◽  
The Us ◽  
Elevated Intraocular Pressure ◽  
Scleral Shell

One of the important events leading to loss of vision in primary open-angle glaucoma — the 2 nd leading cause of blindness in the US [1] — is the death of retinal ganglion cells. Previous research has established a strong correlation between elevated intraocular pressure (IOP) and the incidence of glaucoma [2]. Stiffening of ocular tissues (like sclera) and axonal damage in the optic nerve head (ONH) were found to occur in response to elevated IOPs [3, 4]. As such, the biomechanical environment in and around the ONH, which is surrounded by the sclera and through which the visual information exits the eye, could be important in the incidence of this disease. Additionally, race and ethnicity factors were found to affect the incidence of glaucoma [5].

scholarly journals The Neurophysiology of Backward Visual Masking: Information Analysis

1999 ◽  
Vol 11 (3) ◽  
pp. 300-311 ◽  
Author(s):  
Edmund T. Rolls ◽  
Martin J. Tovée ◽  
Stefano Panzeri
Keyword(s):  
Visual Processing ◽  
Visual Information ◽  
Computational Models ◽  
Direct Evidence ◽  
Visual Masking ◽  
Neuronal Response ◽  
Short Soas ◽  
Stimulus Onset ◽  
Backward Masking ◽  
Neuronal Responses

Backward masking can potentially provide evidence of the time needed for visual processing, a fundamental constraint that must be incorporated into computational models of vision. Although backward masking has been extensively used psychophysically, there is little direct evidence for the effects of visual masking on neuronal responses. To investigate the effects of a backward masking paradigm on the responses of neurons in the temporal visual cortex, we have shown that the response of the neurons is interrupted by the mask. Under conditions when humans can just identify the stimulus, with stimulus onset asynchronies (SOA) of 20 msec, neurons in macaques respond to their best stimulus for approximately 30 msec. We now quantify the information that is available from the responses of single neurons under backward masking conditions when two to six faces were shown. We show that the information available is greatly decreased as the mask is brought closer to the stimulus. The decrease is more marked than the decrease in firing rate because it is the selective part of the firing that is especially attenuated by the mask, not the spontaneous firing, and also because the neuronal response is more variable at short SOAs. However, even at the shortest SOA of 20 msec, the information available is on average 0.1 bits. This compares to 0.3 bits with only the 16-msec target stimulus shown and a typical value for such neurons of 0.4 to 0.5 bits with a 500-msec stimulus. The results thus show that considerable information is available from neuronal responses even under backward masking conditions that allow the neurons to have their main response in 30 msec. This provides evidence for how rapid the processing of visual information is in a cortical area and provides a fundamental constraint for understanding how cortical information processing operates.

Memoirs: On the Intracellular Micro-organisms of some Bostrychild Beetles

1934 ◽  
Vol s2-77 (306) ◽  
pp. 243-253
Author(s):  
K. MANSOUR
Keyword(s):  
Alimentary Tract ◽  
Posterior Pole ◽  
Bursa Copulatrix ◽  
Final Destination ◽  
Rhizopertha Dominica ◽  
Pass Through ◽  
Micro Organisms ◽  
Biological Relation

1. Rhizopertha dominica, F., Sinoxylon ceratoniae, L., and Bostrychoplites Zickeli, Mars., possess paired mycetomes full of bacteria-like micro-organisms. 2. The transmission of the micro-organisms from one generation of the host to the next is carried out in the following way: (a) Micro-organisms from the mycetomes invade the testis lobes, multiply, and mix with the sperms. (b) These micro-organisms pass with the sperms during copulation into the bursa copulatrix of the female. (c) From this region they pass through the micropyle of the fully formed eggs during their passage to the outside, and thus the infection is accomplished. 3. The invasion of the testis lobes by micro-organisms causes abnormality in the process of spermatogenesis. 4. The micro-organisms in the developing egg are first seen near the micropylar region in the peripheral protoplasm. In a later stage these micro-organisms, which have multiplied greatly by then, are to be found in between the yolk globules towards the posterior pole of the egg. From this stage onwards the course these micro-organisms follow till they reach their final destination in the larva has not been followed. 5. The mycetomes throughout life remain quite isolated from the alimentary tract. 6. The biological relation between the micro-organisms and their host is also discussed.

scholarly journals Interspike Interval Based Filtering of Directional Selective Retinal Ganglion Cells Spike Trains

2012 ◽  
Vol 2012 ◽  
pp. 1-17 ◽  
Author(s):  
Aurel Vasile Martiniuc ◽  
Alois Knoll
Keyword(s):  
Retinal Ganglion Cells ◽  
Visual Stimulus ◽  
Visual Information ◽  
Ganglion Cells ◽  
Neuronal Response ◽  
Spike Trains ◽  
Retinal Ganglion ◽  
Stimulus Motion ◽  
Information Rates ◽  
Grating Bars

The information regarding visual stimulus is encoded in spike trains at the output of retina by retinal ganglion cells (RGCs). Among these, the directional selective cells (DSRGC) are signaling the direction of stimulus motion. DSRGCs' spike trains show accentuated periods of short interspike intervals (ISIs) framed by periods of isolated spikes. Here we use two types of visual stimulus, white noise and drifting bars, and show that short ISI spikes of DSRGCs spike trains are more often correlated to their preferred stimulus feature (that is, the direction of stimulus motion) and carry more information than longer ISI spikes. Firstly, our results show that correlation between stimulus and recorded neuronal response is best at short ISI spiking activity and decrease as ISI becomes larger. We then used grating bars stimulus and found that as ISI becomes shorter the directional selectivity is better and information rates are higher. Interestingly, for the less encountered type of DSRGC, known as ON-DSRGC, short ISI distribution and information rates revealed consistent differences when compared with the other directional selective cell type, the ON-OFF DSRGC. However, these findings suggest that ISI-based temporal filtering integrates a mechanism for visual information processing at the output of retina toward higher stages within early visual system.

scholarly journals A method for single-neuron chronic recording from the retina in awake mice

Science ◽  
2018 ◽  
Vol 360 (6396) ◽  
pp. 1447-1451 ◽  
Author(s):  
Guosong Hong ◽  
Tian-Ming Fu ◽  
Mu Qiao ◽  
Robert D. Viveros ◽  
Xiao Yang ◽  
...  
Keyword(s):  
Retinal Ganglion Cells ◽  
Visual Information ◽  
Single Neuron ◽  
Ganglion Cells ◽  
Ex Vivo ◽  
Neural Circuitry ◽  
Retinal Ganglion ◽  
Chronic Recording ◽  
The Brain

The retina, which processes visual information and sends it to the brain, is an excellent model for studying neural circuitry. It has been probed extensively ex vivo but has been refractory to chronic in vivo electrophysiology. We report a nonsurgical method to achieve chronically stable in vivo recordings from single retinal ganglion cells (RGCs) in awake mice. We developed a noncoaxial intravitreal injection scheme in which injected mesh electronics unrolls inside the eye and conformally coats the highly curved retina without compromising normal eye functions. The method allows 16-channel recordings from multiple types of RGCs with stable responses to visual stimuli for at least 2 weeks, and reveals circadian rhythms in RGC responses over multiple day/night cycles.

scholarly journals Oscillatory Dynamics of Perceptual to Conceptual Transformations in the Ventral Visual Pathway

2018 ◽  
Vol 30 (11) ◽  
pp. 1590-1605 ◽  
Author(s):  
Alex Clarke ◽  
Barry J. Devereux ◽  
Lorraine K. Tyler
Keyword(s):  
Visual Information ◽  
Computational Models ◽  
Semantic Information ◽  
Low Frequency ◽  
Visual Pathway ◽  
Semantic Representations ◽  
Low Level ◽  
Oscillatory Dynamics ◽  
Incremental Model ◽  
Ventral Visual Pathway

Object recognition requires dynamic transformations of low-level visual inputs to complex semantic representations. Although this process depends on the ventral visual pathway, we lack an incremental account from low-level inputs to semantic representations and the mechanistic details of these dynamics. Here we combine computational models of vision with semantics and test the output of the incremental model against patterns of neural oscillations recorded with magnetoencephalography in humans. Representational similarity analysis showed visual information was represented in low-frequency activity throughout the ventral visual pathway, and semantic information was represented in theta activity. Furthermore, directed connectivity showed visual information travels through feedforward connections, whereas visual information is transformed into semantic representations through feedforward and feedback activity, centered on the anterior temporal lobe. Our research highlights that the complex transformations between visual and semantic information is driven by feedforward and recurrent dynamics resulting in object-specific semantics.

The Biomechanical Response of Normal and Glaucoma Human Sclera

2010 ◽  
Author(s):  
Baptiste Coudrillier ◽  
Kristin M. Myers ◽  
Thao D. Nguyen
Keyword(s):  
Retinal Ganglion Cells ◽  
Material Properties ◽  
Visual Information ◽  
Ganglion Cells ◽  
Retinal Ganglion ◽  
Progressive Degeneration ◽  
Biomechanical Response ◽  
Elevated Intraocular Pressure ◽  
The Relationship ◽  
The Brain

By 2010, 60 million people will have glaucoma, the second leading cause of blindness worldwide [1]. The disease is characterized by a progressive degeneration of the retinal ganglion cells (RGC), a type of neuron that transmits visual information to the brain. It is well know that elevated intraocular pressure (IOP) is a risk factor in the damage to the RGCs [3–5], but the relationship between the mechanical properties of the ocular connective tissue and how it affects cellular function is not well characterized. The cornea and the sclera are collage-rich structures that comprise the outer load-bearing shell of the eye. Their preferentially aligned collagen lamellae provide mechanical strength to resist ocular expansion. Previous uniaxial tension studies suggest that altered viscoelastic material properties of the eye wall play a role in glaucomatous damage [6].

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