Showing papers on "Night vision published in 2011"

Vision and Visual Navigation in Nocturnal Insects

Abstract: With their highly sensitive visual systems, nocturnal insects have evolved a remarkable capacity to discriminate colors, orient themselves using faint celestial cues, fly unimpeded through a complicated habitat, and navigate to and from a nest using learned visual landmarks. Even though the compound eyes of nocturnal insects are significantly more sensitive to light than those of their closely related diurnal relatives, their photoreceptors absorb photons at very low rates in dim light, even during demanding nocturnal visual tasks. To explain this apparent paradox, it is hypothesized that the necessary bridge between retinal signaling and visual behavior is a neural strategy of spatial and temporal summation at a higher level in the visual system. Exactly where in the visual system this summation takes place, and the nature of the neural circuitry that is involved, is currently unknown but provides a promising avenue for future research.

Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology

Abstract: Variation in daily activity patterns facilitates temporal partitioning of habitat and resources among species. Knowledge of temporal niche partitioning in paleobiological systems has been limited by the difficulty of obtaining reliable information about activity patterns from fossils. On the basis of an analysis of scleral ring and orbit morphology in 33 archosaurs, including dinosaurs and pterosaurs, we show that the eyes of Mesozoic archosaurs were adapted to all major types of diel activity (that is, nocturnal, diurnal, and cathemeral) and provide concrete evidence of temporal niche partitioning in the Mesozoic. Similar to extant amniotes, flyers were predominantly diurnal; terrestrial predators, at least partially, nocturnal; and large herbivores, cathemeral. These similarities suggest that ecology drives the evolution of diel activity patterns.

Bundling night vision and other driver assistance systems (das) using near infra red (nir) illumination and a rolling shutter

Abstract: A system mountable in a motor vehicle. The system includes a camera and a processor configured to receive image data from the camera. The camera includes a rolling shutter configured to capture the image data during a frame period and to scan and to read the image data into multiple image frames. A near infra-red illuminator may be configured to provide a near infra-red illumination cone in the field of view of the camera. The near infrared illumination oscillates with an illumination period. A synchronization mechanism may be configured to synchronize the illumination period to the frame period of the rolling shutter. The frame period may be selected so that the synchronization mechanism provides a spatial profile of the near infra-red illumination cone which may be substantially aligned vertically to a specific region, e.g. near the center of the image frame.

Effects of common anesthetics on eye movement and electroretinogram

Abstract: High-resolution magnetic resonance imaging (MRI) provides non-invasive images of retinal anatomy, physiology, and function with depth-resolved laminar resolution. Eye movement and drift, however, could limit high spatial resolution imaging, and anesthetics that minimize eye movement could significantly attenuate retinal function. The aim of this study was to determine the optimal anesthetic preparations to minimize eye movement and maximize visual-evoked retinal response in rats. Eye movements were examined by imaging of the cornea with a charge-coupled device (CCD) camera under isoflurane, urethane, ketamine/xylazine, and propofol anesthesia at typical dosages in rats. Combination of the paralytic pancuronium bromide with isoflurane or ketamine/xylazine anesthesia was also examined for the eye movement studies. Visual-evoked retinal responses were evaluated using full-field electroretinography (ERG) under isoflurane, ketamine/xylazine, urethane, and ketamine/xylazine + pancuronium anesthesia in rats. The degree of eye movement, measured as displacement per unit time, was the smallest under 1% isoflurane + pancuronium anesthesia. The ketamine/xylazine groups showed larger dark-adapted ERG a- and b-waves than other anesthetics tested. The isoflurane group showed the shortest b-wave implicit times. Photopic ERGs in the ketamine/xylazine groups showed the largest b-waves with the isoflurane group showing slightly shorter implicit times at the higher flash intensities. Oscillatory potentials revealed an early peak in the isoflurane group compared with ketamine/xylazine and urethane groups. Pancuronium did not affect the a- and b-wave, but did increase oscillatory potential amplitudes. Compared with the other anesthetics tested here, ketamine/xylazine + pancuronium was the best combination to minimize eye movement and maximize retinal function. These findings should set the stage for further development and application of high-resolution functional imaging techniques, such as MRI, to study retinal anatomy, physiology, and function in anesthetized rats.

PbSe nanocrystal-based infrared-to-visible up-conversion device.

Abstract: Low-cost hybrid up-conversion devices with infrared sensitivity to 1.5 μm were obtained by integrating a colloidal PbSe nanocrystal near-infrared sensitizing layer on a green phosphorescent organic light emitting diode. A ZnO nanocrystal hole blocking layer is incorporated in the devices for keeping the device off in the absence of IR excitation. The maximum photon (1.3 μm)-to-photon (0.52 μm) conversion efficiency is 1.3%. The extension (until 1.5 μm) of the near-infrared wavelengths, which can be converted to visible light, may be able to improve night vision.

The Phenotype of Severe Early Childhood Onset Retinal Dystrophy (SECORD) from Mutation of RPE65 and Differentiation from Leber Congenital Amaurosis

Abstract: PURPOSE. To describe in detail the characteristic clinical phenotype and electrophysiological features of Severe Early Childhood Onset Retinal Dystrophy (SECORD) caused by mutation of RPE65. METHODS. Ophthalmological examination, color fundus photography, visual field testing, detailed electrophysiological assessment, and screening of RPE65 were undertaken in five subjects. Selected patients also had spectral domain optical coherence tomography. RESULTS. All five patients had life-long, extremely poor night vision. Variable degrees of nystagmus were present; three cases lacked nystagmus at the time of assessment. Bilateral disc drusen were evident in three subjects. While case 1 had an undetectable electroretinogram and features supporting a diagnosis of Leber congential amaurosis (LCA) as an infant, her level of acuity and function into the second decade of life was more consistent with SECORD. In two cases, both vision and electrophysiological responses were seen to improve into the second decade of life. The objective demonstration of improved retinal function over time, with electrophysiological testing, has not been previously reported. Cases 4 and 5 had evidence of fine white retinal dots. The authors propose that these represent abnormal accumulations of retinyl esters, as has been demonstrated in animal models, and has also been observed as lipid droplets within the retinal pigment epithelium (RPE). These white dots were seen to fade with time in the patients and were replaced by RPE changes. CONCLUSIONS. The identification of patients with mutations in RPE65 has attained greater significance now that gene replacement trials have begun. The features presented in this article assist in the recognition of this form of LCA/SECORD. (Invest Ophthalmol Vis Sci. 2011;52:292‐302) DOI:10.1167/iovs.106106

Choroidal involution is a key component of oxygen-induced retinopathy.

Abstract: Purpose Retinopathy of prematurity (ROP) is a major cause of visual handicap in the pediatric population. To date, this disorder is thought to stem from deficient retinal vascularization. Intriguingly, functional electrophysiological studies in patients with mild or moderate ROP and in the oxygen-induced retinopathy (OIR) model in rats reveal central photoreceptor disruption that overlies modest retinal vessel loss; a paucity of retinal vasculature occurs predominantly at the periphery. Given that choroidal circulation is the major source of oxygen and nutrients to the photoreceptors, the authors set out to investigate whether the choroidal vasculature system may be affected in OIR. Methods Rat models of OIR treating newborn animals with 80% or 50/10% alternated oxygen level for the first two postnatal weeks were used to mimic ROP in humans. Immunohistology staining and vascular corrosion casts were used to investigate the vessel layout of the eye. To investigate the effect of 15-deoxy-Δ12,14-PGJ(2) (15d-PGJ(2); a nonenzymatic product of prostaglandin D(2)) on endothelial cells, in vitro cell culture and ex vivo choroid explants were employed and intravitreal injections were performed in animals. Results The authors herein demonstrate that deficient vascularity occurs not only in the retinal plexus but also in the choroid. This sustained, marked choroidal degeneration is specifically confined to central regions of the retina that present persistent photoreceptor loss and corresponding functional deficits. Moreover, the authors show that 15d-PGJ(2) is a prominent contributor to this choroidal decay. Conclusions The authors demonstrate for the first time pronounced, sustained choroidal vascular involution during the development of ROP. Findings also suggest that effective therapeutic strategies to counter ROP should consider choroidal preservation.

G-Protein βγ-Complex Is Crucial for Efficient Signal Amplification in Vision

Abstract: A fundamental question of cell signaling biology is how faint external signals produce robust physiological responses. One universal mechanism relies on signal amplification via intracellular cascades mediated by heterotrimeric G-proteins. This high amplification system allows retinal rod photoreceptors to detect single photons of light. Although much is now known about the role of the α-subunit of the rod-specific G-protein transducin in phototransduction, the physiological function of the auxiliary βγ-complex in this process remains a mystery. Here, we show that elimination of the transducin γ-subunit drastically reduces signal amplification in intact mouse rods. The consequence is a striking decline in rod visual sensitivity and severe impairment of nocturnal vision. Our findings demonstrate that transducin βγ-complex controls signal amplification of the rod phototransduction cascade and is critical for the ability of rod photoreceptors to function in low light conditions.

True color night vision (TCNV) fusion

Abstract: True color images are produced by combining data collected from one or more color cameras with data collected from one or more infrared cameras. The produced images are the result of combining portions of the visible light data with portions of the infrared light data that may have been captured at dark, at daytime or at low light level conditions. These images appear as normal color images, with infrared information highlighted in a non-distracting fashion. The true color images that are produced in this fashion can also facilitate identification and reproduction of various objects that may not be visible or readily identifiable in infrared or false color imagery.

Imaging devices having arrays of image sensors and lenses with multiple aperture sizes

Abstract: An array camera may be formed from an array of lenses, an array of corresponding apertures, and an array of corresponding image sensors. The array of apertures may be configured so that some image sensors receive light through apertures of different size than other image sensors. Providing apertures of smaller size increases the F/# of an array camera and increases the depth-of-field in a captured image. The array of image sensors may include a near-infrared image sensor. Providing an image sensor array with a near-infrared image sensor may enhance depth information in captured images or increase night vision capabilities of an array camera. Combining an array of image sensors that includes a near-infrared sensor with an array of apertures having different aperture diameters may allow increased depth-of-field imaging, enhanced extraction of depth information from an image, improved night vision, enhanced image clarity or other improvements.

Visual threshold is set by linear and nonlinear mechanisms in the retina that mitigate noise: how neural circuits in the retina improve the signal-to-noise ratio of the single-photon response.

Abstract: In sensory biology, a major outstanding question is how sensory receptor cells minimize noise while maximizing signal to set the detection threshold. This optimization could be problematic because the origin of both the signals and the limiting noise in most sensory systems is believed to lie in stimulus transduction. Signal processing in receptor cells can improve the signal-to-noise ratio. However, neural circuits can further optimize the detection threshold by pooling signals from sensory receptor cells and processing them using a combination of linear and nonlinear filtering mechanisms. In the visual system, noise limiting light detection has been assumed to arise from stimulus transduction in rod photoreceptors. In this context, the evolutionary optimization of the signal-to-noise ratio in the retina has proven critical in allowing visual sensitivity to approach the limits set by the quantal nature of light. Here, we discuss how noise in the mammalian retina is mitigated to allow for highly sensitive night vision.

Night Vision Pedestrian Detection Using a Forward-Looking Infrared Camera

Abstract: Conference Name:2011 International Workshop on Multi-Platform/Multi-Sensor Remote Sensing and Mapping, M2RSM 2011. Conference Address: Xiamen, China. Time:January 10, 2011 - January 12, 2011.

Residual electroretinograms in young Leber congenital amaurosis patients with mutations of AIPL1.

Abstract: Leber congenital amaurosis (LCA) is a severe congenital or early-onset inherited retinal dystrophy that classically presents with searching nystagmus, absence of normal pupil responses, flat electroretinograms (ERGs), minimal, if any, vision beyond infancy, and an initially normal fundus appearance, followed by the development of pigmentary changes over time. The term LCA has traditionally been used when these features present within the first 6 months of life, whereas a variety of terms such as juvenile retinitis pigmentosa,1 early childhood onset retinitis pigmentosa,2 or severe early childhood onset retinal dystrophy (SECORD)3 have been used to describe milder forms of the disease that present after 1 year. LCA and SECORD are genetically extremely heterogeneous, and are caused by >16 genes (AIPL1, CEP290, CRX, CRB1, GUCY2D, IMPDH1, IQCB1, LCA5, LRAT, MERTK, RD3, RDH12, RPGRIP1, RPE65, SPATA7, and TULP1). All except CRX and IMPDH1 exhibit autosomal recessive inheritance in which some de novo mutations result in an autosomal dominant trait.3–5 The gene AIPL1 encodes aryl hydrocarbon receptor interacting protein-like 1 (AIPL1), a 384-amino acid protein with three tetratricopeptide repeat motifs. AIPL1 has been suggested to play a role in photoreceptor development6 and protein farnesylation7 and as a chaperone for NUB1, Hsp70, Hsp90, and photoreceptor-specific phosphodiesterases (PDE6β).8–12 Although AIPL1 was initially thought to be expressed only in adult rod photoreceptors,13 its expression in adult rodent cones has now been demonstrated.14 Mutations in AIPL1 are estimated to account for approximately 5% to 10% of all cases of LCA.4,15 Patients usually have severe vision loss (ranging from 20/200 to LP), but milder forms that would fit the definition of a later onset rod-cone dystrophy have also been reported.2,16–19 Other typical features include poorly responsive pupils, nystagmus, hyperopia, and unrecordable ERGs. The fundus appearance in patients with AIPL1 mutations can appear normal early in the disease, but most patients eventually demonstrate a pigmentary retinopathy with a high prevalence of macular atrophy. One series demonstrated that cataracts and keratoconus were common in those with homozygous AIPL1 mutations.18 Spectral domain-optical coherence tomography (SD-OCT) has shown severe loss of outer retinal thickness in the macula, lamellar disorganization, and increased inner retinal thickness.16 Successful gene replacement therapy in AIPL1-deficient mouse models has raised the hope that such methods could be translated for human treatment.20,21 However, Jacobson et al.16 recently studied the feasibility of treatment in a series of patients with AIPL1 mutations and concluded that the severe photoreceptor degeneration seen might mean they were not good candidates for gene replacement therapy unless and that evidence would be needed in much younger patients of some photoreceptor preservation. We herein report three young patients with mutations in AIPL1 who presented with the clinical features of LCA but had residual electroretinograms characterized by slow insensitive scotopic responses and absent photopic responses. The presence of these residual ERG responses potentially indicated greater photoreceptor preservation than seen in older patients and suggested that these patients might be better candidates for gene replacement therapy than previously considered.

From optics to attention: visual perception in barn owls.

Abstract: Barn owls are nocturnal predators which have evolved specific sensory and morphological adaptations to a life in dim light. Here, some of the most fundamental properties of spatial vision in barn owls are reviewed. The eye with its tubular shape is rigidly integrated in the skull so that eye movements are very much restricted. The eyes are oriented frontally, allowing for a large binocular overlap. Accommodation, but not pupil dilation, is coupled between the two eyes. The retina is rod dominated and lacks a visible fovea. Retinal ganglion cells form a marked region of highest density that extends to a horizontally oriented visual streak. Behavioural visual acuity and contrast sensitivity are poor, although the optical quality of the ocular media is excellent. A low f-number allows high image quality at low light levels. Vernier acuity was found to be a hyperacute percept. Owls have global stereopsis with hyperacute stereo acuity thresholds. Neurons of the visual Wulst are sensitive to binocular disparities. Orientation based saliency was demonstrated in a visual-search experiment, and higher cognitive abilities were shown when the owl's were able to use illusory contours for object discrimination.

An illumination invariant and robust apparatus and method for detecting and recognizing various traffic signs

Abstract: The present application provides a robust, illumination invariant apparatus and method for detecting and recognizing various traffic signs. A robust method for detecting and recognizing the traffic signs using images captured by a digital color and night vision camera, the said method characterized in being illumination invariant comprising the processor implemented steps of: transforming RGB image into HSV color model and subsequently extracting desired color components by using color quantization; filtering the noise components in the HSV color model based on object symmetrical shape property; detecting edges of the objects and subsequently detecting the distinct objects in the noise components filtered image; classifying the shapes of the traffic signs based on sha pe of the determined distinct objects; and recognizing the classified shapes of the traffic signs by template matching. Further, the method provides the provision for warning the driver by use of the recognized data of the traffic signs.

Correspondence: Lighting for pedestrians: Is facial recognition what matters?

Abstract: The lighting of residential streets and public spaces is crucial to public safety of pedestrians after dark. One important objective of safety needs is facial recognition at a distance. The authors state that studies in the past have not truly measured illumination required for facial recognition due to the methodology used to conduct them. The authors suggest improved methodology that would more reliably measure the ability to recognize a target's facial expression, as well as gender, age and race, from a distance, in order to make more informed decisions about personal safety. The authors hope that this new approach will lead to a better understanding of how lighting could be used to enhance safety on the streets.

Human scotopic dark adaptation: Comparison of recoveries of psychophysical threshold and ERG b-wave sensitivity.

Abstract: We have compared the time course of dark adaptation of the human scotopic visual system, measured psychophysically and from the b-wave of the electroretinogram (ERG), for bleaches ranging from a few percent to near total. We also measured light adaptation, in order to apply a "Crawford transformation" to convert the raw measurements of dark adaptation into equivalent background intensities. For both the "psychophysical threshold equivalent" intensity and the "ERG b-wave sensitivity equivalent" intensity, the equivalent background declined over much of its range with an "S2" component, though with somewhat different slopes of -0.36 (psychophysical) and -0.22 (ERG) log(10) unit min(-1), respectively. In addition, the magnitude of the equivalent background was approximately 1 log(10) unit lower in the psychophysical experiments than in the ERG experiments. Despite these differences, the two approaches extract a common time course for the decline in level of free opsin following moderately large bleaches. We conclude that the recovery of psychophysical scotopic visual threshold over the S2 region reflects events that are present by the stage of the first synapse of rod vision, stemming ultimately from the presence of unregenerated opsin in the rod outer segments.

Ectopic expression of cone-specific G-protein-coupled receptor kinase GRK7 in zebrafish rods leads to lower photosensitivity and altered responses

Abstract: Non-technical summary When rod and cone photoreceptors in the eye respond to light, they need to recover, and the first step in recovery involves a protein called G-protein receptor kinase (GRK). Rods, which underlie night vision, employ a variant called GRK1, whereas cones, which mediate day vision, typically employ a variant called GRK7. We have engineered rod cells in the zebrafish retina that additionally express the cone variant, GRK7. By recording electrically from these modified rods, we have found that they are less sensitive to light than normal rods, in that regard mimicking cones. We have also found evidence to suggest that the size of the cell's response to a single photon (the smallest particle of light) is normal when recovery is mediated by GRK1, but is small (and hence somewhat cone-like) when mediated by GRK7. These results help us understand the differences between rod and cone photoreceptors.

Augmenting full colour-fused multi-band night vision imagery with synthetic imagery in real-time

Abstract: We present the design and first field trial results of an all-day all-weather enhanced and synthetic-fused multi-band colour night vision surveillance and observation system. The system augments a fused and dynamic three-band natural-colour night vision image with synthetic 3D imagery in real-time. The night vision sensor suite consists of three cameras, sensitive in, respectively, the visual (400–700 nm), the near-infrared (NIR, 700–1000 nm) and the long-wave infrared (LWIR, 8–14 mm) bands of the electromagnetic spectrum. The optical axes of the three cameras are aligned. Image quality of the fused sensor signals is enhanced in real-time through dynamic noise reduction, super resolution and local adaptive contrast enhancement. The quality of the LWIR image is enhanced through scene-based non-uniformity correction. The visual and NIR signals are used to represent the fused multi-band night vision image in natural daytime colours, using the Colour-the-Night colour remapping technique. Colour remapping can also be deployed to enhance the visibility of thermal targets that are camouflaged in the visual and NIR range of the spectrum. The dynamic false-colour night-time images are augmented with corresponding synthetic 3D scene views, generated in real-time using a geometric 3D scene model in combination with position and orientation information supplied by the Global Positioning System and inertial sensors of the system. Initial field trials show that this system provides enhanced situational information in various low-visibility conditions.

Age-related retinal function changes in albino and pigmented rats.

Abstract: PURPOSE: To investigate the effect of old age (3 vs. 18 months) on the retinal function of albino (Sprague-Dawley [SD]) and pigmented (Long-Evans [LE]) rats. METHODS: Electroretinograms (ERG) were recorded in both albino (SD; 3 months old n = 16, 18 months old n = 16) and pigmented (LE; 3 months n = 16, 18 months n = 5) rats. Data are analyzed for photoreceptor, ON-bipolar, and retinal ganglion cell (RCG) amplitudes as well as photoreceptor and ON-bipolar cell sensitivities. RESULTS: In the pigmented strain, senescence results in decreased photoreceptor output, but ON-bipolar and retinal ganglion cell amplitudes were preserved, due to a relative increase in ON-bipolar cell sensitivity. In the albino rats, although ageing decreased both photoreceptor and ON-bipolar cell amplitudes, increased photoreceptor sensitivity produced a relative sparing of retinal ganglion cell amplitude. CONCLUSIONS: Both strains show evidence of retinal plasticity with senescence, albeit at different retinal levels. The exact mechanisms underlying sensitivity changes require further investigation. Nevertheless, given the findings of previous human studies, pigmented rats appear to be a more appropriate model for human ageing. Future work using animals to study the effect of ageing need careful consideration in strain selection.

Quantitative evaluation of night vision and correlation of refractive and topographical parameters with glare after orthokeratology

Abstract: To evaluate night vision disturbance and investigate correlations between pre- and post-treatment parameters and glare scores in orthokeratology patients. Twenty-eight right eyes of 28 patients were enrolled in this study. Corneal topography and a night vision test (NVT) to evaluate the extent of glare were performed after orthokeratology. From the corneal topography, two indices [surface regularity index (SRI) and surface asymmetry index (SAI)] were calculated. Fourier analysis was performed on the topographic data from the central 6 mm, and data were decomposed into asymmetric and higher order components for analysis. There was no correlation between the glare score and pre-treatment keratometric value, pre-treatment cylinder, post-treatment sphere, and post-treatment cylinder. However, there was a statistically significant correlation between pre-treatment sphere and glare score (Pearson correlation coefficient, r = −0.54, p < 0.01). SRI and SAI significantly correlated with glare score (SRI: r = 0.52, p < 0.01, SAI: r = 0.41, p < 0.05). Higher order and asymmetric components were also significantly correlated with glare score (asymmetry: r = 0.61, p < 0.01, higher order: r = 0.67, p < 0.001). The glare score was significantly correlated with corneal irregularity, and appeared to be a beneficial parameter for assessment of night vision performance in patients receiving orthokeratology.

New applications with a SWIR imager employing long wavelengths

Abstract: SWIR imagers can operate at near room temperature with cut-off wavelengths that extended from 1.7μm (for InP lattice matched InGaAs) to beyond 2.0μm with strained InGaAs epitaxial growth on InP substrate. A leading application in the SWIR band - Night vision, requires very low dark current levels, whereas the dark current increases as the cutoff wavelength increases. We demonstrate imaging applications made possible by utilization of dark current reduction, and the physics of background and objects radiance. A newly built imager is presented.

Colorized night vision image brightness enhancement method applicable to automotive assisted driving system

Abstract: The invention provides a colorized night vision image brightness enhancement method applicable to an automotive assisted driving system The method comprises the following steps of: firstly, transforming a night vision colorized image from a red, green and blue (RGB) space to a luma and chroma (YUV) space to overcome the shortcoming of color distortion caused by direct processing of the night vision colorized image in the RGB space; then processing a brightness component image by using an S-curve correction Retinex algorithm so as to enhance the detail and the brightness of the image; enhancing the brightness component image by a selective nonlinear grey level mapping method and keeping good shadow information; and finally, performing weighed fusion on the two enhanced images by a weighed fusion method and inversely transforming the weighed fusion brightness component image and a UV component image to the RGB space for displaying The enhanced image acquired by the method keeps the necessary shadow information and has the detail and the brightness applicable to vision observation; and the night vision colorized image has a good enhancement effect

Post-receptoral contributions to the rat scotopic electroretinogram a-wave.

Abstract: The electroretinogram is a widely used objective measure of visual function. The best characterised feature of the full-field dark-adapted flash ERG, is the earliest corneal negativity, the a-wave, which primarily reflects photoreceptoral responses. However, recent studies in humans and primates show that there are post-receptoral contributions to the a-wave. It is not clear if such contributions exist in the rat a-wave. We consider this issue in the rat a-wave, using intravitreal application of pharmacological agents that isolate post-receptoral ON-pathways and OFF-pathways. In anaesthetised adult long Evans rats, we show that the ON-pathway (2-amino-4-phosphonobutyric acid, APB sensitive) makes negligible contribution to the a-wave. In contrast, CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) or PDA (cis-piperidine-2,3-dicarboxylic acid) sensitive mechanisms modify the a-wave in two ways. First, for bright luminous energies, OFF-pathway inhibition (CNQX or PDA) results in a 22% reduction to the early phase of the leading edge of the a-wave up to 14 ms. Second, OFF-pathway inhibition removed a corneal negativity that resides between the a-wave trough and the b-wave onset.