Visual Field Loss In Glaucoma

The primate visual system is usually separated in two partially independent pathways; the dorsal pathway subserves mostly motion perception, while the ventral one subserves object feature recognition. The primary visual cortex (V1) receives most of its retinal input through the lateral geniculate nucleus (LGN). Anatomical and functional segregation of visual perception starts at the level of the retina, where parvocellular (P) ganglion cells have small receptive fields and have sustained colour-sensitive synaptic response to light, whereas magnocellular (M) ganglion cells have larger receptive fields and a faster adapting achromatic response to light [Livingston et al., 1992]. Both types of cells project to the layers 3-6 and 1-2 of the LGN, respectively, which in turn send most of their outputs to layers 4Cβ and 4Cα of V1, forming what is known as the P and M pathways [Refs].

Fig. __ Feed-forward projections from the eyes to the brain and topographic mapping. In each eye the visual field on the left and right of the fovea (the cut goes right through the fovea!) projects to different cortical hemispheres: the ipsilateral retina projects to the ipsilateral visual cortex, and the contralateral retina crosses the contralateral cortex (hemifield crossing in the optic chiasma). The first synapse of the retinal ganglion cells is in the lateral geniculate nucleus (LGN), but information from the left (L) and right (R) eye remains strictly separated. The LGN consists of six layers, layers 1 and 2 are primarily occupied by the magnocellular pathway, and 3–6 by the parvocellular. Information from both eyes comes first together

According to current research there are about 800,000 ganglion cells in the human optic nerve (J.R. Anderson, 2009,pg. 35). The ganglion cells are where the first encoding of the visual information happens. Encoding is the process of recognizing the information and changing it into something one’s brains can understand and store. Each ganglion cell is dedicated to encoding information from a specific part of the retina. The optic nerve goes then to the visual cortex and the information enters the brain cells. There are two types of cells that are subcortical, or below the cortex; the lateral geniculate nucleus and the superior colliculus. The lateral geniculate nucleus is responsible for understanding details and recognizing objects. The superior colliculus is responsible for understanding where objects are located spatially. This collection of cells working together is called the “what-where” distinction. The division of labor continues, as the information is further processes. The “what” information travels to the temporal cortex, the “where” information travels to the parietal regions of the brain.

How does the progression of optic nerve and RGC damage translate to the clinical symptoms of glaucoma? In a study published by Harwerth and Quigley in 2006, the structure-function relationships of human glaucoma and experimental glaucoma in monkeys are compared, in order to discern a possible correlation between the progressive loss of visual field experienced by glaucoma patients and the gradual neural losses. Previous studies had suggested a large amount of variance between the well-defined relationship of experimental glaucoma and the slightly different system of clinical glaucoma, but the discrepancies could have equally resulted from different methods of data analysis, which would affect the precision of the results. The study compared

Glaucoma is an eye disorder that cause severe blindness. There are multiple types of Glaucoma however, they all have something to do with damage to the optic nerve (usually form high eye pressure) that sends and receives information to the brain form the eye. Glaucoma can be a very dangerous disease although it is no fatal but it can contribute to the failure of one of the bodies most important senses which is blindness. In most cases, glaucoma is correlated with high pressure inside the eye (ocular hypertension),but it also can occur when intraocular pressure (IOP) is normal. If left untreated glaucoma first causes peripheral vision loss and eventually leads to total blindness.

A review of this concept done by Alan Cowey and Petra Stoerig looks at blindsight from a different point of view by first looking at the retinal ganglion cells which receive the visual information from photoreceptors in the eye. They then looked at the particular retinal ganglion cells in a normal retina versus those in a subject with striate cortex damage. The major factors included the amount of degeneration in the retinal ganglion cells and how many remained. The ultimate conclusion came that although there was much degeneration in the cells occurred, there were still some that survived. So what happens with these remaining cells? To try and answer this question they take a look at the ganglion cells in monkeys and see if there is any possible connection from those to the visual cortex that could be causing the phenomenon of blindsight. Cowey and Stoerig discuss the idea of having some other pathways from the ganglion cells to other areas of the brain such as V4, despite the damage of the dLGN that is causing the response to

Glaucoma is several eye conditions that can damage to your optic nerve. Increased pressure in the eye can cause glaucoma, which leads to vision loss or blindness (Healthline). There are five different types of glaucoma, which are open-angle (chronic) glaucoma, angle-closure (acute) glaucoma, congenital glaucoma, secondary glaucoma, and normal-tension glaucoma (Healthline). Open-angle (chronic) glaucoma is the most common type of glaucoma, and there are no signs or symptoms expect gradual vision loss (Healthline). People that over sixty years old are at risk for glaucoma, and African Americans risk starts at forty years old. There is no cure for glaucoma, but surgeries and medicine can help

When the photoreceptors are stimulated they transmit impulses to the bipolar cells that project to the ganglion cells of retina.

The visual system of the cells within the brain contain an area known as the receptive field and is the point in which light enters hits the cell of a receptor (Kalat, 2013). This part of the visual system relies on sensory information, such as light, to either excite or inhibit the cells within the center portion of the receptive field. One of the most significant processes of transmitting information from the visual field is through primary cells of the visual receptors, which include the retinal ganglion cells. In the retina, ganglion cell send information from the eye to the brain. Both the rods and cones within the visual system have a rather small receptive field that connects to bipolar or amacrine cells, of which have their own receptive field consisting of ganglion cells, and then the ganglion cells ultimately make up a larger receptive field (Kalat, 2013).

She will be able to visualize due to primary visual cortex and surrounding areas. V1 & V2 being responsible for orientation, spatial frequency, and color
V3 for integration of information, V4 for object recognition, color perception
V5/MT for motion perception. Cranial nerve II, the optic nerve, is a sensory nerve delivers images of sight to the brain and runs to the visual cortex in the occipital lobe .This nerve is activated when Laila sees her friends around a margarita pizza. The visual information is initially processed from her eyes. Her pupils absorbed light, which enters the eye and then travels to the lens. The lens refracts the light and focuses the light into the retina. The optic nerve (II), is responsible for carrying the visual impulse from the eye to the optic chiasm. This nerve is located in the posterior of the eye. It transfers visual information to the visual centers in the brain. The optic chiasm contains temporal fibers that run

Glaucoma is a group of eye diseases characterized by increased intraocular pressure, resulting in atrophy of the optic nerve. (Venes, D. 2013) This disease is known to gradually cause the loss of peripheral vision which can eventually lead to total blindness. Glaucoma is the third most prevalent cause of visual impairment and blindness in the U.S, although the incidence of blindness is decreasing due to early detection and treatment. (Venes, D. 2013) Glaucoma comes in two major categories: closed-angle glaucoma, and open-angle glaucoma. (Holistic Nursing Practice, Vol. 24)

There are many types of Glaucoma, but the most common one is Open-Angle Glaucoma, but the most common type of Glaucoma. This happens when the passage for eye drainage is narrow, but still open. Usually Glaucoma develops in older adults, but they could start having symptoms of Glaucoma at the age of 5. Glaucoma is also the leading cause in preventable blindness in the U.S., and is the 3rd leading cause of blindness worldwide. Some of the signs and Symptoms of Open-Angle Glaucoma are vision loss,and tunnel vision. Since there are no treatments for the optic nerve and vision loss caused by Glaucoma,it is impossible to cure it. But it is possible to to prevent further visual loss by lowering eye fluid pressure. You can take certain medications to increase eye fluid drainage through the mouth or eye drops. Also you can get Laser eye surgery or microsurgery to open the drainage canals can be effective in increasing drainage of eye

Striate cortex in vision is the first area in the cerebal cortex where visual information is processed and received. Neurons from

These characteristics of the glaucoma patient can progress to blindness. Regularly, glaucoma and its treatment have been closely connected with intraocular pressure. In normal tension glaucoma, damage to the optic nerve occurs without any increase in intraocular pressure. Normal tension glaucoma most often occurs in the elderly and can lead to loss of sight and significant disability. Numerous studies indicate that glaucoma patients have altered retinal circulation. Extensive morphological studies describe endothelial proliferations in the retinal vessels of glaucoma patients. [Charlson2011] In study [Evans1999] Evans et al. assert that glaucoma patients demonstrate faulty autoregulation in the retina during posture change: their CRA response to posture variation shows no change. The CRA directly feeds and is the only source of blood supply for the retinal arteries. These distal vessels nourish the retinal ganglion cells and the confluence of unmyelinated nerve fibers anterior to the lamina

Glaucoma is a group of eye disorders that cause blindness by hurting the optic nerve, which is the large nerve that is responsible for vision. In glaucoma, the optic nerve damage is related to a change in the fluid pressure that circulates around the eyeball. In many cases, Glaucoma occurs when the eye's fluid pressure is high, but it can also occur when the pressure is measured as normal.