User:Briantoussaint0/Ganglion cell layer

Ganglion Cell Analysis in Glaucoma Research
When studying glaucoma, it is necessary to observe the morphological differences in different species. Glaucoma, a chronic disease that is caused by the degeneration of retinal ganglion cells and the activity within the optic nerve, subsequently leading to the loss of vision. One of the major risk factors if the occurrence of the elevation of intraocular pressure (IOP) which is mediated by the aqueous outflow pathway tissue. The same classification and analysis of glaucoma in humans were introduced in animals by establishing animal models of glaucoma and ocular hyperextension (result of poor drainage of the fluid inside the eye). The importance and necessity of the establishment of the animals models allows the analysis of the number of ganglion cells in the layers and how it may affect the diagnosis of glaucoma or vision impairment in the following animals: mouses, rats, rabbits, pigs, dogs, cats, chickens, and quails.

Rodents
According to Glaucoma research, it was discovered that there were clear differences observed in the inner retina; mainly associated with the appearance of ganglion cell layer (GCL). It was also determined that amacrine cells are present in GCL with different relative numbers as opposed to the ganglion cell count.

Most of the relevant changes in the number of ganglion cells are prevalent in different mouse strains: varying between 32,000 and 87,000. In terms of rats, there is less of a strain variation. However, in albino and pigmented animals, there are notable differences in strain-variation: more than 100,000 ganglion cells in albino and approximately 72,000 in pigmented animals. Not only do both rodents exhibit ganglion cells in the GCL layer but an innumerable amount of amacrine cells were also present, making up 59% in mouses and 50% in rats.

Rabbit
In the rabbits retina, it can observed that they posses a relatively low number of ganglion cells (250,000-394,000). One profound findings that explains the low number of ganglion cells is the restriction of the avascular retina. This is significant as it will cause the restriction of astrocytes in the retina. Astrocytes are relevant in terms of GCL as they regulate the development and maturation of retinal ganglion cells that are derived from Human Pluripotent Stem Cells.

Birds
On the contrary, the retina of birds (chickens and quails) is completely avascular (having few blood vessels ). In addition, a glia-cell barrier (peripapillary glia) restricts the the vessels from arriving in the retina. Since the oligodendrocytes are stationed throughout the avian retina, this creates a high number of ganglion cells in the avian retina. Furthermore, it is twice that of primates (quails having 2,000,000 ganglion cells while chickens posses 2,400,000 ganglion cells). The reason being for the expressed ganglion cells being less in quails compared to chickens is due to the presence of amacrine cells in chickens, while no amacrine cells were observed in quails: 35% of the cells located in the GCL were amacrine cells. The importance of amacrine cells in relation to GCL is due to the amacrine cells being major carriers of rod signals to the ganglion cells in the retina. In fact, they also play an important role in assisting the slow potential rod messages that are sent in the ganglion cells.

Pigs
442,629 retinal ganglion cells were present in pigs while also having 31% of amacrine cells in GCL. These results demonstrates similarities to the rabbit. The distribution of astrocytes in the inner retina were similar to the human eye.

Carnivores
The number of retinal ganglion cells is 148,303 in dogs and 193,000 in cats. When comparing the size of the eyes of both, the density of the ganglion cells for both animals are low. On the contrary, they both emerge an area centralis (small region located in the temporal retina in which the neuron density is at its highest ) with an increased number of retinal ganglion cells. In fact, the cat has been intensively studied in terms of the ganglion cell differentiation. In dogs, the density of the astrocytes varied as the the number of retinal blood vessels increased in the peripapillary retina. Nevertheless, the astrocytes in cats were located around the axon bundles and less intense around the blood vessels. An explanation for the higher number in ganglion cells in cats compared to dogs is simply due to the 80% of amacrine cells located in the GCL.

Primates
The most comparable animal to the human eye are primates. Simply due to the fact that they posses 900,000-1,500,000 ganglion cells which is the closest to humans (700,000-1,500,000).

Conclusion
Based on the table, it is observed that humans, monkeys, chickens, and quails have a fairly large number of ganglion cells which allows them to become more dubious to having glaucoma or vision impairment compared to the rest of the animals in the table. When analyzing the results, it can be observed that monkeys have a similar amount of ganglion cells compared to humans; which is significant as it demonstrates closest relation to the human anatomy. Furthermore, the pig eye has numerous advantages compared to the animals (cats, dogs, rodents, rabbits) discussed as they have a fairly large amount of retinal ganglion cells. On the contrary, rodents, rabbits, cats, and dogs are more susceptible to inheriting glaucoma or the occurrence of a vision impairment.