Visual Perception - Essay Example

In the myopic eye, the point forms before the fovea centralis of the retina, and therefore, distant objects seem blurry. From a pathophysiological viewpoint, myopia is usually caused because of an elongated eyeball, but it can result from a too much refractive power in the lens system of the eye. There are two types of myopia, benign and malignant. Benign myopia usually occurs around puberty and it is usually stabilized by the end of 25 years of age, but malignant myopia occurs in early childhood, during which slow but steady elongation of the sclera occurs.

This elongation occurs in the back of the eye, while the frontal part does not change, and this can lead to a serious elongation of the internal membrane of the eye, causing atrophy of the pigmented epithelium and the chorioidea, or the layer of blood vessels in the eye, and the appearance of a myopic cone. Visual acuity is measured using the Snellen chart, where the letters (optotypes) decrease in size in each row, from top to bottom. The smallest row that can be read accurately indicates that person's visual acuity in that eye.

The patient is placed at 6 meters distance from the chart and asked to read the letters. Near each row there is a number, indicating the length at which a person with normal visual acuity would be able to read it, or the distance at which a person can discern 2 separate points on the chart. A patient with 6/6 visual acuity means that he has normal vision, while the results show us that the person we measured has slight myopia. It is easily treatable by placing concave spherical lenses in front of the eyes, reducing the excessive refractive power and diverging the rays to fall on the retina.

In modern times, refractive surgery is also available, which uses laser to reshape the curvature of the cornea and reduce the refractive power.2. The person obviously is healthy, as it is able to observe motion, even though he was unable to observe shape during the motion. This is normal eye physiology, as there are more rod cells that detect motion, than cone cells that detect color in the periphery of the fovea centralis. While not in motion, more cones are stimulated and therefore, can detect color and shape.3. Miosis is the process of decreasing the size of the pupillary aperture.

It is caused by the stimulation of the parasympathetic nerves, which excite the pupillary sphincter muscle, and it represents an integral part of the pupillary light reflex. When light hits the retina, some of the impulses pass through the optic nerves to the pretectal nuclei. Secondary impulses then arrive at the Edinger-Westphal nucleus, which send signals through parasympathetic nerves to the papillary sphincter muscle. The reason why the pupil of the other eye remains the same when light is shined in one eye is because the two separate signals coming from the two eyes are relayed through separate nerves and neuronal layers, even after they arrive at the dorsal lateral geniculate nucleus, which then sends the signals to the visual cortex.

This separation of signals throughout the entire visual neural pathway allows for an independent miosis in each eye.4. When a sudden pulse of light strikes the retina, the receptor potential that occurs in the rods reaches a peak in 0.3 seconds and lasts for more than a second. It is also