Converting Visible Light Into Neural Activity - Essay Example

Exploring Human Eye’s Conversion of Visible Light Into Neural Activity and Conveying of Visual Information into Visual Cortex This essay highlights the importance of human eye including its anatomy and physiology, and the mechanism by which light rays that enter in an eye are converted to images on the retina. Some defects of eye are also mentioned in this essay these defects are associated with the increasing age due to physiologic changes like cataract and presbyopia. Similarly, alteration in anatomy also causes defects like myopia, hypermetropia, and astigmatism. However, various methods are also included in this essay to overcome these eye problems. Human eye acts as a camera and detects light rays which are eliminated in the form of packets of energy known as photons or waves of various frequencies. These rays of light surround use everywhere. Rays of light are also emitted by various objects present around us. (SK277 Course Team, 2004, p.62) However, light rays first come in contact with cornea which helps in maintaining the anterior chamber of an eye. The light rays travel via small hole known as a pupil , it contains iris muscles in its surrounding which later pass on to the lens, it aids in converging the beam of light to focus the object depending on the distance. (SK277 Course Team, 2004, p.63) This phenomenon is also known as accommodation reflex. Human eye comprises of two chambers namely the anterior chamber and posterior chamber. The anterior chamber is situated between cornea and lens and is filled with a fluid knows as aqueous humour. The activity of visual light is under control of an autonomic nervous system. The amount of light entering in the eye is based on the diameter of the pupil; as soon as the light enters the radial and smooth muscle start their activities. The diameter of the aperture is enhanced by the activity of radial muscle, whereas as the diameter is decreased when circular muscles act. The image is finally produced on the retina which is made up of several distinct layers; it also possesses receptors for light known as photoreceptors. (SK277 Course Team, 2004, p.63) Before the formation of an image, the light has to pass through the several layers and receptors present in the retina. These photoreceptors can be categorized as rods and cones. Both rods and cons have a distinct function. Data gathered from the rods play a vital role in night vision.These receptors are highly sensitive to the low level of light and are unable to give the details of the object at night. Due to this fact, we can see objects more clearly during daytime as compared to the night. Whereas, cons are responsible for viewing the object during the daytime. The photopigment that is present within rods and cons are capable of absorbing light in them. These pigments are 125 million in numbers and are made up of a protein known as opsin; they also carry a chemical named as retinene (SK277 Course Team, 2004, p.64) The role of this photoreceptor is to convert the energy generated from the light into biochemical signals via electrical activity which in the end reaches retinal ganglion cells. These cells take the information to the brain for final processing. Now axons present in retinal ganglion cells leads to the production of the optic nerve and optic chiasm, it has overlapping fibers forming optic tract, they end up as a lateral geniculate nucleus in the area of the thalamus. (SK277 Course Team, 2004, p.68) Later, the signals are transferred to the primary visual cortex and secondary visual area. The processing of visual information takes place in the following ways 1- According to movement, region and spatial arrangement 2- According to Anatomy 3- According to color. There are a number of anatomical and physiological defects which impair vision. Due to variation in anatomy light rays are unable to focus on the retina leading to impaired vision. This kind of refractive errors can be categorized as 1- myopia (nearsightedness) 2- farsightedness (hypermetropia). Myopia occurs when the image is focused in front of the retina, whereas in case of hypermetropia the image is formed far behind the retina. Another variety of anatomical eye defect includes astigmatism; in this condition, there is an irregularity in the curvature of cornea instead of being smooth and even in all directions allowing the lens to produce a number of focal points giving rise to improper images. Astigmatism leads to blurring of vision; it can occur in conjugation with myopia and hypermetropia. However, these conditions can be corrected by the use of glasses and contact lens. Nearsightedness can be corrected via the use of concave lenses and farsightedness can be corrected by the help of using a convex lens. Astigmatism often does not require correction however the treatment option includes surgery and lenses. (SK277 Course Team, 2004, p.65) Physiologic defects of the eye include cataract and presbyopia. Both are linked with the old age. The incidence of presbyopia is common with the increasing age. In this defect, the lens of the eye gets hard and loses its capability to adjust focal point the of an eye. Presbyopia can be corrected by using glasses for activities like reading newspaper or books. Distant vision is barely affected by this condition; it only impacts the near vision in the beginning. Cataract is another physiologic abnormality of an eye. There are a clouding and swelling in the lens of either one or both eyes altering an individual’s vision. It is chiefly a disease of the older group, particularly over 60 years. Cataract cannot spread from one eye to another. It needs prompt attention, or it can lead to complete blindness. Other than old age some other factors also contribute to cataract like malnutrition, smoking habits, prolong exposure to sun and injuries of an eye. Surgical intervention is helpful in individuals suffering from cataract. In such surgeries the cloudy lens is removed which is replaced by an artificial small lens made up of plastic is placed inside the eye. Use of sunglasses helps to protect the eye and delay the occurrence of cataract in an individual. ( (SK277 Course Team, 2004, p.70) Many systemic conditions also lead to alteration in vision. One of such condition includes diabetes. It causes a disturbance in sight and can also lead to blindness. Diabetes can impact the capillaries that supply oxygen and other nutrients to retina causing the blood to move in this region. Capillaries which are formed are fragile and could bleed in vitreous humour (SK277 Course Team, 2004, p.70) Macular degeneration also increases with age causing irreversible blindness. In this condition, there is thinning of macula causing degeneration of macular tissues producing distorted images, blurred vision, and formation of dark spots in the field of vision. To sum up, it is important to know the proper anatomy and physiology of eye for knowing the conversion of visible light into neural activity and how visual information is then converted to the visual cortex. With the take-home message, all the defects of the eye demand prompt attention as these defects can result in a complete loss of sight. Older people must pay attention to the condition of their eye by the help of regular checkups as the frequency of eye disease increase with age particularly after 45 years. Hence, early detection of the problem helps in better prognosis and reduces the chances of complications. Reference List SK277 Course Team.(2004). Control and Communication: SK277-Human Biology. 2nd ed. Open University Worldwide. Read More