The visual system is part of the central nervous system which allows human being to see. This system is said to bring about complicated tasks such as the response of eyes to light, the arrangements of monocular representations, formation of a binocular perception from a pair of two dimensional projections, the identification and grouping of visual objects, and measuring distances to and between objects [1].
During light reflection to one of the eyes, the pupils will constrict to avoid abnormality of light rays. Visual acuity can be experimented using a Snellen chart which has a few lines of big letters. The size of the letters shrinks at a descending order from each line. A number next to each line is the distance readable for individual with normal vision.
Astigmatism is usually caused by an irregularly shaped cornea resulting in blurriness of vision at some distances. This symptom can be detected by using an astigmatism fan. If certain part of the lines is blurry or greyish, then that person has astigmatism. The line which is perpendicular to the axis of the sharpest line will be generally the axis of astigmatism (blurriest).
Colour blindness can be tested using Ishihara colour chart. It is a test on red-green colour deficiencies.
Next, in determining the range of what an individual are able to see peripherally can be done through visual field testing using a perimeter in order to assess the potential of blind spots or scotomas (Marilyn Haddrill, 2007).
While for auditory system, both Rinne test and Weber test is used to test our sense of hearing. With the Rinne test, when a tuning fork is held next to a person ear, that person will hear the sound of the vibration longer and louder rather than when it is held against the mastoid bone. For the Weber test, the tone produced when the tuning fork is placed along the centre of the skull, or face, sounds about the same volume in each ear (Altha Roberts Edgren, 2002).
The least amount of sound that an average ear with normal hearing can hear in a quiet environment called the absolute threshold of hearing (Durrant & Lovrinic 1984, Gelfand 2004). One’s deafness can be detected by doing a simple experiment on masking where noises are made when a person is talking. The person’s voice should increase if he is not deaf.
References :
[1] http://en.wikipedia.org/wiki/Visual_system
[2] http://www.answers.com/topic/hearing-tests-with-a-tuning-fork-normal-results
[3] http://www.lifesteps.com/gm/Atoz/ency/hearing_tests_with_a_tuning_fork.jsp
[4] http://www.allaboutvision.com/conditions/astigmatism.htm
[5] http://www.allaboutvision.com/eye-exam/visual-field.htm
[6] http://en.wikipedia.org/wiki/Absolute_threshold_of_hearing
[7] http://ezinearticles.com/?Blurry-Vision-in-One-Eye&id=919222
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