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Standard vision tests are different from eye exams. Vision exams are a function of an eye physcial exam to conclude if there is any diminution in the capacity to see. Most vision tests check visual acuity that is the sharpness of central vision. Refractive mistakes such as nearsightedness (shortsightedness), hypermetropia (hypermetropia) as well as astigmatism are the most frequent causes of visual keenness. The primary stage in the eye screening examination is to determine the persons visual acuity through utilizing probably a standardized visual acuity chart or a near card meant for bedside handling. Snellen test serves as a standard method for examining eyesight. It is performed with the benefit of a snellen chart and a phoropter. A Snellen chart shows block letters and numbers decreasing in size from the top to bottom. Phoropter is a simple system to store different lenses in front of each eye. The patient is placed at a distance of twenty feet (or fourteen inches if near card is being used) from the snellen chart. Patients read lines on the Snellen chart that get smaller and smaller while the Snellen line emphasizes if the patient can read more than fifty percent accuracy. The lenses in the phoropter are changed until the lettering near the bottom of the chart can be interpreted. An optometrist determines the refraction by Phoropter by placing oclur lenses with different powers and asking the patient to select lens of the best power. Each eye is tested separately. After this course of action the corresponding vision is predictable for each eye. Normal value is 20/20 or 6/6 if the distance is in meters. For example, OD=20/200 and OS= 20/200. OD stands for ocular dexter that represents the right eye. OS stands for ocular sinister that represents the left eye. The numerator of this fraction represents the distance of the patient from the chart. The bottom number value reveals the distance from which a person with regular visual acuity would comprehend the line with better than 50% accuracy. Testing for shortsightedness is completed if the Snellen test is impracticable. It's less less precise than snellen exams. This particular test is like the Snellen test as the optometrist holds the near vision card approximately fourteen inches from the eyes and following similar steps of the Snellen test. If the patient already has reading glasses or bifocals they should be worn for the exam. Snellen tests may not be the right test for a patient that has vision less than 20/400 which means a patient can accurately observe an object from 20 feet that a normal person can see at 400 feet. More primitive assessments have been needed to consider such problems to examine visual keenness. Three assessments are executed step by step at the time the previous one reveals no results. Counting fingers tests is administered which the patient is able to count the fingers held by the examiner is reported. A documented vision CF 3 feet means the patient is able to add up the fingers at a distance of three feet. The use of hand movement exams are useful if patients are not able to count the examiner's fingers from a short distance. Light perception testing is executed if the patient's vision has been affected to an extent that he or she is not capable to respond to hand activities. Light perception can be tested when the examiner shines a bright light right on the patient's eye while covering the other eye.
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