By: Jerry Rogers
Submitted: 2010-08-15 14:12:23 | Word Count: 647
Standard vision tests are different from eye exams. Vision assessments are a function of an eye exam to resolve if there is any diminution in the capability to see. Most vision tests check visual acuity that is the sharpness of central vision. Refractive mistakes such as myopia (shortsightedness), hypermetropia (farsightedness) as well as astigmatism are the most common reasons of visual acuteness.
The initial stage in the eye screening physcial exam is to assess the persons visual keenness via employing probably a uniform visual acuity chart or a near card meant for bedside handling. Snellen test serves as a customary technique for examining vision. It's accomplished with the support of a snellen chart as well as a phoropter. Snellen chart displays lines of numbers and block letters with the size decreasing from top to bottom. Phoropter is a simple tool to accommodate numerous lenses in front of each eye.
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The patient is placed at a distance of twenty feet (or fourteen inches if near card is being used) beginning with the snellen chart. The patient is asked to read progressively smaller lines on the chart while the snellen line determines that he or she can read with greater than 50% accuracy. The lenses in the phoropter are changed until the lettering close to 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 particular procedure the corresponding vision is documented 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 which represents the right eye. OS stands for ocular sinister which represents the left eye. The numerator of this fraction represents the distance of the patient from the chart. The denominator value shows the distance from which a person with regular visual acuity would figure out the line with greater than fifty percent precision.
Near vision test is performed only when the standard snellen test is impracticable. It is less less accurate than snellen tests. This test is similar to snellen test while the optometrist places the near vision card roughly 14 inches away from the eyes repeating the same steps as of snellen test. Providing the patient already has reading spectacles or bifocals they should be worn for the examination.
Snellen test maybe unable to use if the patient has vision less than 20/400 which means the patient can see an object from 20 feet what can be seen by a normal eye at a distance of 400feet. More primitive checks are considered necessary to manage such problems to test visual keenness. Three exams are carried out step by step at the time the prior one demonstrates no results.
Counting fingers tests is administered which the patient is able to count the fingers held by the examiner is reported. A standard vision CF 3 feet means the patient is able to calculate 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 carried out providing the patient's vision has been exaggerated to an extent that he or she is incapable to respond to hand activities. The examiner can test for light perception by shining bright light directly on the patients eye covering adequately the opposing eye.
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