The Equipment Doctor’s Use To Test Eyes
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Vision tests are not equivalent to eye examinations. Vision assessments have been a function of an eye physcial exam to determine if there is some reduction in the ability to see. Most vision tests check visual acuity that is the sharpness of central vision. Refractive errors such as myopia (myopia), farsightedness (farsightedness) plus astigmatism are the most general causes of visible keenness.
The primary step in the eye screening examination is to determine the persons visual keenness via employing possibly a standardized visual acuity chart or a near card meant for bedside use. Snellen test serves as a typical system for examining eyesight. It's accomplished with the help 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 instrument to hold numerous lenses in front of each eye.
The patient is positioned at a distance of twenty feet (or fourteen inches if near card is being used) from 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 letters next to the bottom of the chart can be read.
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 method the corresponding vision is acknowledged 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 bottom number value indicates the distance from which a person with regular visual acuity would interpret the line with better than fifty percent correctness.
Near vision test is performed only when the standard snellen test is impracticable. It's less less accurate 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 ought to 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 required to manage such cases to test visual sharpness. Three assessments are performed step by step at the time the prior one shows no results.
Finger counting tests are utilized that consist of the patient counting the examiners fingers. A standard vision CF 3 feet means the patient is able to tally the fingers at a distance of three feet.
Hand movements exam is needed if the patient is unable to count the fingers from very short distance. Light perception testing is completed providing the patient's vision has been exaggerated to an extent which he or she is incapable to act in response 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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Author Resource:-
To learn what types of high tech vision instruments are used to test vision visit titmus vision screener
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By :
Jerry Rogers
Submitted
2010-08-15 14:19:55 |
Article From Article Mayhem
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