Vision tests are not equivalent to eye examinations. Vision tests have been a role of an eye examination to determine if there is any decrease in the capability to see. Many vision tests determine visual acuity which is the sharpness of central vision. Refractive mistakes such as nearsightedness (shortsightedness), farsightedness (hypermetropia) in addition to astigmatism has been the most widespread causes of visible keenness.
The initial phase in the eye screening physcial exam is to evaluate the persons visual keenness by means of using either a uniform visual acuity chart or a near card intended for bedside use. Snellen test serves as a typical technique for checking vision. It's accomplished with the assistance 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 system to accommodate several lenses in front of each eye.
The patient is situated at a distance of 20feet (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 altered until the print 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 process 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 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 denominator value indicates the distance from which a person with typical visual acuity would comprehend the line with greater than fifty percent accurateness.
Near vision test is performed only when the standard snellen test is impracticable. It's less less accurate than snellen exams. 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 exam.
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 assessments are required to deal with such cases to examine visual acuteness. Three assessments are accomplished step by step at the time the prior one shows 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 executed providing the patient's vision has been affected to an extent that he or she is incapable to act in response 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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