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Perimetry visual field Akram Rismanchian MD Farabi Hospital

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The field of vision is defined as the area that is perceived simultaneously by a fixating eye. The limits of the normal field of vision are 60 into the superior field, 75 into the inferior field, 110 temporally, and 60 nasally

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THE NORMAL VISUAL FIELD. Traquair, in his classic thesis, described an island of vision in the sea of darkness. The island represents the perceived field of vision, and the sea of darkness is the surrounding areas that are not seen. In the light-adapted state, the island of vision has a steep central peak that corresponds to the fovea, the area of greatest retinal sensitivity.

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The single filed printout

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There are several different packets of information present on the printout, including Basic identification of patient and test Indicators of test reliability Raw unprocessed threshold sensitivity measurements

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Deviations of measured sensitivity from age normal ( total deviation ) Deviation from normal after adjustment for the patients overall sensitivity( pattern deviation ) Overall indices of normally ( global indices ) Plain language analysis ( the glaucoma hemi field test )

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STRATEGY Fastpac _ Full Threshold Sita _ Swap

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Reliability parameters fixation loss fixation loss false positive response errors false positive response errors false negative response error

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Gaze stability The accuracy of the test result can be strongly affected by the strength or weakness of the patients ability to stay focused on the fixation target during test The Heiji Krakau blind spot method can be used to monitor and record a patients fixation loss ( FL ) rate during the test

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Perimeters equipped with a gaze monitor show fixation errors on the screen during the test so that perimetrist can make adjustments or instruct the patients when necessary A tracing appears at the bottom of the printout

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False positive error rates The perimetric false false positive (FP) error rate in the non SITA strategies is the frequency with which the patient presses during FP catch trials, which are pauses during which no stimulus is presented The letter X is printed twice next to the FP ratio when it exceeds 33%

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The SITA strategies do not make explicit FP catch trials but calculate FP rates from responses at unexpected times during the test m

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False negative error rates The perimetric false negative (F N) error rates the frequency with which the patient fails to press the response button when a visible stimulus is presented

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For tests run using the full threshold and Fastpac strategies.the false negative rate (FN) is expressed the printout as the ratio of the number of times patients failed to respond to a stimulus 9 db more intense than the previously determined threshold estimate divided by the number of such FN catch trials As with false positive responses an XX appears next FN rate on the printout when it exceeds 33%

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For tests using the SITA strategies the result is displayed as a percentage instead of ratio The recorded parameter more closely represents the percentage of time the patient fails respond to visible stimuli because of inconsistency or inattentiveness because the strategy dose not consider any failure to respond during the test that might be caused by disease

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Test labeled as having low reliability Filed were excluded if the fixation loss rate was greater than 20% or if either the false positive rate or the false positive rate the false negative rate exceed 33%( in sita stratgy false +ve =8% false ve =12% )

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Raw test results a) Threshold sensitivity values Decibel threshold sensitivity values are displayed as a ( sensitivity value table ), except that the sensitivity value at the fovea is listed over to the side along with the reliability parameters b) Gray scale

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Total deviation ( from normal values for age) The total deviation display has two parts : a table of numeric values, which represents the actual decibel deviation from age normal, and below that, a probability plot showing symbols that indicate the statistical significance of each measured deviation

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Deviations of less than 5 db may be note worthy near the center of the filed and that even 10 db deviations near the edge of the visual field may well within the normal range

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Pattern deviation ( localized loss ) The function of the pattern deviation plot is to expose localized defects that may be masked by either a generalized depression or an elevation of the hill of vision This is accomplished by making an adjustment of the threshold values according to the general height ( GH) of the visual filed

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Thus, of the 51 points that are finally considered, the seventh highest sensitivity value relative to age normal is taken to represent the overall general height of hill of vision

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A key to the probability symbols is shown near the bottom of the printout. The symbols increase in darkness as the deviation become more significant

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Marking a test location with the symbol for p