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Abstract Automated perimetry is a ready means to obtain standardized, quantitative measurements of the visual field, has prompted valuable clinical research, and has improved the care of patients with glaucoma. Static threshold measurements are sensitive to shallow depressions of the visual field. This increases the detection rate of early glaucomatous defects compared to routine manual techniques. Although static threshold measurements are not new to practitioners, the computerized format and the generation of a large amount of numeric data present new challenges. The increased sensitivity of the method has increased the ”noise” of the measurements and demands careful attention to the many variables that may affect the measured threshold. Visual field measurements should never be interpreted in the absence of other clinical information. It is necessary to integrate intraocular pressure, appearance of the optic nerve, and other ocular and systemic factors when making decisions about diagnosis and therapy. Patient reliability IS an important initial consideration when inter preting visual fields. This may be assessed by the rates of false - positive and false - negative answers, the operator’s assessment of reliability, the fluctuation of repeated threshold measurements, the number of fixation 120 losses, and the number of stimulus presentations required to complete a visual field examination. The operator must adequately explain the testing procedure and encourage patient cooperation and alertness during the examination if reliable results are to be obtained. Abnormalities of the visual field can be recognized in two ways: by point-by-point comparison with data from normal individuals of similar age, and by comparison with thresholds in adjacent areas of the visual field, in the opposite hemifield of the same eye, or in the visual field of the contralateral eye. The classic glaucomatous visual field defects are often preceded by widespread, shallow depressions throughout the visual field, though the concept of uniform diffuse depression in early glaucoma is debated. Diffuse depressions is not specific for glaucoma and is frequently caused by media opacity, inaccurate refraction, miosis, retinal disease, or poor test performance. Computer-assisted comparisons with normal data may help identify early glaucomatous defects. The visual field indices mean defect (or mean deviation), corrected loss variance (or corrected pattern standard deviation), and short-term fluctuation, seem useful to evaluate sequential examinations but may not be suited to detect the earliest glaucomatous defects. Careful comparison of sequential visual field often appropriately directs glaucoma treatment. Knowledge of the conditions under which 121 Careful comparison of sequential visual field often appropriately directs glaucoma treatment. Knowledge of the conditions under which valid comparisons can be made is essential .It is best to avoid changes in treatment, whenever possible, based on the comparison of only two visual fields. A series of examinations may show the true course of the disease when only two examinations would be misleading. There are no generally accepted criteria for progression of defects, but some guidelines can be offered. A new, confirmed defect that meets reasonable criteria for abnormality can be considered progression. In areas of a previous defect, a further decrease in the threshold of greater than or equal to 5dB would be suggestive, where as a decrease of greater than or equal to IOdB can usually be considered a significant change. A number of confounding variables make the interpretation of visual fields difficult, particularly for progression. The differentiation of longterm fluctuation (test-retest variation) from true progression of visual field loss remains one of the important challenges in modem perimetry. longterm fluctuation in glaucomatous eyes increases with the depth of the defect and with distance from fixation. The comparisons of sequential visual fields is enhanced ifthese factors are considered. Computer-assisted analyses have been developed to evaluate sequential visual field examinations for evidence of progression beyond that which might be 122 explained, at a given level of probability, by long-term fluctuation. The practitioner must be cautioned, however, that statistical significance should not be equated with clinical significance. Changes in pupil area can be significantly affect the visual field, and may be exaggerated in the presence of even minor media opacities. Pupil size should be measured and recorded at every visual field examination; when it is less than 3.0Imn,patients’pupils should be dilated before testing whenever possible. When tills is not possible, examinations should be repeated at the same pupil size. Cataract can have a profound effect on measured visual thresholds, especially in the presence of a small pupil. A subjective evaluation of the media is useful, but such evaluations are rarely sensitive enough to detect small changes that can significantly affect visual field measurements. In difficult situations in which changes in media clarity have occurred, it helps to correlate apparent deterioration of the visual field with change in optic nerve appearance. Refractive errors of only one diopter can cause a significant decrease of measured central visual thresholds. Aphakic eyes are best tested after placement of contact lenses, since aphakic spactacle correction induces significant peripheral artifact . t23 The results of psychophysical tests generally improve as subjects gam experience. This learning effect is small in most patients who have previous experience with manual perimetry, but some patients still show a dramatic improvement on their second automated test compared to their first. The variability of test results decreases significantly with experience. Whenever possible, the patient’s second visual field test should be used as a baseline for subsequent comparisons. The weight given to perimetric finding in decision making depends on the reliability of the patient, the visibility and appearance of the optic nerve, the level of intraocular pressure, and ocular and systemic factors. Computerized static threshold perimetry has increased the validity of routinely performed visual field examinations. It has made compansons of multiple examinations more meaningful, but also more problematic. Automated perimetry has properly shifted the emphasis away from intraocular pressure measurements and toward the visual field in the diagnosis and treatment of glaucoma. Perimetric results, when they are reliable, should play prominently in the minds of practitioners when making diagnostic and theraputic decisions. Future work to enhance the value of automated perimetry will undoubtedly include the development of summary indices with improved sensitivity and specificity for early glaucomatous defects; better strategies to differentiate true progression from long-term fluctuation; and timesavmg testing algoritlnns with acceptable detection rates for early defects. Automated perimetry has, perhaps, provided more questions than answers about the early functional abnormalities in glaucoma. The sensitivity of the technique has made us more aware of the ’noise’ inherent in psychophysical testing; improved techniques to separate the ”signal” from the ”noise” must be developed. Conclusion • The automated perimetry has been shown to be superior (0 manual perimetry in detecting early glaucomatous visual field defect. • The best strategy for detection and follow up is full-threshold strategy and it must be done twice at least. • The only accurate judge of the success of the treatment is the frequent visual field test. |