Principles of Visual Field Testing
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Measurement of structural and functional damage is very important in the diagnosis and evaluation of progression in glaucoma. Retinal ganglion cell death and nerve fiber layer damage leads to visual field loss. Progressing disease results in progressing visual field defects and causes irreversible blindness.
Principals of visual field testing describes the main terminology, used in the evaluation of visual field and main types of visual field defects are discussed.
Visual field testing is routine procedure in diagnosis and monitoring of glaucoma patients and standart automatic static perimetry is the main functional test for evaluation of glaucomatous visual field defects. Humphrey field analyser (Carls Zeiss Meditec, Dublin CA) is dominating system used for testing in many countries. Tests for central visual field examination are used—central visual field 30, 24 degrees and central 10 degrees from the fixation point (for advanced visual field loss). Most glaucomatous visual field defects occur in central 30 degrees area, paracentral scotomas—between 10 and 20° from the fixation point. Minimal criteria for grading abnormality in central visual field according to Capriolli (1991) and Hodapp classification for the severity of visual field loss are presented.
For evaluation of glaucoma progression Humphrey field analyser uses the software and event and trend analyses of the visual field in follow up can be performed.
Short wavelength and frequency doubling technology perimetry are also used for identifying visual field loss in glaucoma and earlier detection of glaucomatous damage than using standart automated perimetry was observed in several studies.