Glaucoma Case Study
Visual
Fields
in
Glaucoma
Evaluation of the field of vision is the mainstay of the diagnosis and management of glaucoma. The use of manual perimetry for defining glaucomatous defects is an art that is highly dependent on the perimetrist's skill. With the advent of computers and automation, perimetry has changed from an art to a more quantitative science. Understanding glaucomatous abnormalities detected with both manual and automated techniques requires a thorough understanding of the normal and glaucomatous visual field and the factors that influence test results.
THE NORMAL VISUAL FIELD
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 …show more content…
These perimeters measure the ability of the eye to detect a difference in contrast between a test target and the background luminance. The differential light threshold is designated as the dimmest target seen 50% of the time. Suprathreshold stimuli are brighter than threshold stimuli, and they will be seen more than 50% of the time. Infrathreshold stimuli are dimmer than threshold stimuli, and they will be seen less than 50% of the time.
Threshold at a specific retinal location can be measured directly from a frequency-of-seeing curve. The frequency-of-seeing curve is generated by testing one retinal location multiple times with different stimulus intensities. The frequency-of-seeing curve is the graph of the percentage of stimuli seen at each intensity level. Threshold is read off the graph at the 50th percentile (Fig. 8).
Unfortunately, it is impractical to perform frequency-of-seeing curves at the large number of locations required to assess the visual field accurately for glaucomatous damage. Therefore, different perimeters use a variety of strategies to estimate threshold. These strategies are described below under Automated Perimetry: Testing Strategies: Threshold
Fields
in
Glaucoma
Evaluation of the field of vision is the mainstay of the diagnosis and management of glaucoma. The use of manual perimetry for defining glaucomatous defects is an art that is highly dependent on the perimetrist's skill. With the advent of computers and automation, perimetry has changed from an art to a more quantitative science. Understanding glaucomatous abnormalities detected with both manual and automated techniques requires a thorough understanding of the normal and glaucomatous visual field and the factors that influence test results.
THE NORMAL VISUAL FIELD
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 …show more content…
These perimeters measure the ability of the eye to detect a difference in contrast between a test target and the background luminance. The differential light threshold is designated as the dimmest target seen 50% of the time. Suprathreshold stimuli are brighter than threshold stimuli, and they will be seen more than 50% of the time. Infrathreshold stimuli are dimmer than threshold stimuli, and they will be seen less than 50% of the time.
Threshold at a specific retinal location can be measured directly from a frequency-of-seeing curve. The frequency-of-seeing curve is generated by testing one retinal location multiple times with different stimulus intensities. The frequency-of-seeing curve is the graph of the percentage of stimuli seen at each intensity level. Threshold is read off the graph at the 50th percentile (Fig. 8).
Unfortunately, it is impractical to perform frequency-of-seeing curves at the large number of locations required to assess the visual field accurately for glaucomatous damage. Therefore, different perimeters use a variety of strategies to estimate threshold. These strategies are described below under Automated Perimetry: Testing Strategies: Threshold