Visual Field Testing Methods

Tangent Screen & Bowl Perimeter

• Larger targets are used to assess functional detection ability when scotomas are found
• Coarse screening for peripheral field loss can be performed by confrontation or similar techniques
• In confrontation testing, the patient’s visual field is compared with the clinician's visual field
• This is done by both clinician and patient looking through a mid-point between their eyes
• If no peripheral field deficits are present, the point of appearance and disappearance of the test target should be at approximately the same location for both clinician and patient
• Pseudoperimeter technique is used by sweeping a target along an arc starting behind the patient
• This technique helps test the peripheral regions of the field, especially in the temporal side
• The Amsler grid examines central visual function and characterizes disturbances of central vision

Automated Perimetry

• Short wavelength automated perimetry (SWAP) presents a large blue target on a bright yellow background
• Automated perimetry procedures often involve detection of flickering stimuli, motion, or displacements
• High-pass resolution perimetry presents rings with a light center and two dark circles on either side
• Automated perimeters include programs that present stimuli beyond 30 degrees
• Automated visual field testing procedures have advantages from consistent control of test stimuli, procedures, and the analysis of results
• The classic perimetric techniques of tangent screen and bowl perimeter examination are not as commonly used today
• They remain the best methods for determining scotoma shape and location
• Illumination conditions must be controlled

Visual Field Testing

• Kinetic perimetry involves a clinician moving the target across the visual field
• Static perimetry techniques involve the turning on and off of a target at specific locations
• Graphic display printouts typically show regional variations in visual sensitivity
• Most automated perimetry devices concentrate on testing the central 25 to 30 degrees of the visual field
• The glaucoma hemi-field test analyses threshold data and compares the relative sensitivity of selected regions in the superior and inferior visual fields
• New visual field tests specify visual processing of information originating in different regions of the visual field
• These tests attempt to identify deficits in neural processing mechanisms that may be vulnerable to diseases

Frequency-Doubling Perimetry

• A central visual field test where a 5-degree square of flickering grating is presented at 17 different locations
• The grating has a spatial frequency of less than 1 cycle per degree
• When presented in rapid counterphase flicker (more than 15 Hz), there is the illusion of twice as many stripes in the target pattern
• The visibility of the stimulus is relatively unaffected by optical defocus, ambient illumination, pupil diameter, or media clarity
• The frequency-doubling illusion relies on the sparse large-diameter magnocellular nerve fibers, which are vulnerable to glaucoma
• This test is reported to be sensitive for the early detection of glaucoma

This quiz covers various methods of assessing visual fields, including tangent screen testing, confrontation techniques, and automated perimetry. Explore the principles behind functional detection ability and the usage of tools like the Amsler grid and pseudoperimeter techniques. Test your knowledge on these important diagnostic approaches in ophthalmology.