Visual field Testing
A visual field testing is a diagnostic procedure used to measure the entire scope of a person's vision, including central and peripheral (side) vision. It assesses how well the eyes can detect objects across the visual field without moving the eyes. The test is commonly used to diagnose and monitor conditions affecting the visual system, such as glaucoma, optic nerve damage, retinal disorders, or neurological conditions like stroke or brain tumors.
Visual field testing encompasses several methods, each designed to assess the scope and sensitivity of a person’s central and peripheral vision. Below are the different types of visual field tests, their techniques, and their specific uses:
1. Automated Static Perimetry
The most common modern method, using a computerized device (e.g., Humphrey Field Analyzer, Octopus Perimeter) to present stationary light stimuli of varying intensity at fixed points in the visual field. Patient sits in front of a bowl-shaped instrument and focuses on a central point. Lights of different brightness flash at various locations, and the patient presses a button when they see them. The machine maps the visual field based on responses.
- Threshold Testing: Measures the faintest light detectable at each point, providing detailed sensitivity maps (e.g., used for glaucoma monitoring).
- Suprathreshold Testing: Screens for gross defects by presenting brighter stimuli (faster, used for screening).
Diagnosing and monitoring glaucoma, optic nerve disorders, retinal diseases, and neurological conditions. Highly precise, reproducible, and standardized. Requires patient cooperation and concentration; can be tiring (5–15 minutes per eye).
2. Kinetic Perimetry
Uses moving stimuli (e.g., a light or object) to map the boundaries of the visual field, often with a Goldmann perimeter. The patient fixates on a central target. A moving light or object is brought from the periphery toward the center until the patient detects it. The examiner plots the points where the stimulus becomes visible, creating a map of the visual field. Useful for detecting peripheral vision loss (e.g., in advanced glaucoma, retinitis pigmentosa, or stroke). Effective for mapping large defects or in patients with poor fixation; allows manual adjustments by the examiner. Less automated, depends on examiner skill, and less sensitive for subtle defects.
3. Confrontation Visual Field Testing
A simple, manual screening test performed by an examiner without specialized equipment. The examiner faces the patient (about 1 meter apart) and asks them to cover one eye. the patient fixates on the examiner’s nose or eye. The examiner moves a target (e.g., finger, pen, or white pin) from the periphery toward the center in different quadrants, asking the patient to signal when they see it. Often compared to the examiner’s own visual field for reference. Quick screening in clinical settings, often for neurological conditions like stroke or brain tumors. Fast, portable, no equipment needed; useful in bedside exams. Low sensitivity, misses subtle defects, subjective.
4. Tangent Screen Test
A manual test using a flat, usually black, screen at a fixed distance (1–2 meters) to map the central visual field. The patient sits in front of the screen and fixates on a central point. The examiner moves a test object (e.g., a white disc) across the screen, and the patient indicates when it appears or disappears. Blind spots and defects are plotted on a chart.
Detects central and paracentral defects (e.g., in macular degeneration or optic neuritis). Simple, focuses on central vision, customizable. Limited to central field (within 30 degrees), less precise, and examiner-dependent.
5. Amsler Grid Test
A handheld or printed grid (usually 10x10 cm) with a central fixation point, used to test the central 20 degrees of the visual field.
The patient holds the grid at reading distance (about 30 cm) and covers one eye.They focus on the central dot and report any distortions, wavy lines, or missing areas in the grid. Primarily for detecting central vision defects, especially in macular degeneration or other retinal disorders. Simple, self-administered, portable, and quick. Limited to central vision, subjective, and not suitable for peripheral defects.
6. Frequency Doubling Technology (FDT) Perimetry
Description: A specialized automated test that uses a flickering pattern (low spatial frequency, high temporal frequency) to assess visual field function, particularly magnocellular pathways. The patient views a screen with flickering black-and-white patterns and presses a button when they see them. The test targets specific retinal ganglion cells sensitive to motion and contrast. Early detection of glaucoma and other optic nerve disorders. Quick (3–5 minutes per eye), portable, less affected by cataracts or poor visual acuity. Less comprehensive than standard perimetry, may miss certain defects.
Notes:
Depends on the suspected condition, patient cooperation, and available equipment. Automated perimetry is the gold standard for most clinical settings. Tests require focus and cooperation; fatigue, poor attention, or motor issues can affect results. May be repeated periodically to monitor progressive conditions like glaucoma.