Peripheral vision, often called side vision, is the ability to see objects and movement outside of the direct line of sight. This broad awareness of the surrounding environment is important for navigating spaces, driving safely, and detecting potential hazards. Testing the visual field, which encompasses both central and peripheral sight, is a routine practice in eye care to identify potential loss early on. Detecting a reduction in peripheral vision can indicate the presence of various eye diseases or neurological issues, such as glaucoma or damage from a stroke.
Quick Screening Checks
The simplest initial assessment for peripheral vision is the Confrontation Visual Field Test, which requires no specialized equipment and is often performed in a general doctor’s office. During this test, the patient and the examiner sit facing each other, about an arm’s length apart. The patient covers one eye while focusing their gaze on the examiner’s opposite eye. The examiner then brings a target, typically wiggling fingers, inward from the extreme periphery into the patient’s field of vision. The patient signals the moment they first detect the target, and the examiner compares the patient’s field of view to their own, which serves as a benchmark for a normal field.
This method is a fast screening tool, providing a gross assessment of all four quadrants of the visual field. Although it lacks the detailed sensitivity of automated tests, it is useful for rapidly identifying large or obvious defects before referring a patient for more comprehensive testing.
Automated Static Field Testing
For a detailed assessment, the standard method is Automated Static Perimetry. This technique uses a specialized machine, referred to as a visual field analyzer, to map the sensitivity of the entire visual field. The patient sits with their head positioned inside a bowl-shaped dome and is instructed to look at a fixed central point.
The term “static” refers to the fact that the test uses stationary flashes of light that appear briefly at specific, fixed locations across the inner surface of the dome. The machine systematically varies the intensity of these light stimuli to determine the threshold, which is the dimmest light the patient can see. When the patient perceives a flash, they press a response button, and the machine records the point’s light sensitivity level, measured in decibels (dB).
This automated process is standardized and reproducible, making it the preferred method for monitoring progressive diseases like glaucoma. The typical test covers the central 30 degrees of vision, which is the area most frequently affected by many ocular and neurological conditions. By repeating the testing sequence, the machine generates a detailed map of the patient’s visual sensitivity, allowing doctors to track subtle changes over time.
Mapping Vision with Moving Targets
Kinetic Perimetry is another specialized method for mapping the visual field, exemplified by the Goldmann perimeter. This test contrasts with static testing because it uses a stimulus that is in motion. Instead of measuring the sensitivity at fixed points, this technique is designed to map the boundary of the patient’s peripheral vision.
During the test, a target of a specific size and brightness is moved slowly from the non-seeing area outside the periphery toward the center of the dome. The patient signals when they first see the moving target, and the examiner marks that point on a chart. This process is repeated along several different meridians radiating from the center.
Connecting these marked points creates a boundary line known as an isopter, representing areas of equal retinal sensitivity to that specific stimulus. By using multiple targets of varying sizes and brightness, the practitioner can generate a series of nested isopters. Kinetic perimetry is particularly useful for evaluating the extreme edges of the visual field or for identifying specific visual defects caused by neurological disorders.
Understanding the Test Results
The results of automated perimetry are presented as a detailed printout, which typically includes numerical data and a corresponding grayscale map. The numerical chart displays the sensitivity value in decibels for every tested point. The grayscale map visually translates these numbers, where darker areas indicate reduced sensitivity or vision loss, while lighter areas represent normal sight.
Doctors look for specific patterns of vision loss, known as scotomas, which are blind spots within the visual field. Certain patterns suggest particular diagnoses; for example, an arc-shaped loss is often characteristic of glaucoma damage. The printout also provides global indices, such as the Mean Deviation (MD), which gives a single number representing the overall amount of vision loss compared to a healthy baseline.
These data points allow the clinician to objectively quantify the extent and depth of any visual impairment. By comparing current results to previous tests, the doctor can determine if a condition is stable or progressing, which is vital for adjusting treatment plans to protect the remaining functional vision. The interpretation focuses on matching the location and shape of the defects to known pathways in the optic nerve and brain.