Visual field testing maps the entire area an individual can see, including peripheral vision, while looking straight ahead. Standard assessments typically test each eye separately, creating two distinct maps of vision. The Esterman Visual Field Test is a specialized assessment that moves beyond this monocular approach to focus on measuring functional vision. It provides a standardized, quantifiable score of a person’s overall visual capabilities. This score is used for important administrative and medical evaluations, determining how well an individual can perform daily activities that require the use of both eyes together.
What the Esterman Visual Field Test Measures
The Esterman Visual Field Test is unique because it is primarily a binocular test, evaluating the combined visual field of both eyes simultaneously, which mirrors real-world sight. This approach differs fundamentally from traditional perimetry tests, which measure the sensitivity of each eye in isolation. The Esterman test assesses functional vision, or the practical visual capacity needed for navigating the environment.
Peripheral vision loss caused by conditions like glaucoma, stroke, or traumatic brain injury may not seem severe in a single eye but poses a significant hazard when performing tasks requiring wide, unobstructed sight. The assessment measures visual efficiency, which is the percentage of the normal visual field an individual retains. It covers a substantial area, typically spanning approximately 136 degrees horizontally, providing a comprehensive view of the patient’s side vision. Evaluating this wide field is critical because it helps identify visual field defects that impact daily activities, such as detecting obstacles or vehicles while driving.
How the Esterman Test is Performed
The Esterman test is performed using a computerized device called a perimeter, which is a large, bowl-shaped instrument. The patient sits with their head placed on a chin and forehead rest and focuses intently on a central point of light inside the bowl.
During the test, the computer presents standardized light stimuli, or targets, at various locations across the visual field. These targets are set at a fixed, relatively bright intensity, a method known as suprathreshold testing. This method determines if a point is simply seen or not seen, rather than measuring the precise sensitivity threshold.
The binocular test uses a grid of 120 predetermined points arranged to cover areas important for functional vision. The patient presses a response button immediately upon detecting a light stimulus in their peripheral vision, while maintaining fixation on the central target. The test covers a wide area, extending far into the temporal visual field of both eyes. It is often performed while the patient wears any corrective lenses they normally use, ensuring the assessment reflects their functional capacity.
Calculating the Esterman Score
The outcome of the test is converted into a single, objective figure known as the Esterman Disability Score (EDS), expressed as a percentage of visual field efficiency. The calculation is not a simple count of missed points because the scoring system applies a weighting to different regions of the visual field. This weighting reflects the principle that certain areas of sight are more important for everyday function than others.
For instance, the central field and the lower half of the visual field are considered more valuable for navigating and performing activities like walking or driving. To account for this functional importance, the Esterman grid has a higher concentration of test points in the inferior visual field, containing roughly twice as many points as the superior field. Consequently, missing a point in the lower half has a greater impact on the final score.
The very center of the visual field, the area within three to five degrees of fixation, is intentionally excluded from the Esterman grid, as acuity in this area is assessed separately. The final percentage score indicates the remaining visual function, with 100% representing a full, unimpaired functional visual field.
Real-World Uses of the Esterman Field Score
The Esterman Field Score provides a universally accepted metric for quantifying visual disability, making it highly valuable in administrative and legal contexts. Its most widespread application is assessing fitness to drive, where licensing authorities require a minimum score to ensure peripheral vision meets safety standards. The score’s binocular nature is particularly relevant for driving, as it accurately reflects the combined visual field available to the driver.
The score is also a standard component in determining visual impairment for disability ratings. This includes its use in guidelines such as the American Medical Association’s (AMA) Guides to the Evaluation of Permanent Impairment. The standardized percentage score allows clinicians and agencies to convert a complex visual defect into a clear number for purposes like worker’s compensation, insurance claims, and disability benefits. This objective, functionally-weighted measure helps ensure fair and consistent evaluation of permanent visual loss.