How to Get Better Visual Field Test Results

Visual field testing plays a pivotal role in diagnosing and managing various eye conditions. To ensure the accuracy and reliability of these tests, thorough training of technicians is paramount. This article outlines essential strategies for technicians conducting visual field tests, covering patient preparation, equipment setup, and result interpretation. By following these best practices, eye care professionals can ensure accurate assessments and improved patient outcomes.

Train Your Technicians for Visual Field Testing

To ensure smooth and accurate visual field testing, it's imperative to train your technicians comprehensively. Begin by ensuring that all technicians receive thorough training on the equipment they will be using. This includes understanding the functionalities of the visual field testing equipment and how to operate it effectively.

Some companies, like Virtual Field, offer a comprehensive training package for technicians. It includes access to an online user manual that covers all aspects of the equipment's operation, as well as a quick start guide for immediate reference during testing procedures. Virtual Field also provides unlimited onboarding calls with a dedicated customer success manager. These calls are designed to address any questions or concerns technicians may have, ensuring that they are confident and proficient in conducting visual field tests.

By investing in proper training and support for your technicians, you can enhance the accuracy and efficiency of visual field testing in your practice, ultimately leading to improved patient outcomes.

Prepare Patients Before Taking a Visual Field Test

When it comes to preparing patients for a visual field test, effective communication and understanding of their condition are paramount. There are a couple of things you can do ahead of time to ensure a smooth experience.

For example, consistency in instructions is critical for accurate visual field test results. Developing a standardized script for technicians to follow ensures that patients receive uniform guidance, minimizing variations that could affect the outcome. Clear and consistent instructions, such as when to press the button during the test, help maintain the integrity of the results.

Additionally, engaging in pre-test conversations with patients is essential. Assessing their well-being, especially regarding factors like fatigue or recent disruptions to their sleep, can significantly impact test accuracy. Understanding the patient's condition before the test allows for adjustments or rescheduling if necessary, preventing misleading results.

By implementing standardized protocols for instruction and considering patients' well-being pre-test, eye care professionals enhance the reliability and validity of visual field assessments.

Get Patients Ready During the Exam

Here is a list of strategies that each technician should use when getting a patient ready to take a visual field test. Although some of these may seem minor, they can greatly impact the reliability and success of a test. 

Establish optimal lighting conditions.

Although virtual visual field exams are able to be performed in any environment, you will get the best results in a dimly lit room. Dim lighting reduces glare and distractions, allowing the patient to focus better during the examination. Additionally, it enhances the sensitivity of the equipment used for the test, ensuring precise measurements of the visual field.

If the patient is coming into the exam from a brightly lit area, begin by allowing their eyes time to adapt to dim lighting. This step is crucial as it helps the eyes adjust to the testing environment. 

Address any language barriers.

Take into account any potential language barriers between yourself and the patient. One way to do this is by utilizing Virtual Field. It offers audio instructions, corrections, and encouragements available in 38 languages. This ensures clear communication and comprehension throughout the test.

Provide a clear explanation of the test process.

Providing a clear explanation of the visual field test process is essential for several reasons. First, it alleviates any anxiety or confusion the patient may have about the procedure. When patients are too anxious, they may start pressing the button even though they don’t see any visual stimuli, thus causing false positives. Explain that it is not a test of skill – they aren’t trying to “win” or “beat the machine”. A clear explanation can help minimize this behavior.

When explaining how to perform the test, reassure the patient that blinking is allowed. This helps to ensure that they maintain a natural and comfortable eye posture throughout the examination, which is vital for accurate results. 

You will also want to inform the patient that they can request to restart the test at any time. This encourages open communication and ensures that the test proceeds smoothly without unnecessary interruptions. Virtual Field makes it easy to restart the exam and may even pause an exam if the general depression is bad enough.

Address existing eye conditions.

Considerations for eyelid conditions and dry eyes are essential aspects of preparing patients for a successful visual field test. Eyelid conditions, such as ptosis or dermatochalasis, can obstruct the visual field or cause artifacts in the test results. Addressing these issues, such as by taping up the eyelids if necessary, minimizes potential sources of error and ensures more accurate data collection during the examination.

Additionally, patients with dry eyes may experience discomfort, irritation, and blurred vision, all of which can impact their ability to perform the test accurately. Allowing these patients to use artificial tears before testing not only enhances their comfort but also optimizes their visual acuity during the examination.

Ensure the patient is seated comfortably.

Ensuring the patient is seated comfortably throughout the test is essential for their cooperation and engagement during the examination. Comfortable seating reduces the likelihood of fidgeting or movement that could affect test results. It also promotes relaxation, which is beneficial for maintaining stable fixation and concentration during the visual field assessment.

If you need to make your exams more accessible, use a virtual visual field test like Virtual Field. Virtual visual field testing devices allow patients to lie back or even lie down if that’s more comfortable. They can even take the exam in a wheelchair. 

Place the lens in the correct position. 

Correctly placing lenses is critical for obtaining accurate and reliable visual field test results. Trial lenses correct refractive errors and optimize the patient's vision during the examination. Properly aligned lenses ensure that the patient's visual acuity is optimized, eliminating potential sources of error that could arise from uncorrected refractive issues.

Optimize virtual reality setups.

For virtual reality (VR) visual field tests, optimizing headset positioning is crucial for obtaining accurate and consistent test results. Properly centered headsets ensure that the patient's field of view aligns correctly with the virtual stimuli presented during the examination. Misaligned headsets can lead to distortions or inaccuracies in the test results, compromising the clinical validity of the visual field assessment. 

For example, if the headset is too high or too low, it can impact test results by causing a general depression or localized defects. By following precise headset positioning procedures, you enhance the reliability and reproducibility of VR-based visual field testing.

Best Practices for Conducting the Exam

When conducting a visual field exam, it’s important to play an active role as the technician. Here are a few best practices to ensure you get accurate results:

• Active monitoring – During visual field exams, technicians may actively monitor patients' performance to ensure accuracy. Watch for proper fixation, response patterns, and patient engagement. If issues arise, technicians can intervene promptly, offering guidance or restarting the test as needed for reliable results. Monitoring the fixation monitor is crucial to detect problems like closed eyes or poor fixation, prompting potential test repeats for accuracy.
  If you use a company like Virtual Field, it does the heavy lifting for you by giving instructions, corrections, and encouragements in the patient's native language throughout the exam. However, the technician should still monitor the exam enough to know whether the exam needs to be restarted. 

• Reacting to patient responses (or lack thereof) – During visual field exams, technicians must be attentive to patient responses or lack thereof. Virtual Field devices will also be monitoring activity and may automatically pause the exam if the patient doesn’t respond for an extended period of time. If a patient shows minimal or no response to stimuli, especially in advanced glaucoma cases, technicians may want to consider adjusting the testing strategy. For instance, switching from a 24-2 test to a 10-2 testing strategy may be more appropriate for detecting vision changes efficiently. 
  While experienced technicians can often make these decisions independently, it's important to consult with the doctor before altering the testing strategy. This ensures that changes align with the overall treatment and monitoring plan, maintaining the continuity and comparability of test results for disease progression assessment.

• Setting new baselines – If you’re using a new machine, make sure to rebaseline your patients. When comparing results with another visual field machine, do not directly compare the absolute value graph (on the top left) or the grayscale graph (on the bottom left). Instead, compare the general pattern shown on the total and pattern deviation graphs. The exact deviations will vary between devices.

How to Know if You Should Discard a Result

When assessing visual field exam results, it's crucial to identify situations where the data may be compromised, leading to potentially misleading interpretations like false positives, false negatives and fixation losses.

False Positives

One key indicator to watch for is a high false positive rate, which can significantly impact the reliability of the test findings. False positives occur when patients respond as if they see a stimulus that wasn't presented or when they over-respond due to factors like anxiety or misunderstanding the test instructions.

A false positive rate above 15% to 20% is often considered problematic, as it can distort the results and mask actual visual field defects, especially in conditions like glaucoma. Such results may erroneously suggest improvement or stability in the patient's condition, leading to incorrect clinical decisions. In cases where false positives are excessively high, typically indicating patient-related issues rather than disease progression, it's advisable to discard that particular test result.

However, it's essential to consider other factors alongside false positives before discarding a test entirely. 

False Negatives and Fixation Losses

Fixation losses and false negatives, while also important indicators of test reliability, may not always warrant test rejection on their own. Fixation losses, for instance, may not significantly impact visual field results, and false negatives can be elevated in advanced glaucoma cases.

Consistency of Reliability Indices 

The decision to discard a test should also consider the consistency of reliability indices across multiple tests. Significant changes in fixation losses, false negatives, or false positives from one test to the next may indicate variability in patient cooperation or test conditions, potentially affecting the reliability of the results. Consistency in reliability indices between tests suggests greater reliability in the data obtained, guiding clinicians in making informed interpretations and treatment decisions based on accurate visual field assessments.

For example, when using a virtual reality visual field test like Virtual Field, consider potential reliability factors like headset positioning, trial lenses worn, and patient temperature and comfortability.

When to Use Various Virtual Field Exams

Different exam patterns serve distinct clinical purposes based on the specific visual field area being assessed and the conditions under evaluation.

• Central 24-2 & Central 30-2: These patterns are commonly used to assess the central 24 or 30 degrees of vision, respectively, providing comprehensive information about central visual function. They are valuable for detecting and monitoring conditions affecting the macula and central retina, such as macular degeneration and diabetic retinopathy.
• Central 24-2C: The 24-2C pattern, with additional points in the central region, enhances the detection of macular field loss. It's particularly useful for monitoring both peripheral and central vision.
• Central 10-2: This pattern specifically targets the central 10 degrees of vision and is ideal for evaluating patients with central vision issues like macular degeneration, diabetic retinopathy, and late-stage glaucoma. It's also used for monitoring patients on medications like Plaquenil (Hydroxychloroquine) that can impact vision.
• C-40 & N-30 Screening: These fast screening patterns evaluate the central 30 degrees (C-40) or 20 degrees (N-30) of vision efficiently, making them suitable for quick assessments or initial screenings. Follow-up exams may be conducted based on initial findings.
• Superior 36: Primarily used for ptosis assessment, the Superior 36 pattern targets superior visual fields. It's performed with and without eyelids taped, providing insights into visual field changes associated with eyelid conditions.
• Esterman & Full Field Exams: Esterman patterns assess peripheral vision extensively, crucial for tasks like state licensing exams. Full Field 120 and Full Field 70 (Kinetic) exams also evaluate peripheral vision, offering a broader assessment of visual field integrity.

Choosing the appropriate exam pattern depends on the clinical context, the area of interest within the visual field, the condition being assessed, and the desired level of detail required for diagnosis, monitoring, or screening purposes. Understanding the strengths and applications of each pattern helps optimize visual field testing for enhanced patient care and management.