The importance of visual field (VF) testing cannot be overstated. It may qualify a patient for surgery, document vision loss for disability, or serve as data for the doctor to prescribe glaucoma drops. The technician plays a major role in VF testing. It may be routine, but, like many skills of an ophthalmic technician, performing a VF is science, art, and a bit of math.
Still, VF is often performed by the testing technician, the front desk receptionist (pulling double duty), or the technician who has least seniority. Usually these staff members are taught which buttons to press and are not provided a well-rounded education, which is crucial to have reliable, accurate, and reproducible fields. To address this challenge, this article offers steps ophthalmic professionals can take to move from button pressing to becoming proficient in VF testing. You, too, can be a VF superhero—learn on!
Pay attention to data entry
Human factors can cause a litany of possible errors. With a slip of the key, the patient’s name, date of birth or refraction could contain errors. Following an office protocol of how to enter the patient’s name (all lowercase, all caps, or initial caps) creates a smooth list rather than a mishmash of styles. Before hitting enter, double check your entries.
Follow a script
I break the ice calling VF an “old video game.” This also helps to alleviate, with humor, some of the patient’s testing anxiety. A suggested best practice is to have written scripts (English, Spanish, Farsi, or any language common in your area) available. Even better, personalize the scripts for the different tests—10-2, 24-2, Superior 36, etc. This benefits both the patient and the newly learning VF technician. Put the scripts in plastic sheet protectors or laminate them for durability; add to a binder kept with the machine.
The following details can help improve your script:
- Fovea threshold pre-test. “Click when you see the white dot, dim or bright, which will appear in the middle of the four orange dots.” (Make sure the fovea threshold is turned "on" with your machine. Measuring the fovea threshold collects information that would have been missed if it were "off." It also serves as a reliability check. If the fovea threshold is 38 dB and if you see a 38 anywhere else, then the patient was likely looking around during the test.)
- Patient fixation. “Now the machine is going to take a picture of your location. Blink and hold steady on the yellow-orange light straight ahead.”
- Final instructions. “There will be times where you do not see the light, which is normal. It’s the machine testing you to be sure you are looking where you should, which is straight ahead at the yellow-orange light. Blink whenever you want to; however, the best time to blink is right after you have clicked the button. The test can be paused, if needed.”
- Test commentary. At the very least, let the patient know when they are about halfway done. I also give a note of about a minute or so left. Some patients will need additional commentary to keep them alert (“eyes wide open,” “be sure to blink,” “ keep your gaze steady,” etc.).
Monitor the patient during testing
Stay with the patient in the room (or just outside if able to monitor appropriately during this special pandemic time) to monitor the reliability indices (fixation losses, false negatives, false positives). A technician will monitor the patient’s head (so it stays still), teeth (together), and forehead and chin in position. Once these indices get above 20%, an “XX” appears indicating an unreliable test. Reliability indices shown on screen during most testing are fixation losses and false negatives. The graph or the “printout” also lists the false positives. One common graph result of the patient’s inattention results in a clover-leaf or a mouse pattern.
At times during the pandemic, I have found an uptick of unreliable tests. A patient who has a large beard or mask may have a harder time finding the chinrest. I suggest this patient uses their hand to help guide them into place.
Also, fogging on the trial lens can occur. Taping down the top half of the mask may reduce fog.
Designate a clinical trainer
Some offices train like the operation of a phone tree—one person teaches the next. Information can get lost or forgotten, leading to mistakes. Invest in and designate a technician, preferably IJCAHPO certified, as the clinical trainer. Not all excellent technicians are excellent trainers, so resources and time to hone the craft should be provided. This will raise the education level, one key in improving the quality of the VFs.
Recover from fixation losses
If fixation losses happen fast and early, restart the test. Suggested best practice is to repeat the test, depending on your office protocol and scheduling demands. [For more on monitoring fixation, see “Efficiency in glaucoma testing,” Ophthalmic Professional January/February 2020 (bit.ly/OP2020JanVF ).]
Other reliability errors include:
- False negatives. These are a result of the patient seeing a dim stimulus, but, when tested again, the patient did not respond. It could be a result of the patient tiring. Use gentle prompts and commentary to keep the patient alert. Note on the field or chart if the patient was falling asleep or had a difficult time.
- False positives. These occur when the patient pushed the button when no stimulus was presented. When preparing the patient’s VF, take a quick glance at their old tests, if available. See whether the patient has a history of unreliable tests, and even if they are a regular patient, provide quality instructions with your script. If they have a higher level of false positives, remind them that it is normal to not see all the targets.
Develop knowledge and skills
While we can’t cover the large topic of VFs in a single article, we’ll address main topics for further education. It is good to know why the test was ordered. Which specialty does it concern: glaucoma, neuro-ophthalmology, or retina? Knowing this allows you to double check to ensure the order matches the doctor's concern. The order gives you a clue of what to look out for, such as tunnel vision for end-stage glaucoma, hemianopia in a stroke patient, etc. Note that not all doctors specify, so the default test for glaucoma can be done in error.
The technician also should be familiar with these core areas:
- Anatomy of the VF pathway. Light has to be able get to the retina, so anything that gets in the way of that can cause a VF defect. Some may be artificial, like a lens edge rim, droopy eyelid, or natural, like a cataract. The retina nerve fibers are split into quadrants (SN, IN, ST, IT); the nerve fibers continue along forming the optic nerves, through the chiasm, splitting into the optic tracts, lateral geniculate bodies, and optic radiations, ending to form the visual cortex in the occipital lobe of the brain.
- Anatomical mapping terminology. By anatomy they are fovea and optic nerve but on the VF graph they correspond to fixation and blindspot. The blindspot is about 15° temporal to the fixation. Remember fixation is 0° on the graph. The VF is inverted and reversed from the retina.
- Pupil size. Small pupils and medications that cause small pupils can artificially constrict a VF. Consult with the doctor to see their preference if the VF is performed pre- or post-dilation, particularly in this case. For example, patients being treated for dry mouth may be prescribed pilocarpine, which can cause pinpoint pupils (1-2mm).
- Target size. For patients who have moderate to severe vision loss (20/200 or worse), consider increasing the size of the target (stimulus). The typical size of the target is the equivalent of an III4e (4mm2) but can be changed to a V4e (64mm2) with a different test strategy. This takes switching software strategies; so again, consult with a doctor for their preference.
- Visual issues. It’s crucial to have the patient’s BCVA for testing, otherwise false defects can occur. To reduce possible errors learn how to correctly calculate depending on: age, if dilated, monovision, or contact lenses. Don’t forget to pick up the correct lens, don’t assume!
To provide quality care to our patients, seek education to learn the “how” and the “why” in the art, science, and math of VFs. Learn from your co-workers and manager (clinical trainer). Read the manual. Read the manual?! Skim the table of contents and read one section at a time. Seek an accredited training program, for example, icaccreditation.org/find_a_program/find_a_program.html . Join an ophthalmic tech Facebook group, ask questions, and lean on the community. You too can be a VF superhero! OP