CPO FREE CPO Visual Field Testing (Perimetry) Questions and Answers 2 — Questions and Answers
Question 1: A visual field printout shows a dense superior defect that appears arcuate in shape on the pattern deviation plot. However, the grayscale plot shows a distinct 'cloverleaf' or quadrantanopic pattern. What is the most likely cause of this specific artifact?
- Incorrect trial lens placement creating a rim artifact.
- Patient fatigue and inattention, leading to a high number of false negatives. (Correct answer)
- A 'trigger-happy' patient with a high false positive rate.
- Ptosis or a prominent brow obstructing the superior visual field.
Correct answer: Patient fatigue and inattention, leading to a high number of false negatives.
The 'cloverleaf' pattern is a classic sign of high false negatives. This occurs when a patient becomes fatigued or inattentive during the test and stops responding. Because the testing algorithm often checks the four central quadrant points first before spiraling outwards, the patient may respond initially but then fail to respond to dimmer or more peripheral stimuli, creating a pattern where only the central points in each quadrant are seen.
Question 2: A patient with a known pituitary adenoma is undergoing visual field testing. Which of the following less common visual field defects would most specifically indicate that the tumor is exerting pressure on the *uncrossed* nasal retinal fibers at the optic chiasm?
- Bitemporal Hemianopia
- Junctional Scotoma (of Traquair)
- Binasal Hemianopia (Correct answer)
- Homonymous Hemianopia with Macular Sparing
Correct answer: Binasal Hemianopia
Binasal hemianopia, the loss of the inner (nasal) halves of the visual field in both eyes, is a rare defect. It can be caused by pressure on the uncrossed temporal nerve fibers in both optic nerves, often from conditions like hydrocephalus or, in some cases, bilateral internal carotid artery aneurysms compressing the nerves from the side. While bitemporal hemianopia is classic for chiasmal compression, binasal defects point to pressure on the lateral, uncrossed fibers.
Question 3: Kinetic perimetry, such as Goldmann perimetry, is preferred over standard automated static perimetry in which of the following clinical scenarios?
- Detecting subtle, early-stage glaucomatous changes near fixation.
- Quantifying the depth of a known central scotoma for research purposes.
- Screening for plaquenil toxicity which affects the parafoveal region.
- Mapping the peripheral visual field boundaries in a patient with advanced retinitis pigmentosa. (Correct answer)
Correct answer: Mapping the peripheral visual field boundaries in a patient with advanced retinitis pigmentosa.
Kinetic perimetry, which uses a moving stimulus of a set size and brightness, excels at mapping the outer boundaries (isopters) of the visual field. It is particularly useful for assessing peripheral vision in conditions like advanced retinitis pigmentosa, evaluating complex neuro-ophthalmic defects, or for patients who cannot perform static perimetry well. Static perimetry is more sensitive for detecting and quantifying the depth of scotomas in early glaucoma or for central field defects.
Question 4: When performing perimetry on a patient who is wheelchair-bound and has difficulty maintaining a stable head position in a conventional automated perimeter, which modification is most critical to obtaining a reliable test?
- Using a larger stimulus size (Goldmann V) throughout the test.
- Switching from a SITA-Standard to a SITA-Fast strategy to reduce test time.
- Utilizing a virtual reality (VR) headset-based perimeter. (Correct answer)
- Performing the test without a trial lens to reduce discomfort.
Correct answer: Utilizing a virtual reality (VR) headset-based perimeter.
Conventional perimeters pose significant accessibility challenges for patients with mobility issues or those who cannot maintain the required posture. A virtual reality (VR) headset-based perimeter is an ideal solution as it eliminates the need for a chin/forehead rest, allows the patient to remain in their wheelchair, and can be performed in a reclined or comfortable position, greatly enhancing stability and reliability for this patient population.
Question 5: The Visual Field Index (VFI) is a global index on a Humphrey printout that stages the total amount of visual field loss. How does it primarily differ from the Mean Deviation (MD)?
- VFI is expressed in decibels, while MD is a percentage.
- VFI gives more weight to peripheral visual field points than central points.
- VFI is less affected by generalized depression, such as from a cataract, than MD. (Correct answer)
- VFI is only calculated for 10-2 tests, whereas MD is used for 24-2 and 30-2 tests.
Correct answer: VFI is less affected by generalized depression, such as from a cataract, than MD.
The Visual Field Index (VFI) is designed to be less sensitive to generalized depressions in the visual field, such as those caused by cataracts. It is a staged percentage (100% is normal, 0% is perimetrically blind) that gives greater weight to central points and is derived from the pattern deviation plot to minimize the effect of media opacity. Mean Deviation (MD), in contrast, reflects the overall mean departure from the age-corrected normal field and is significantly affected by cataracts.
Question 6: A patient with early glaucoma has a repeatable visual field test with fixation losses of 2/17, false positives of 1%, but false negatives of 35%. While this indicates inattention, what other clinical interpretation is possible for such a high false negative rate?
- The patient has an unusually large physiological blind spot.
- The test is unreliable and must be discarded without any interpretation.
- It can be an early indicator of significant, established visual field loss. (Correct answer)
- The patient was not wearing the correct near-add correction.
Correct answer: It can be an early indicator of significant, established visual field loss.
While a high false negative rate often signifies inattention or fatigue, it can also be a sign of significant, established disease. In areas of deep visual field loss, there is high threshold variability. The perimeter may determine a threshold and then re-present a brighter stimulus in that same damaged area that the patient, due to the disease, still fails to see. This is recorded as a false negative, making it a potential indicator of disease severity, not just poor test-taking.
CPO FREE CPO Visual Field Testing (Perimetry) Questions and Answers 2
A visual field printout shows a dense superior defect that appears arcuate in shape on the pattern deviation plot.
However, the grayscale plot shows a distinct 'cloverleaf' or quadrantanopic pattern.
What is the most likely cause of this specific artifact?