Visual Field Flashcards
Test 1 Material (46 cards)
Define Visual Threshold
The visual threshold is the intensity at which a stimulus is first visible, or visible 50% of the time.
How much does a patient’s threshold vary in normal individuals? What about those with disease processes?
Normal: 3dB per day
Disease: 6-8dB per day
This fluctuation can make it hard to tell if there is a disease present or if it’s normal fluctuation.
Explain the stimulus intensity scale associated with the visual threshold.
Stimuli intensity vary from 50dB-0dB. The higher dB values are dimmer stimuli intensity, and lower dB values are brighter stimuli intensity. The average, healthy individual will have a threshold range of lower/mid 20’s to upper 30’s on the dB scale. The foveal vision limit is 40dB.
What is the range of the normal hill of vision?
Temporally: 90 degrees
Nasally/Superiorly: 60 degrees
Inferiorly: 70 degrees
What are the two types of visual field testing? Explain the differences.
Static and Kinetic.
Static is most common, as it takes less time per eye and there are norms to compare results to. The stimulus is stationary.
Kinetic takes a long time and usually is only used for specific purposes, like special drivers licenses or disability testing. The stimulus moves. Kinetic testing has no norms to compare data to. Similar to confrontations, the stimulus starts peripheral and is moved central until the patient reports seeing the stimulus.
What are the standard illumination, stimulus duration, and stimulus size/intensity that are used for automated perimetry?
Standard illumination: 10Cd/m^2
Stimulus Duration: 200ms
Size/Intensity: Goldman Size III
When might you use a Goldman size V stimulus size?
When the person has very poor acuity.
Explain the two types of suprathreshold testing.
Suprathreshold testing is a screening system that utilizes a stimulus that is well above the expected threshold at all test points. If a patient has a defect/depression, that will be caught by the screening process.
Single Intensity Screening: While the threshold varies for each individual threshold, the stimulus intensity is constant (25dB). Therefore, the pass-fail criterion is variable by position.
Threshold Related Screening: The stimulus intensity varies based on the expected threshold for each point. Therefore the pass-fail criterion is constant by position.
Threshold Related Screening is more sensitive than Single Intensity Screening, but neither gives quantitative information. Threshold testing, which is the gold standard of visual field testing is required for quantitative information.
Explain threshold testing.
Threshold testing is the gold standard of visual field testing. It utilizes a repetitive bracketing method to estimate the threshold of the patient. This means a stimulus is presented suprathreshold, and then infra threshold, and then back and forth until the threshold point is estimated. Threshold testing gives both quantitative and qualitative information
What degree of the visual field does each of the following test?
- 30-2
- 24-2
- 10-2
- 30-2: Central 30 degrees, 76 points
- 24-2: Central 30 degrees, 54 points
- 10-2: Central 10 degrees, 68 points
What are the differences between the Humphrey FDT and the Humphrey Matrix FDT?
The Humphrey FDT:
Frequency Doubling
Tests M-Pathway (more susceptible to glaucoma)
Screening:
1. C-20: 17 points central field
2. N-30: C-20 + 2 points tested above/below midline
Limitations:
1. Large stimulus size (hard to detect subtle defects)
2. Few stimuli
3. No fixation monitoring
4. Small screen, had to change fixation for N-30
The Humphrey Matrix FDT:
Sought to fix the flaws of the original FDT.
Frequency Doubling
Targets M-Pathway
Improvements from original FDT:
1. Can perform screening and full threshold.
2. Smaller stimulus size
3. Fixation monitoring
4. Larger Screen size, no longer need to change fixation for N-30
How do you describe a scotoma?
- Position: Can be peripheral, paracentral, central, cecal, or centrocecal.
- Shape: Can be arcuate, ring-shaped, or oval/round
- Size: Described by the extent in degrees
- Intensity/Depth: Quantifies how much sensitivity is lost
- Uniformity: Constant or irregular
- Margins: Steep, sloping
- Onset/Course: Rapid, slow
- Laterality: Unilateral, bilateral
Define a scotoma.
Scotoma: Any area of decreased sensitivity from the norm, whether it be partial/relative (depression) or absolute/complete (contraction). Scotomas can also be positive or negative, meaning the patient is aware of the scotoma (positive) or unaware of the scotoma (negative).
What is a depression in a visual field?
An area that exhibits a decrease in visual sensitivity from expected. Depression is the most general classification of a visual field defect. Depressions can be either localized or generalized. Generalized depressions occur when there is a uniform decrease in the visual field. The patient’s entire field is depressed. This can be due to medial opacities, small pupils, and/or inadequate RE. Localized depression occurs when only one area shows a decrease in patient sensitivity. A depression can further be categorized in the same way as a scotoma.
Differentiate between a depression and a scotoma.
A depression is any decrease in sensitivity in a visual field. A depression can be localized to one specific area, or it can be a general reduction in sensitivity across the entire field. A scotoma is any reduction in sensitivity that is surrounded by normal/near-normal vision. A scotoma is the same as a localized depression.
Explain the different positions of a scotoma.
Peripheral: Outside central 30 degrees
Paracentral: Inside central 30 degrees but not involving fixation
Central: Involving fixation
Cecal: Involving the optic nerve (normal blind spot)
Centrocecal: Involving the optic nerve (normal blind spot) and fixation
What are some examples of causes of a positive scotoma?
New retinal detachment
Advanced glaucoma
Macular degeneration
What are some examples of causes of a negative scotoma?
Long-standing retinal detachment
New-onset glaucoma
Optic nerve (blind spot)
What are the different shapes of a scotoma? What is the likely cause of each shape?
Arcuate: Superior/Inferior arcuate bundle defects due to glaucoma
Ring: Retinitis Pigmentosa
Round/Oval: Central or centrocecal scotoma
What is the difference between sloping and steep margins in a visual field?
Steep usually means more advanced or end-stage
Sloping usually means more recent/active
What is the difference between a slow and rapid onset/course of a visual field defect?
Slow usually is due to toxic effects, a tumor, or glaucoma
Rapid usually is due to vascular compromise such as hemorrhage, infarction, inflammation, etc
How does the location of a lesion in the visual pathway relate to a visual field?
Pre-chiasmal is unilateral
Chiasmal, post chiasmal, or lesions of both nerves pre-chiasmal are bilateral
What are some potential causes of a generalized threshold depression?
Inadequate refractive error correction
Small pupils
Cloudy media
Slow reaction time (specific to kinetic testing)
Describe a pre-chiasmal lesion and how the corresponding visual field will appear.
Pre-chiasmal lesions will produce unilateral defects. The only time a bilateral lesion may be present is if there is an abnormality present in both eyes before the chiasm.
If the pre-chiasmal lesion is mostly superficial (not involving the retina/choroid, but instead due to medial opacity/uncorrected RE/small pupil) then the field defect will likely be more general and not have any characteristic pattern.
If the pre-chiasmal lesion involves the outer retina/choroid, there will be no respect for the vertical or horizontal midlines.
If the pre-chiasmal lesion involves the inner retina/NFL/Optic nerve, the lesion will correspond to the distribution of the NFL bundles. These defects will respect the HORIZONTAL meridian and an RAPD may be present. An RAPD may be present because pupillary fibers have not left the visual pathway at this point.
