- 1.
What are the main types of visual-field tests?
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Confrontation visual fields
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Kinetic perimetry
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Static perimetry
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Amsler grids
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- 2.
How are confrontation fields used in practice?
Confrontation fields are used as a screening tool because they are a simple, quick, qualitative method for finding gross defects in the peripheral field. The test is performed with the examiner facing the patient and asking if the patient can see fingers in all four quadrants while looking directly at the examiner, testing one eye at a time. In clinical practice, this is more of a screening test. A defect picked up by confrontation fields can be described more definitively with formal field testing.
- 3.
What is the normal field of vision?
From the fixation point, the visual field is 60 degrees nasally, 110 degrees temporally, 75 degrees inferiorly, and 60 degrees superiorly.
- 4.
What is the difference between kinetic and static perimetry?
With kinetic perimetry, a stimulus of a particular size and intensity is moved throughout the visual field. The area within which a given target is perceived is known as that target’s isopter. These are marked with different colors to easily differentiate the multiple stimuli used. Central vision is mapped with dimmer, smaller stimuli. Larger, more intense stimuli are used for peripheral vision. The Goldmann perimeter and tangent screen are examples of kinetic techniques. With static perimetry, a test site is chosen and the stimulus intensity or size is changed until it is large enough or bright enough for the patient to see it. The Humphrey and Octopus machines are examples of static perimetry.
- 5.
When is kinetic perimetry used?
The test can be helpful in patients who require significant supervision to complete visual-field testing, i.e., children, stroke victims, and patients with dementia and other mental challenges. Patients with low vision due to central vision loss are another indication.
Highly trained personnel are needed to administer these tests.
- 6.
What is full-threshold testing?
Full-threshold testing refers to static visual-field testing in which the exact threshold of the eye is measured at every point tested. This technique differs from suprathreshold testing in which test objects are presented at a fixed intensity. Suprathreshold testing is used mainly in screening programs and may miss early defects. Also, a shallow defect will appear the same as an extremely deep defect.
- 7.
You order a Goldmann visual field, and the isopters are labeled with notations such as I2e and V4e. What do these notations mean?
The target size and intensity are indicated by a Roman numeral (I to V), an Arabic numeral (1 to 4), and a lowercase letter (a to e). The Roman numeral represents the size of the target in square millimeters. Each successive number is an increase by a factor of 4. The Arabic numeral represents the relative intensity of the light presented. Each successive number is 3.15 times brighter than the previous one. The lowercase letter indicates a minor filter. The “a” is the darkest, and each progressive letter is an increase of 0.1 log unit.
- 8.
How is an Amsler grid used to test visual field?
The grids can be used to detect central and paracentral scotomas. If held at one-third of a meter, each square subtends 1 degree of visual field.
- 9.
Where is the physiologic blind spot located?
It is in the temporal visual field. The fovea is the center of the visual field. The blind spot is 15 degrees temporal and just below the horizontal plane. On the Humphrey visual field, it is marked by a triangle.
- 10.
When looking at a visual field, how do you differentiate the right eye from the left eye?
The right and left eyes are differentiated by noting where the blind spot is located. The right eye has the blind spot on the right side in its temporal field, and the left eye has the blind spot on the left in its temporal field. If the field loss is so great that the blind spot cannot be identified, the top of the printout should say which eye was tested.
- 11.
What are causes of fixation errors? What can be done to decrease them?
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Poor patient fixation
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“Trigger-happy” patient
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Mistake in locating the blind spot
Try replotting the blind spot, reinstructing the patient, or changing the fixation diamond to one that does not require central vision in patients with macular disease or central scotoma. If the fixation loss is greater than 20%, the test is not reliable. Small defects may be missed and the depth of large defects can be underestimated. A kinetic field may be more helpful clinically.
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- 12.
What are false-negative errors?
False negatives occur when a stimulus brighter than threshold is presented in an area where sensitivity has already been determined and the patient does not respond. The patient is usually inattentive and the field will appear worse than it actually is. They may also occur in patients with extremely dense defects.
- 13.
What are false-positive errors?
Most projection perimeters are fairly noisy, and there is an audible click or whirring while the machine moves from one position to another in the field. False positives occur when the projector moves as if to present a stimulus but does not and the patient responds. The patient is “trigger-happy,” and the field will look better than it actually is.
- 14.
On a Humphrey visual field, what is the difference between total deviation and pattern deviation?
The total deviation is the point-by-point difference from expected values for normal patients that are in the same age range. It cannot confirm a scotoma, but shows only generalized depression. The pattern deviation adjusts for the generalized depression or elevation and confirms the presence of a scotoma.
- 15.
What is a scotoma?
A scotoma is an area of lost or depressed vision within the visual field surrounded by an area of less depressed or normal visual field. On the pattern deviation plot, three or more nonedge points, clustered in an arcuate area, are suspicious for a scotoma.
- 16.
On a Humphrey printout, what do MD, PSD, SF, and CPSD mean? Are they important?
Mean deviation (MD) is similar to the total deviation plot, i.e., generalized depression. Pattern standard deviation (PSD) is a measure of the degree to which the numbers are different from each other, i.e., local irregularity. This shows more information regarding potential scotomas. Short-term fluctuation (SF) is a measure of intratest error in determining thresholds. Ten predetermined points are each tested twice. Corrected pattern standard deviation (CPSD) is the PSD corrected for the SF. If the SF shows unreliability, the CPSD is better. If the SF is due to true pathology, the PSD is better. If the CPSD or PSD is depressed with p < 5%, it is likely the patient has scotoma.
- 17.
What are false field defects? What are some of their causes?
False field defects occur when the interpreter overlooks physical factors and interprets them as true field defects:
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Ptosis and dermatochalasis can cause loss in the upper parts of the field. Taping the lid up will clear these defects.
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A tilted optic disc can cause local variations in retinal topography, giving the impression of a field defect for refractive reasons alone. When a patient has bilateral tilted discs, the effect can mimic a bitemporal visual field loss.
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A small pupil may give a false impression of true field loss. Dilation of the pupil will clear these defects. This is especially important in patients on miotic therapy ( Fig. 6-1 ).
Figure 6-1
A small pupil can create a false impression of visual-field defects. Note that a majority of the defects disappear or lessen when the pupil is dilated from 2 to 8 mm.
(From Gross R: Clinical glaucoma management, Philadelphia, 2001, W.B. Saunders.)
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The rim of the trial lens will give a defect in the periphery of the central visual field. This will be noted if the patient pulls the head back from the machine while taking the test ( Fig. 6-2 ).
Figure 6-2
Rim artifact caused by the lens and lens carrier. This is most commonly seen in patients on whom a hyperopic correction is being used. A clue to the presence of a rim artifact is the abrupt change from a fairly normal reading to a sensitivity of 0 dB.
(From Alward WLM: Glaucoma: the requisites in ophthalmology, St. Louis, 2000, Mosby.)
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Media opacities: cornea, lens, and vitreous opacities may cause routine test objects to be invisible. Using larger, brighter test objects may help clarify this problem. This generalized decreased sensitivity can be noted on the total deviation on a Humphrey visual field, but the pattern deviation may show no defects.
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- 1.
Ptosis
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Tilted optic disc
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Small pupil
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Rim defect
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Media opacities
- 18.
What is hemianopia?
Hemianopia is defective vision or blindness in half of the visual field of one or both eyes.
- 19.
Define the terms homonymous and congruous in relation to visual-field defects.
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Homonymous: Pertaining to the corresponding vertical halves of the visual field of both eyes. In plain language, the term is used for defects that occur after neurologic insults that cause loss of a portion of the visual field subsumed by both eyes.
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Congruous: Matched visual-field defects. The more congruous the defect, the more posterior the lesion.
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- 20.
How do you describe a visual-field defect?
- 1.
Position: Central (defined as the central 30 degrees), peripheral, or a combination of both. Note if the defects are unilateral or bilateral.
- 2.
Shape: Very helpful diagnostically. Visual-field defects can be monocular or binocular. The most common form of monocular sector defect is found in glaucoma. The shape is determined by physiologic interruption of nerve fiber bundles. The typical binocular sector defect is a hemianopia.
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Intensity: This refers to the depth of the defect.
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Uniformity: This refers to the depth of the defect throughout the defect.
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Onset and course : This is determined by serial visual fields.
- 1.
- 21.
What are the different types of hemianopia?
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Homonymous, total: Loss of temporal field in one eye and nasal field of the other eye. The vertical midline is respected. The fixation point may be included or spared. This defect implies total destruction of the visual pathway beyond the chiasm unilaterally, anywhere from the optic tract to the occipital lobe. A complete homonymous hemianopia is nonlocalizing.
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Homonymous, partial: The most common visual-field defect. It may be caused by injury to postchiasmal pathways. Again, it can result from damage at any point from the optic tract to the occipital lobe ( Fig. 6-3 ).
Figure 6-3
Bitemporal hemianopia: incongruous noted on both the Goldmann perimeter (above) and the Humphrey perimeter (below).
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