Chapter 11: Principles and Techniques of Perimetry Flashcards
Perimtery
The measurement of the expanse and sensitivity of peripheral vision and the visual field to pinpoint possible defects, typically done one eye at a time.
Functions:
1) Detect abnormalities in visual field
2) Monitor changes over time
Visual Field
The full view seen by an eye that is fixating straight ahead
The visual field of each eye overlaps on the nasal side
Visual Pathway
The route that is taken by light-generated nerve impulses after they leave the eye
Physiological Blind Spot
The sightless “hole” in the normal field corresponding t the optic disc where there are no photoreceptors. This is due to the like of rods or cones in that area.
This is typically located at 15 degrees eccentricity on the 0/180 degree meridian, very close to the central point of fixation.
Optic Chiasm
The point behind the eyes in the brain where the 2 optic nerves merge and the axon fibers from the nasal retina of each eye cross to the opposite side.
Circles of Eccentricity
A series of concentric circles at intervals of 10 degrees from the point of visual fixation, providing coordinates for mapping the visual field
Radial Meridians
Dividing sections radiating from the point of central fixation on a visual field chart
Quadrants
One of 4 quarters of the visual field: upper left, upper right, lower left and lower right
Horizontal and Vertical Meridians
The radial meridians that divide the visual field into 4 quarters: upper right, lower right, upper left, and lower left.
Any point in the visual field is located through denoting the degrees of eccentricity and the meridian.
Orientation of a Visual Field Map
Images focused on the retina are INVERTED and REVERSED!
Images that are seen by the patient on temporal side, are actually focused on the nasal portion of the retina. So damage to the superior portion of the retina, will cause a field defect on the nasal portion of their visual field.
Types of Perimetry
Kinetic Perimetry- uses a fixed object that moves to different locations
Static Perimetry- uses a fixed object and varies the brightness at each test location
Kinetic Perimetry
The type of perimetry that uses a moving the test object of a predetermined size and brightness. The simplest form of this is to move a hand or finger in the visual field of a patient that is fixated on a distance target. and noting when the patient first sees the finger/hand (CVF- Confrontational Visual Fields)
Advantages: simple to understand
Disadvantages: accurate results rely in patient and examiner capabilities
Static Perimetry
The type of perimetry that uses a target tat can be varied in size, brightness, and position within the visual field but is only displayed when stationary
Isopter
In visual field tests, a line connecting the points denoting areas of equal sensitivity to a stimulus; similar to contour lines denoting equal elevations to a topographic map
Scotoma
An area within the field of vision where vision is reduced
Shallow Scotoma
A mild visual field defect that appears as a depression in the island of vision
Deep Scotoma
A visual field defect more serious than a shallow scotoma; appears as a pit or well in the island of vision
Absolute Scotoma
A severe visual field defect in which the largest and brightest stimulus cannot be seen; blindness at that specific location
Tangent Screen Test
A type of manual perimetry used for identifying visual field defects within 30 degrees of a fixation point. The patient sits in front of a black screen, with one eye occluded and fixated on a central dot. The examiner will then move a wand with a target on it into the field of vision until the patient notes when they see it.
Advantages: simple to perform
Disadvantages: difficult to replicate all variables between testing
Goldmann Perimeter
A bowl-like instrument for testing visual fields which targets (lights) of different sizes and intensities are projected onto a standardized background illumination
Advantages: Reproducible for each testing
Suprathreshold Static Perimetry
A type of perimetry in which a light or target of a specific size, brightness, or intensity is chosen so that the patient should be able to see it when it is placed at a particular site in the visual field
Decibel
The unit ( one tenth of a log) of measure of the brightness of a test object
Threshold Static Perimetry
The type of static perimetry in which the threshold is that level of brightness at which the patient can just detect a test object about half of the time
Automated Threshold Perimetry
This is the visual field most commonly used today, and is used to determine the sensitivity ti light at each retinal location.
Advantages: more sensitive at detecting subtle defects, and eliminates technicians performing the exam
Disadvantages: Increase risk of errors and is more difficult for patients to understand, also more difficult for patients with limited mobility
