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