visual fields I Flashcards
what is the visual field ?
- all the space that an eye can see at any given time
what is the normal level of visual field ?
- superiorly is approximately 60 degrees
- inferiorly is 70 degrees
- nasally 60 degrees
- temporally 100 degrees
what is visual field limited by ?
- limited by facial anatomy
. forehead
. eyebrows
. nose
what does the full field measure to ?
- the full field measures to a 200 degrees across
what is the binocular visual field ?
- 120 degrees
what is the vertical extent of the visual field ?
- the vertical extent of the visual field is the same monocularly as it is binocularly
example- if you put your finger up high, and close either one of your eyes , you will still be able to see
how to do a central visual field ?
- you must do within the central 30 degrees
how to do a peripheral visual field ?
- beyond central 30 degrees
where does nasal retina project ?
- projects temporally
where does superior retina project ?
- projects inferiorly
what does every point in the retina correspond to ?
- every point in the retina corresponds to a certain direction in the visual field
where do you see damage in the superior temporal retina in visual field ?
- inferior nasal retina
where is the highest density of cones ?
- centre of the macula and fovea
where is the blind spot largest ?
- blind spot is larger vertically than horizontally
where is the the blind spot ?
- always approximately 15 degrees from fixation ( from the fovea )
where is the blind spot in the right eye ?
- blind spot on the right
where is the blind spot in the left eye ?
- blind spot on the left
what is difference between visual field and fundus exam ?
- the visual field is what the patient sees
- so right is on right
- left is in the left
- the fundus exam is what the clinician sees
- right eye on left
- left eye on right
what is the measurement of visual field ?
- perimetry is the measurement of the visual field
what are two types of perimetry ?
- kinetic perimetry - stimulus is moving
2. static perimetry - stimulus stays down
what is hill of vision ?
- height of the hill is threshold sensitivity
- everything inside the hill you can see except the blind spot
- everything outside the hill you cant see
what is kinetic perimetry ?
. stimulus of fixed/luminance is moved from non-seeing to seeing until it is detected by the patient
how to carry out kinetic perimetry ?
- move the stimulus from where they can’t see it until where they can and mark on map
- move about 15 - 30 degrees
- keep doing until you go around 360 degrees
- join together ( called an isopter )
how to record kinetic perimetry ?
- eccentricity that the stimulus is seen at is then recorded
- points of equal sensitivity form together to make an isopter
- different isopters are measured using different stimulus sizes or light intensities or colour can be shown
how is kinetic perimetry repeated ?
- procedure is repeated with a smaller/lower luminance stimulus
what is reliable kinetic perimerty ?
- a minimum of 3 isopters is required to obtain a good ‘ contour map’ of the visual field
- thew higher the Roman numeral the higher the number the brighter the stimulus
what are the manual types of kinetic perimetry ?
- gross perimetry
- goldmann perimeter
how to do gross perimetry ?
- patient faces practitioner
- occlude one eye
- patient told to constantly fixate examiners nose
- target held 35cm from the patient’s eye outside the field of view
- patient reports when they are first aware of the target
- carried out in uniform surrounding if possible
- target moved at constant velocity in an imaginary arc
- once patient notices target ( mental note made of it ) and the target continues to the centre
- repeated in eight directions ( superior, superior temporal, temporal)
- repeated with other eye
- only very gross defects detected
what are the advantages of gross perimetry ?
- quick
- cheap
- only method possible with young children/ elderly with stoke
- will detect gross field defects
what are the disadvantages of gross perimetry ?
- virtually useless for small areas of loss
- no control of stimulus luminance/contrast
- no control over background
- recognition of defect entirely dependent on judgment of practitioner
what is in goldmann perimetry ?
- patient’s side
- projector - put the light on to screen
- head rest
- button response - to press every time they see light
- practitioner’s side
- pantoscopic arm
- target luminance and size control
- chart
how to set up goldmann bowl perimeter ?
- occlude one eye
- adjust chin/head rest so patient’s eye is in the centre of the telescope’s field
- instruct patient to look at light in the centre and let you know when they see light
- put up correct refractive correction
what are the rules for refractive correction ?
- inside 30 field degrees always give reading correction ( distance correction + reading addition which is appropriate machine)
- Reading correction= distance correction + reading addition.
- outside 30 degrees no correction unless >+/- 8DS
what is goldmann’s table near addition to use when doing the calculation?
. 40-44 +1.50 DS
. 45-49 + 2.00 DS
. 50-54 +2.50 DS
. 55 and older or cyclopleded +3.00 DS
what is the rule of thumb of refractive correction in goldamm perimeter ?
1- cylinder correction < or equal to 1 dioptre convert to mean sphere
mean sphere = sphere + 0.5 x CYLINDER (half the cyl)
2- cylinder correction > 1.00 insert actual cylinder
how to carry out goldmann perimeter ?
- select stimulus
- move stimulus in from periphery ( non-seeing to seeing )
- recored where they can see it
- continue to move the stimulus to the centre asking the patient to report if it disappears
- repeat for at least 2 other stimulus size/luminance combinations
- repeat for other eye
what is the goldmann perimetry with the octopus ?
- age matched normal values: for immediate judgment or normality
- repeatable tests: automatic repetition and follow up of kinetic examination
- quantification : measurement of isopters for the quantification of progression
- automatic repetition of kinetic examinations using follow up button
- manual or automated kinetic testing
how to plot kinetic perimetry manually with the humphrey ?
- choose the following . size of stimulus . intensity of stimulus . colour of stimulus . no of meridian tested . no of isopters tested . special mapping ( plot blind spot, plot scotoma ) . does not monitor fixation constantly
what are the advantages of kinetic goldmann perimetry ?
. useful for detecting contraction of the visual fields
. useful for detecting neurological problems
. useful in young children when automated not possible
what are the disadvantages of kinetic goldmann perimetry ?
. requires skilled operator with manual perimetry
. results are operator dependent with manual perimetry
. time consuming with manual perimetry
. difficult to quantify results with manual perimetry
. children/adults with stroke may find manual perimetry easier
. poor sensitivity for detecting small scotomas both manual and automated
-scotomas are easily missed.
