Visual Fields Flashcards
what is the visual field?
all the space that an eye can see at any given time
what is the extent of VF?
60 derees towards nasal
100 degrees to periphery
60 degrees up to forehead
75 degrees down to nose
how is visual field limited?
limited by facial anatomy -forehead eyebrows nose cheek bone
how much is central Visual Field?
30 degrees
how much is peripheral Visual Field?
more than 30 degrees
how does the visual field work in the retina?
every point in the retina corresponds to a certain direction in the visual field
what does the retinal image look like?
image will be upside down and back to front
how does the retinal sensitivity work?
retina most sensitive at macula
retina least sensitive at the optic disc
why is the retina most sensitive at the macula
high density of cones
why is the retina least sensitive at the optic disc?
low density of cones
why is the physiology of the blind spot?
Blind spot is the temporal projection of optic nerve 5.5 degree wide 7.5 degree high 15 degree from fixation 1.5 degree below horizontal midline
where is the blind spot in the R eye ?
Blind spot on the R hand side
Where is the blind spot in the L eye?
Blind spot on the L hand side
What is the definition of Visual Field?
Perimetry is the measurement of the Visual Field
what types of perimetry are there?
Kinetic perimetry
Static Perimetry
what is Kinetic perimetry?
A stimulus of fixed size and luminance is moved from a non seeing area top the seeing area until it is detected by the patient
How is Kinetic perimetry recorded?
Go all around the 360 degree and points are shown eccentricity that stimulus is seen is then recorded as an isopter
what is an Isopter?
Points of equal sensitivity form together to make an isopter
If you change size and light sensitivity what changes?
isopter changes
what is the shape of the isopter for a large and bright stimuli?
big round isopter
what is the shape of the isopter for a small and dim stimuli
small isopter
what do you get if the isopter is repeated three times?
Contour map of visual field
What manual Kinetic Perimeter are there?
Gross Perimetry
Goldmann Perimetry
How do you do gross perimetry?
1) patient faces practitioner
2) occlude one eye
3) patient fixate at practitioner nose
4) target held at 35cm from patients non seeing field of view
5) patient reports when target first seen
6) carried out uniform surrounding in all 8 position of gaze
7) tell patient when they cannot see it
what do you take care of when doing gross perimetry?
- -target is moved at constant velocity in an imaginary arc
- -take a mental note of when px see the target
- -repeat in all 8 directions
- -only very gross defects detected
- -repeat other eye
what are the 8 position of gaze?
Superior, superior nasal, nasal
inferior nasal, inferior, inferior temporal, temporal, superior temporal
what is the advantage of gross perimetry?
Quick
Cheap
Only method possible with young children and elderly with strokes
will detect grodd field defects
what is the disadvantage of gross perimetry?
- Useless for small area defect
- no control on stimulus contacts/luminance
- no control on background
- recongintion of defect depends all on the practitioners judgment
How does the goldmann Bowl perimetry work?
1) Occlude one eye
2) ajdust chin rest head rest so that px eye is in centre of telescope vies
3) instruct px
4) put up correct refractive correction
5) select stimulus and record what they see
6) continue to move to the centre and report when it dispears
7) repeat again for 2 other stimulus
8) repeat other eye
when can you have refractive correction for Visual Field?
inside 30 field degrees always give reading correction or >+/- 8DS
What is the reading correction?
distance correction + reading addition
what are the goldmann reading additions?
age 40-44 = +1.50D
age 45-49= + 2.00D
age 50-54= +2.50D
age 55+ = +3.00 D
when do you not give reading correction?
when outside 30 degrees of field of view
When do you give cylinder correction?
if cylinder is less that 1D give mean sphere
if cylinder is 1D or more give actual cyl
what is mean sphere?
mean sphere= sphere + half cyl
What is good about octopus goldmann perimetry?
- aged matched normal values- for immediate judgment of normality
- repeatable tests: automatic repetition and follow up kinetic examinations
- quantification: measurement of isopter for the quantification of progression
- Automatic repition of kinetic examinations using follow up bottom
- manual or automated kinetic testing
what can you do with manually humphrey ?
choose: size of stimulus intensity of stimulus speed of stimulus colour of stimulus no of meridian tested no of isopters tested special mapping ( blind spot plot and scotoma plott)
what does the humphrey not do?
It does not monitor fixation constantly
what is the overall advantage of kinetic perimetry?
useful for detecting contraction of visual field
useful for detecting neurological problems
useful in young children when automated not possible
children/ adults with stroke may find find it easy to use manual perimetry
what is the overall disadvantage of Kinetic perimetry?
..required skilled operator with manual perimetry
..results are operator dependent with manual
..time consuming with manual perimetry
..difficult to quantify results with manual
.. poor sensitivity for detecting scotomos both manual and automated
what is missed with kinetic perimetry?
Scotomas
How is gross perimetry recorded?
PERL(A)
What does perl(A) mean?
pupil equally responsive to light and accommodation
