LEC 1: INTRODUCTION & TYPES OF FIELDS LOSS

Question 1

What is meant by visual field?

Answer 1

Visual field is that portion of space in which objects are visible at the same moment during steady fixation of the gaze in one direction.

Question 2

Maximum extent of the visual field: superior, inferior, temporally & nasally?

Answer 2

Superior and nasally: 60 degrees
Inferiorly: 75 degrees
Temporally: 100 degrees

Question 3

Fovea is used to measure?

Answer 3

Visual acuity alone.

Question 4

Visual field exam role?

Answer 4

Used to measure peripheral vision.

Question 5

Describe how information moves from the retina down to the visual pathway?

Answer 5

Image is centrally transduced from photochemical response to electric response. This electric response moves down the visual pathway. - (Crossing at the chiasm).

Question 6

3 purposes of routine visual field exam?

Answer 6

Early detection, the assessment and the follow-up of functional loss of the visual system.

Question 7

What is the instrument used to measure visual field called? And what is its use? What is the operator called?

Answer 7

Perimetry or Perimeter
Use: Measure perimeter of visual field.
Operator: Perimetrist

Question 8

Describe how perimeter is used?

Answer 8

(Normally) involves the presentation of a small spot of white light (the stimulus) against a white background of uniform luminance. Patient is asked to report the first time they see the presentation of that small spot of light and press the button.

Question 9

What does perimeter measure?

Answer 9

Detection threshold- detecting the presence of that white light in the visual field when it is superimposed upon the background with white light at constant brightness.

Question 10

2 types of perimetry?

Answer 10

1. Static perimetry- spot of light stationery within the visual field.
2. Kinetic perimetry- spot of light moving edge of the visual field until it is first detected then it is moved in towards fixation and px indicates if it disappears.

Question 11

2 types of static perimetry?

Answer 11

1. Threshold
2. Suprathreshold

Question 12

The results from static perimetry is in decibels (dB)- what do this numbers indicate?
What does it mean if this number is very large?
The lower the number indicates?

Answer 12

The numbers relate to the brightness of the spot of light.
If numbers are very large- this indicates that the eye is very sensitive to very dim and small spots of light.
Lower the number: worse the vision.

Question 13

The results from static perimetry, a triangle is seen under a certain number, what does this triangle indicate?
Why is the number below this triangle reduced in value?

Answer 13

The triangle indicates the position of the blind spot.
Reduced value of number: shows the location around the edge of the blind spot.

Question 14

Damage to the visual field is described as?

Answer 14

Visual field loss or visual field defect.

Question 15

When looking at grey scale diagram in test results- what does this dark shaded region indicate?

Answer 15

This is the position of the blind spot.

Question 16

Describe the colour allocation in grey scale diagram- dark and light greys.

Answer 16

Black dots are allocated to very poor vision- numbers around 0. Light grey numbers are allocated to the very high numbers.

Question 17

Describe how kinetic perimetry is performed?

Answer 17

A white stimulus is moved from the area where it is not seen towards the area where it is just seen (radially from the periphery to fixation).
The specific location where the stimulus is just seen is recorded as threshold.

Question 18

Bitemporal Hemianopia meaning and area of the visual pathway defect?

Answer 18

Ocular defect that leads to impaired peripheral vision in the outer temporal halves of the visual field of both eyes. Area of visual pathway defect: in optic chiasma.

Question 19

Hemianopia meaning

Answer 19

Hemianopia: Where there is a loss of one half of your visual field.

Question 20

Describe why the retina is said to be reversed?

Answer 20

Light passes through retinal nerve fiber layer (axons of RGCs). Light then progresses to rods and cones.

Question 21

Nasal and temporal RGCs, which ones cross and which one stays on the same side?

Answer 21

Nasal RGC axons cross, Temporal RGC axons stay on the same side.

Question 22

Nasal and temporal RGCs, which ones cross and which one stays on the same side?

Answer 22

Nasal RGC axons cross, Temporal RGC axons stay on the same side.

Question 23

Describe how rods and cones are scattered in the RNFL vs axons of ganglion cells?

Answer 23

Rods and cones are scattered all over the RNFL. Axons of ganglion cells swipe in a very arcuate manner into the optic nerve head. They do not cross over the horizontal mid-line.

Question 24

Glaucoma damages the optic nerve head area in what o’clock region?

Answer 24

Glaucoma damages the optic nerve head area in the 6 and 12 o’clock region.

Question 25

In the results of the visual field test- on the grey scale, optic disc is on which side?

Answer 25

Blind spot is projected temporally. Left eye: blind spot on the left side.

Question 26

The dark areas shown on the grey scale asides from the blind spot indicate ?

Answer 26

Abnormal areas

Question 27

When the defect crosses the horizontal line it is unlikely to be ?

Answer 27

Unlikely to be in retinal nerve fiber layer defect.

Question 28

When the defect crosses the vertical line it is unlikely to be ?

Answer 28

It is unlikely to be a neuron abnormality.

Question 29

Conclusion when clumping seen in fundus that crosses the horizontal and vertical mid line?

Answer 29

Retinitis Pigmentosa- Rod defect

Question 30

Characteristic seen in grey scale for px with retina pigmentosa?

Answer 30

Ring formed around that is darker than the rest of the field.

Question 31

When a defect does not cross horizontal line- this indicates?

Answer 31

Retinal Nerve Fiber Layer problem

Question 32

Difference between eye pressure between 2 eyes is significantly very important for diagnosis above?

Answer 32

Pressure difference between 2-3mmHg.

Question 33

Stroke on the left-hand side of the brain- hence likely to affect which visual field?

Answer 33

Right visual field

Question 34

Stroke affects vision- where in the visual pathway is this effect seen?

Answer 34

Optic Chiasma related visual field loss - including optic radiations.

Question 35

Does visual field measure the integrity of the entire visual pathway?

Answer 35

Yes

Question 36

How do you alter visual field exam in Px with cataract or a corneal problem?

Answer 36

The spot of light can be reduced in brightness.

Question 37

What is seen in visual field test results for Px with a cataract or corneal opacities or dystrophy?

Answer 37

Generalised visual field loss

Question 38

Describe abnormality crossing for Receptor Level Visual Field Loss?

Answer 38

Crossing over the horizontal and vertical midline.

Question 39

Describe abnormality crossing for Nerve Fiber Layer Visual Field Loss

Answer 39

Abnormality does not cross over the horizontal but crosses over the vertical.

Question 40

Describe abnormality crossing for Chiasma Related Visual Field Loss And Beyond- in the optic radiation-

Answer 40

Abnormality crosses horizontal line but not vertical line.

Question 41

What are the 3 types of field loss?

Answer 41

1.Generalized (overall) damage to the visual field.
2.Localized (focal) damage within the visual field (scotoma; focal defect)- Related to glaucoma
3.Damage at the edge(s) of the visual field (constriction/ contraction). - Related to stroke

Question 42

Structural and functional assessments used for detecting glaucoma?

Answer 42

Structural assessment: OCT
Functional assessment: Visual fields