LEC 2: TYPES OF FIELDS LOSS & REPRESENTATION OF SENSITIVITY

Question 1

Describe what happens to fibers as they move down the optic nerve?

Answer 1

As you move down the optic nerve the fibers re-arrange themselves.

Question 2

Does abnormality only occur on retinal levels or even in the optic nerve?

Answer 2

Abnormality can occur anywhere from the optic nerve to even in the retina.

Question 3

What is Relative afferent pupillary defect-

Answer 3

A condition in which pupils respond differently to light stimuli shone in one eye at a time due to unilateral or asymmetrical disease of the retina or optic nerve. – it is indicative of the fact that there is damage in 1 eye.

Question 4

What is the defect called that does not cross over horizontally. It only crosses the vertical?

Answer 4

This is called superior/ inferior altitudinal loss.

Question 5

Altitudinal loss refers to?

Answer 5

Refers to damage in either the superior or inferior hemi-field. Hence, it can be superior or inferior loss only.

Question 6

Px with Altitudinal loss are said to suffer a min-stroke in the optic nerve called?

Answer 6

AION- Anterior ischemic optic neuropathy

Question 7

Where does AION- Anterior ischemic optic neuropathy defect occur in the visual pathway?

Answer 7

This defect occurs anteriorly in the visual pathway. NOT RETINA. It occurs in one eye.

Question 8

AION- Anterior ischemic optic neuropathy occurs in both or 1 eye?

Answer 8

1 eye

Question 9

Whenever performing evolutions both eyes need to be checked, why?

Answer 9

Because contribution from each eye occurs simultaneously to each visual field.

Question 10

Left temporal fibres correspond to what what visual feild

Answer 10

Left temporal fibres correspond temporally to the nasal field in the right eye.

Question 11

Hemianopia (Hemianopsia) meaning?

Answer 11

Loss of half of the visual field (with respect to the VERTICAL midline).

Question 12

Quadrantanopia (Quadrant anopsia) meaning?

Answer 12

Loss of one quadrant of the visual field (with respect to the VERTICAL midline). MUST INDICATE SUPERIOR OR INFERIOR.

Question 13

Left Vertical field loss corresponds to damage to which side of the brain?

Answer 13

Right side of the brain

Question 14

Homonymous meaning?

Answer 14

Loss on the “same side” (e.g. right or left homonymous hemianopia).

Question 15

Congruous meaning?

Answer 15

Similar shaped defect in both eyes (e.g. congruous or in-congruous hemianopia).

Question 16

Unilateral or bilateral eye problems at optic nerve and beyond chiasma?

Answer 16

Optic nerve problems are 1 eye defected problems. As soon as you get to the chiasma and beyond (because fibres cross)- the 2 eyes are involved in the defect.

Question 17

What is Bi-temporal hemianopia?

Answer 17

VERY RARE:
Hemianopia is on the temporal side in the RE & LE on the temporal. Therefore, called bi- temporal hemianopia.
Occurs from pituitary trauma

Question 18

Optic radiations move to which 2 lobes?

Answer 18

Temporal and parietal lobe.

Question 19

Defect in Temporal Lobe causes?

Answer 19

Superior quadrantic defect (‘pie in the sky’).

Question 20

Defect in Parietal Lobe causes?

Answer 20

Inferior quadrantic defect. (‘pie on the floor’)

Question 21

Describe in scientific terms what- right side pie on the floor defect means?

Answer 21

Defect on the right sided optic radiations parietal lobe causing left sided inferior defect.

Question 22

Role of Threshold perimetry

Answer 22

It records the depth and severity of a defect.

Question 23

Why do you record the depth of visual field defect?

Answer 23

Human eyes are most sensitive at the fovea and the ability to see the smallest or dimmest light declines as you move to the periphery.

Question 24

Equation for threshold perimetry and sensitivity

Answer 24

Threshold perimetry: ∆L/L
Sensitivity: L/∆L

Question 25

Is threshold perimetry an estimation of the threshold or the exact threshold?

Answer 25

It is an estimate.
To get the exact threshold- FOS curve is used.

Question 26

Staircase method is used to?

Answer 26

Used to estimate the exact threshold.

Question 27

What does crossing the threshold mean?

Answer 27

This is the movement from the not seen to seen part in the visual field.

Question 28

What is true value?

Answer 28

Once you have crossed the threshold- you move in the opposite direction- with changed dB values and cross the threshold value again to obtain the true value.

Question 29

In the stair case method the threshold is crossed how many times?

Answer 29

2 times

Question 30

Accuracy in staircase method increases with?

Answer 30

Smaller step sizes, more reversals, more repetitions and time influenced by start level. More times you cross the threshold- more data you have- more accurate.

Question 31

Absolute values are generated by?

Answer 31

Staircase method

Question 32

Absolute values are the highest at the centre of the grid, why?

Answer 32

Vision is the best here- BECAUSE OF FOVEA. Values decrease as you move from fovea.

Question 33

How does field defect correlate to absolute numbers?

Answer 33

Small number- deeper the field defect.

Question 34

Absolute values are in which unit?

Answer 34

dB ( decibel)

Question 35

Brightness of spot of light is reduced by?

Answer 35

Neutral density filters

Question 36

Strength of each neutral density filters can be quantified in terms of?

Answer 36

log units and dB.

Question 37

Limitations of grey scales? -3

Answer 37

• Not age compensated.
• Not eccentricity compensated.
• Can mask/underestimate loss

Question 38

Relation between grey and sensitivity in the grey scale?

Answer 38

Darkest grey represents the lowest sensitivity.