entoptic phenomena

Question 1

define entoptic phenomenon (2)

Answer 1

visual sensations/perceptions produced by structures within the eye itself

• often noticed under specific circumstances
• cannot be imaged/recorded

Question 2

identify the 5 types of entoptic phenomena

Answer 2

1. mechanical (phosphenes)
2. shadow-cast (opacities, floaters, purkinje trees)
3. diffraction (haloes)
4. polarisation (haidinger’s brush)
5. nerual (blue arc)

Question 3

outline mechanical phosphene EP types (1) (1+2)

Answer 3

visual sensations that occur when retina is stimulated by energy other than light

1. pressure
   - pressing eyeball produces dark spot at opposite end due to pressure activation of retinal cells
2. traction
   - retinal detachment
   - Moore’s lightning streak

Question 4

outline shadow-cast EP and its causes (1) (3)

Answer 4

defects affecting light transmission will cast a shadow on the retina, producing an entoptic phenomenon

causes:

1. anterior
   - tear film (debris)
   - anterior chamber (foreign body)
2. near nodal point
   - lenticular (cataract)
3. posterior
   - vitreous (floaters)
   - retina (purkinje trees)

Question 5

define the troxler effect

Answer 5

eye movements are critical to maintain vision

-> when fixation is maintained for 30sec, periphery objects will dim

Question 6

outline diffraction EP (1) and its causes

Answer 6

occular structures can act as diffraction gratings (eg. cornea)

1. haloes caused by:
   - physiological (normal)
   - pathological (abnormal -> larger, more noticeable) (corneal oedema)

Question 7

outline polarisation EP (1)

Answer 7

haidinger’s brush:

- appearance of paired brush-like structures projected into space when looking at a clear blue sky

Question 8

outline nerual EP (2)

Answer 8

blue arc

• fixating just past the edge of a bright soure in a dark environment, a pblue arc and spike is seen
• not seen when fovea directed to source