Title: Entoptic Phenomena of Retinal Origin
1Entoptic Phenomena of Retinal Origin
Page 2.36
2Retinal Adaptation
- Retinal receptors (actually receptive fields)
require constantly changing stimulus - Attempted steady fixation ? eyes in constant
motion - small amplitude, rapid tremor
- larger drifts
- correcting saccades
- Result ? images always moving over retina
- Receptor stimulation therefore constantly
changing - minimizes retinal adaptation
- prevents image fading
3The Troxler Effect
4The Troxler Effect
- Retinal receptive fields smallest at the fovea ?
11 correspondence cone ? ganglion cell - Receptive fields much larger in peripheral retina
? many cones feeding into a single ganglion cell
5High cone density
Central Retina
Peripheral Retina
Thick ganglion cell layer
6The Troxler Effect
- Larger receptive fields in peripheral retina ?
will see retinal adaptation here first with very
steady fixation
7View center of pattern with one eye for 30
seconds
Fig 2.23, Page 2.36
8Retinal Adaptation
- Switches off our perception of pre-retinal
vessels (cast very distinct shadow on retina)
under normal conditions
9Entoptic Perception of Retinal Vessels
Page 2.37
10Purkinje Tree
- Can overcome normal adaptation that prevents us
seeing shadows of retinal vessels - shine light into eye at a very oblique angle
- keep light moving to prevent adaptation
- See shadows of retinal vessels entoptically
- Projected into visual field based on inverted
receptor map
11Purkinje Tree
See projection of larger vessels with penlight
12Purkinje Tree - Optimum Conditions
Directional light shone into eye (point source at
first focus) ? perceive retinal vessels down to
capillary level Avascular fovea visible (no
branches). Can map foveal diameter by entoptic
perimetry
13Avascular Fovea
14(No Transcript)
15Luminous Darting Points - Yellow Dancing Spots
- View a uniform white background ? see yellow
spots moving in short, arcuate patterns in
paracentral visual field - Optimum Conditions view uniform, bright, blue
background ? dark spots against blue background - Origin leukocytes in pre-retinal capillaries
- Erythrocytes absorb blue ? create a dark
background - Leukocytes transmit blue ? light interruptions on
dark background
Page 2.37
16Blue Field Entoptoscope - Optimized Viewing
Conditions
- Diagnostic device to detect/monitor retinal
pre-occlusive and occlusive conditions - Brightly back-illuminated blue filter viewed
through magnifying eyepiece - Field divided into quadrants by large cross-hair
reticle - Can perceive avascular fovea with steady
fixation ? area that spots never enter
Page 2.38
17Blue Field Entoptoscope
See many spots Follow short, arcuate paths
Diagnosis Looking for difference in number and
speed of motion between quadrants (and eyes)
18Phosphenes
Page 2.38
19Phosphenes Proof of the Inverted Retinal Map
N
20Phosphenes Proof of the Inverted Retinal Map
N
21Phosphenes Proof of the Inverted Retinal Map
- Phosphenes produce the same inverted retinal map
as light shone into the eye. - Obtaining the same projection without light
proves that the retina is an inverted map of the
visual field
N
22Phosphenes - Flashes of Light
- Clinically significant ? may indicate posterior
vitreous detachment or retinal detachment
23Posterior Segment Anatomy
24Posterior Vitreous Detachment
Page 2.38
25Posterior Vitreous Detachment
- Vitreous loosely attached to retina by vitreous
membrane (stronger at ora seratta and optic
disc). - With age vitreous gel shrinks and becomes more
fluid (loss of hyaluronic acid support for
collagen) - Shrinkage creates traction ? may lead to
posterior vitreous detachment - Rare in patients younger than 50
26Posterior Vitreous Detachment
Vitreous pulls away from the retina at the
posterior pole
27Posterior Vitreous Detachment - Symptoms
- Patient sees vertically oriented lightning
streaks in temporal visual field (nasal retina) ?
Moores Lightning Streaks - At the same time, a cluster of floaters appear at
the posterior pole (tend to resolve with time)
28Posterior Vitreous Detachment - Symptoms
- Lightning Streaks probably due to detached
vitreous bumping into retina during eye movements
(vitreous ballotment) - Floaters due to vitreous degeneration and
possibly minor vitreous hemorrhage. Usually
resolves with time as vitreous detachment expands
to periphery - Risk of retinal tears or detachment, but this
only occurs in a small percentage of cases ? as
the vitreous detaches from the underlying retina,
traction can produce a retinal tear
29Retinal Tear with Vitreous Detachment
30Retinal Detachment
Page 2.39
31Retinal Detachment
- Retinal detachment is a clinical emergency
- Signs (all more likely with a detachment near the
fovea) - Photopsia (flashes of light) ? entoptic
- Scotomas (visual field defects)
- Floaters (possibly large) ? entoptic
- Metamorphopsia (distortion of central vision)
32Types of Retinal Detachment
- Rhegmatogeneous Retinal Detachment - due to a
retinal break (liquefied vitreous enters space
between RPE and sensory retina ? detachment) - Tractional Retinal Detachment - due to vitreous
traction on the underlying retina - Serous (Exudative) Retinal Detachment - due to
fluid accumulation beneath the sensory retina
without a retinal break
33Types of Retinal Detachment
Inner limiting membrane
Tractional
VITREOUS
Break
RPE
Serous
Rhegmatogeneous
CHOROID
Bruchs Membrane
SCLERA
34Blue Arcs of the Retina
NO clinical significance
Page 2.39
35Blue Arcs of the Retina
- Due to secondary electrical activity in the
retina - One neuron firing stimulates adjacent neurons all
the way back along the arcuate nerve fiber bundle
to the optic disc - Seen best when fixation target parallel to
arcuate nerve fiber bundle in stimulated retinal
region
36Blue Arcs
Fig 2.24, Page 2.40
37Blue Arcs
Nasal Field
Temporal Field
N
Disc
38Blue Spike - Target Horizontal
Fig 2.25, Page 2.40
Fixating nasal edge of horizontal rectangle
(orange)
39Entoptic Phenomena of Macular Origin
Page 2.41
40Plane Polarization
41Plane Polarization Rope Analogy
Zero energy in horizontal plane
42Plane Polarization Rope Analogy
- Snapping a taut rope vertically at the free end
causes a vertically oscillating wave to propagate
horizontally along the length of the rope. - This is analogous to plane polarized light
- Some crystals (e.g. tourmaline) freely transmit
light along one crystal axis and totally
extinguish light along a perpendicular axis ?
emit plane polarized light from unpolarized
incident light. Many are also dichroic
(absorbing some ?s more than others)
43Vertically Polarized Light
- Vertical plane of vibration (maximum energy)
- Horizontal plane of extinction (zero energy)
zero energy
44Vertically Polarized Light
- Polarizing sunglasses are plane polarizers with
vertical transmission axis (cut out horizontally
polarized light) - Most reflected glare (e.g. from a lake surface)
is horizontally polarized
45Vertically Polarized Light
- Plane polarized light looks no different from
unpolarized light under normal conditions - Need an analyzer (second polarizer) to detect
polarization of incident light - Crossing two polarizers (one with vertical
transmission axis second with horizontal
transmission axis) results in total extinction of
light
46Crossed Polarizers
Knowing the transmission axis of one polarizer
(the analyzer) we can rotate the second polarizer
until it is crossed with the analyzer. This
locates the transmission axis of the second
polarizer.
- Polarizing sunglasses are plane polarizers with
vertical transmission axis (cut out horizontally
polarized light) - Most reflected glare (e.g. from a lake surface)
is horizontally polarized - Plane polarized light looks no different than
unpolarized light under normal conditions - Need an analyzer (second polarizer) to detect
polarization of incident light - Crossing two polarizers (one with vertical
transmission axis second with horizontal
transmission axis) results in total extinction of
light
47Entoptic Phenomena of Macular Origin
48Haidingers Brushes - the Eyes Analyzer
- Human macula contains an analyzer that (under
specific viewing conditions) can entoptically
differentiate the transmission and extinction
axes of P-state light ? transmits differently - Macular analyzer has polarizing properties and is
dichroic (selectively absorbing blue light)
49(No Transcript)
50Macular Pigment - Xanthophyll
Macular pigment xanthophyll creates a yellow
filter for light under normal conditions ? blue
cones appear to turn up their sensitivity to
compensate
51Neuroglial Fibers (Muller Cells)
52Muller Cell Fibers in Macular Region
Inner retinal layers sloped away from center in
foveal region ? supporting fibers on Muller cells
form a radial pattern
53Radial Analyzer
Xanthophyll tends to associate with Muller cell
fibers ? yellow radial analyzer
54Appearance of Haidingers Brushes
- Haidingers brushes appear optimal when viewing a
rotating plane polarizer through a blue filter
55Appearance of Haidingers Brushes under optimum
conditions
Fig 2.26, Page 2.41
56Mechanism of Haidingers Brushes
- Xanthophyll pigment aligned with radial Muller
fiber arrangement in macular region ? analyzer
radial - Polarized blue light affected differently
depending on state of polarization - in transmission axis ? free transmission?
effectively overcomes yellow filter ? greater
transmission of blue - light perpendicular to transmission axis ? fully
absorbed by xanthophyll pigment ? blue ? blue
dark (dark)
57Mechanism of Haidingers Brushes
- Remember under normal conditions, polarized
light does not look any different from
unpolarized light - Need the analyzer to see the state of
polarization of light
58Haidingers Brushes Dichroic RA Theory
WHITE LIGHT
BLUE LIGHT
Fig 2.28, Page 2.43
59Haidingers Brushes Dichroic RA Theory
If we did not have the radial analyzer, what
would we see? Blue light
WHITE LIGHT
BLUE LIGHT
If we did not have xanthophyll at the macula,
what would we see? Blue light
If we did not have the rotating polarizer, what
would we see? Blue light
Fig 2.27, Page 2.41
60Haidingers Brushes - Clinical Applications
- Diagnosis of macular edema - even small amount of
macular edema (hard to see with BIO) disrupts
Muller cell fiber radial analyzer? Haidingers
brushes not seen - Detection of eccentric fixation (strabismus
patient) ? when fixating eccentrically, do not
see Haidingers Brushes - Training central fixation seeing Haidingers
Brushes ? tells patient when they are centrally
fixating (feedback)
61Recap Key Objectives
- The most clinically important entoptic phenomena
are phosphenes (possible retinal detachment),
entoptic haloes (possible corneal edema), and
macular entoptic phenomena (Haidingers brushes
macular integrity, central fixation training for
eccentric fixation