1. Entopic Phenomenon in
Eye
Gauri S. Shrestha, M.Optom, FIACLE
Lecturer
B.P. Koirala Lions Centre for Ophthalmic Studies
2. What Does ‘Entopic Phenomenon’
Mean?
This is any sensation that comes from INSIDE the
eye
Ent-Optic: ‘inside the optics’
Visual sensation can also be raised from shadows
of opacities within the eye
Eg mechanical pressure on the globe
Entoptic phenomena are produced when
something other than light stimulates the retina
These sensation not directly due to the formation
of an optical image by the refracting system of the
eye
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3. What Is An Example?
Can be seen especially when looking at a bright
blue sky
What Does It Look Like?
Small, rapid pin-point sparks of light darting about
in the central vision.
We all have the potential to see this phenomenon,
but most of us ignore it.
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5. What Causes It?
Some people think these sparks are floaters.
They actually represent white blood cells moving
through the blood capillaries of the retina.
Red blood cells are not seen
Compact and close to the retina
This is a normal finding, and actually may indicate
normal retinal function
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6. Patients and Entopic Phenomenon
Some people become suddenly aware of this
phenomenon.
Sudden awareness can lead to the idea that there is a
problem with the eyes, when actually there is not
Sparkles that can be seen illuminating in the central
vision
Most visible when we look at something bright then close
our eyes or immediately look at something dark.
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7. Causes of Entoptic Phenomena
Refractive Effects Xanthophyll Effects
Tear film Maxwell's spot
Corneal corrugation Haidinger's brush
Diffraction Effects
Pressure Phosphenes
Corneal haloes
Corneal corona Digital Pressure
Ciliary corona Eye Movement
Asterism Moore’s Lightning
Shadows Streaks
Ocular opacities Electrical Phosphenes
Purkinje tree
Blue field
Battery stimulation
entoptoscope Blue arcs of the
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retina
8. Refractive effect
Small surface changes across the cornea can
redirect light outside the retinal image.
Tear film
When the eye blinks, a horizontal ridge of tears is
left momentarily where the lids came together
Some observers report a “shadow” effect seen as a
horizontal striation
Mucous strands can do the same thing, but they
last longer and move around with the blink
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9. Refractive effect
Corneal corrugations
Squeezing the lids tightly shut gives transient
ridges on the cornea that can give “shadow”
streaks, monocular diplopia, and even
decreased visual acuity, which in extreme
cases can last longer than an hour
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10. Diffraction effects: Corneal Halos
The stroma of the cornea is composed of collagen
fibrils between 19-34 nm in thickness.
The interfibrillar separation is much smaller than
the wavelength of light
light scattered by one fibril can’t constructively
interfere with another fibril.
No diffraction pattern is formed.
In addition, there is destructive interference
between scattered and non-scattered light,
further reduce the effects of the scatter
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12. Diffraction effects : Corneal Corona
With corneal edema, the regularity of the
collagen fibrils is disrupted and the normal
beneficial destructive interference no
longer occurs
With severe edema and water droplets
or water clefts in the epithelium, even
more scattering occurs.
With monochromatic light, an Airy-disc
like appearance is seen.
With white light, a white center will be
surrounded by chromatic rings or red-
yellow, purple, etc. This is called the
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corneal corona.
13. Ciliary corona
Spread of light around an isolated bright source of
light eg street lamp
Diffraction of particles with in the eye
No color fringe is seen
Only central disc is perceived
Diameter of disc depends upon the source
brightness
Normal phenomenon
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15. Diffraction effects: Corneal Colored
Halos
Corneal edema can be caused by increased
intraocular pressure that forces water into the
cornea producing water clefts, which act as
diffractive particles.
e.g., patients may report colored haloes around
small bright lights during episodes of acute
glaucoma.
Swimming in chlorinated pools and overwear of
contact lenses may give a similar effect.
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16. Diffraction effects : Lenticular Halo
The lens also has regularly-arranged fibers. With
the exception of the zonular area and the anterior
cellular area, its fibers are laid out in a radial
fashion.
The axial part of the lens is uniform, so no halo is
seen with small pupil diameters (< 3mm).
Under low light conditions or when dilated, the
effects of the peripheral zones become apparent
and a halo is seen.
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18. Emsley-Fincham test
A lenticular halo is normal!
Since the corneal and lenticular halos look similar
and the corneal halo is not normal, they must be
differentiated via the Emsley-Fincham test.
Move a stenopaeic slit across the pupil.
The corneal halo is reduced in brightness a bit no
matter where the slit.
The lenticular halo changes in shape as the slit
moves!
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20. Asterisms
Small bright objects against a dark background
usually have spikes surrounding their geometric
images.
An example of this is bright stars where the effect is
so prominent that artists frequently depict stars with
spikes.
This effect is assumed to be due to diffraction off
the suture lines of the crystalline lens.
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22. Shadows
The passage of light through the ocular media
may be affected by localized heterogeneities in
refractive index that scatter light, or by opacities
that absorb or scatter light.
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23. Shadows
1. Ocular opacities
2. Purkinje tree
3. Blue field entoptoscope
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24. Shadows
Unless an opacity is nearly the same size as the pupil or
close to the retina, it won’t cast a significant shadow.
Objects in a room lit by a single window won’t have
strong shadows, except for those near the walls.
We use a small light source to make the shadows denser
and more defined.
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26. Shadows and Parallax
By using parallax, the location of an opacity can
be localized.
If the opacity is behind the exit pupil, against
motion is seen.
If the opacity is in front of the exit pupil, with
motion is seen.
The farther away from the exit pupil, the more
motion seen.
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28. Ocular opacities
Visualization of striae, folds, vacuoles, cysts and corneal nerves,
lens vacuoles vitreous opacities, mucous, oil globules, lens
sutures, Muscae volitantes
Entoptic image of eye lashes and corneal opacity shows with
movement
Lenticular and vitreous opacity downward movement
• Corneal scars, lens opacities, intraocular foreign bodies, vitreal
floaters and blood cells would all be expected to cast shadows.
• The effect is strongest for opacities nearest to the retina because
objects near the retina project an umbra rather than just a
penumbra onto the retina.
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29. Opacities may not be noticed at all by the patient if
completely opaque.
•An example is asteroid hyalosis, which are calcium deposits in
the vitreous.
•To the doctor looking in, they look very bright and may make a
good view of the fundus difficult due to glare; but because they
are opaque, from the retinal side they are dark and the patient
may be unaware of them.
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32. Muscae Volitantes
Cellular debris, probably from the embryonic
hyaloid vascular system.
Cast shadows and refracts light into bright
circular spots and other shapes such as wavy
filaments or cobwebs.
Most commonly seen when viewing a bright
background like a bright sky or white wall.
They move on eye movement.
Become more noticeable with age as the vitreous
liquifies.
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33. Vitreous Opacities
Most vitreous opacities are harmless.
A sudden onset of floaters may be serious,
especially if accompanied by photopsia (flashes of
light).
The sudden appearance of a “film, haze or cloud”
of opacities may be caused by bleeding into the
vitreous or vitreous detachment.
Vitreous opacities may be removed by vitrectomy.
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34. Purkinje Tree
Because the branching retinal blood vessels are in
front of the photoreceptors, they can cast a shadow
that resembles a tree.
They are normally not seen, but a small bright
light can reveal them as a branched pattern
stopping short of the avascular zone around the
fovea
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35. Purkinje Tree
Since stable images on the retina quickly fade (the
Troxler effect), the Purkinje tree is best seen if the
light source is constantly moved over a large
angle.
Patients sometimes comment on the Purkinje tree
when they are examined with bright lights, such as
the slit lamp or BIO.
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39. Blood Cells and the Blue-Field
Entoptoscope
When looking at a bright blue background such as the sky,
a person may see bright spots moving along curved lines
and their flow may even seem to pulse with the heartbeat.
These are thought to be white blood cells, which interrupt
the columns of red blood cells in the smaller retinal blood
vessels.
The white blood cells allow blue light to pass,
whereas red blood cells absorb blue light.
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40. Blood Cells and the Blue-Field
Entoptoscope
This entoptic image has been
incorporated into a machine
known as a blue field
entoptoscope to serve as a gross
subjective assessment of the
vascular function of the retina.
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42. Maxwell’s Spot
If a blue filter is quickly placed in front of your eye as you
view a bright, uniform white background, a dark disk appears
in the macular area.
This is due to a Xanthophyll pigment (zeaxanthin) in the
macula.
This acts like a yellow filter, which excludes more of the blue
light than the surrounding retina does so that a relatively dark
spot appears in the part of the visual field that corresponds to
the macula. gs101lg@hotmail.com
43. Maxwell’s Spot
Maxwell’s spot is used in vision therapy to “tag” where the
patient is fixating.
Maxwell’s spot can also be used to measure the density of
macular pigment. The darker Maxwell’s spot, the denser the
pigment.
e.g., cigarette smoking reduces the amount of macular
pigment, which makes a person more susceptible to UV
damage and to ARMD.
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45. Haidinger’s Brushes
Propellar like figure seen in polarized light near the fixation
point
Uniformly illuminated white screen is viewed through a rotating
polarizer and blue filter= yellow brushes appear.
Haidinger’s brush is due to birefringence induced by
Xanthophyll, which is radially polarizing.
A competing theory is that radially oriented receptor cell
axons form a birefringent layer in the macula.
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46. Haidinger’s brushes
Some structure in eye behaves as radial analyzer
of blue filter-yellow macular pigment
(Xanthophyll) radial analyzer
Vertical vibration falls on analyzer and horizontal
vibration on plane of transmission perpendicular
to plane of incidence
Vertical element transmit more blue light- so blue
brush is seen
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47. Haidinger’s Brushes
Dichroism=the effect of absorption of light polarized in
one direction and transmission in the plane at right angles
The figure fades rapidly due to visual adaptation, so it
must be kept in view by rotating the Polaroid filter so that
the hourglass also appears to rotate and exposes new
retina.
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48. Haidinger’s Brushes
The effect is less pronounced or absent in macular
edema. This can occur even before ophthalmoscopic
signs of macular edema.
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49. Haidinger’s Brushes
Because Haidinger's brush corresponds to the macula, it is
sometimes used as a gross subjective test of macular
function and sometimes as a training technique in
amblyopia to improve fixation.
Haidinger’s brush can determine whether amblyopic
patients fixate with their foveas or not (eccentric fixation)
since the fovea always corresponds to the center of the
hourglass and the center of rotation.
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50. Pressure Phosphenes
1. Digital Pressure
2. Eye Movement Phosphenes
3. Moore’s Lightning Streaks
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51. Digital Pressure Phosphenes
Phosphenes of all kinds are weak stimuli and
therefore have to be viewed in the dark.
If pressure is applied in the dark to the side of
the eyeball through the closed lid, a circular
bright spot will be seen
The pressure directly activates retinal cells.
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54. Pressure Phosphenes
Pressure phosphenes are now being used to
monitor patient’s intraocular pressure at home
with a device called the Proview.
The patient applies pressure through the eyelid
until a pressure phosphene is seen. The pressure
needed to produce the phosphene is read off the
instrument.
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57. Pressure Phosphenes
Mechanical traction on the retina also can cause
phosphenes.
Patients will complain of photopsia -- flashes of
light.
This is why a complaint of flashes of light must
be treated with utmost concern. Retinal
detachments are ocular emergencies.
Vitreous liquifaction and detachment can also
cause photopsia.
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58. Eye Movement Phosphenes
If you close your eyes and move them all the way to the
left or right, then try to move them even further, you’ll
see a bright half-ring shaped light with a dark center on
the opposite side of the field.
This is due to the extreme contraction of the rectus
muscle deforming the globe a bit and mechanically
stimulating the photoreceptors under the muscle’s
insertion site.
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59. Moore’s Lightning Streaks
When the vitreous liquefies with age (syneresis), the
points of remaining adherence between vitreous and
retina may tug on the retina, especially during eye
movements.
This produces pressure phosphenes, which appear as
lightning streaks at points in the visual field that
correspond to the locations of adherence.
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60. Moore’s Lightning Streaks
These may be benign, but the clinician
should check carefully for the possibility of
retinal tears and detachments because they
are more likely to occur in patients who
experience these events.
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61. Electrical phosphenes
1. Battery stimulation
2. Blue arcs of the retina
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62. Electrical and X-ray phosphenes
Battery stimulation
If a low-voltage battery (<10 V) is placed in the mouth
between tongue and upper lip in the dark, a faint glow
will be seen over the visual field.
Do not try this with high voltage battery
X-rays stimulation of the retina (typically higher doses)
can also produce phosphenes.
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64. Blue Arcs of the Retina
If a red patch of light (such as a very small red LED light) is
viewed in a dark room monocularly, blue arcs will be seen
emerging from the light source and heading towards the blind
spot.
This is sometimes seen when looking at the red LEDs on a
digital clock in a darkened room.
The effect is subtle, but is a little easier to see if one fixates
slightly to the side of the red light.
The arcs follow the course of the ganglion cell axons in the
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69. Blue Arcs of the Retina
Some people explain the effect as due to an electrical
“short circuit” between the axons from ganglion cells
under the red stimulus and ganglion cells encountered
along the path of those axons.
Others claim it is due to the electrical signals in the
ganglion cells in the fiber bundles stimulated by the red
light abnormally causing the photoreceptors below them
to respond.
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71. Orientation and location of obstruction
The erect retinal shadow of
An axial opacity behind the
a pin, placed between the
exit pupil casting a shadow on
pinhole and the eye,
the retina in the centre of the
appears inverted
illuminated retinal area
Downward movement of pin Downward movement of
hole casts image in opposite pinhole casts image on the
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same side
Bennett & Rabbetts (Clinical Visual Optics) Figure 22.8. (a) The Emsley-Fincham test for distinguishing a lenticular halo. The stenopaeic slit is passed across the pupil, isolating differently orientated groups of lens fibres responsible for the sections of the halo shown in (b).
Tunnacliffe Fig. 7.58 a & b (a) Shadow cast by an opacity close to the retina. Note there will probably be a detectable shadow on the retina. Such shadows are usually only seen when looking at a bright surface. (b) An opacity further forwards may not cast its shadow on the retina. (c) A lenticular opacity (cataract) may be made visible by placing a pinhole at the anterior focal point of the eye and looking at a bright surface.
Bennett & Rabbetts (Clinical Visual Optics) Figure 22.3. The use of parallax to locate the site of an opacity. The circles on the right represent the entoptic field and the apparent relative position of a central opacity as seen by the subject. (a) Opacity behind pupil, pinhole central. (b) Effect on (a) of downward movement of pinhole. (c) Opposite effect of pinhole shift when opacity is in front of pupil.
Ring shaped floater (probably vitreous detachment)
