Entoptic phenomena are visual sensations and effects caused by structures within the eye itself. When light enters the eye, it interacts with tissues like the lens, vitreous humor, and blood vessels, causing the observer to see shadows, colors, or movements. Some entoptic phenomena are normal, while others may indicate eye problems. Examples include floaters caused by vitreous strands, or the blue field phenomenon where white blood cells are visible in retinal capillaries against a blue sky. The variations in density and structure within the eye play important roles in the formations of these phenomena.

2. Entoptic Phenomena literally translates as
"phenomena inside the eye". They are visual effects and
sensations that occur from causes within the human eye
itself. So the eye sees itself.
These phenomena may result from either normal
anatomic components of the eye or pathologic
imperfections.

3. The optical illusions are caused by the visual system by
causing things doesn't exist, or pictures that we perceive
differently than they really are.
Because entoptic images are caused by phenomena
within the observer's own eye, the observer cannot share a
direct and specific view of the phenomenon with others (the
same with illusions) .

5. The optical density and the refractive index of the structures
are important in the formation of entoptic phenomena.
The location of the inner-eye structure and changing the
illuminating angle, the eye can detect the direction of the
movement of the shadow that the structure caused it according
to the location from the pupil:
1. Opacity in a structure behind the pupil: the shadows are
cast on the retina will move in the opposite direction to the
illuminating source.
2. Opacity in a structure in front of the pupil: the shadows
are cast on the retina will move with the direction of the
illuminating source.

6. The structure's distance from the pupil also plays an important
role. The further away the structure is from the pupil, a greater
shift of the shadow is observed; so patients are most disturbed by
opacities that are located in the posterior vitreous body.
Entoptic phenomena occurs because of the Optic media, are
resulting from:
1. Refractive causes: occur when the light passes through
structures with different density, changing its direction, which is
perceived as a shadow
2. Diffractive causes: occur from the light bending and
dispersing on the fringes of imperfections of the optical system,
which is perceived as a halos

8. Vitreous changes and the Floaters (musca volitans)
- Floaters or flying flies: are small spots, most of them are small
protein called collagen.
- Floaters usually happen because of normal changes in the eyes with
the age (and more likely in myopic eye).
- With the age; the vitreous body starts to liquefy and the structure of
collagen fibrils breaks down and stick together to cast shadows on the
retina.
- The shadows of those opacities appear as the floaters (spots).
- They usually don't totally go away, and they move as the eye moves.
- Blinking does not remove the floaters.
- Floaters could be also due to internal eye inflammation and infection.

9. Vitreous changes and the Floaters
- They become most noticeable when looking into a bright and
uniformly illuminated light source (the sky or a white paper).
- It does not need a treatment, but if the patient saw a flash, a
sudden increase in the number of floaters, loss of side vision and
a drop in the vision, he needs to see a doctor immediately,
because this means there is:
- Retinal detachment
- Vitreous detachment
- Bleeding in vitreous
*Visual aura can come with a migraine headache and last
for 30 minutes.

13. -Different structure inside the eye cause diffraction when the
light bend from their edges. The result is a decline in the
contrast of the image and the onset of rainbow halos.
- The size of the perceived halos depends on the distance from
the structure, of which the light is diffracted, to the retina. The
closer it is to the retina, the smaller the halo will be.
- These phenomena can occur in normal eye (physiological),
and also in (pathologic) conditions.

14. - Pathological phenomena include corneal halo
- Corneal halo occurs because of corneal edema,
causing light scattering in all directions.
-When viewing white light, a white central circle can
be perceived, surrounded by multicoloured rings.
- Physiological phenomena include the ciliary corona,
and lenticular halo.

15. - Ciliary corona occur when watching a singular illuminated
object in the dark (e.g., a street lamp), the illumination source is
surrounded by a halo with slightly coloured needles.
- This is the result of the light reflecting from numerous tiny
particles (proteins) in the lens nucleus, and the tiny
irregularities in the structure of other ocular parts (deposits on
the corneal endothelial cells, the cells in the anterior chamber
and the anterior lens capsule).
- Lenticular halo may occur when the pupil is dilated in a dim
area, a ribbon of colour around the illumination source will
appear.
- It is caused by light bouncing from the zonular and anterior
parts of the lens.

18. - Under normal conditions retinal vessels are not
visible because of neuron adaptation.
- The entoptic view of the retinal vessels has many
characteristics of an after image. It remains visible
after the intermittent short stimulus has stopped.
- This include Purkinje tree and Blue field.

19. - The Purkinje tree (Retinal vessels image)
- If we shine a light into the eye from an usual angle, the
shadows of the vessels will cast on the retina. This allows
patients to briefly see the retinal vascular image (Patients being
examined by a biomicroscope often notice the retinal vascular
image).
- It can be seen by shining a bright, moving light like a penlight
onto the sclera in a darkened room.
- The shadows cast by the retinal vessels, remain in fixed
position, even during eye movements because of the (after
image).

20. - The Blue field phenomenon (Scheerer's Phenomenon).
- The blue sky sprites are tiny bright dots moving quickly along
squiggly lines in the visual field, especially when looking into
bright blue light such as the sky.
- The dots themselves are the result of white blood cells moving
along capillaries in front of the retina (the dots themselves are
small and white, and they appear slightly elongated with dark
tails which are red blood cells).
- Spherical white blood cell is too wide for the capillary, and red
blood cells get backed up behind them (creating the appearance
of a white dot with a tail).

21. - The Blue field phenomenon (Scheerer's Phenomenon).
- Blue light is absorbed by the red blood cells which fill the
capillaries. And the white blood cells, which are much less than
the red ones and do not absorb blue light, but allowed to pass to
the retina making gaps appear as the spots.
- The dots appear in the central field of view, within 10 to 15
degrees from the fixation point. The dots will not appear at the
very center of the visual field, because there are no blood
vessels in the foveal avascular zone.

22. - The Blue field phenomenon (Scheerer's Phenomenon).
- Scheerer's phenomenon can be distinguished from visual snow
because it appears only when looking into bright light, whereas
visual snow is constantly present in all light conditions including
the dark.
-Visual snow syndrome (VSS):
is an uncommon neurological
condition that cause the patient
to see persistent flickering white,
black, transparent, or coloured
dots across the whole visual field.
-It has no cure and treatment yet.

24. - The center of the retina is the macula, and the center of it
there is the fovea macula lutea-yellow spot) which
responsible for central vision. It's the point at which visual
acuity is at its highest.
- In the fovea, there are NO rods (only cones), and there is
no blood vessels (avascular).
- Central vision phenomena is due to the absorption of blue
light by a yellow pigment in the macula called xanthophyll
which acts as yellow filter.
- It is include Haidinger's brushes and Maxwell's spot
phenomena.

25. • Haidinger's brushes phenomenon
- A pale interlinked blue and yellow bar or bow tie shape,
visible in the center of the visual field against the blue sky
viewed while facing away from the sun. Or on any bright
background, due to light polarization.
- Central vision phenomena is due to the absorption of blue
polarized light as a result of dichroic xanthophyll pigment.
- The direction of light polarization is perpendicular to the
yellow bar (i.e., vertical if the bar is horizontal).
- Haidinger's brush is formed only on the macula and
centered on the fovea, so we can use it to measure eccentric
fixation and detect any macular problem early.

26. • Maxwell spot
- A dark spot can be seen in the center of the visual field
surrounded by a brighter circle with a halo when a white
surface is viewed by a normal observer through a dichroic
filter transmitting red and blue lights.
- The central dark circle is the result of blue light absorption
in the xanthophyll pigment of the central fovea.
- The phenomenon can be used to test eccentric fixation.
* Eccentric fixation means the eye uses a portion of
the retina other than the fovea for fixation.

28. • The stimulation of the retinal receptors with an energy other than the
light energy, may lead to those phenomena, which include Blue arc and
Phosphene.
• Blue arcs
- It is viewing two pale blue arcs above and below the fixation point for a
short period of time coming from electronic devices or artificial lighting
in dark room as a result of secondary electrical stimulation of the retina.
- The position and orientation of the arcs are correspond to arcuate nerve
fiber bundles extending to the optic disk.

29. • Photopsias and Phosphene
- Photopsias are perceptions of light without an actual light because of
the pressure on the retina which results in activation of retinal ganglion
cells.
- Photopsias occur as result of direct retinal stimulation.
- The person sees colorful shapes and light, geometric patterns, sparks
and zig-zag lines, floating shapes, moving dots, ... etc.
- Photopsias can occur because of numerous pathological ocular or
systemic conditions.
- Phosphenes are a subgroup of photopsias.
- Phosphenes is can be induced by mechanical, electrical, or magnetic
stimulation of the retina, visual cortex, or any part related to the eye, they
are more intense and of shorter duration.

31. • Phosphene Causes
1. Mechanical stimulation: The most common phosphenes are
pressure phosphenes, caused by rubbing or applying pressure on
the closed eyes.
Pressure mechanically stimulates the cells of the retina.
Another common phosphene is "seeing stars" from a sneeze,
laughter, a heavy and deep cough, blowing of the nose, a blow on
the head or low blood pressure.
Less commonly, phosphenes can also be caused by some diseases
of the retina and nerves, such as multiple sclerosis.

32. • Phosphene Causes
2. Electrical stimulation: Phosphenes can be created by electrical
stimulation of the brain.
3. Others:
Transcranial magnetic stimulation and magnetic field.
Radiation of space or radiotherapy cause phosphenes (patients reported
seeing blue flashes of light).
Phosphenes can be caused by some medications, such as Ivabradine (used
to treat heart failure).

33. • Photopsias Causes
- Causes:
1. Peripheral vitreous detachment: if it occurs too rapidly, it can cause
photopsia which manifests in flashes and floaters in the vision, separation
of posterior vitreous from the optic disk results in appearance of central
large annular opacity (Weiss ring).
2. Macular degeneration: the second most common cause of photopsia.
3. Retinal detachment.
4. Ocular migraine cause visual auras.
5. Optic neuritis; an inflammation that damages the optic nerve.
6. Neurological causes: such as poor blood flow to the back of the brain.

34. • Photopsias Causes
7. The presence of the permanent violet flashing indicates a retinal
ischemia (no enough blood).
8. Proliferative diabetic retinopathy.
9. Charles Bonnet Syndrome (CBS): A phenomenon affecting
people who have partially or completely lost their sight, in which
they still "see" things that aren't there.
10. Retinitis pigmentosa.
11. Blood pressure problems.