This document discusses various types of visual hallucinations and their potential causes. It covers formed hallucinations of objects, animals, people and scenery as well as unformed hallucinations of dots, colors, flashes and geometric patterns. Potential causes discussed include temporal lobe lesions, Charles Bonnet syndrome, migraine, and occipital lobe lesions. The document also examines several occipital lobe disorders and related phenomena such as the Riddoch phenomenon, visual anosognosia, alexia, prosopagnosia, hemiachromatopsia and palinopsia. Charles Bonnet syndrome is described in detail. Finally, the document presents several examples of optical illusions.

1. Can You Trust Your Eyes ?!!Can You Trust Your Eyes ?!!
By
Dr.Ahmed Alsherbiny
MSc. Ophth, FICO , FRCS Ophth (Glasg(

2. Chapter III

4. Visual Hallucinations

5. Types of Visual Hallucinations
Formed
-Objects
-Animals
-People
-Scenery
Unformed
-Dots
-Colors
-Flashes
-Geometric Patterns

6. Causes of Visual Hallucinations
(For Ophthalmology Interest)
Formed
-Temporal Lobe
Lesions
-Charles Bonnet $
Unformed
-Migraine
-Occipital Lobe
Lesions

7. Occipital Lobe Disorders Related
Phenomena
Riddoch phenomenon
Riddoch and Holmes observed that individuals recovering
from occipital lobe injuries first perceive moving objects
but not stationary ones. The Riddoch phenomenon can
be observed during confrontation field testing by
comparing the patient’s responses to moving and still
targets. More recently it has been shown that rare
patients with uni- or bilateral occipital lesions lose object
recognition but in some instances may have
“blindsight,” an unconscious ability to locate light
sources and detect moving targets in affected fields

8. Occipital Lobe Disorders Related
Phenomena
Visual Anosognosia (Anton Syndrome (
• The main characteristic of this disorder is
the denial of blindness by a patient who
obviously cannot see. • The patient acts as
though he could see, and in attempting to
walk, collides with objects, even to the
point of injury. • The lesions in cases of
negation of blindness extend beyond the
striate cortex to involve the visual
association areas.

9. Higher Visual Functions Affections
- Alexia (inability to read( with agraphia(inability to write( : occipitoparietal (dominant( Angulate
gyrus
- Alexia without agraphia : occipital cortex (dominant(
- Prosopagnosia (the inability to recognize the faces of familiar people( Occipitotemporal
- Hemiachromatopsia (Impaired color perception with relative preservation of form vision(
Occipitotemporal
- Palinopsia (Parietooccipital – migraine - LSD(
a visual disturbance defined as the persistence or recurrence of a visual image after the
stimulus has been removed.
- Visual Agnosia occipitotemporal

10. Charles Bonnet Syndrome
History
In about 1760, Charles
Bonnet, a Swiss naturalist
and philosopher, described
the vivid hallucinations
experienced by his 87-
year-old grandfather. In
1936 de Morsier (whom,
like Charles Bonnet, was a
native of Geneva
Switzerland), named the
phenomenon after Charles
Bonnet.

11. Charles Bonnet Syndrome
Initially used to designate elderly
patients with eye-related visual loss
and hallucinations, the label
Charles Bonnet syndrome has been
used as a “wastebasket” term to
describe patients with visual
hallucinations without psychiatric
disease or drug use but with
insight into the artificial nature of
their visions. Most patients with
Charles Bonnet syndrome are
elderly and have visual deficits of
varying degree due to age-related
macular degeneration, diabetic
retinopathy, glaucoma, cataracts,
and corneal disease. However,
visual loss has not been a
consistent criterion for the
diagnosis, and patients with
homonymous hemianopias and
children have also been labeled

12. Charles Bonnet Syndrome

13. Terminology meanings
(Related to Parietal Lobe Disorders)
Acalculia : loss of the ability to perform simple
calculations, typically resulting from disease or injury
of the parietal lobe of the brain.
Agraphia : is an acquired neurological disorder causing a
loss in the ability to communicate through writing
Apraxia : is a motor disorder caused by damage to the
brain (specifically the posterior parietal cortex). In
which the individual has difficulty with the motor
planning to perform tasks or movements when asked,
provided that the request or command is understood
and he/she is willing to perform the task.

14. Optical Illusions

15. Rotating Rings
If you stare at the dot in the center and move your head away from the screen
the rings will start to rotate. Now gradually get closer again…they change
direction!

16. Hermann Grid
This is a classic optical illusion named after Ludimar Hermann who discovered
it in 1870. At every point where the white lines intersect our eyes perceive a gray,
shadowy blob. If you look directly at one of the intersections though, the blob
disappears.

17. Scintillating Grid
This is a variation of the Hermann Grid where black dots appear and disappear
at the intersections of the gray lines. Interestingly enough, if you cock your head
at a 45 degree angle the effect is reduced (but not eliminated).

18. Monster Illusion
Found in virtually every psychology textbook in the world, the two monsters in
this optical illusion are in fact the same size. Your brain automatically adjusts
images that it perceives to be distant in order to compensate for the fact that
they are larger than they seem.

19. Jastrow Illusion
Named after Robert Jastrow in 1889, the bottom figure appears to be larger
although they are both the same size. This is because the shorter edge of “A” is
directly adjacent to the longer edge of “B”.

20. Blue vs Green
There are several variations to this optical illusion but the effect is the same. The
“blue” and “green” backgrounds are in fact the same color (open it in
photoshop).

21. Zöllner Illusion
This optical illusion was named after Johann Karl Friedrich Zöllner and consists
of parallel lines that appear to be diagonal. You may need a ruler for this one.

22. Hering Illusion
Although the two red lines seem to be bowed outwards they are perfectly
straight and parallel. This optical illusion is attributed to Ewald Hering, a German
physiologist who believed that the distortion was derived from the mind
overestimating the angles at the points of intersection.

23. Titchener Circles
Also known as the Ebbinghaus Illusion, there is still a debate in
psychological circles as to the exact mechanism and implication of this
effect. Essentially, the orange circle on the left appears to be smaller
than the one on the right although in reality they are the same size.

24. Leaning Tower
Yes, the leaning tower of pisa does actually lean, but these two images are in
fact one and the same. Although the image on the right appears to be leaning
away from the one on the left this is only in your head. Go ahead and try the
same thing with the empire state building…it will lean too, promise.

25. Static Motion
No, this is not an optical illusions GIF. The image really is static. Notice that when
you look at any individual point dead on, it will stop moving. This powerful optical
illusion is derived from interacting color contrasts and shape positions within the
image.

26. Cafe Illusion
Another famous optical illusion, this one was recently rediscovered in a cafe wall at
the bottom of St. Michael’s Hill. Although the lines appear to be diverging from one
another they are in fact quite parallel.

27. Checker Shadow Illusion
Probably one of the most unbelievable illusions out there, this one was
first optical illusions pictures published by Edward Adelson, a professor at
MIT. Although the square labeled “A” appears to be darker than the square
labeled “B”, they are actually exactly the same shade of gray. It’s okay if
you don’t believe it, we didn’t either, but Photoshop proved us wrong.

29. Color Illusion
t may look as if the two arms of the "X" use different shades of red, but in
face the whole "X" only uses a single shade of red. Likewise, only one
shade of green is present throughout the image.

30. Curvature Blindness Illusion
What do you see in the center of the above image: curvy lines or zigzag
ones? Most people see both — double wavy lines and double angled lines
alternating. Now look at the lines as they appear over the black and white
area of the photo. What do you see now? The truth is all the lines are wavy.

31. Simultaneous Contrast Illusion
In this image, the horizontal bar in the middle of the picture is one solid color.
However, the changing gradient behind the bar makes it seem like the color of
the bar itself is changing as it goes from left to right. If the viewer uses their
hands to block the background, it becomes obvious that the whole bar is indeed
only one shade of gray.

32. Ponzo Illusion
The Ponzo Illusion relies on geometric shapes to trick the eye. The idea is
similar to the Simultaneous Contrast Illusion: People will make assumptions
about an object based on the information that they get from the background.

33. Rotating circles
When your eyes dart to one seemingly spinning circle, the others around
them appear to start rotating

34. All about perspective
Can you figure out which of these windows is bigger? Not only are they the
exact same size, but their tops and bottoms are also directly in line with
each other. Talk about a new perspective.

35. Spinning colors
Optical illusions like this will leave you dazed and confused. The colors
seem to be swirling around, even though it’s a still image.

36. These two circles are not warped. They're perfectly round

38. This image is not just lines and boxes. There are 16 circles in there as well

39. You can not see all 12 of the black dots in this image at once, no matter how
hard you try

40. Long and short
Which horizontal line is shorter: the top or the bottom? Trick question—
they’re the same size, even though your mind perceives the one with
outward wings to be longer.

41. What do you see?!!

42. What is the direction of the
bus?!!

43. Thank You