A THOUGHT EXPERIMENT:
Imagine yourself sitting in a dark room. I mean, really dark — pitch black all around you, so that you can see absolutely nothing. As the minutes creep on slowly, you start becoming restless…
An hour has almost gone by, and… well, nothing has happened. You start wondering why, after all, you are sitting here in this darkness. Deciding that the experiment has been a failure, you start to get up when…suddenly, you see a burst of colours before your eyes. Whoa! You sit back down. Initially, it’s merely a formless display of colours. But gradually, you feel like you can decipher shapes, albeit vague, through the psychedelic mist that surrounds you. Is that a person there to your right? But no one was in the room with you just five minutes ago. And right in front of you, that certainly seems like a tiled pattern on the wall. But hey, you think, the wall is painted pale violet. You should know, it is your room. You turn to your right again, but now there is no trace of the person you saw just a few moments ago. What?! You turn your head around frantically, searching for that missing person. Where could he have gone to? Or was it a she? But there is no sign of a person in the room. Instead…back in the corner, behind you, to your right, there is a dog, a small and fluffy dog, its skin white with intermittent brown patches, its tail bushy, and its ears pricked, looking intently back at you with its head slightly tilted. The image is crystal clear: all the features of the dog are perfectly discernible. Again, you wonder, the room was supposed to be empty of a dog too. You turn back to face the front, but lo — the tiled pattern is no more, it has morphed into a model of a building…well, not really a building, but a maze of interconnected steel rods. The top of the structure is hidden by clouds, coloured in a strange mixture of blue, green and red.
In the meantime, as you turn around the room taking in these extraordinary visions, a disturbing thought pops into your mind quite unbidden, but entirely natural under the circumstances: am I going soft in the head?
This is exactly what a person affected with Charles Bonnet Syndrome experiences from time to time, commonly known as a ‘hallucination’. 
Now, hallucinations are typically brought on by recreational drugs and mental disorders (a pertinent example being schizophrenia). They carry a stigma of being weird — if you claim to be having hallucinations, your worth, as a human, drops somewhat in the estimation of your fellow humans and they tend to take you less seriously. And quite understandably. But the hallucinations which are characteristic of the Charles Bonnet Syndrome are not induced by either drugs or mental disorders. Their origins are entirely distinct, as I shall try to explain below.
THE PROTAGONIST OF OUR STORY:
The Charles Bonnet Syndrome (hereafter referred to as CBS) is named after Charles Bonnet, a Swiss naturalist who, in 1760, observed his grandfather having vivid visions of things that were clearly non-existent in the real world. His observation was all the weirder because his grandfather was almost blind from cataract in both his eyes. How could the man, Charles wondered, be having clear, vivid visions of things which did not exist around him, and which he could not conceivably see even if they were to exist? 
Today, we know significantly more about this phenomenon than Charles Bonnet did. It arises in people who have lost either entirely, or a part of, their vision. Such persons “see things that aren’t really there — medically known as having a hallucination”. The content of such hallucinations ranges from the very simple, for instance, “patterns of lines, dots, or other geometric shapes”, to the very complex, for instance, “vivid detailed pictures of people, animals, objects or buildings”, “landscapes, such as mountains or waterfalls”, and “imaginary creatures, like dragons”. These hallucinations also often mesh with a person’s familiar surroundings. They are especially intense during the first few weeks or months after a considerable deterioration of eyesight. They may last for mere seconds, minutes or even long hours. Besides, they are purely visual and do not affect any other senses at all, a vital point of difference when compared to conventional hallucinations. 
A significant characteristic of people with CBS is that they’re aware of having hallucinations, even though their visions may be exceptionally vivid.  Yet the prevalence of this condition cannot be ascertained correctly, primarily due to the reticence of people in disclosing whether they have symptoms of CBS, for fear of being labelled insane. 
TL; DR: The brain invents images for itself to see in the absence of visual stimuli from the external environment.
Under normal conditions, light waves enter our eyes and fall on the retina, which processes them and converts them into electrical impulses which are carried to the brain via the optic nerves — “the information, received from [the] eyes, actually stops the brain from creating its own pictures”. When normal vision is impaired, the retina is unable to receive visual stimuli from the external environment as under normal conditions. The nerves which used to transport impulses from the retina to the brain are, as a consequence, left without any stimulation. In such situations, the brain occasionally attempts to generate, on its own and by the combined forces of memory and imagination, inputs to the optic nerves. The result of the occipital lobe of the brain interpreting the resultant impulses from the optic nerves is the hallucination that characterises CBS. 
TL; DR: There is no getting past.
There is no medical cure for CBS, at present. But there a few actions, recommended by victims and experts alike, that could potentially mitigate the effects of CBS:
(1) Talking about the hallucinations: Sharing details about the hallucinations and reminding oneself that this affliction is not caused by any mental disorder is highly recommended,
(2) Changing environments: If hallucinations tend to happen in a particular environment, then effecting a change in that environment may be able to reduce further occurrences of the hallucinations,
(3) Using the eyes: Moving the eyes side-to-side or up-and-down; looking away from, or staring at, these hallucinations; and even blinking have been claimed to be of help in reducing these hallucinations,
(4) Rest and relaxation: Stress and fatigue have been suggested as possible triggers for such hallucinations; taking care to have adequate rest and avoid stressful situations is thus recommended. 
Highly unusual at first sight, the Charles Bonnet Syndrome is one of the lesser-known phenomena in psychology and psychiatry. If more and more of the population come to be aware of this medical condition, the persons who actually have this syndrome could be persuaded to speak out. And maybe, in the future, more scientific resources would be allocated to study this phenomenon, and hallucinations in general, so that more could be understood and discovered about the brain itself, the ultimate enigma.
By Subhrangshu Ghosh, Student, Electrical Engineering, Jadavpur University, Kolkata, India.
1. Ted-Ed. “How much of what you see is a hallucination? – Elizabeth Cox”
2. “Visual release hallucinations”: www.en.m.wikipedia,org/wiki/Visual_release_hallucinations
3. “Charles Bonnet Syndrome”. www.rnib.org.uk/eye-health/eye-conditions/charles-bonnet-syndrome-cbs
4. “What Is Charles Bonnet Syndrome?”: www.aao.org/eye-health/diseases/charles-bonnet-syndrome
5. Mogk et al. (2000). “Charles Bonnet Syndrome In Adults with Visual Impairments from Age-Related Macular Degeneration”.
6. “How Is Charles Bonnet Syndrome Treated?”: www.aao.org/eye-health/diseases/charles-bonnet-syndrome-treatment
Featured Image and Fig.1 “A Comic Representation” Source: https://medcomic.com/medcomic/visual-release-hallucinations-charles-bonnet-syndrome/
Fig.2 “Charles Bonnet” Source: Ref.
Fig.3 “What it’s like” Source: http://www.precisionfamilyeyecare.com/charles-bonnet-syndrome/
Fig.4 “Global Distribution” Source: https://www.dailyinfographic.com/this-underreported-impairment-causes-hallucinations
About the author: Hi! I am Subhrangshu Ghosh, freelance writer. I am also a student, presently in my third year of study in Electrical Engineering at Jadavpur University, Kolkata, India. Whenever I’m not studying (which is almost always), I either read books or write about stuff that interests me. If I have to name one thing I would want to have while I’m stranded on an island, it would be the book Meditations, by Marcus Aurelius. If I have to name one thing that I would like to do before I die, it would be to visit Iceland. If I have to name one person that I would like to meet, be it from the past or the present or the future, it would be Swami Vivekananda. For the future, I plan to be known far and wide, as an author and life-enthusiast (borrowing from Mark Manson, my idol).
Other blog by the author: Blue Light Blues-What Blue Light Means For Your Eyes and Health