Sankhajyoti Saha, M.Optometry

Clinical Optometrist, I for Eye-Care, Falakata, India


Hallucinations are sensory experiences that appear real but are created by the subconscious mind. They may affect all your senses (vision, smell, taste, hearing , and/or touch). Charles Bonnet Syndrome (CBS) is a condition that causes people with decreased vision, to have visual hallucinations like seeing patterns, or more complex images such as people, animals, buildings, etc. CBS is named after the Swiss scientist, Charles Bonnet, who described this condition experienced by his grandfather, and who later developed it himself. (1)

Criteria for diagnosing CBS include visual hallucinations, absence of hallucinations in other sensory modalities, absence of psychological disorders, preserved cognitive skill, no lower limit of visual acuity, and no specific age. (2) It is important to consider visual pathway pathology as a contributing factor to visual hallucinations in patients with previously diagnosed underlying dementia (Alzheimer’s disease, etc.), psychosis (psychological disorders, etc.), Parkinson’s disease, and delirium. (3) 

Visual hallucination reported by patients:

  • A woman sees a little girl wearing an apron, knowing the fact that it cannot be real. (1)
  • Another woman saw a pink grid filling the whole visual field, which was very disturbing to her. (1)
  • An old lady reported seeing different people from her dreams, with a history of blindness after cataract extraction. (4)
  • An old man with a prosthetic left eye, experienced ghost images with “flower- like” and “lamp-like” appearance. (4)



Deafferentation Theory (Sensory Deprivation Theory) is the most widely accepted hypothesis.  Deprivation of visual inputs into the brain, due to the absence of visual stimulation, eventually leads to spontaneous firing of neuronal discharge in the visual association cortex. Increasing excitability within the visual cortex area results in visual hallucinations.  (2) These physiological changes liberate visual images from the conscious to the subconscious.

CBS can be experienced without an acuity loss in glaucoma, where Deafferentation takes place in ganglion cells, conversely,  in ARMD, there is a loss of central retinal ganglion cells resulting in acuity loss to occur in CBS.(2)

Risk factors:

  • Visual impairment
  • Older age (because of increased incidence of eye disease in the elderly) (2)
  • Isolation (1)
  • Dark environments (1)


Treatment Regimen:

  • Optical Intervention: Enhancing the residual vision with spectacles, contact lenses, and/or low vision devices may reduce the frequency of visual hallucination. (2)
  • Surgical Intervention: With surgical intervention, treating the underlying cause of visual impairment can halt visual hallucinations. (2)
  • Mindfulness-based interventions: For a greater acceptance and insight into their hallucinations.
  • Patient Education: Eye care professionals play a critical role in reassuring patients and family members that it can be a normal consequence of their vision loss. (2)


Although acknowledgment of CBS in the Optometric and Ophthalmologic literature has increased over the past few decades, adequate information about CBS is still a missing link that needs to be renovate for proper diagnosis and management. Despite having some well-recognized theories, the actual mechanism is still under the scanner. Before diagnosing CBS, all other aetiologies which cause visual hallucination must be investigated properly.



  1. The American Society of Retina Specialists. Charles Bonnet Syndrome – The American Society of Retina Specialists. ASRS. Retrieved from (Last accessed: January 17, 2021, 16:00 IST)
  2. Pang L. (2016). Hallucinations Experienced by Visually Impaired: Charles Bonnet Syndrome. Optometry and Vision Science, 93(12), 1466–1478.
  3. Osa A, Bowen T & Whitson J. (2020). Charles Bonnet Syndrome in a Patient with Parkinson’s Disease and Bilateral Posterior Capsule Opacification. International Medical Case Reports Journal, Volume 13, 7-10.
  4. Paradowski B., Kowalczyk E., Chojdak-Łukasiewicz J., Loster-Niewińska A., & Służewska-Niedźwiedź M. (2013). Three Cases with Visual Hallucinations following Combined Ocular and Occipital Damage. Case Reports in Medicine, 2013, 1-5.