More than meets the eye

 

Despite awareness initiatives, Charles Bonnet syndrome continues to languish at the margins of medical interest. One of the consequences of this state of affairs is that outdated information and misconceptions thrive. One such misconception is that eye disease (or injury) is the sole cause of the syndrome. This covers well known eye conditions such as macular degeneration, cataracts and glaucoma. 

What is less understood is that the syndrome can be triggered even when a person’s eyes are (structurally) fine. CBS can occur when there is damage anywhere along the visual pathways: from the optic nerve to the visual region of the brain (back of the head). Common medical causes for such damage includes stroke, brain tumour or traumatic head injury.

A recently published case adds a further layer to how susceptible the visual pathways can be to a negative outcome. A 60 year old woman with very good vision (6/6 in one eye [20/20] and 6/9 in the other [20/30]) was found to have a tumour behind the top of the nose and at the base of the brain. The vast majority of this tumour was successfully removed. She was subsequently given radiation therapy to attack the small remnants of the tumour that remained.

All seemed to be going well after the first 10 months as evidenced by another good eye test result and no unwanted symptoms. However, just two months later (ie. 12 months since completing her radiation therapy), it was discovered that the woman had suffered significant damage to the optic nerves. It was around this time that the woman first began to encounter unusual visual experiences including seeing “geometric patterns, lions with manes and women’s faces”.  

 

(Image courtesy of Mariola Grobelska) 

It was determined that the radiation therapy had led to the deterioration of the optic nerves and its effects were still being felt. Since then, her vision has continued to decline. Alongside her progressive sight loss, her CBS visions have increased. 

This case highlights that any damage to the optic pathways (beyond the eye itself) can be sufficient to activate CBS.

 

 

 

REFERENCE:  A case of vision loss from radiation-induced optic neuropathy resulting in Charles Bonnet syndrome (2023). Applied Radiation Oncology, Vol 12(2): 34-38.