How a cancer treatment can leave people with 'night vision'
Among all the different types of cancer treatment, photodynamic therapy – where light is used to destroy malignant cells – might have one of the strangest side effects: Patients are often better able to see in the dark.
Photodynamic treatment is used to treat certain malignancies, and patients frequently report an odd side effect.
Many people claim to have a feeling of better "night vision" in addition to seeing unusual patterns and silhouettes in the dark.
Photodynamic therapy involves the use of light-sensitive medicine that is activated by a light source.
The photo-active substance (chlorine e6) is injected into the circulation through a vein or applied to the skin, depending on the portion of the body being treated, and eventually finds its way into malignant cells.
The medicine is "turned on" when a specific laser is blasted over the damaged area, and it generates a chemical that kills the rogue cells.
Researchers eventually discovered out why this occurred last year: Rhodopsin, a light-sensitive protein found in our eyes' retinas, interacts with chlorin e6, a photosensitive chemical that is a critical component of this sort of cancer treatment.
The research relied on what scientists already understood about retinal, an organic substance found in the eye that is normally insensitive to infrared radiation.
The science of vision
When light is collected by a succession of cones and rods in the retina, "seeing" occurs.
Rods have a lot of rhodopsin, a photosensitive protein that absorbs visible light thanks to a substance called retinal that it contains.
When exposed to visible light, the retina separates from rhodopsin.
This allows the light signal to be translated to an electrical signal, which our brain's visual cortex perceives as sight.
In fact, during the night there is "less light," which means light radiation is not in a domain visible to humans.
The retina is not sensitive to higher wavelengths (the infrared level).
As a result, unlike many species, we are unable to see in the dark.
(With inputs from agencies)