Intrinsically photosensitive retinal ganglion cells

Specialized retinal cells involved in non-image-forming vision

Classification
External resources

Intrinsically photosensitive retinal ganglion cells (ipRGCs) are a type of retinal ganglion cell that are directly sensitive to light. Unlike the majority of retinal ganglion cells, which rely on input from rod cells and cone cells, ipRGCs contain the photopigment melanopsin, which allows them to respond to light independently.

Function

IpRGCs play a crucial role in various non-image-forming visual functions. They are primarily involved in the regulation of the circadian rhythm, the pupillary light reflex, and other physiological responses to ambient light levels. These cells project to several brain regions, including the suprachiasmatic nucleus (SCN), which is the central circadian clock in mammals.

Circadian Rhythm

IpRGCs are essential for the entrainment of the circadian rhythm to the light-dark cycle. They convey information about ambient light levels to the SCN, which adjusts the body's internal clock accordingly. This process is vital for maintaining synchrony with the external environment.

Pupillary Light Reflex

The pupillary light reflex is another function mediated by ipRGCs. These cells send signals to the pretectal area of the brain, which controls the constriction of the pupil in response to light. This reflex helps protect the retina from excessive light exposure and aids in visual acuity.

Melanopsin

Melanopsin is the photopigment found in ipRGCs. It is sensitive to blue light, with a peak sensitivity around 480 nm. This sensitivity makes ipRGCs particularly responsive to the blue light present in natural daylight, which is important for their role in circadian regulation.

Clinical Significance

Dysfunction of ipRGCs can lead to various disorders, including circadian rhythm sleep disorders and seasonal affective disorder. Understanding the role of ipRGCs in these conditions can help in developing therapeutic strategies.

Research

Recent studies have focused on the role of ipRGCs in mood regulation and their potential involvement in depression. The ability of ipRGCs to influence mood and alertness highlights their importance beyond traditional visual pathways.

See also

• Retina
• Photoreceptor cell
• Visual system

External links

• Intrinsically photosensitive retinal ganglion cells on WikiMD