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An eye on the arts–the arts on the eye
Journal of AAPOS Volume 7 Number 4 August 2003
230 SCN of the hypothalamus. Rods and cones are not required for this photoentrainment process; thus, this neural circuit demonstrates an apparent independence from conventional retinal photo-transduction. Melanopsin, an opsin-like protein whose coding messenger RNA has been found in a subset of mammalian ganglion cells, may be the visual pigment of the phototransducing ganglion cells that set the circadian clock and initiate other non–image-forming visual functions. Hattar et al6 found that intrinsic photosensitive ganglion cells were invariably melanopsin positive, whereas conventional ganglion cells lacking intrinsic light responses were melanopsin negative. Although melanopsin may be the best candidate as the circadian photopigment, this has not been determined with certainty. Another photopigment, cytochrome, has been found in some RGCs and may also play a role. This system of light-sensitive ganglion cells, with its projections to the SCN (the circadian pacemaker), may explain why the circadian pattern could be altered by prolonged daylight exposure. According to Provencio,8
the discovery of this specialized network might also lead to treatment of disorders such as jet lag and seasonal depression. References 1. Muchnick RS, Sanfilippo S, Dunlop EA. Cyclic esotropia developing after strabismus surgery. Arch Ophthalmol 1976;94:459-69. 2. Clarke WN, Scott WE. Cyclic third nerve palsy. J Pediatr Ophthalmol Strabismus 1975;12:94-9. 3. Metz HS, Searl SS. Cyclic vertical deviation. Trans Am Ophthalmol Soc 1984;82:158-65. 4. Reimann HA. Periodic disease. Medicine 1951;30:219-45. 5. Metz HS, Bigelow C. Change in the cycle of circadian strabismus. Am J Ophthalmol 1995;120:124-5. 6. Hattar S, Liao HW, Takao M, Berson DM, Yau KW. Melanopsincontaining ganglion cells: architecture, projections, and intrinsic photosensitivity. Science 2002;295:1065-70. 7. Berson DM, Dunn FA, Takao M. Phototransduction by retinal ganglion cells that set the circadian clock. Science 2002;295:1070-3. 8. Provencio I, Rollag MD, Castrucci AM. Photoreceptive net in the mammalian retina. Nature 2002;415:493. 9. Baringa M. How the brain’s clock gets daily enlightenment. Science 2002;295:955-7.
An Eye on the Arts – The Arts on the Eye
Zenzen’s eyes opened. The doctor took out a penlight and shined it into Zenzen sensei’s eyes, back and forth. The sensei’s eyes blinked, but didn’t follow the light. “What’s his condition?” Tina asked. “He had a hemorrhagic stroke in the left lobe, with some damage to the prefrontal area as well. He was stabilized well in the emergency room, the brain swelling reduced. He was lucky that he got here when he did, just minutes after the hemorrhage. They were able to reduce the ischemic cascade, limit the area of the infarct, using drugs and cooling.” He glanced at Tina to see if she was following. She nodded at him to go on. He flipped through the pages in the file and said, “However, the damage was extensive.” His fingers dipped into the file and extracted a film image. “Yes, extensive damage.” He handed it to her. Tina studied the image. With its black-and-white blobs, she recognized a coronal section of the brain. Where the normal tissue would have shown as light gray, large portions of the left hemisphere were black. Tina looked from the image to the sensei, his eyes focused on her now, though his face was expressionless. She kneeled near him; his eyes followed her. “Sensei?” His focus dissolved, and his eyes closed. —Todd A. Shimoda (from The Fourth Treasure: A Novel)
230 SCN of the hypothalamus. Rods and cones are not required for this photoentrainment process; thus, this neural circuit demonstrates an apparent independence from conventional retinal photo-transduction. Melanopsin, an opsin-like protein whose coding messenger RNA has been found in a subset of mammalian ganglion cells, may be the visual pigment of the phototransducing ganglion cells that set the circadian clock and initiate other non–image-forming visual functions. Hattar et al6 found that intrinsic photosensitive ganglion cells were invariably melanopsin positive, whereas conventional ganglion cells lacking intrinsic light responses were melanopsin negative. Although melanopsin may be the best candidate as the circadian photopigment, this has not been determined with certainty. Another photopigment, cytochrome, has been found in some RGCs and may also play a role. This system of light-sensitive ganglion cells, with its projections to the SCN (the circadian pacemaker), may explain why the circadian pattern could be altered by prolonged daylight exposure. According to Provencio,8
the discovery of this specialized network might also lead to treatment of disorders such as jet lag and seasonal depression. References 1. Muchnick RS, Sanfilippo S, Dunlop EA. Cyclic esotropia developing after strabismus surgery. Arch Ophthalmol 1976;94:459-69. 2. Clarke WN, Scott WE. Cyclic third nerve palsy. J Pediatr Ophthalmol Strabismus 1975;12:94-9. 3. Metz HS, Searl SS. Cyclic vertical deviation. Trans Am Ophthalmol Soc 1984;82:158-65. 4. Reimann HA. Periodic disease. Medicine 1951;30:219-45. 5. Metz HS, Bigelow C. Change in the cycle of circadian strabismus. Am J Ophthalmol 1995;120:124-5. 6. Hattar S, Liao HW, Takao M, Berson DM, Yau KW. Melanopsincontaining ganglion cells: architecture, projections, and intrinsic photosensitivity. Science 2002;295:1065-70. 7. Berson DM, Dunn FA, Takao M. Phototransduction by retinal ganglion cells that set the circadian clock. Science 2002;295:1070-3. 8. Provencio I, Rollag MD, Castrucci AM. Photoreceptive net in the mammalian retina. Nature 2002;415:493. 9. Baringa M. How the brain’s clock gets daily enlightenment. Science 2002;295:955-7.
An Eye on the Arts – The Arts on the Eye
Zenzen’s eyes opened. The doctor took out a penlight and shined it into Zenzen sensei’s eyes, back and forth. The sensei’s eyes blinked, but didn’t follow the light. “What’s his condition?” Tina asked. “He had a hemorrhagic stroke in the left lobe, with some damage to the prefrontal area as well. He was stabilized well in the emergency room, the brain swelling reduced. He was lucky that he got here when he did, just minutes after the hemorrhage. They were able to reduce the ischemic cascade, limit the area of the infarct, using drugs and cooling.” He glanced at Tina to see if she was following. She nodded at him to go on. He flipped through the pages in the file and said, “However, the damage was extensive.” His fingers dipped into the file and extracted a film image. “Yes, extensive damage.” He handed it to her. Tina studied the image. With its black-and-white blobs, she recognized a coronal section of the brain. Where the normal tissue would have shown as light gray, large portions of the left hemisphere were black. Tina looked from the image to the sensei, his eyes focused on her now, though his face was expressionless. She kneeled near him; his eyes followed her. “Sensei?” His focus dissolved, and his eyes closed. —Todd A. Shimoda (from The Fourth Treasure: A Novel)