Nav: Home

A first glimpse into disc shedding in the human eye

October 13, 2016

WASHINGTON -- An elusive biological cycle in the eye - the daily disposal and regeneration of the end tips of photoreceptor cells - has been captured in images for the first time in a living human eye. Photoreceptors are light-sensitive cells responsible for initiating vision. This glimpse into the inner workings of the eye will help scientists better understand, prevent and manage major eye diseases that affect photoreceptors like age-related macular degeneration and retinitis pigmentosa.

The physiological processes of disposal and regeneration -- called "disc shedding" and "disc renewal" -- are fundamental to maintaining the health of photoreceptors. The novel imaging method devised by these scientists detects disposal at the level of individual photoreceptor cells and clears a path for deeper explorations of vision and eye health.

The report on the collaborative work between Indiana University's School of Optometry, Indiana, USA, and the University of California, Davis, Department of Ophthalmology and Vision Science, California, USA, appears in the current issue of the journal of the Biomedical Optics Express, from The Optical Society (OSA).

Photoreceptors are conic or cylindrical structures that capture and convert light into an electrical response. The light, itself, is toxic as it leads to photo-oxidative compounds that would kill the cells if left to accumulate. To remain healthy, the cells must discard the membranes that contain the toxic compounds and then renew those that were lost. The difficulty lies in the fact that the cells have to maintain a constant length as they undergo this dynamic process each day. They cannot add too many renewing bits in the assembly process that the cell becomes too big, or too few that it becomes too small to work correctly.

"Shedding must be offset by renewal," said Omer P. Kocaoglu, a biomedical engineer at Indiana University and the first author on the paper. "Dysfunction at any stage or loss in synchronization -- such as loss of diurnal rhythm -- can lead to photoreceptor and retinal pigment epithelium (RPE) dystrophy, and ultimately blindness." The RPE is a thin but critically important layer of cells that nourishes and detoxifies photoreceptor cells.

"We and other imaging groups have been trying to detect this important physiological event for many years and have always come up short," said Donald T. Miller, the lead researcher on the project. The end tips that the team is looking for are tiny - only a few microns in size - and are believed to break off the larger photoreceptor cell only once a day, after which they are quickly gobbled up by neighboring cells. This makes them difficult to capture.

"In some ways it is like looking for a needle in a haystack," Miller said.

A key feature of their work is the discovery of the optical signature of this transient event as measured with their new imaging method. Their method combines two imaging technologies: adaptive optics, a technology first used in ground-based telescopes to correct aberrations induced by atmospheric turbulence, and optical coherence tomography (OCT), which makes cross-sectional images. Combined, the two methods provide exquisite optical resolution, permitting individual cells in the retina to be captured in all three dimensions - length, width and depth.

But the researchers wanted to take it a step further and actually track and monitor these cells over time - four dimensions. This required sophisticated post-processing algorithms, which the team developed. The team verified their observations with quantitative analyses of the spatial and temporal properties of the cone shedding dynamics in three healthy human subjects whose vision they were testing.

Previous research into this process, which has been taking place for decades, often used the eyes of dead animals for their model. Until the current study, no one knew exactly how this cycle was executed in humans.

"These first experiments establish a clear path for further investigation of photoreceptor shedding, which are now underway in our laboratory. Much awaits, and we have a great team to do it." Miller said.
-end-
Paper: Omer P. Kocaoglu, Zhuolin Liu, Furu Zhang, Kazuhiro Kurokawa, Ravi S. Jonnal, and Donald T. Miller, "Photoreceptor disc shedding in the living human eye," Biomed. Opt. Express 7, 4554-4568 (2016).

About Biomedical Optics Express

Biomedical Optics Express is OSA's principal outlet for serving the biomedical optics community with rapid, open-access, peer-reviewed papers related to optics, photonics and imaging in the life sciences. The journal scope encompasses theoretical modeling and simulations, technology development, and biomedical studies and clinical applications. It is published by The Optical Society and edited by Christoph Hitzenberger, Medical University of Vienna. Biomedical Optics Express is an open-access journal and is available at no cost to readers online at: OSA Publishing.

About The Optical Society

Founded in 1916, The Optical Society (OSA) is the leading professional organization for scientists, engineers, students and entrepreneurs who fuel discoveries, shape real-life applications and accelerate achievements in the science of light. Through world-renowned publications, meetings and membership initiatives, OSA provides quality research, inspired interactions and dedicated resources for its extensive global network of optics and photonics experts. For more information, visit osa.org/100.

The Optical Society

Related Photoreceptors Articles:

Researchers pinpoint how detecting social signals may have affected how we see colors
The arrangement of the photoreceptors in our eyes allows us to detect socially significant color variation better than other types of color vision, a team of researchers has found.
Photoreceptor cell death leads to blindness in CLN5 form of Neuronal Ceroid Lipofuscinosis
Researchers from the University of Eastern Finland have discovered a likely cause for visual impairment and eventual loss of vision in the Finnish variant of Neuronal Ceroid Lipofuscinosis (NCL).
Honey bees have sharper eyesight than we thought
Research conducted at the University of Adelaide has discovered that bees have much better vision than was previously known, offering new insights into the lives of honey bees, and new opportunities for translating this knowledge into fields such as robot vision.
Fish eyes to help understand human inherited blindness
Discovery of a gene in zebrafish that triggers congenital blindness could lead to a suitable cure for similar disease in humans.
NIH scientists deploy CRISPR to preserve photoreceptors in mice
Silencing a gene called Nrl in mice prevents the loss of cells from degenerative diseases of the retina, according to a new study.
Fish eyes may hold key to regenerating human retinas
Research into retinal regeneration in zebrafish has identified a signal that appears to trigger the self-repair process, raising the possibility that human retinas can also be induced to regenerate, naturally repairing damage caused by degenerative retinal diseases and injury, including age-related macular degeneration and retinitis pigmentosa.
Fighting blindness: TSRI scientists bring a key protein into focus
Scientists from the Florida campus of The Scripps Research Institute (TSRI) have discovered how a protein called α2δ4 establishes proper vision.
Flirting on the 'fly', what blow flies can tell us about attraction & dating apps
A study led by Simon Fraser University biologist Gerhard Gries found that the photoreceptors in blow fly eyes do more than help them navigate the environment.
Improving longevity of functionally integrated stem cells in regenerative vision therapy
One of the challenges in developing stem cell therapies is ensuring that transplanted cells can survive long enough to work.
New transplant technique restores vision in mice
Researchers at the RIKEN Center for Developmental Biology in Kobe, Japan have shown that retinal transplants derived from induced pluripotent stem cells can restore visual function in mice.

Related Photoreceptors Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#SB2 2019 Science Birthday Minisode: Mary Golda Ross
Our second annual Science Birthday is here, and this year we celebrate the wonderful Mary Golda Ross, born 9 August 1908. She died in 2008 at age 99, but left a lasting mark on the science of rocketry and space exploration as an early woman in engineering, and one of the first Native Americans in engineering. Join Rachelle and Bethany for this very special birthday minisode celebrating Mary and her achievements. Thanks to our Patreons who make this show possible! Read more about Mary G. Ross: Interview with Mary Ross on Lash Publications International, by Laurel Sheppard Meet Mary Golda...