May 8, 2006, 11:37 PM CT

Genetic Insights Into Retinoblastoma

Investigators at St. Jude Children's Research Hospital have discovered the role of several key genes in the development of the retina, and in the process have taken a significant step toward understanding how to prevent or cure the potentially deadly eye cancer retinoblastoma. Retinoblastoma is the third most common cancer in infants after leukemia and neuroblastoma (nerve cancer). Retinoblastoma that has spread outside the eye is among the deadliest childhood cancers, with an average survival rate of less than 10 percent.

A key finding of the new study is that humans are more susceptible to developing retinoblastoma than mice, because mice can compensate for the loss of a gene critical to normal retinal development while humans cannot. The results of the study appear in the open-access journal BMC Biology.

"Our study gives us important new information on the normal development of the retina and suggests new studies that could lead to the design of more effective drugs to treat retinoblastoma," said Michael Dyer, Ph.D., an associate member of the Department of Developmental Neurobiology at St. Jude and senior author of the paper.

The scientists discovered that during the development of the retina in mice, three genes that belong to the Rb gene family are expressed at different times. Specifically, the p107 gene is active before birth in cells that are going to become the retina. This gene ensures that the retinal cells stop multiplying at the proper time during development of this tissue. The Rb gene is expressed after birth in those cells that are actively multiplying as they also help form the retina.........

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April 26, 2006, 6:52 PM CT

Virtual 'forest' used to measure navigation skills

A new study recently published in Journal of Vision, an online, free access publication of the Association for Research in Vision and Ophthalmology (ARVO), shows that an individual's navigation skills can be measured by using an immersive virtual "forest" in which peripheral visual field losses are simulated.

The study, conducted by scientists from the Lions Vision Center, Wilmer Eye Institute, Johns Hopkins University in Baltimore, Md., involved varying the study participants' visual field of view and recording several performance measures such as walking time and path efficiency. Participants were then identified as either "good navigators" or "poor navigators." The results suggest that poor navigators rely on visual information to solve the task while good navigators are able to use visual information in conjunction with an internal representation of the environment. As a result of these differences, the performance of the poor navigators improved more than the performance of the good navigators as the amount of available visual information increased.

"By simulating peripheral visual field losses during navigation, we were able to create a paradigm that systematically controls the amount of external visual information available to participants. This allows us to directly test the extent to which participants rely on this type of information, and identify those individuals who are able to rely on alternative sources of information to learn about their environments," said lead researcher Francesca Fortenbaugh, BS. "Knowing what types of information individuals use when navigating and how performance deteriorates when that information is removed is important not only for understanding human navigation in general, but also for the development of rehabilitation protocols for individuals with visual impairments."........

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April 24, 2006, 6:53 PM CT

Eyeglass Injuries May Lead To Hospital Visit

Injuries correlation to wearing glasses sent an estimated 27,000 people to the emergency department in 2002 and 2003, a new study suggests.

But the scientists say that such injuries could be avoided if people would wear protective eyewear during activities that put them at high risk of eye injury.

The scientists estimated that, in 2002 and 2003, some 27,000 people went to the emergency department seeking therapy for injuries correlation to wearing glasses. More than 1,000 of these cases were admitted to the hospital for further therapy.

"We also found that injuries correlation to wearing glasses vary by age and gender," said Huiyun Xiang, a co-author of study and an assistant professor of pediatrics at Ohio State University.

For example, people 65 and older were much more likely than younger adults to fall and hit their head, thus causing a glasses-related injury. Sports-related eyeglass injuries were more common in children 17 and younger.

The scientists also found that injuries to the eyeball were much more prominent among people age 18 to 64, compared to children and elderly adults.

Xiang and colleagues report their findings in a recent issue of the journal Ophthalmic Epidemiology. Xiang conducted the study with lead author Sara Sinclair, a research associate at the Center for Injury Research and Policy at Columbus Children's Hospital, and Gary Smith, the Center's director.........

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April 20, 2006, 9:37 PM CT

Insights Into Lazy Eye Theory

In a study that challenges conventional thinking about the condition known as lazy eye, scientists at MIT's Picower Institute for Learning and Memory show that it's the quality, not the quantity, of images and light striking the retina that causes one eye to lose function.

The study will appear in the recent issue of the Journal of Neurophysiology.

Amblyopia, or lazy eye, is a developmental disorder characterized by poor or blurry vision in an eye that is structurally normal. The problem is caused by either no transmission or poor transmission of visual images to the brain for a sustained period during early childhood. Amblyopia has been estimated to affect 1 percent to 5 percent of the population.

"It's been known for a long time that if you are born with cataracts in one eye, you will go blind in that eye," said co-author of study Mark Bear, Picower Professor of Neuroscience. "Depriving one eye of crisp images rapidly causes cortical neurons to lose responsiveness to the deprived eye".

While it was thought that inactivity caused the neurons associated with the deprived eye to wither -- a case of "use it or lose it" -- Bear and his colleagues at Brown University report that a blurry image is worse than no image at all.

The conventional therapy for lazy eye is to wear a patch over the good eye in the hope that the weaker eye will get stronger. "It's a zero-sum game," Bear said, "because as the weak eye gets stronger, the strong eye gets weaker. The challenge is to promote recovery of the weak eye without impairing the other eye".........

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April 20, 2006, 9:05 PM CT

Laser Therapy For Melanoma Of The Eye

Mayo Clinic scientists report that transpupillary thermotherapy (TTT) appears to be a successful therapy for most patients who have small choroidal melanomas -- a primary cancer of the eye. The results of the study are in the recent issue of Archives of Ophthalmology.

In TTT, a wide laser beam is directed at the choroidal tumor through a contact lens, causing tumor cell death. In 1996, Mayo became one of the first centers in the nation to use TTT. Three years later, Mayo scientists published the results of TTT for the first 20 patients seen (available online at http://archopht.ama-assn.org/cgi/content/full/117/11/1512).

"We wanted to reaffirm the effectiveness of TTT for our original patients by examining their follow-up data," said Colin McCannel, M.D., Mayo Clinic ophthalmologist and study co-investigator. "In addition, we hoped to show continued success with the procedure as a stand-alone therapy for choroidal melanoma."

The choroid is the vascular layer of the eye between the retina and the sclera. It is responsible for limiting reflection of light within the eye as well as providing blood supply and oxygen to the retina. Choroidal melanoma can cause vision loss and eventually spread to other parts of the body. While cancers of the eye are not very common, they historically were treated by removal of the eye to prevent spread of the cancer. There are limited therapy options beyond removing the eye, but the Mayo team showed that at least for small tumors, TTT is a very good option.........

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April 15, 2006, 2:30 PM CT

Gene Decreases Retinal Degeneration In Fruit Flies

Johns Hopkins scientists have discovered a gene in fruit flies that helps certain specialized neurons respond more quickly to bright light. The study, reported in the April 4 issue of Current Biology, also has implications for understanding sensory perception in mammals.

In teasing apart the molecular interactions and physiology underlying light perception, the scientists studied a gene they dubbed "Lazaro" that is expressed 15 times higher in the fly eye than the rest of the fly head. They found that this gene is mandatory for a second biochemical pathway that controls the activity of a protein called the TRP channel. TRP channels are found in fruit fly neurons responsible for sensing light. The fly TRP channel is the founding member of a family of related proteins in mammals that are essential for guiding certain nerves during development and for responding to stimuli including heat, taste and sound.

By shining bright light onto and recording electrical changes in single nerve cells in the fly eye, scientists found that neurons carrying a mutation in this gene cannot respond as well to light as compared to neurons carrying normal copies of this gene. In fact, the mutant neurons turn off their response to light four times faster than normal neurons. Because Lazaro helps fly TRP channels work at their maximum, it is possible that a Lazaro-like gene in mammals might also play a role in how well mammalian TRP channels work.........

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April 10, 2006, 7:57 PM CT

Macular Degeneration May Lead To Cognitive Impairment

Older patients with advanced age-related macular degeneration and reduced vision may be more likely to also have cognitive impairment, or problems with thinking, learning and memory, as per a research studyin the recent issue of Archives of Ophthalmology, one of the JAMA/Archives journals.

Age-related macular degeneration (AMD) develops when the macula, the portion of the eye that allows people to see in detail, deteriorates. AMD is a leading cause of irreversible vision loss in elderly Americans, as per background information in the article. Cognitive impairment also affects a number of elderly adults, reducing their ability to function independently.

The Age-Related Eye Disease Study (AREDS) Research Group examined the relationship between vision problems and cognitive impairment in 2,946 patients enrolled in AREDS, an 11-center study of AMD and age-related cataracts. Between July 2000 and March 2004, the patients took a series of six tests to gauge their cognitive function. Participants' visual acuity (sharpness) was measured every year, and the progression of AMD was assessed and categorized at regular intervals throughout the study using photographs of the retina. Category 1 indicates no AMD and Category 4 is the most advanced stage.

At the time they took the test, 23 percent of the participants were classified as AMD Category 1, 29 percent Category 2, 26 percent Category 3 and 22 percent Category 4. In addition, 72 percent had 20/40 vision or better, 18 percent had worse than 20/40 vision in one eye and 10 percent had an overall visual acuity of less than 20/40. Those who had more severe AMD had poorer average scores on the cognitive tests, an association that remained even after scientists considered other factors, including age, sex, race, education, smoking, diabetes, use of cholesterol-lowering medications and high blood pressure. Average scores also decreased as vision decreased.........

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April 5, 2006, 10:54 PM CT

Fish Oil May Protect Against Retinal Diseases

A invited paper published in Trends in Neuroscience this week by Nicolas G. Bazan, MD, PhD, Boyd Professor and Director of the Neuroscience Center of Excellence at LSU Health Sciences Center in New Orleans, reports on the role that the omega-3 fatty acids in fish oil play in protecting cells in the retina from degenerative diseases like retinitis pigmentosa and age-related macular degeneration, the leading cause of loss of vision in those older than 65. The paper is titled, Cell survival matters: docosahexaenoic acid signaling, neuroprotection and photoreceptors.

In these blinding eye diseases, photoreceptor cells (rods and cones) degenerate and die. Eventhough this process can be triggered by a number of different things, one of the most significant protective factors may be the close association of retinal pigment epithelial (RPE) cells and the amount of docosahexaenoic acid (DHA) in them. The main role of RPE cells is photoreceptor maintenance-they conduct the daily shedding, internalization, and degradation of the tips of the photoreceptor outer segments. It now appears that RPE cells are also key to the survival of photoreceptor cells.

Both photoreceptor and RPE cell types are normally exposed to potentially damaging factors such as sunlight and high oxygen tension.........

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January 10, 2006, 6:24 PM CT

Treating Glaucoma Early

Treatments that delay the progression of glaucoma may significantly reduce the economic health burden on people with the disease and on the U.S. health system, according to a new study by scientists at Duke University Eye Center and elsewhere. Their findings appear in the January 9, 2006, issue of Archives of Ophthalmology.

The team determined that patients with early-stage or suspected glaucoma use approximately $623 per year in health care resources, while patients with end-stage disease consume approximately $2,511. The cost of medicine was responsible for one-third to half of the total direct cost to consumers.

"It is imperative that patients with glaucoma be well-monitored for changes in their disease," said Paul Lee, M.D., a glaucoma specialist at Duke University Eye Center and lead author on the study. "Our results prove what we've thought for a long time - that the disease gets more expensive as it worsens. With effective therapys at earlier stages, the progression of disease can be slowed or halted - saving both the patient and society from greater economic burden."

Glaucoma is a leading cause of blindness in the U.S., affecting an estimated 2.2 million adults, the scientists said. Experts anticipate the overall number of people living with glaucoma to rise as the number of elderly Americans increases. Glaucoma is a group of eye diseases that damage the cells and fibers of the optic nerve, interrupting the transmission of visual signals from the eye to the brain. The disease is believed to be caused by a level of intraocular pressure (IOP) that is too high, eventhough other mechanisms are likely to be involved since people can develop the disease and have a normal IOP. A number of people go undiagnosed during early stages of the disease because symptoms are virtually undetectable without an eye exam.........

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January 7, 2006, 4:55 PM CT

Mysterious Eye Cells Adapt To Light

A new retinal photoreceptor adjusts its sensitivity in different lighting conditions, according to researchers at Brown University, where the rare eye cells were discovered.

The results, published in Neuron, are a surprise. Though rods and cones, their biological cousins in the retina, clearly adjust to light levels, these new cells - intrinsically photosensitive retinal ganglion cells, or ipRGCs - were assumed not to adapt this way. Still, the adaptation process in ipRGCs is weaker and slower than it is in rods and cones.

The findings provide further evidence that the eye has complementary brain-signaling systems at work. Rods and cones rapidly communicate changes in brightness, signals which allow us to glimpse a baseball streaking across the sky or a deer darting into a darkened road. But ipRGCs work differently. They send signals about overall brightness, telling the brain when it is night and when it is day.

"These cells operate like a light meter on a camera," said David Berson, the Sidney A. Fox and Dorothea Doctors Fox Professor of Ophthalmology and Visual Sciences. "They tell the brain to constrict the pupil based on the amount of light registered over time".

Berson discovered ipRGCs in his Brown neuroscience lab three years ago. These cells number no more than 2,000 in the eye and have a direct link to the brain, sending electrical messages to an area regulating the pupil as well as a region controlling the body clock. This circadian rhythm controls alertness, sleep, hormone production, body temperature and organ function.........

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