The Neuronal Organization of the Retina

The mammalian retina consists of neurons of >60 distinct types, each playing a specific role in processing visual images. They are arranged in three main stages. The first decomposes the outputs of the rod and cone photoreceptors into ∼12 parallel information streams. The second connects these streams to specific types of retinal ganglion cells. The third combines bipolar and amacrine cell activity to create the diverse encodings of the visual world—roughly 20 of them—that the retina transmits to the brain. New transformations of the visual input continue to be found: at least half of the encodings sent to the brain (ganglion cell response selectivities) remain to be discovered. This diversity of the retina’s outputs has yet to be incorporated into our understanding of higher visual function.

Abnormal Involuntary Eye Movements in the “Lazy Eye” Disease Amblyopia Linked to Changes in Subcortical Regions of the Brain

The neural mechanism underlying amblyopia, also called “lazy eye” is still not completely clear. A new study now reports abnormal eye movements of the lazy eye, which suggests that disturbed functioning of eye movement coordination between both eyes and not primarily the dysfunction of the visual cortex may be a cause of amblyopia (Xue-feng Shi et al.).

Little is known about oculomotor function in amblyopia, or “lazy eye,” despite the special role of eye movements in vision. A group of scientists has discovered that abnormal visual processing and circuitry in the brain have an impact on fixational saccades (FSs), involuntary eye movements that occur during fixation and are important for the maintenance of vision. The results, which raise the question of whether the alterations in FS are the cause or the effect of amblyopia and have implications for amblyopia treatment, are available online in advance of publication in the November issue of Restorative Neurology and Neuroscience.

“Although FSs are of great functional significance in neural coding, visual perception, and visual task execution, their behavioral characteristics in visual and neurological disease have been rarely studied,” says lead investigator Xue-Feng F. Shi, MD, PhD, of the Tianjin Key Laboratory of Ophthalmology and Visual Science, Tianjin Eye Institute, College of Clinical Ophthalmology, Tianjin Medical University, and the Department of Pediatric Ophthalmology and Strabismus, Tianjin Eye Hospital, Tianjin, China. “We carried out quantitative and detailed analysis of fixational saccades in amblyopia for the first time.”

Nobel Winner’s Stem Cells to Be Tested in Eye Malady in 2013

Stem cells derived from a mouse’s skin won Shinya Yamanaka the Nobel Prize. Now researchers in Japan are seeking to use his pioneering technology for an even greater prize: restoring sight.

Scientists at the Riken Center for Developmental Biology in Kobe plan to use so-called induced pluripotent stem cells in a trial among patients with macular degeneration, a disease in which the retina becomes damaged, resulting in loss of vision, Yamanaka told reporters in San Francisco.

Companies including Pfizer Inc. (PFE) are already planning trials of stem cells derived from human embryos. The Japanese study will be the first to use a technology that mimics the power of embryonic cells while avoiding the ethical controversy that accompanies them.

“The work in that area looks very encouraging,” John B. Gurdon, 79, a professor at the University of Cambridge who shared the Nobel with Yamanaka, said in an interview in London.

Yamanaka and Gurdon shared the 8 million Swedish kronor ($1.2 million) award for experiments 50 years apart that showed that mature cells retain in latent form all the DNA they had as immature stem cells, and that they can be returned to that potent state, offering the potential for a new generation of therapies against hard-to-treat diseases such as macular degeneration.

Fruit flies’ eyes shrink a little to see

I spy, with my mechanical eye. It seems a simple mechanical change plays a role in sensory perception in fruit flies, and possibly in many other animals, including humans.

The eyes of the common fruit fly (Drosophila melanogaster) contain clusters of light-sensitive cells organised into rods. When light strikes one of these cells, it triggers a series of chemical reactions. These cause a protein called a transient receptor potential (TRP) ion channel to open. When it’s open, the TRP allows charged particles to flow into the cell, causing the cell to send a signal to the fly’s brain.

TRP channels play a part in sensory perception in many animals, from nematodes to humans. But nobody knew how the chemical signals make the TRP channel open.

Easier test for blindness cause

Scientists from Australia’s Vision Centre have demonstrated a quick, accurate test under lights for one of the world’s leading causes of blindness.

A new study shows that age-related macular degeneration (AMD) can be just as effectively and more rapidly and inexpensively diagnosed under bright lights, instead of requiring patients to sit for 20 minutes in a darkened room.

“AMD accounts for half of the legal blindness cases in Australia,” says Professor Ted Maddess from The Vision Centre and The Australian National University. “It affects one in seven people over the age of 50, costing the nation $2.6 billion a year. Globally, it affects 25 to 30 million people, with an annual cost of $343 billion.

“While current tests for AMD are done in the light, scientists have proposed that it might be better if the patient has their vision adapted to the dark prior to the test,” he says.

“This is because they had found that rod receptors – vision cells that we use to see in black and white and in low light – die earlier in AMD than the cone receptors we use to see in colour during the day. So it had been suggested that AMD tests would be more accurate if they were based on the health of a person’s rods.”

How Do Blind People Picture Reality?

Paul Gabias has never seen a table. He was born prematurely and went blind shortly thereafter, most likely because of overexposure to oxygen in his incubator. And yet, Gabias, 60, has no trouble perceiving the table next to him. “My image of the table is exactly the same as a table,” he said. “It has height, depth, width, texture; I can picture the whole thing all at once. It just has no color.”

If you have trouble constructing a mental picture of a table that has no color — not even black or white — that’s probably because you’re blinded by your ability to see. Sighted people visualize the surrounding world by detecting borders between areas rich in different wavelengths of light, which we see as different colors. Gabias, like many blind people, builds pictures using his sense of touch, and by listening to the echoes of clicks of his tongue and taps of his cane as these sounds bounce off objects in his surroundings, a technique called echolocation.

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Artificial cornea gives the gift of vision

Blindness is often caused by corneal diseases. The established treatment is a corneal transplant, but in many cases this is not possible and donor corneas are often hard to come by. In the future, an artificial cornea could make up for this deficiency and save the vision of those affected.

“We are in the process of developing two different types of artificial corneas. One of them can be used as an alternative to a donor cornea in cases where the patient would not tolerate a donor cornea, let alone the issue of donor material shortage,” says IAP project manager Dr. Joachim Storsberg.

The scientist has considerable expertise in developing and testing of next-generation biomaterials. Between 2005 and 2009 he collaborated with interdisciplinary teams and private companies to successfully develop an artificial cornea specifically for patients whose cornea had become clouded – a condition that is extremely difficult to treat. Such patients are unable to accept a donor cornea either due to their illness or because they have already been through several unsuccessful transplantation attempts. Dr. Storsberg was awarded the Josef-von-Fraunhofer Prize 2010 for this achievement. “A great many patients suffering from a range of conditions will be able to benefit from our new implant, which we’ve named ArtCornea®. We have already registered ArtCornea® as a trademark,” reports Storsberg.

Caffeinated Coffee Linked to Loss of Vision

Consumption of caffeinated coffee is associated with an increased risk of developing exfoliation glaucoma, the leading cause of secondary glaucoma worldwide, according to a new study led by Dr Louis Pasquale of Brigham and Women’s Hospital in Boston.