The importance of being protected: How to choose your sunglasses

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Posted on 2nd September 2016 by Pacific ClearVision Institute in General |Retina

Experts from the University of Alicante (UA) have found that prolonged exposure to the sun increases the chance of developing alterations in the lens by 4%. Choosing the right pair of sunglasses can reduce such complications.

Despite the fact that the vast majority of the harmful radiation from the sun is absorbed by the atmosphere, enough ultraviolet rays do reach Earth’s surface to cause skin burns and eye complications in structures like the retina and cornea. In this sense, studies highlight that each hour spent exposed to the sun in the summer increases the chance of developing alterations in the lens by 4%.

The researchers, from the UA’s Department of Optics, Pharmacology and Anatomy, stress that using approved sunglasses from 10 to 4pm can reduce this chance by around 2%.

But how do we choose the right pair of sunglasses?

One of the biggest ‘musts’ is that the glasses bear the European ‘CE’ seal, since this means they adhere to European safety standards.

Further advice from UA professor David Piñero urges us to remember “that sunglasses are very important for visual health and, therefore, their purchase should be supervised by an optician-optometrist.”

Filter category

Another important thing to know when you’re buying a part of sunglasses is what filter category you need. This is determined by your location and activity. In accordance with European regulations on sunglasses, UV filters are classified into five categories, from 0 to 4.

When driving, for instance, you need use a category 1, 2 or 3 filter lens, depending on the conditions; never a 4, since this can interfere with your perception of traffic signs. Piñero tells us that “in the summer in Alicante a category 2 or 3 filter is more than enough, though if we’re going out onto the water or into the mountains, where light is reflected much more strongly, protection level 4 would be advisable.”

Special care should be paid to the glasses worn by children and old people. Children are especially sensitive to ultraviolet radiation, since the lens is still very transparent until adolescence. Category 2 or 3 is recommended, and very sturdy lenses and frames. Old people should wear the same category lens.

Debunking myths

Just as price is not an indicator of quality, neither is the colour of the lense an indicator of the level of protection offered. “There are very dark lenses that do not correctly filter ultraviolet light, leading to greater pupil dilation and an increase in the radiation that enters the eye,” says Piñero.

Ultraviolet radiation is a risk factor for our eyes and “has an accumulative effect that can, in some cases, set off problems in the photoreceptors in the retina (the rods and cones), progressively bad vision, macular degeneration, or the onset of pterygion, where tissues invade the cornea, known colloquially as Surfer’s Eye.”

New test needed to assess the quality, safety of sunglasses

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Posted on 2nd September 2016 by Pacific ClearVision Institute in General |Retina

Revision of standards is needed to test sunglasses quality and establish safe limits for the lenses’ UV filters, according to research published in the open access journal Biomedical Engineering OnLine.

Exposure to the sun may deteriorate your sunglasses over time and the lenses may become lighter and so alter the category under which they are classified. It may also diminish the impact resistance of lenses (how ‘shatterproof’ the lens is). Current national and regional standards require that sunglasses provide levels of UV protection linked to the luminous transmittance, which decides the category of the lenses.

The aging test, used in Europe, Brazil, New Zealand and Australia, calculates the extent to which the lenses’ category deteriorates as a result of exposure to the sun. The test exposes sun glasses to a sun simulator for 50 hours at 30cm from a 450 W lamp. The lamp exposure is equivalent to two days in a natural environment on a summer’s day, or four days in winter.

Liliane Ventura, the corresponding author, from São Carlos School of Engineering, University of São Paulo, Brazil, said: “50 hours of exposure to the sun simulator equates to 23.5 hours of exposure to natural sun in Sao Paulo in Brazil. Most Brazilians replace their sunglasses every two years. To test the sunglasses are safe to wear for these two years, with the assumption they are worn for a period of two hours a day, they should be tested for 134.6 hours at a distance of 5cm. Although our calculations are mainly based on Brazilian cities, other countries may also benefit, especially those located at similar latitudes.”

Exposure will vary among world latitudes, with tropical countries being of most concern, as UV indexes are extremely high in summer and remain high in the winter. Therefore, sunglasses worn in the southern hemisphere may need replacing more often than in those worn in the northern hemisphere.

Liliane Ventura adds: “We need adequate lamp power, exposure time, distance from the bulb and controlled temperature. To overcome the current limitations one may either increase the time the lenses are exposed to the lamp or decrease the distance of the lenses from the lamp. We could also consider using a higher power lamp, switching from a 450W to 1600 W lamp.”

A Brazilian national survey indicated that most Brazilians wear the same pair of sunglasses for a minimum of two years for a period of two hours a day. Therefore, the standard must guarantee that the sunglasses are safe over this period.

The study calculations were carried out in 27 Brazilian state capitals and data for 110 national capitals in the northern hemisphere were also included. Calculating the equivalence of the simulator to natural light is an estimate because when an individual wears sunglasses, the lenses are not directly exposed to the sun, as they are usually worn in the vertical position.

Lenses should provide adequate UV filters, because insufficient protection could lead to pathological modifications to the cornea and to the internal structure of the eye. This could cause edema (swelling of the eye which can distort vision), pterygium (growth of pink, fleshy tissue on the white of the eye that can interfere with vision), cataract (clouding of the lens of the eye) and retina damage.

Artificial retinas: Promising leads towards clearer vision

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Posted on 2nd September 2016 by Pacific ClearVision Institute in General |Retina

A major therapeutic challenge, the retinal prostheses that have been under development during the past ten years can enable some blind subjects to perceive light signals, but the image thus restored is still far from being clear. By comparing in rodents the activity of the visual cortex generated artificially by implants against that produced by “natural sight,” scientists from CNRS, CEA, INSERM, AP-HM and Aix-Marseille Université identified two factors that limit the resolution of prostheses. Based on these findings, they were able to improve the precision of prosthetic activation. These multidisciplinary efforts, published on 23 August 2016 in eLife, thus open the way towards further advances in retinal prostheses that will enhance the quality of life of implanted patients.

A retinal prosthesis comprises three elements: a camera (inserted in the patient’s spectacles), an electronic microcircuit (which transforms data from the camera into an electrical signal) and a matrix of microscopic electrodes (implanted in the eye in contact with the retina). This prosthesis replaces the photoreceptor cells of the retina: like them, it converts visual information into electrical signals which are then transmitted to the brain via the optic nerve. It can treat blindness caused by a degeneration of retinal photoreceptors, on condition that the optical nerve has remained functional[1]. Equipped with these implants, patients who were totally blind can recover visual perceptions in the form of light spots, or phosphenes. Unfortunately, at present, the light signals perceived are not clear enough to recognize faces, read or move about independently.

To understand the resolution limits of the image generated by the prosthesis, and to find ways of optimizing the system, the scientists carried out a large-scale experiment on rodents. By combining their skills in ophthalmology and the physiology of vision, they compared the response of the visual system of rodents to both natural visual stimuli and those generated by the prosthesis.

Their work showed that the prosthesis activated the visual cortex of the rodent in the correct position and at ranges comparable to those obtained under natural conditions. However, the extent of the activation was much too great, and its shape was much too elongated. This deformation was due to two separate phenomena observed at the level of the electrode matrix. Firstly, the scientists observed excessive electrical diffusion: the thin layer of liquid situated between the electrode and the retina passively diffused the electrical stimulus to neighboring nerve cells. And secondly, they detected the unwanted activation of retinal fibers situated close to the cells targeted for stimulation.

Armed with these findings, the scientists were able to improve the properties of the interface between the prosthesis and retina, with the help of specialists in interface physics. Together, they were able to generate less diffuse currents and significantly improve artificial activation, and hence the performance of the prosthesis.

This lengthy study, because of the range of parameters covered (to study the different positions, types and intensities of signals) and the surgical problems encountered (in inserting the implant and recording the images generated in the animal’s brain) has nevertheless opened the way towards making promising improvements to retinal prostheses for humans.

This work was carried out by scientists from the Institut de Neurosciences de la Timone (CNRS/AMU) and AP-HM, in collaboration with CEA-Leti and the Institut de la Vision (CNRS/INSERM/UPMC).

Surprise discovery in the blink of an eye

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Posted on 2nd September 2016 by Pacific ClearVision Institute in General |Retina

We probably do it every day, but scientists have only just discovered a distinct new way in which we move our eyes.

The team from the University of Tübingen in Germany assessed the eye movements of 11 subjects using tiny wires attached to the cornea and with infrared video tracking. In results published in eLife, they discovered a new type of eye movement that is synchronised with blinking.

The movement they discovered helps to reset the eye after it twists when viewing a rotating object. It is like avoiding tiny rotations of a camera to stabilise the image we perceive. We don’t notice the eye resetting in this way because it happens automatically when we blink.

“We were really surprised to discover this new type of eye movement and it was not what we had anticipated from the experiment,” says lead author Mohammad Khazali.

“We had expected to find that another, already well-known type of eye movement is synchronized to blinking.”

Although it is brief, blinking creates an interruption in our visual perception. We spend up to a tenth of our waking hours blinking but hardly notice it. It serves an essential role in lubricating the eye and may even provide the brain with small, frequent mental breaks.

The scientists sought to investigate whether a reflexive, involuntary eye movement called torsional optokinetic nystagmus (tOKN) occurs at the same time as blinking. The theory was that this reflex also creates a break in the visual system so synchronising them minimises downtime.

The subjects’ eye movements were tracked as they viewed a rotating pattern of dots. As their eyes twisted to follow the dots, they frequently reset, via tOKN, to avoid moving beyond the mechanical limits of the eye muscles. However, this resetting was imperfect and the eyes gradually twisted until the muscles couldn’t twist any more. This varied between subjects from three to eight degrees of rotation.

Once they reached their maximum, the eyes reset so they were no longer twisted at all. This happened at the same time as blinking. The scientists have called this newly-discovered movement blink-associated resetting movement (BARM).

“The eye’s sharpest vision is enabled by a spot on the light-sensitive sheet of the retina called the fovea and this needs to stay balanced to ensure objects of interest can be scrutinised in an optimum way,” says Khazali.

The frequency and size of the movement is determined by how far the eyes have deviated from a neutral position. It helps to reduce strain in the eyes as they move to assess the world around us. In further experiments, the scientists discovered that it even occurs when the eye is not tracking a rotating object.

“To discover such a ubiquitous phenomenon in such a well-studied part of the human body was astonishing to us and we’re very grateful to the volunteers who took part in the study,” says Khazali.