CONTENTS OF #7 2006
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Laseroptronix AB located in Sweden has been a leading innovator of electro-optical and laser-based systems since 1977 and a reseller and integrator of products in its local markets. Laseroptronix products are based on proprietary sensor technology and patents controlled by Laseroptronix. |
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Laseroptronix AB manufactures and sells products under the names of Ladar, LaserSnap and LaserGrab with primary applications in security and counter-terrorism. Its products are in use at major airports, governmental buildings, military installations and nuclear power plants.
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-Wear a tie that's too tight and you run the risk of the eye disease glaucoma. That's the controversial contention of a study that says snug neckwear can increase intraocular pressure (IOP) in the eyes, possibly leading to glaucoma. "If men wear tight neckties when their IOP is measured, it can raise their IOP," says Dr. Robert Ritch, lead author of the study and a professor of clinical ophthalmology at The New York Eye and Ear Infirmary. Ritch became aware of the phenomenon during his regular practice. "I just noticed that some patients had tight neckties, and I just loosened their neckties and their IOP would go down several points," he says. |
To quantify his observation, Ritch and his colleagues studied 20 healthy men and 20 men with open angle glaucoma, the most common form of the disease. The researchers measured IOP while the men weren't wearing neckties, three minutes after they put on a tight necktie, and three minutes after the tie was loosened. Ritch's team found that in 70 percent of the healthy men, a tight necktie increased mean IOP, as it did in 60 percent of those with glaucoma. Increases in IOP while wearing a tight necktie ranged from more than 2 mmHg to more than 4 mmHg, compared to IOP readings when no ties were worn and after ties were loosened. Ritch speculates that when a necktie exerts too much pressure on the jugular vein in the neck, pressure is increased in the entire venous system, including in the eye. Although there are no reported cases of glaucoma caused by a tight necktie, Ritch says it's theoretically possible. |
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"Most people have no symptoms and no early warning signs," the foundation says. "If open angle glaucoma is not diagnosed and treated, it can cause a gradual loss of vision. This type of glaucoma develops slowly and sometimes without noticeable sight loss for many years. It usually responds well to medication, especially if caught early and treated." George Shafranov, an assistant professor and director of the glaucoma section at Yale University, says tight neckties "certainly don't cause glaucoma. Ties do increase IOP if the tie is really pressing on the neck and may make some ophthalmologists believe that glaucoma is present." Neckties can affect the measurements of IOP, Shafranov says. And a tight necktie is something physicians should be aware of when measuring IOP, in addition to other factors that can increase the pressure during an examination. |
According to the Glaucoma Research Foundation, open angle glaucoma is the most common type of glaucoma and affects about 3 million Americans. Open angle glaucoma develops over time as the eyes' drainage canals become clogged.
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If you have two roughly equivalent eyes you will see a ‘sausage’ floating in front of you in mid air, by following these steps: |
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- Hold your hands in front of you, at 20–30 cm distance from you, at eye level.
- Point your index fingers against each other, leaving about 2 cm distance between them.
- Now look “trough” your fingers, into the distance behind them.
- The sausage should appear now, and you can change its length by varying the distance between the finger tips.
- For most observers, the sausage will look blurred, at least initially.
- If you try to look at the sausage, it will disappear, it is only present if you look at something more distant than your fingers.
- It helps if the background is rather homogenous and has a color very different from your fingers.
Explanation
Basically, this ‘sausage’ is caused by two mechanisms, (1) physiological double images and (2) interocular rivalry and suppression.
| When you look at your fingers, the gaze direction of your two eyes is angled towards each other, so that their lines of sight meet at the target. When you then look into the distance, your eyes shift slightly outward, making their lines of sight nearly parallel. For close objects the image in the two eyes is consequently no longer at the right position, the images are no longer merged and can appear double for your “inner eye”. This is quite normal and occurs all the time, usually these double images are suppressed. So, if the two images overlap, why then doesn't the compound image look like the neighbouring figure on the right? |
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At the end of the image of each finger, there is a rivalry between the image from the two eyes when the brain tries to combine them. In one eye the finger ends, in the other it continues. So what does your brain do in such rivalry situations? If the two images are rather similar, the percept can oscillate between the alternatives. Here, however, we have a high contrast step in one eye, namely the end of the finger, where it is replaced by the background. |
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In rivalry the eye with the higher contrast wins, at least locally; this is here meant by the term ‘suppression’. In the figure on the left this high contrast step is symbolised by the yellow halo.
More reading about rivalry: Randolph Blake’s pages (with demos) or in Wikipedia
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