Sea-U
Sea-U was a contact lens from contact lens specialist Rainer Holland ( Holland & Dorider Contactlinsen, Hamburg ), which should enable freedivers to see clearly underwater without a diving mask . It was manufactured by HERZ Submicron Lathing srl in Catania / Sicily . However, after Rainer Holland's retirement and due to a lack of demand, production was discontinued.
Origin of name
The name Sea-U is a play on words by a British journalist who didn't like the word underwater lens, derived from the phrase see you! (English for see you! ) and the term sea (English for sea ). The name symbolizes the function of being able to see clearly in the water.
Physical background
The human eye is adapted to the refractive index of the air . If the front surface of the eye, i.e. the cornea, gets into the water , the optical effect on the cornea is reduced to almost zero. The reason for this are the almost identical refractive indices of the cornea and the water. An optical error of around 44 diopters arises - a person can only see dimly underwater without a mask, with a maximum of fingers counting directly in front of the eyes. A diving mask is usually put on for a clear view underwater. The eye still borders on the air inside the mask, which in turn is separated from the water by a flat pane. This system provides a sharp, but 3 magnified view.
The pressure inside the diving mask must be consciously adjusted several times while diving. It does this by blowing air from your lungs through your nose. This fact is only possible to a limited extent for freedivers, as they only have one lung filling of air with them and the repeated pressure equalization in the mask leads to a significant loss of air and thus to shorter dives. Especially at greater depths, the volume of the compressed lung is too small for this.
In order to reduce the mask volume, many freedivers inject their mask completely with a filling material such as silicone, except for a small viewing channel. This significantly reduces the volume of air required for mask pressure compensation. However , when swimming goggles (i.e. without a nosepiece) are used for freediving, the pressure cannot be equalized via the nose, since it is in the water and is closed with a clamp to prevent water from entering the lungs.
properties
In order to compensate for the resulting optical error, an extremely strong contact lens that still has 44 dioptres of effect in the water is required. Since the refractive index of soft lenses is only slightly higher than that of water, this lens has to be extremely strong. The Sea-U therefore had an approx. +240 diopters strong, almost hemispherical lens with a diameter of only 2 mm in the center. You couldn't make it much bigger because it was almost a hemisphere.
On land, only a centrally blurred view was possible with this lens. Sharp images could only be made outside the small central optics. However, the user was able to see sharply with the center after additionally putting on a diving mask or swimming goggles filled with water. With the entry into the water these swimming goggles were then removed.
Since the eye with the Sea-U adjoined the surrounding water without any distance, the increased perception that arises with air-filled diving masks due to the distance of the eye to the water was eliminated.
Fixation
To ensure a well-centered and immovable fit of the lens on the eye, the user put on swimming goggles, which were then filled with fresh water. The osmotic differences between water and the conjunctiva (conjunctiva) lead to swelling (edema) of the uncovered conjunctiva. There it becomes thicker than the edge of the lens and a circumferential bead is created that fixed the Sea-U as if in a shape.
Contact with salt water causes the conjunctiva to swell and the Sea-U can move freely again after about 15 minutes, so use in salt water is limited to a maximum of 15 minutes.
If the lens is used in fresh water, it will always stay firmly in place. In order to loosen it afterwards, isotonic or even hypertonic saline solution is filled into the attached swimming goggles , the edema of the conjunctiva is reduced, the lens becomes mobile again on the eye and can then be removed.
Testing in the diving tower of the German Navy
In order to determine how good the visual acuity actually is with the Sea-U , freediver Benjamin Franz , on whose request the lens had been developed, and Rainer Holland received the approval to use the 32 m deep diving tower of the German Navy in Neustadt together with a camera team . Here the visual performance was determined under water at a distance of 5 m and at close range. Since Benjamin Franz's pupils became quite narrow with the bright lighting in the water there, there was hardly any interference from images outside the small optics and a visual acuity of 0.80 at distance and 1.00 at close range was outstandingly good. In open water, especially at greater and thus darker depths, the effect of the lens was smaller, since the pupils there are significantly larger.
Used in Benjamin Franz's attempt to record
With the Sea-U lens, freediver Benjamin Franz broke the German record in the No Limits discipline on the panoramic reef off Port Safaga in the Red Sea in 1999 .
During his record attempts in the cold Attersee , he put larger swimming goggles filled with freshwater over the lenses to protect the eyes from the cold and at the same time avoid the disadvantages of air-filled swimming goggles.
Further missions
Underwater models were equipped with the Sea-U so that they can see the cameraman without a mask and follow his signs. At the same time, the cornea was protected from the effects of chlorinated water.
Similar developments
Also in order to reduce the volume inside the mask, Eric Fattah invented a mask called Fluid Goggles in 1988 , in which a saline solution is injected into the space between the mask and the eye. It also has a lens to allow a clear view. Pressure equalization is therefore no longer necessary.
The Trygons company has also been producing a flexible mask called Fluid Goggles since 2007 , which also has no air space between the eye and the water.
Individual evidence
- ↑ a b dict.cc: German-English translation for: See you. Retrieved March 9, 2017 .
- ^ A b Rainer Holland: Diving with contact lenses. Neues Optiker Journal (NOJ), July 2001, accessed January 25, 2017 .
- ↑ Dr. Dieter Schnell: Modern diving medicine manual for diving instructors, divers and doctors . Ed .: Ch. Klingmann and K. Tetzlaff. 1st edition. 2007, ISBN 978-3-87247-645-6 , pp. 449–458 ( gentner.de ). Modern diving medicine handbook for diving instructors, divers and doctors ( Memento of the original from January 31, 2017 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ Michael Goldschmidt: Benjamin Franz: German record NO LIMIT 100 meters. (No longer available online.) UnderWasserWelt History, November 1999, archived from the original on August 25, 2010 ; Retrieved January 25, 2017 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Unterwasser-Bild.de: Geo - Seeing like a fish. Retrieved February 1, 2017 .
- ↑ a b Blue Eye Divers: Diving without a mask - the forgotten project “Sea-U”. August 21, 2013, accessed February 1, 2017 .
- ↑ Liquivision: Fluid Goggles. Retrieved January 25, 2017 (English).
- ↑ Trygon's Designs: Fluid Goggles. Retrieved January 25, 2017 (English).
