NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Telescope danger to sight.
From: Ken Gebhart
Date: 2004 May 14, 10:54 -0500
From: Ken Gebhart
Date: 2004 May 14, 10:54 -0500
on 5/14/04 5:58 AM, Jim Thompson at jim2@JIMTHOMPSON.NET wrote: > Kieran, > > Excellent case report; thank you. I made the stupid mistake (once) of > starting to view the sun to check index error with the index arm set to zero > degrees after viewing the horizon, without swinging down the horizon mirror > shades. Fortunately I sensed the very bright light just starting to flare > in the periphery of my field of vision before I got a retinal blast, and > quickly turned away. I did not have any immediate or subsequent symptoms. > I have had laser surgery a couple of times: it really flared my vision green > for several minutes after the procedure, and was far more stimulating than > that brief peripheral solar exposure. > > Being a physician you stimulated my professional curiosity, so I did a > brief, limited literature search on Pubmed to learn more about solar eye > injury. I posted the literature search results in a separate email. I > found not a single reference to navigational sextants in Pubmed, for any > health reason whatsoever. Interestingly the world's medical literature > appears to be completely silent on navigatonal sextants! No news is good > news, I guess. > > I get the sense that humans are well adapted to moderate sun exposure. > Although sun-gazing can definitely cause damage, much of it appears to be > reversible, probably because sufferers are quick enough to turn away soon > enough. I am by no means expert on this issue, but I get the sense from my > reading so far that for significant damage to occur, the eye has to be > exposed to direct sunlight for relatively lengthy periods, or has to suffer > repeated exposures over long periods of time. My conclusion is that human > eyes are well adapted to deal with limited exposures to direct sunlight, but > that we do not want to push the edge of that envelope. > > As Kieran pointed out there are risk groups, such as the intoxicated. But > hunters, sailors and other people who occupationally stare at bright skies > are also at risk of acute and chronic eye damage. > > Sunlight can acutely damage all the tissues of the eye in different ways: > - Lids and conjunctiva: sunburn (UV). > - Cornea: sunburn (UV damage, same as welders' flash). > - Lens (UV, heat). > - Vitreous. > - Retina (heat, UV, and components of light). > There is also a link between UV exposure and ocular melanoma. > > I think it is clear that, as with all things in health, minimizing exposure > to noxious stimulus is ideal, so scrupulous eye care is wise when using a > sextant, or when out in bright sunlight for any other reason. I recommend > sunglasses between sights, as Kieran suggested, lots of sunscreen, minimal > observation time, careful attention to the condition of the shades, deep > caution when swinging up to view the sun, and very careful attention to use > of the shades. > > Jim Thompson > jim2@jimthompson.net > www.jimthompson.net > Outgoing mail scanned by Norton Antivirus > ----------------------------------------- > Thanks to Jim, Kieran and George for picking up on this side of the thread. Armed with your posted information, those involved with sextant manufacturing can breathe a little easier in our litigious society. Ken Gebhart