Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Telescope danger to sight.
    From: Ken Gebhart
    Date: 2004 May 14, 10:54 -0500

    on 5/14/04 5:58 AM, Jim Thompson at jim2{at}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{at}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

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site