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| Author | Subject: Confused on RGP assesment |
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 sasaria
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Confused on RGP assesment
Jul 18, 2006 17:31:55 Im a bit confused with assesing an astigmatic cornea with a spherical RGP...not to sure on how to interpret the fluoriscean patterns any help? |
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Stephen Meynell
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RE: Confused on RGP assesment
Jul 18, 2006 21:12:16 In a spherical cornea the flourescene picture is of circles - of touch or flourescence where there is flourescene pooling. And the ideal is faint flourecence disk centrally showing 'minimal corneal clearance' followed by a thin wedge of flourescen that surrounds the central area like an anulus followed by an edge lift at the edge -ie : increasing pooling at the far edge. If there is any bubbles the chances are that you are 0.2 mm out from corneal clearance, if there is touch then its dark. Now in astigmatic corneae - its basically the same BUT you are compromised by the astig cornea -so some parts of the flourecen pattern will show touch and further round it will show clearance. So it either looks like a horizontial dogs bone of touch in with the rule astig corneas or vertical dogs bone in against the rule. Your flourescen picture is compromised by the ride of the lens - as you need to get a central ride to allow clear, unfluctuating vision, and a good flourscen picture to allow proper tear exchange under the lens (and no bubbles either! bubbles anywhere at the edges will encourage dry spots and discomfort and local dissication). If you can't get an acceptable compromise - then you move to gps with a toric rim or a full toric. To start - if you get a trial lens averaging the corneal k's ( best done by averaging the sum of the reciprocals of the k's - and taking the reciprocal of that) and place that on the eye you will see a big edge lift and at 90 degrees to that a narrow edge. Leave it for 20 minutes and review the fit. If you having bubbling at the big edge lift you need to think about toric edged gps. If you have poor low riding lens - but a good fl. picture then you need a smaller lens and a bit steeper. Any residual atstig comes through the lens at about 10% of the spectacle astig - so its not a big deal. hope it helps - all the best to you steve |