Eyesight Tropia vs Phoria
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Eyesight Tropia vs Phoria
I've had a fairly extensive search through the various vision threads and haven't been able to find much in the past decade or so about the above conditions.
From a young age I've had a constant squint and last year I got it looked at professionally, it turns out I have Heterotropia. The deviations of the non-dominant eye are outside of those are allowed for a Class 1 for Phorias (latent squints) but there is absolutely no mention of limitations for Tropias (constant squints). I've seen a thread from many years ago that Phorias are taken much more seriously becuase the latent nature of the squint means that there is no suppression of the non-fixating eye whenever a squint is induced, hence a risk of Diplopia.
I have deep suppression of any overlapping images from the non-dominant eye when using my dominant eye as the fixating eye, my medical records from the Opthalmologists state clearly that I don't experience Dipopia. I've found that I can induce it deliberately by choosing to switch my fixating eye (so that my non-dominant eye becomes the fixating eye) and looking at things from certain angles but that requires a bit of effort and it's possible to switch back to my dominant eye in an instant, after all most people can induce diplopia deliberately by crossing their eyes. I have 20:20 vision in both eyes uncorrected so there's no Amblyopia that I know of.
I've looked at surgery but there is a small risk of Intractible Diplopia, I'm aware that there is now an adjustable suture technique which reduces the risk but if I can get a Class 1 without needing it I think that may well be the better option. Would the CAA be likely to grant a Class 1 with Heterotropia being present and there being deep suppression of any Diplopia-induced images when fixating using the dominant eye?
From a young age I've had a constant squint and last year I got it looked at professionally, it turns out I have Heterotropia. The deviations of the non-dominant eye are outside of those are allowed for a Class 1 for Phorias (latent squints) but there is absolutely no mention of limitations for Tropias (constant squints). I've seen a thread from many years ago that Phorias are taken much more seriously becuase the latent nature of the squint means that there is no suppression of the non-fixating eye whenever a squint is induced, hence a risk of Diplopia.
I have deep suppression of any overlapping images from the non-dominant eye when using my dominant eye as the fixating eye, my medical records from the Opthalmologists state clearly that I don't experience Dipopia. I've found that I can induce it deliberately by choosing to switch my fixating eye (so that my non-dominant eye becomes the fixating eye) and looking at things from certain angles but that requires a bit of effort and it's possible to switch back to my dominant eye in an instant, after all most people can induce diplopia deliberately by crossing their eyes. I have 20:20 vision in both eyes uncorrected so there's no Amblyopia that I know of.
I've looked at surgery but there is a small risk of Intractible Diplopia, I'm aware that there is now an adjustable suture technique which reduces the risk but if I can get a Class 1 without needing it I think that may well be the better option. Would the CAA be likely to grant a Class 1 with Heterotropia being present and there being deep suppression of any Diplopia-induced images when fixating using the dominant eye?
Last edited by Chris the Robot; 22nd Dec 2023 at 02:35.
Caveat that I have had no dealings with the CAA; Transport Canada has its own set of criteria and miseries.
A conscientious optometrist can produce a prescription with prisms that, at least in my case, can get both eyes working together. If you have not yet had prisms, be very careful walking down any steps leaving the optometrist/optician.
My first landing with prisms was three feet high. My brain clued in promptly afterwards and my landings improved considerably.
Diplopia has happened late at night on the road, especially without prisms.
A conscientious optometrist can produce a prescription with prisms that, at least in my case, can get both eyes working together. If you have not yet had prisms, be very careful walking down any steps leaving the optometrist/optician.
My first landing with prisms was three feet high. My brain clued in promptly afterwards and my landings improved considerably.
Diplopia has happened late at night on the road, especially without prisms.
This side of the border, +-1 is acceptable vertically, and +-6 laterally. When I have an airman who exceeds these limits, without obvious Diplopia, and I call OKC for guidance, the answer is invariably “Issue, and inform the airman that he might receive a request for additional evaluation from CAMI”.
To my knowledge, during my tenure as an AME, none ever have…
To my knowledge, during my tenure as an AME, none ever have…
