I don’t know for sure, but it would make sense if it had to be fairly severe. If it were not enough to meaningfully distort one eye vs the other it would not se

I don’t know for sure, but it would make sense if it had to be fairly severe. If it were not enough to meaningfully distort one eye vs the other it would not seem to be detrimental. It’s only when the two images can’t be correlated any more that the problem shows up. In my recent years I have developed some astigmatism, but I can still do them without difficulty.