You may want to read up on The Irlen Method.
Having comprehension problem may be due to either your vision or
your ability to reason.
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Comprehension is the understanding and interpretation of what is
read. To be able to accurately understand written material, need to
be able to
1) decode what they read;
2) make connections between what they read and what they already
know; and
3) think deeply about what they have read.
One big part of comprehension is having a sufficient vocabulary, or
knowing the meanings of enough words.
Note: Your C6 score in English probably is one factor you don't do
well in Comprehension.
Readers who have strong comprehension are able to draw conclusions
about what they read what is important, what is a fact, what
caused an event to happen, which characters are important. Thus
comprehension involves combining reading with thinking and
reasoning.
If vision is not the problem,
you can,
Use outlines, maps, and notes when you read.
Read stories or passages in short sections and make sure you know
what happened before you continue reading.
Ask yourself, "Does this make sense?" If it doesn't, reread the
part that didn't make sense.
Read with a buddy. Stop every page or so and take turns summarizing
what you've read.
As you read, try to form mental pictures or images that match the
story.
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