The most common and most likely answer to this crossword clue is the 9 letter word EYESTRAIN
E
Y
E
S
T
R
A
I
N
More clues leading to the result EYESTRAIN
- Difficulty seeing coach behind back of vehicle, certainly
- What might give you an irritated look?
- Problem caused by too much reading, of course, in English school
- Irritation right inside retina needing treatment
- Reader's issue with English agreed by school
- Disturbed serenity, receiving a tired look
- Before tutor, English certainly suffering when reading, perhaps?
- Looks at rail transport as a source of irritation to observers
- Exhaustion experienced when observing fine English school dons
- . European certainly next to file complaint
Buddy explains!

The straight part
We know that "an issue for The Observer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case an issue for the observer = eyestrain.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EYESTRAIN mean?
EYESTRAIN noun- Tiredness or pain in the eyes, sometimes accompanied by headache, caused by excessive or improper use of the eyes, or by uncorrected defects of vision