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I know that the ability to adapt to dark conditions does get worse as you get older but IIRC plateaus around age 42 and doesn't get worse. Also when we carry out visual field tests the accepted norm for "brightness" for a young person is different from that of an older person.
A lot of people also find that they do need more light to read around about the time you begin to need a separate reading presription which is typically around 45.
Other reasons can be the beginnings of cataract which is unlikely at your age but more common if you are very myopic.
Do you usually have a visual field test when you have an eye exam? If so and if results are normal, it would be unlikely that anything serious is the matter.
I have a visual field test at each eye test. I presume it's OK because I've never been told otherwise.
But at my last eyetest my optician referred me to a specialist (I'll see them in a week or so) because she was not happy with the results. She said that what I was reporting did not match with what she could find - which was nothing physically wrong.
I have -7 point something. The myopia seems to be stabilising, it -7 about five years ago, when the changes started slowing down, but the astigmatism still changes at every appointment, and 2-3 years ago the presbyopia began.