How do I know if I need glasses? Could I be straining my eyes to see clearly and think it's normal?

The best way to know if you need glasses is to go to an eye doctor and have an eye examination performed.

sorry I cant answer as I dont have my glasses on to read the question!

Firstly when did you last have an eyesight test?
Have you your sekf noticed a change in yiur eyesight?
Do you have difficulty seeing things at distance?
Do you get headaches when reading a Book etc?
They are a few signs ypou will notice whenyour eyesight is failing lol

GT YOUR EYES TESTED EVERY TWO YEARS OR LESS WHEN U NOTICE CHANGE GO DONT WAISTE TIME

i found out i needed glasses when i put someone else's glasses on and found i could see individual leaves on the trees and individual blades of grass on the lawn. Straining to see clearly wont really damage your eyes but will make them tired and cause wrinkles around your eyes.

If you find yourself squinting or you get headaches or if you are seeing "halos" around lights at night.

If you're getting frequent headaches, or squinting, or having a hard time reading road signs, chalkboards or anything else, you should visit an eye doctor. Generally, you should get your eyes checked every few years, regardless of whether you think you need glasses or not. Eye deterioration is a very gradual process, and some problems can be slowed in their progress with proper treatment.

It may sound obvious that you will know when you need glasses - but declining eyesight in most cases sneaks up on you, and it can be difficult to realise that you need some support or that the "symptoms" have become more than just casual or intermittent....read more here - https://www.fashionspecsdirect.co.uk/article8.php