Brief: When your eyes suggests that it needs extra eyes(eyeglasses).

I dont like glasses and I know many who uses it don't also like it but have no choice since their eyes suggests it needs another extra eye. Lol
Get oriented:
It’s estimated that about half of all Americans wear corrective lenses. But there are millions more who could use a pair.1 Many people
have lived with poor vision for such a long time, they simply don’t realize they would benefit from or see better with vision correction. Others might be aware they have a vision problem but put off going to the eye doctor until it’s a struggle to perform everyday functions. The fact is that as soon as you notice your eyesight is changing, it’s time to see your eye doctor.
As soon as you notice your eyesight is changing, it’s time to see your eye doctor.
Wondering if it’s time to get a pair of glasses?
Dr. John Lahr, divisional vice president, EyeMed Provider Relations, and medical director, offers the following 10 symptoms that you might need an eye exam.

1. Blurred close-up vision, indicating
farsightedness (hyperopia)
2. Poor distance vision, or
nearsightedness (myopia)
3. Difficulty seeing objects both close up and at a distance (astigmatism)
4. Difficulty seeing at night
5. Increased difficulty adjusting from dark to light surroundings
6. Difficulty in reading or working at a
computer
7. Eye strain or eye fatigue
8. Frequent headaches
9. Double vision
10. Seeing halos around light
If you have one or more of these symptoms, it doesn’t always mean you have a problem.
However, it’s important to have your eyes checked by a qualified eye professional to understand the cause behind these changes.
But trust me, when you start having this, then it's time you visit and optician.