Your glasses are not worn out. Three screws and pads have moved.

A hinge screw is a thread that unscrews itself

Every time you fold or unfold the glasses, the two barrels of the hinge rotate around that one tiny screw. Each cycle hands a whisper of friction to the screw, and over thousands of cycles that whisper walks the screw out of its thread. Skin oil and sweat creep into the barrel and lubricate the process. Nothing is defective — this is simply what a hinge does with a screw in it. Which is why the fix is not "buy better glasses", it is "put the screw back and then keep it there".

That is also why the tightening has to stop at snug. Snug means the arms fold with light, even resistance and hold any position you leave them in. Past snug you are not adding security, you are grinding the threads down. Every over-torqued turn costs you a little of the material that is holding the screw in — and a stripped hinge barrel cannot be tightened back.

Three ways glasses go loose, three different fixes

• The screw backed out — the most common cause by a wide margin. The arm wobbles, flaps, or droops instead of holding its angle. Turn it clockwise in eighth-turns until snug. If the same screw keeps coming loose every few weeks, a drop of removable threadlocker (or clear nail polish) on the threads fixes it permanently.
• The temples splayed — the frame slides forward all day and leaves pressure marks. Check the gap between temple and the side of your head: past about 5 mm and it is guaranteed to slide. Correct it in steps of no more than 2 mm, testing on your face after each one. Acetate must be warmed first — at room temperature it is brittle and will snap at the hinge. Metal is bent cold. Titanium and TR90 you leave alone.
• The nose pads drifted or hardened — the frame sits too low or too close, and the bridge gets red marks. Pad spacing should be about 15–18 mm between centres. Squeeze the pad arms in to raise the glasses, out to lower them — a millimetre or two is a visible change. Silicone pads harden and go glossy in 6–12 months; once they are slick they will not grip no matter how you bend them.

The test that beats the mirror

You cannot judge whether your own glasses are crooked by looking in a mirror — your face is not symmetrical and your eye will split the difference wrong. Set them upside down on a flat table, lenses down, arms open. Both temple tips must touch the table at the same time. If one floats, that side's ear bend is off — and note that this is a temple problem, not a hinge problem, so tightening the screw will not fix it.

The habit that halves the frequency

Take your glasses off with both hands. One-handed removal puts the entire load of the removal on one hinge, so that side loosens first and the frame ends up crooked. Store them in a case, never lenses-down on a desk — a rim pressed flat against a table is the one failure on this page that cannot be undone. Take them off before a sauna, a hot shower or a car parked in the sun: heat is what lets acetate move, and you do not want it moving on its own.