Glasses break in ordinary ways. A screw works itself loose over a few weeks, the lens drops out of the rim, someone sits on the frame, or the arm gets bent out of shape in a bag. None of it is dramatic and most of it is fixable in a few minutes. The problem is that the wrong fix at home turns a five-minute job into a new pair of glasses.

Here is how to tell the two apart.

A loose or missing screw

The screws that hold the hinges and the rim are about a millimetre across, and they back out slowly with use. You notice it when one arm goes floppy or the lens starts to shift in the frame.

If the screw is still in place and just loose, a jeweller's screwdriver will tighten it. Turn until it stops and then stop. Over-tightening strips the thread in the hinge, and once the thread is gone the whole hinge has to be replaced, which is a much larger job than the screw was.

If the screw has fallen out, do not substitute anything. A pin, a wire, or a bit of tape holds for a day and usually damages the hinge in the process. Optical screws come in different diameters and lengths, and a shop will have a tray of them. This is a walk-in job.

Never use glue on a hinge. It seizes the joint, and removing cured glue from a metal hinge normally destroys it.

A lens that has popped out

What happens next depends on the frame.

Full-rim plastic frames hold the lens by tension. The frame is warmed until the plastic softens slightly, the lens is pressed back into the groove, and the frame cools around it. Warming plastic at home with hot water usually works badly, because too much heat distorts the shape of the rim permanently and then the lens never seats properly again.

Full-rim metal frames hold the lens with a screw at the rim. The lens goes back in and the rim screw is tightened. Same rule as above about not stripping the thread.

Rimless frames hold the lens on mounting posts that pass through drilled holes. If a lens has come off a rimless frame, do not press it back on. The holes are drilled to a tolerance and forcing the post can crack the lens outward from the hole. Take it in.

In every case, pick the lens up by the edges and put it somewhere safe. A loose lens sliding around in a bag picks up scratches that no cleaning will remove.

A bent frame

Arms bend at the hinge and at the point where they curve behind the ear. A slight bend is why your glasses sit crooked on your face or slide down.

Small adjustments are done by hand at the shop and take under a minute. Metal frames flex readily. Plastic frames need heat first, which is why bending a plastic arm cold at home tends to snap it at the hinge.

If one lens sits noticeably higher than the other, the frame is out of alignment, not your face. It gets straightened rather than tolerated.

Nose pads

On metal frames the pads sit on small arms that can be squeezed closer or spread wider. Pads that are too wide let the glasses slide down. Pads that are too narrow leave red marks either side of the bridge and press the lenses too close to your eyes.

The pads themselves are consumable. Yellowed or hardened pads get replaced, and the replacement takes seconds.

A scratched lens

This one has no repair. Polishing compounds and toothpaste, which come up in every online thread on the subject, remove the anti-glare coating and leave a hazy patch that is worse than the original scratch.

If the scratch sits in your line of sight, the lens gets replaced. If it sits at the edge, you can usually live with it.

What to do about it in Colaba

We do repairs and adjustments while you wait. Screws, refitting lenses, straightening bent temples and hinges, and nose pad replacement are all done in the shop, and none of it needs an appointment. Bring the glasses in and, if a lens has come out, bring that too.

If the frame is beyond repair, we can usually fit your existing lenses into a new frame instead of remaking the prescription, provided the lens shape works with the frame you pick.

Optica Eyewear is on Shahid Bhagat Singh Road in Colaba, near INS Shikra. Open Monday to Saturday, 10am to 8pm.