Contact lenses are remarkably safe when used correctly. The complications that do occur are almost never caused by the lens itself — they are caused by a handful of ordinary habits that feel harmless right up until they are not.

These are the nine that eye doctors see most often, roughly in order of how much damage they cause.

1. Sleeping in your lenses

This is the big one. When your eyes are closed, tear exchange under the lens nearly stops and oxygen flow to the cornea drops sharply. That combination is exactly what opportunistic bacteria need.

Sleeping in lenses not approved for extended wear raises your risk of microbial keratitis — a corneal infection — by several times over daily wear. Keratitis can scar the cornea permanently and, in serious cases, cost you vision in that eye.

A twenty-minute nap counts. Take them out.

2. Letting lenses touch water

Tap water, bottled water, river water, swimming pool water and saliva all belong nowhere near a contact lens. The specific danger is Acanthamoeba, a microorganism common in ordinary water supplies that is harmless to intact eyes but can cause Acanthamoeba keratitis when trapped against the cornea by a lens.

It is rare. It is also one of the most painful and treatment-resistant eye infections there is, sometimes requiring months of therapy or a corneal transplant.

That means no showering, no swimming, and never rinsing a lens or case with water — not even “clean” water, not even once.

3. Topping up old solution instead of replacing it

Multipurpose solution works by neutralising microorganisms, and it is consumed doing so. Yesterday’s solution is spent. Adding a splash of fresh solution to a case that still holds old solution dilutes the new disinfectant and leaves you soaking a lens in an ineffective mixture.

Empty the case fully, every time. Refill with fresh solution, every time.

4. Neglecting the lens case

The case, not the lens, is the most common source of contamination. Cases develop bacterial biofilm — a layered growth that ordinary rinsing does not remove and that disinfectant struggles to penetrate.

After each use: empty it, rinse with solution rather than water, wipe with a clean tissue, and leave it face down to air dry. Replace the case every three months. They are cheap; corneal ulcers are not.

5. Wearing lenses longer than their replacement schedule

A monthly lens expires 30 days after you open the blister, whether you wore it thirty times or four. The replacement schedule is not about wear count — it is about protein and lipid deposits building up on the lens surface and about material degradation over time.

Deposits are not just uncomfortable. They give bacteria a surface to adhere to and can provoke giant papillary conjunctivitis, an inflammatory reaction under the upper eyelid that can end your ability to wear lenses at all.

Write the opening date on the box. Everyone thinks they will remember. Nobody does.

6. Overwearing during the day

Eight to ten hours is a reasonable daily maximum for most people in most lenses. Fourteen-hour days in lenses — common among students and office workers — leave the cornea oxygen-starved for too long.

The early warning sign is eyes that stay red for an hour or more after you take the lenses out. Over time, chronic oxygen deprivation can trigger corneal neovascularisation, where new blood vessels grow into the cornea. It is usually painless and often unnoticed until an optometrist spots it, and it is not fully reversible.

7. Sharing lenses

This happens more than people admit, particularly with cosmetic colour lenses passed between friends before an event. Two problems: you are transferring whatever is on someone else’s ocular surface directly onto your cornea, and their lens is fitted to the curvature of their eye, not yours.

A lens that is too tight restricts tear flow. A lens that is too loose slides and abrades. Neither is visible to you when you put it in.

8. Buying lenses without a fitting

Cosmetic zero-power lenses are still medical devices. They still sit on your cornea and still need to match your base curve and diameter. Buying by colour alone, from a seller who never asks for a prescription, means the fit is a guess.

It also usually means the lens has no verifiable manufacturer, batch number or expiry date — which matters, because you cannot assess sterility by looking at a blister pack.

9. Pushing through red eye instead of stopping

The instinct is to take the lens out, rinse it, and put it back in because you have somewhere to be. This is how a minor abrasion becomes an ulcer.

Remove the lens and leave it out if you have any of the following:

• Pain rather than mild irritation
• Redness that does not settle within an hour
• Sensitivity to light
• Discharge or excessive watering
• Any blurring or drop in vision

Pain plus light sensitivity plus reduced vision together is the combination that warrants same-day attention from an eye doctor. Keep the lens in its case and take it with you — it can be cultured.

The routine that prevents nearly all of this

• Wash and dry your hands before touching lenses, every time.
• Fresh solution in a clean case, every time.
• Rub the lens for twenty seconds — do not just soak it.
• Air-dry the case face down daily; replace it quarterly.
• Respect the replacement date.
• Keep to eight to ten hours, and take a lens-free day where you can.
• Never sleep in them, never swim in them, never share them.
• See an optometrist annually even if nothing feels wrong.

That is roughly ninety seconds a day, and it is the difference between decades of comfortable lens wear and a preventable injury.

If you are just starting out, our step-by-step guide for first-time wearers covers insertion and removal in detail, and every lens in our Ego Vision range ships in sealed blisters with base curve, diameter, batch number and expiry printed on the pack.

This article is general information and does not replace medical advice. If you have eye pain, light sensitivity or reduced vision, contact an eye care professional promptly.