Prescription or not? The question that actually matters

Why this matters more than the filter

Uncorrected refractive error produces the exact symptom set people attribute to blue light: tired eyes, intermittent blur, headache after sustained close work. The mechanism is straightforward — the focusing system is compensating continuously for something the lens should be correcting, and muscles held under load for eight hours ache.

Two cases catch people out. Small amounts of astigmatism often go undiagnosed for years because distance vision seems fine; the effort only shows up during long near work. And presbyopia, the gradual loss of near focusing range that begins around the early forties, arrives slowly enough that people adapt by holding things further away and blame the screen.

If you already wear glasses

Add the filter to a prescription lens or skip it. Buying a non-prescription pair to wear at the computer means either working without your correction — which is worse for your eyes than any lighting condition — or stacking two pairs, which nobody does for long.

Two things are worth more than the blue filter when you order:

An anti-reflective coating, which reduces reflections between the lens surfaces and is genuinely noticeable under office lighting.
If you are presbyopic and spend all day at a monitor, ask your optometrist about an intermediate-distance or occupational lens. A standard progressive is optimised for reading distance, not screen distance, and that mismatch causes a lot of neck-craning.

Both of those are conversations to have with the person doing your eye test, not decisions to make on a retail website.

If you do not wear glasses

Start with the exam rather than the purchase. If it comes back clear, then a non-prescription pair is a low-cost thing to try, and the honest framing is that you are buying an accessory with an unproven optical benefit — which is fine if you know that going in.

If it does not come back clear, you have found something a $20 filter would never have fixed.

Buying prescription lenses online

Online retailers sell prescription lenses at a fraction of high-street prices, and for a simple single-vision prescription the result is often indistinguishable. Some practical notes:

You need a current, valid prescription from an eye exam. The retailer cannot produce one, and an out-of-date prescription defeats the purpose.
You also need your pupillary distance. Ask for it at the exam — measuring it yourself introduces error that shows up as eye strain, which would be an unfortunate irony.
Complex prescriptions — strong powers, significant astigmatism, progressives — are where online ordering most often disappoints. That is the case for buying in person.
Blue-light filtering is sold as a paid add-on. It is optional. The prescription is the part doing the work.
Check the returns policy for prescription orders specifically. It is often stricter than for plain frames.