If you need prescription glasses to read a sign at the end of the street, you need them on the bike. Yet glasses are designed for a desk, not for something pressing against your temples for an hour at 40 km/h. The problems are predictable: pressure points, fogging, and glasses that migrate down your nose exactly when you need to check a mirror.
Frame choice
Thin, flexible arms matter more than lens quality under a helmet. Chunky spring-hinge temples create pressure where the helmet’s padding grips your head; after an hour that becomes a headache people blame on the helmet. Frames with straight, slim arms slide in without lifting the padding and without breaking the helmet’s fit. Trying glasses on with your helmet on — before buying either — is the only honest test. The helmet’s own fit rules are in helmet-fit-guide-vietnam.
Fogging
In Hanoi’s drizzle season, eyeglasses under a closed visor fog like a bathroom mirror. Warm, humid air inside; cool, wet outside. Fixes that work: crack the visor open a notch at low speed (vented airflow clears both surfaces), keep the visor’s anti-fog treatment intact as described in visor-care-anti-fog-motorbike, and wipe lenses with a drop of mild soapy water and let them air-dry — the invisible film noticeably delays fogging. If fogging is constant, a Pinlock-style visor insert helps the visor; the glasses still need airflow.
Tinted and photochromic lenses
Sunglasses and photochromic lenses have a place in Vietnamese sun — the tint selection logic is in helmet-visor-tinted-photochromic and the broader eye-protection picture in eye-protection-riding-motorbike-vietnam. Two cautions for prescription wearers: very dark tints at dusk turn a manageable ride into a blind one, and photochromic lenses depend on UV reaching the lens — some visors block enough UV that the lens never darkens, or darkens late. Test your own combination rather than trusting the marketing.
Practical habits
Carry a microfibre cloth; Vietnamese dust films a lens in a day. Never wipe dust-dry — it scratches coatings. Keep a hard case in the underseat box so spare glasses survive the humidity. And if your helmet presses your frames into your temples hard enough to leave marks, fix the problem — different glasses, different helmet, or contact lenses for longer rides — instead of riding with the pain and half your attention.