How to keep glasses dry in the rain?

The easy answer is a wide-brim hat or long visor on your helmet. This does work, at least at low speeds. You will have to experiment with options, as nothing like this is sold for this purpose as far as I can tell.

Over about 20kph the length of brim you need gets silly, and by 30kph you need half a metre or so (there are some velomobile owners that do this). But if you're willing to slow down, the brim will work.

I wear glasses, and haven't found a water-shedding coating that works well enough to be worth the hassle. In practice I use a clip-on visor on my bike helmet, extended a little so it's about 10cm in front of my forehead. That keeps the worst of the rain off. Then I ride fast enough that my glasses get wet anyway. But not as wet as without it.

The visor/brim also reduces the amount of water running down my head and into my eyes, especially as that always seems to wash stale sweat out of the helmet pads and that stuff stings. A sweatband or headsock helps there.

The visor certainly helps - mine broke away 6 months ago, but the helmet is undamaged. Its almost impossible to find replacement brims.

So you might want to think about your technique. Try riding more defensively:

• Learn to See rather than Look - that's noticing motion through a raindrop or obstruction.
• Position yourself on the road to avoid possible problems.
• Light yourself and your bike up like the Eiffel Tower / Blackpool Tower / Big Glowing thing. More lights and high-vis the better.

Finally check with your optometrist whether rainx or friends might damage your glasses. It should be fine on glass lenses, but coatings might suffer. I wouldn't want to guess on plastic lenses.

If you're getting a new prescription soon, consider getting custom cycling glasses.

Here's a set that put the rain barrier in front of the corrective lens, so the light focussing is less distorted by rain.

Here's another photo showing from the side. Notice how the tinted plastic bit comes much further around the head, reducing that eye-drying side-buffeting on a fast downhill. The corrective lens part can be ground to your prescription by your optometrist. Depending on model, the front shield may be removable, and may even come with up to 5 or 6 different shades for different riding conditions. You can even get some models with a safety strap instead of two temples, so they're almost like baby's glasses or slightly like swimming goggles.

On later thoughts - that foam top band could be both awesome for sweat control, and horrible once it saturates.

I can't wear contacts because they irritate, and I have to wear glasses all the time, so would have to carry normal glasses on a ride too.

In a heavy rain, I just take my glasses off. Hats or similar don't really protect the glasses enough to be worth the trouble.

There are sevral options to prevent wet glasses.

1. Do not ride in rain
   This is absolutely foolproof, but it doesn't solve the problem if you want/need to ride.

2. Do not wear glasses in the rain
   You will have clear view, but in heavy rain and/or higher wind this is painful and may be dangerous. They who must wear corrective glasses cannot use that option for sure.

3. Wear helmet with visor
   When riding relatively slow the helmet makes sort of roof over your face protecting your glasses from the rain. Visor gives extra room for protection. (Thanks, @Criggie) In high winds and heavy rain it is useless.

4. Use hydrophobic-coated glasses
   Such (super-)hydrophobic coatings repell water from the surface. Some are polymer-based which are relatively cheap but are vulnereable to scratching and oils. Rare earth ceramics are investigated to sort these drawbacks out, but might be very expensive. Surf sunglasses, Adidas glasses are available.

5. Use MotoGP helmet for wet races
   These helmet have double visor with sealed gap. Regradless how you sweat, the visor is still bright without any fogging. The visor is also cvered with set of hydrophobic foils (when worn out, they tear one layer away uncovering new one), or there are two cassettes for hydrophobic tape covering the visor (one cassette with unused tape and second for the used part, when the visor is wetting, racer can roll out new part), or the visor is covered by hydrophobic coating. This option is most expensive, Byt you will have ultimate head protection and comfort in cold weather.

Note that hydrophobic film will create separated water droplet that will easily move on the surface - on the bike they will be blown sideways and drop off. Superhydrophobic surface will repel the water droplets as a wall repels tennis balls.

I have a 10 mile commute to work and then back again, I’ve found that polishing your glasses with ( I use Mr Sheen Multi Surface Polish ) before setting off helps a little with repelling the rain and certainly helps when you have to stop and wipe your glasses, my glasses are glass and I’ve had no problems with it affecting the glass.

Many cycling gloves are designed with a chamois or microfibre panel on the thumb section. This allows you to wipe glasses with the back of your thumb. It sounds rubbish, but it works really well, even when the gloves are saturated with water. Of course you have to wipe your glasses quite frequently, but in my experience not so much as to impair my riding.

Tip: Use the left hand for the left lens and the right hand for the right lens. Hold the thumb vertical, start at the inside and wipe towards the outside.

Additional suggestion is to turn your head a little, and often rather than holding the head still and moving your eyes.

As you move your head, your eyeballs get a "line of sight" around any particular drop, and your brain ends up "gluing" the image together.

Its a subconscious thing, but works well enough when combined with the other physical solutions presented.

Give it a try next time it raining.

I've been struggling with this problem & considering getting a full motorbike helmet with the water repellant on visor as nothing else seems to help

As a halfway to wearing a full face helmet, there are helmets with eye-shields like

or one with less tail:

Or there are add-ons to your existing helmet which may fit.

https://bikerumor.com/2015/11/12/rcc15-wide-eyez-flips-any-helmet-into-integrated-visor-mode/ and https://www.wideeyez.com/

The vision it mostly interfered by raindrops sticking on the glass when the glass between raindrops is still dry. This happens in the beginning of the rain.

It helps to sweep the glass with the finger, so that all surface becomes equally wet and drops find they way down faster. It is not the same as the dry glass in good weather but the vision improves.