You've identified the exact reason I don't wear transition lenses or even sunglasses when shooting with my cameras.

Why in the world would you only shoot in manual?

Pros know how to use all the different exposure modes, because they each have their purpose. Yes, there are times and places where manual exposure might be the best... but those are usually when there's little to no variation in lighting, so it's sort of a "set it and forget it" thing. While shooting manual, you shouldn't need to be constantly changing your settings.

If you shoot a lot in manual mode, you might want to consider getting a handheld exposure meter. I always carry one... to check on my settings occasionally, particularly when I'm shooting manual.

I recommend using an "incident" meter. This type measures the light falling onto a subject, rather than the light being reflected off of it. A reflective meter, which is what's inside all cameras, is highly influenced by the tonality of subjects... an unusually light subject will cause the meter to recommend or set an underexposure, while an unusually dark subject will want to overexpose. Fortunately, much of the world works out pretty average tonality, so this is only a problem when things are lighter or darker than usual.

An incident meter largely resolves those "problems". Since it's measuring the light falling onto the subject, there's little need for "exposure compensation" corrections that are common with reflective meters. Unfortunately, an incident meter cannot be built into a camera (when you use one, it makes sense why this is the case... you point the meter toward the light source, not toward the subject like you do the camera and its reflective meter).

But I also recommend you learn to use the other exposure modes of your camera. Sure, they rely upon that internal meter, but it can serve a lot of the time and you can easily tweak what it's doing when needed.

I shoot a lot of sports, as well as some wildlife, and any sort of action photography pretty much requires I use one or another of the auto exposure settings. Following subjects as they move through different lighting conditions I simply don't have time to make the necessary adjustments manually. Often shooting fast, I don't have time to think about exposure.

For a long time my favorite auto exposure mode (AE) has been Aperture Priority. I prefer it because I want to control depth of field (DoF) and background blur effects... I need enough DoF to get all the subject sharp, but also usually want to blur the background as much as possible to make the subject stand out (often shooting sports the background is busy and distracting when it's not sufficiently blurred... same can be true with wildlife). In Aperture Priority AE mode ("Av" on our Canon cameras), you set the ISO and select the aperture, but let the camera choose a shutter speed it feels will make for a "correct" exposure.

Some other people prefer to use Shutter Priority AE for sports action and wildlife, to be sure to freeze movement (fast shutter speed) or to deliberately blur some of it (slow shutter speed). Shutter Priority mode on our Canons is "Tv". Here you choose an ISO and set the shutter speed, then let the camera select an aperture it thinks will make a correct exposure.

However, the cameras I use now have a good implementation of Auto ISO, so I've begun using that a lot more often in conjunction with M (manual) mode. This is actually another AE mode, even though the camera set to M. Here I select both the aperture and shutter speed I want, then let the camera choose an appropriate ISO. This lets me take care of both freezing movement and controlling DoF/background blur... though I have to keep an eye that too high ISO that would make for "noisy" images isn't being selected. If it is, I may need to slow the shutter or increase the aperture size, or a little of both.

I DO NOT use Auto ISO in conjunction with Av, Tv or P AE modes... that makes for sort of a "double auto" exposure situation that's likely to be unpredictable. I don't care for that, so I only use Auto ISO with Manual mode.

More and more I've been using M with Auto ISO AE... Probably just as much as I use Aperture Priority AE. My third most used AE mode is Shutter Priority and my least used is Program (P). I only use the latter on very rare occasions when I need to shoot under radically different lighting conditions, don't have time to think about my settings and after a few shots will be returning to what I was doing previously (my prior settings in the other exposure mode are retained).

I'm not saying don't ever use Manual exposure mode. By all means, there are times it can be ideal. It's certainly good for more sedate subjects such as scenery, architecture, macro, even a lot of portraiture (especially under controlled lighting conditions, such as in a studio). You should have little need for frequent changes to the settings. If not, you might be better served using one of the AE modes: Av, Tv, M + Auto ISO or even P.

If you decide to get a reflective meter, many of those also are excellent flash meters. They can be used to set up lighting ratios and much more. Personally I have been using a Sekonic L358, which is no longer being made. However, the Sekonic L308 is nearly identical and costs less (the only significant difference is that the L358 can be fitted with radio trigger modules that can be handy with studio lighting).

If you prefer not to use a separate meter, and don't need the quickness of AE exposure modes, you should start to use your camera's rear LCD screen. The "Q" button gets you to all the exposure setting info instantly and the Touch Screen allows you to relatively quickly access them and make changes. The "trick" will be to frame your subject, half press the shutter button to "take a meter reading" and then press the Q button and to do your adjustments. The camera holds the readings from the half press for something like 10 or 15 seconds. If you wait too long, you'll be taking readings of the ground while looking at the rear screen of the camera. Using the camera's reflective meter, you do need to think about any tweaks that might be needed due to unusually bright or dark subjects or scenes.