Summary
This page offers some suggestions for ways to block light while you're sleeping without putting pressure on your eyes.
Note: I'm not an expert on this topic, so my recommendations here may be misguided.
Contents
The problem
I often sleep during the daytime, so I regularly need to block out light while I'm sleeping. In the past, I wrapped a shirt or pants around my eyes for this purpose, but I wondered if the weight of this clothing on my eyes could be harmful.
UNSW (2008) warns about putting pressure on your eyes and says: "Even for those who lie on their sides when sleeping, there is the possibility of pillow contact on the eye lids and increased pressure for dangerously long periods through the night. Wearing a sleep mask that touches the eyelids can cause a similar problem."
Solution 1: Curved sleep masks
My first attempt at a solution was to buy a sleep mask that bends upward in the middle (AmazonSmile "3D ..."). When the sleep mask is in the proper position, I can open my eyes, with only my eyelashes touching it, so it hopefully doesn't add pressure on the eyes.
However, the mask sometimes slides a bit during the night, and sometimes the positions it slides to are not obviously harmless from the perspective of eye pressure. One possible solution is to keep the mask very loose to reduce the downside risk from in-the-night movement of the mask. On the other hand, keeping the mask very tight can reduce sliding from happening in the first place. Is there any long-term harm in having a tight sleep mask pressed against your face (without touching your eyes) for ~8 hours each day? I've also found that completely unstrapping the mask in the back reduces sliding and pressure on my face, although the mask doesn't block out light as well.
Solution 2: Dark goggles
Many forms of eyewear avoid touching your eyes, including glasses and goggles. I tried buying dark sunglasses to block light, but they didn't block light around the edges of the glasses.
So instead I tried buying brazing goggles (AmazonSmile "Lincoln ..."), which cover the sides of the eyes as well as the front but without touching the eyes. These goggles still allow a small fraction of the original light through, but the reduction in light intensity is enough to allow for sleep, especially if you also have blinds on the windows.
UNSW (2008) notes that "wearing swim goggles" can increase eye pressure. Therefore, I imagine that if you wear goggles while sleeping, you should make them extremely loose. You could even not use the strap that goes behind your head at all and just let the goggles sit on top of your face.
TODO: I should learn more about goggles and eye pressure.
The AmazonSmile ("Lincoln ...") goggles have the following notice on the back of the package:
WARNING: This product contains or produces a chemical, including DEHP, known to the State of California to cause cancer or birth defects (or other reproductive harm)[.] Wash hands after use. (California Health and Safety Code 25249.5 et seq.)
TODO: Research how much of a concern this is and how it compares to other common consumer products.
Solution 3: A homemade light-blocking mask
I cut my own mask out of a paperboard box, as is shown below. I cut the box to fit my face by trial and error—cutting a bit, seeing if the box fit, and cutting a bit more.
This box works about as well as the brazing goggles at blocking light, but it's presumably less toxic, and it's lighter in weight, so it has less risk of putting too much pressure on my face. I put tape over the bottom edges to avoid papercuts, which would be especially bad in the unlikely event of a box edge touching an eye while it was open.
The main problem with this mask is that it has a high center of mass and is liable to fall over. I'm not sure how best to fix this, but one hacky solution is to stick it to your face, with tape or sticky tack. You could add weight to the bottom of the mask to lower the center of mass, but this would make the mask heavier on your face.
References
AmazonSmile ("3D ..."). "3D Sleeping Mask Eye Mask for Sleeping Contoured Shape Ultra lightweight & Comfortable Sleep Mask for Travel, Nap, Shift Works 2 Pack (Black & Purple)".
AmazonSmile ("Lincoln ..."). "Lincoln Electric KH976 Goggles, IR5 Lens, Black/Green".
UNSW (2008). "Watch how you rub: warning on eye spikes". UNSW Science for society.