It turns out that the expensive Google Glass prototype isn't just a pain in Explorers' wallets, it's also causing a few early adopters headaches.

The eye muscle discomfort is caused by looking in unnatural directions, specifically the top right corner of your vision, admitted Google's own optometrist Dr. Eli Peli to BetaBeat.

Google Glass headaches are said to go away after a few days, which the company likened this to owning a new pair of prescription glasses.

"When anyone gets a new pair of glasses or starts wearing them for the first time there is always an adjustment period until people get used to them," a Google spokesperson told TechRadar.

"For some it's the same with Glass. We encourage Explorers to ease into Glass, just as they would a new pair of glasses."

First-hand experience

Google doesn't see a need for warning labels, but it did caution this reporter not to overuse Glass when I sat down for our Google Glass fitting in December 2013.

Sure enough, there was minor discomfort when I disobeyed this order, like any early adopter would do. It went away within a week.

The problem was that I was focusing just the right eye on a screen while the left eye goes into what can only be described as a "dead zone." Really, Glass is good for short notifications beamed to the eye.

"As we note in our Help Center, Glass is designed for micro-interactions," said the Google spokesperson.

"[It's] not for staring into the screen, watching Friday night movie marathons or reading 'War and Peace.'"