Short answer, it depends on the screen size and the distance you’re sitting away from the screen. It also depends on the brightness of the screen, not the resolution and the amount of blue light it emits.
The longer answer is below
It has been stated that having increased sharpness in a display can be better for eye health. Increasing resolution has been said to actually lower the risk of eye strain, by making print and objects more comfortable to focus on.
It’s difficult to determine whether particular resolutions exceed the discriminating ability of the eye since the retinas don’t output easily understood and convenient parameters and because not every eye is the same.
It has been said that the eye can’t differentiate detail beyond 300 PPI (pixels per inch). It has also been said by a retinal neuroscientist from the University of Utah, that the human eye can’t discern more than 287 pixels per inch at a distance of more than 12 inches.
If this same individual would view content at 24 inches away (the standard distance for desktop use), the max discernible density would drop to below 150 PPI.
The brightness of a display (as mentioned above) is a major factor in determining if a display will cause eye strain. If the display is too bright or dim for the environment the eyes will have to squint to block or let in excess light.
Another thing that’s important is sitting at an appropriate distance. It’s been said that one should sit at least 20 inches away from any computer display. While it’s natural instinct to sit closer to see small details, it’s counterproductive because the eyes will have to work harder to focus the screen’s objects.
A weak relation to resolution can be made here. Text and images that are not scaled will seem smaller on 4K monitors than they would on others, resulting in the urge to lean in. Individuals will have to fight the urge to do so and focus on the scaling features that come built into the monitors (such as the magnifier).
The sweet spot is 24 inches
Even though 4K doesn’t really come with health implications, individuals can have more trouble getting used to it with certain monitors. This is due to the fact that 4K is used for a number of display sizes. While the pixel count may remain the same, 28 inch monitors will not be as dense as a 24 inch screen would. Every pixel will be larger, meaning that there will be less scaling to make the text more readable.
One will see a noticeable difference. 28-inch 4K displays will have 157 pixels per inch, while a 24-inch 4K display will offer 183 pixel per inch. This means, essentially, that every pixel on the 28-inch monitor will be around 15 percent bigger than the pixels on the 24-inch screen, and the images and text will be 15 percent bigger as well.
It’s essentially like going to a 16 font from a 12 point one.
32 inch displays have more dramatic effects, and will increase the size by 30 percent in relation to 24 inch monitors – the pixel density will reduce to less than 140 PPI. This will reduce clarity as well. This is why 28 inches is the sweet spot between clarity and size because it goes over the max discernible pixel density but also renders text readable without the need for excess scaling.
4K displays are no more likely to cause eyestrain than 1080p ones. Actually, the higher clarity will benefit you. Evenn though one can still experience eye strain, it will be due to improper positioning, excess brightness etc. not the resolution.