In newer versions of optifine, for fullscreen mode there is a slider with which you can immediately select the desired resolution; in optifine 1.7.10, there is only a button, which is why you have to click on it several times to select the desired resolution (if the monitor has a large resolution, and you need to make it smaller, you need to click on it a lot of times, also, you can click one extra time, and you will have to click again)
My suggestion is to port the resolution selector slider from newer versions of optifine

here is an example:

new versions:

1.7.10:

yes, it's quite a small thing, but it's actually very convenient