Can straining my eyes cause cross eyes?

Question

Straining such as looking at the computer screen for too long

Answer 1

Long computer use can cause different types of eye strain depending on the monitor and the monotony of activity. For instance, "large white areas" like on a word processing documents are bad for the eyes. Similarly, small text also strains the eyes. The second sight below recommends doing word processing with different colors; i.e. yellow text against brown background.

Regarding cross-eyes, I found the following text:
The basic brain mechanisms are present from birth in the visual cortex, but only experience leads to binocular interpretation becoming "hardwired". If one eye has poor muscles ("cross eyes") it is suppressed and binocular cues may never be worked out properly, which means a squint must be treated early in childhood.

Answer 2

In almost all cases, no.
There is a condition called accommodative esotropia (and esophoria). In this condition, if you look close it will cause the eyes to cross. The treatment for these people is reading glasses.