This article shows how myopia is caused:http://www.myopia.org/ebook/07chapter2.htm Indeed the whole website is worth a read.
Relevant journal articles:
Effects of Nitric Oxide Donors and Nitric Oxide Synthase Substrates on Ciliary Muscle Contracted by Carbachol and Endothelin for Possible Use in Myopia Prevention
The FIRST thing to note is that HUMAN eyes are designed to look at the distance (infinity) for most of the time, in which position they are most relaxed, and therefore least likely to cause stress on any part of the eye.
According to Hitoshi Nakaishi and Yuichi Yamada, "Abnormal Tear Dynamics and Symptoms of Eyestrain in Operators of Visual Display Terminals", Occupational and Environmental Medicine, Vol. 56, No. 1 (Jan., 1999), pp. 6-9, "Our data suggest that dry eyes might be a more common cause of, or at least more associated with, symptoms of asthenopia than refractive errors among VDT workers. As other researchers have mentioned,15 our results indicate that dry eye syndrome and refractive errors might both be causes of asthenopia in VDT workers, rather than be mutually exclusive. There have been much experimental data supporting an increase in the prevalence of drying of the eyes, as well as a report on dry eyes and VDT work in a clinical setting.