Thank you for you questio. My name is***** I have been a small animal veterinarian for 12 years.
At the moment of death, the muscles relax completely— they eyes open at this point because it is actually muscle contraction that closes them. But about 2-4 hours later the muscles begin to stiffen (rigor mortis). This can cause the eyes to close.
I hope that helps, but if you have more questions or need more imformation please let me know.