What could be the reason for occasional blurred vision and tiredness of eyes?

Time for eye exam. Tired eyes are often a sign of either dry eyes or eye strain. Both can be related to long hours spent on a repetitive near task (like being on the computer for hours) and can also be caused by a need fro prescription glasses. Occasional blurred vision can be related to dry eyes or prescription changes also. You would be well off having an eye exam to be sure.
Dry eyes. There can be many reasons, however the most common reason 99% of time would be dry eyes or ocular surface disease.
Dry eye. The number one cause for intermittent blurred vision, especially when associated with tired eyes is dry eye. Try some warm compresses and otc lubricating drops for a few days. If your symptoms continue, see your ophthalmologist.
Tired eyes . This could be due to dry eyes. Using artificial tears, taking breaks from intense computer work or reading, may also alleviate some of the strain. A good exam with an eye doctor will help you uncover any other issues.
Many causes. Syncope, mild double vision due to many causes, TIA etc can cause. Your problem include cardiac etc causes for syncopr.