Hi. I'll be happy to help you with your question.
If it seems like your headaches and feelings of eyestrain resolve after not using your eyes for a bit, for instance after a nap or waking up in the morning, then I agree that your symptoms are related primarily to your eyes. If this is not true, then you may want to consider being evaluated by your primary care MD for other causes of headaches.
That being said, I believe your eye strain, headache and difficulty focusing could be related to your prior history of strabismus (squint) surgery as a child, lifelong use of prism in your glasses and (a normal) condition called presbyopia. As we get around 40 years of age the natural lens in our eye is no longer strong enough to focus clearly on objects up close. That is why you see us older folks wearing reading glasses all the time!
The amount of effort used to focus up close is tied to the amount of "crossing" of our eyes. (A/V ratio) Normally this system works great....just enough crossing for just the right amount of power for near tasks. Problems arise when there is already a mismatch between the amount of "focus power" we use and how much our eyes cross. Many times, in people who have had squint surgery and/or needed prisms in their glasses, this normal match is messed up... when you add to this lifelong problem the fact that you are now over 40 and presbyopic( needing reading glasses)you can get symptoms just like you have described.
The fact that two different optometrists got two different results on different days is possible because in many cases the amount of prism/glasses you need varies from day to day with this condition.
What should you do? Well, I would suggest that you have an evaluation done by an ophthalmologist who specializes in crossed eyes/eye strain. This can be a pediatric ophthalmologist or a neuro-ophthalmologist. They may have to examine you twice. Once with strong drops to dilate your eyes and paralyze accommodation (the muscle used to see up close) -- called a "wet refraction" and, once the drops wear off, repeat the tests without the drops (dry refraction). Many times these tests will give different results. This is where extensive training and experience come in to help order the best glasses possible to solve your issues.
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