Significant change in prescription

I have just had an eye test, and whilst the optometrist said my eyes were healthy, there has been a significant prescription change that has me worried and wondered if anyone else had seen this kind of change. I get my eyes tested every 2 or 3 years and I am age 57. Over the past 20 years my prescription has ranged from -0.25 to -0.75 with an astigmatism (cylinder) of -0.5 in both eyes since 2009. My vision has never been that bad that I have felt the need to wear glasses and I also read without glasses although as I am getting older I do struggle now in low light or with very small text. My eyesight does not appear to have changed much in the past three years, I can still read OK and my distance vision more than meets UK DVLA driver standards (I can read a number plate at 20m easily and actually up to 30m). So my concern is that my prescription has suddenly gone from negative to positive and my astigmatism has become significantly worse although I can't really tell any difference in my actual vision. See previous and latest test results below:

2014 Sphere R -0.5 L -0.25 Cylinder -0.5 in both Axis R 115 L 72

Today Sphere R+0.75 L +1.00 Cylinder R-1.25 L -2.00 Axis R 94 L 83

Any thoughts? Is this something I should be concerned about? Could it indicate some other health problems?

 

I do not know anything about how the lenses are made or how the prescription is applied, but I have noticed one thing. If I add the sphere and cylinder dioptres together, they are not too dissimilar.

2014 R -1.0 L -0.75
2017 R -0.5 R -1.0

Is this a valid thing to do, are the two correction factors in the lens combined in this way? If so the one thing that still confuses me is the long and short sighted element. My wife is long sighted and has been for years. She needs glasses to read her phone, the news paper, use a computer and generally see anything close up, I do not. I can easily read all but the smallest print. On the other hand, my wifes distance sight is much better than mine, she can read road signs and bus numbers much sooner than I can. So how can we now both have a +ve sphere factor, and hers is actually less than mine at +0.75 in both eyes. This does not make any sense to me and I hope someone who knows more about it than I do can shed some light on it.