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There is more than one type of surface irregularity and vision fluctuation being discussed here so I think it might be useful at this point to back up and talk about the parts of the eye for a moment... if not just ignore my mini-lecture 
The front of the eye has three layers that provide the eye's refractive function, that is, clear layers that work to bend light so that it hits the back of the eye (retina) just so. That means three places things can go wrong that affect the stability of your vision:
1) The preocular tear film
In any kind of dry eye disease, obviously the preocular tear film is not fully performing its job and since tear production and distribution are affected, it's totally to be expected that vision will fluctuate as spmcc said. This affects some more than others. I know people whose ONLY dry eye symptom is poor, fluctuating vision. I know people who have bone-dry eyes and who amazingly enough still see 20/20. - Takehome point is that tears are not just there for comfort and to protect the eye - they are the first refractive surface of the eye and essential to clear, stable vision.
2) The cornea (which has 5 layers)
After lasik or other refractive surgeries there are a number of things that can go wrong here that will cause fluctuating vision. It could be small surface irregularities that make it impossible to maintain a smooth tear layer across the cornea (though over time these tend to improve). It could be a small 'effective optical zone' i.e. the diameter of the area that was FULLY treated by the laser (and I don't mean what they programmed into the machine but what actually came out after all healing which can be quite different... this is something verified with a high res corneal topography) - if this is smaller than the pupil gets when it expands, then we can be particularly prone to a widely fluctuating RX in different lighting circumstances.
Some of us have irregular corneas, where the dioptric power varies greatly across the surface of the cornea. There are certain patterns to this (esp. in the earlier days of LASIK things like central islands or decentrations) but often they're all lumped together under a somewhat poorly named category of 'irregular astigmatism'. What it really means is the thickness of the cornea is uneven - in other words, a multifocal cornea. (Suppose you had a pair of glasses with different strengths at different parts of the lens - it's like that but built in.) Long story short, for those of us who have ANY of the other reasons for fluctuating vision - dry eye, small effective optical zone, etc - these irregularities will make the the fluctuations seem even worse.
Then of course there's extremes, like keratoconus (or corneal ectasia as it's known if caused by refractive surgery). Hirentherock that's really different from corneal irregularity in the common sense of the term because keratoconus/ectasia is progressive while irregularity (depending on the cause) can be static.
One of the things that makes this so confusing is that ALL of the cornea-based fluctuation problems get very difficult to diagnose accurately when your eyes are severely dry. The scanning technologies depend to a significant extent on the presence of a decent tear layer. I haven't really kept up with those technologies in the past 5-ish years so there may be better ways to compensate now but that's what I recall historically as often being a problem.
3) The lens (that's the part that flexes to change focus from far to near)
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Hirentherock, yes, BSLs (really any RGP theoretically, but realistically only sclerals can usually be worn by people with dryness as severe as SJS causes) can stabilize this, because the liquid + hard lens provides an artificially smooth, stable surface to compensate for whatever's going on on/in the cornea.
The front of the eye has three layers that provide the eye's refractive function, that is, clear layers that work to bend light so that it hits the back of the eye (retina) just so. That means three places things can go wrong that affect the stability of your vision:
1) The preocular tear film
In any kind of dry eye disease, obviously the preocular tear film is not fully performing its job and since tear production and distribution are affected, it's totally to be expected that vision will fluctuate as spmcc said. This affects some more than others. I know people whose ONLY dry eye symptom is poor, fluctuating vision. I know people who have bone-dry eyes and who amazingly enough still see 20/20. - Takehome point is that tears are not just there for comfort and to protect the eye - they are the first refractive surface of the eye and essential to clear, stable vision.
2) The cornea (which has 5 layers)
After lasik or other refractive surgeries there are a number of things that can go wrong here that will cause fluctuating vision. It could be small surface irregularities that make it impossible to maintain a smooth tear layer across the cornea (though over time these tend to improve). It could be a small 'effective optical zone' i.e. the diameter of the area that was FULLY treated by the laser (and I don't mean what they programmed into the machine but what actually came out after all healing which can be quite different... this is something verified with a high res corneal topography) - if this is smaller than the pupil gets when it expands, then we can be particularly prone to a widely fluctuating RX in different lighting circumstances.
Some of us have irregular corneas, where the dioptric power varies greatly across the surface of the cornea. There are certain patterns to this (esp. in the earlier days of LASIK things like central islands or decentrations) but often they're all lumped together under a somewhat poorly named category of 'irregular astigmatism'. What it really means is the thickness of the cornea is uneven - in other words, a multifocal cornea. (Suppose you had a pair of glasses with different strengths at different parts of the lens - it's like that but built in.) Long story short, for those of us who have ANY of the other reasons for fluctuating vision - dry eye, small effective optical zone, etc - these irregularities will make the the fluctuations seem even worse.
Then of course there's extremes, like keratoconus (or corneal ectasia as it's known if caused by refractive surgery). Hirentherock that's really different from corneal irregularity in the common sense of the term because keratoconus/ectasia is progressive while irregularity (depending on the cause) can be static.
One of the things that makes this so confusing is that ALL of the cornea-based fluctuation problems get very difficult to diagnose accurately when your eyes are severely dry. The scanning technologies depend to a significant extent on the presence of a decent tear layer. I haven't really kept up with those technologies in the past 5-ish years so there may be better ways to compensate now but that's what I recall historically as often being a problem.
3) The lens (that's the part that flexes to change focus from far to near)
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Rebecca or any other BSL wearers can let me know if they face such problems and get benifited with BSLs?Im really curious to know this coz im banking upon BSL to get me out of this problem of varying vision. My other eye is aphakik and has finger counting vision.So i need the best vision in my recently operated eye.
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