hi... as your son has been suffering from multiple systemic disorders...his myopia
may or may not be because of that. as for his intermittent blurring of vision...it may be because of his systemic illness...or drug reaction...or eye problem. because he had suffered neurocystecersis...he may have occular cystecercosis..so ask your eye specialist to do his retinal examination and occualr sonography
do not stop any of his medicines by yourself. consult your physician.