Why did my lepord gecko die?

i got a female lepord gecko aas a baby, and rasied it for three years. and it looked healthy, but i did notice that its eye sight was not at its best. i looked closly and one pupil had almost completly closed. so i had figured it was blind in that one eye, i thought maybe sand got in it or some thintg but iover a corse of about 6 months. it went totally blind. dissabling it from catchin prey. so i did what i was told and fedd it crickets with tweezers and serenged special formula into its mouth. but as it kept getting skinnyier and skinner it died... what happend to my lizard that caused it to go blind? and die?