The title of the question asks if most blindness solved by cadaver donation? The World Health Organization states that:
According to the latest assessment, cataract is responsible for 51% of
world blindness 
So, cataracts are responsible for the majority of blindness. Cataracts are readily treated by replacement of the lens of the eye with an artificial intra-ocular lens made of a type of plastic.
Cadaveric eyes are only used to provide donor corneas ( transparent front part of the eye) for grafting. The lens of the cadaveric eye is not used.
Corneal blindness ( often monocular ) is the second most common cause of blindness, and figures about 1/4 that caused by cataracts 
Diseases affecting the cornea are a major cause of blindness
worldwide, second only to cataract in overall importance. The
epidemiology of corneal blindness is complicated and encompasses a
wide variety of infectious and inflammatory eye diseases that cause
corneal scarring, which ultimately leads to functional blindness. In
addition, the prevalence of corneal disease varies from country to
country and even from one population to another. While cataract is
responsible for nearly 20 million of the 45 million blind people in
the world, the next major cause is trachoma which blinds 4.9 million
individuals, mainly as a result of corneal scarring and
vascularization. Ocular trauma and corneal ulceration are significant
causes of corneal blindness that are often underreported but may be
responsible for 1.5–2.0 million new cases of monocular blindness every
However, the authors conclude that surgery is not cost-effective way of treatment, and most cases are actually preventable. Note also that corneal transplant requires the use of eye banks, and other sophisticated medico-surgical infrastructure.
The message is clear that medical and especially surgical intervention
is not cost-effective in eliminating corneal blindness in developing
countries. Prevention, in the case of almost every disease involved,
is more cost-effective and ultimately more successful in decreasing
the prevalence of blindness. Schwartz et al. estimated that 95.5% of
all blindness in the population they studied in the Central African
Republic was preventable or treatable
So, the answer to the question, is no. The message being passed around Facebook doesn't understand the cause of common blindness and the treatment.
 Whitcher et al Corneal blindness: a global perspective http://dx.doi.org/10.1590/S0042-9686200100030000