Besides corneal dystrophies, other causes of corneal crystals are
associated with systemic conditions. Gammopathies are a group of
conditions caused by monoclonal proliferation of immunoglobulins.
Corneal crystals caused by monoclonal gammopathies have
been well described since 1934, most commonly associated with
multiple myeloma, as presented in a review of corneal involvement
because of systemic paraproteinemias. The crystals in gammopathies
range from subepithelial to stromal in location.
Another systemic condition that causes corneal crystals is cystinosis,
which is a metabolic disorder. This is a rare condition and occurs in
0.0005% of the population. Cystinosis is an autosomal recessive disorder,
and ocular signs appear after the age of 6. This disorder is due to
a defective transport of cystein out of lysosomes which causes intracellular
crystals to form.5 Ocularly, these present as needle shaped