Corneal changes in the dislipoproteinaemias.

The corneal changes in the hyper- and hypoproteinaemias may affect vision and/or provide a diagnostic clue to a systemic disorder. This article describes the structure and function of the major lipoprotein classes and the means by which dietary lipid is absorbed and by which exogenous and endogenous lipid is distributed to and cleared from the tissues. In hyper-beta-lipoproteinaemia, lipid arcus formation may be related to the duration and height of the raised cholesterol levels. The peripheral location of the lipid deposit is presumed to be related to peripheral trapping of low-density lipoprotein (LDL) by glycosaminoglycan binding and tight stromal packing with maintained central clearing by high-density lipoprotein (HDL), whose smaller molecular diameter should allow freer stromal diffusion. In the hypolipoproteinaemias, e.g., Tangier disease, generalised (alpha and beta) lecithin cholesterol acyltransferase (LCAT) deficiency, and alpha-LCAT deficiency (fish-eye disease), the absence or abnormality of HDL may impair clearance of endogenous and possibly exogenous stromal lipid. The hyperlipoproteinaemia that sometimes accompanies Schnyder's crystalline corneal dystrophy is thought to modify the effects of a primary failure of corneal stromal lipid metabolism.