[Corneal arcus and hyperlipoproteinemia (author's transl)]

Correlating corneal arcus with atherosclerosis in familial hypercholesterolemia

BACKGROUND

A relationship between corneal arcus and atherosclerosis has long been suspected but is controversial. The homozygous familial hypercholesterolemia patients in this study present a unique opportunity to assess this issue. They have both advanced atherosclerosis and corneal arcus.

METHODS

This is a cross-sectional study of 17 patients homozygous for familial hypercholesterolemia presenting to the Clinical Center of the National Institutes of Health. Plasma lipoproteins, circumferential extent of arcus, thoracic aorta and coronary calcific atherosclerosis score, and Achilles tendon width were measured at the National Institutes of Health.

RESULTS

Patients with corneal arcus had higher scores for calcific atherosclerosis (mean 2865 compared to 412), cholesterol-year score (mean 11830 mg-yr/dl compared to 5707 mg-yr/dl), and Achilles tendon width (mean 2.54 cm compared to 1.41 cm) than those without. Corneal arcus and Achilles tendon width were strongly correlated and predictive of each other. Although corneal arcus was correlated with calcific atherosclerosis (r = 0.67; p = 0.004), it was not as highly correlated as was the Achilles tendon width (r = 0.855; p < 0.001).

CONCLUSION

Corneal arcus reflects widespread tissue lipid deposition and is correlated with both calcific atherosclerosis and xanthomatosis in these patients. Patients with more severe arcus tend to have more severe calcific atherosclerosis. Corneal arcus is not as good an indicator of calcific atherosclerosis as Achilles tendon thickness, but its presence suggests increased atherosclerosis in these hypercholesterolemic patients.

Ocular lipid deposition and hyperlipoproteinaemia

In all species there are potential ocular manifestations when circulating lipoproteins are raised and these may be transient or permanent Many factors, both systemic and local, influence lipid influx and accumulation (progression) and lipid mobilisation and efflux (regression). In both humans and animals some types of lipid deposition will regress if the local and systemic factors involved in pathogenesis can be modified. There are inescapable parallels with the same phenomena in other tissues.Three types of corneal lipid deposition have been linked with hyperlipoproteinaemia. In corneal arcus, lipid is deposited preferentially in the warmest part of the cornea initially and, in people, the lipid remains almost exclusively extracellular. In animals, corneal arcus is associated with initial extracellular lipid deposition followed by the appearance of intracellular lipid and vascularisation, so that established corneal arcus tends to become more typical of lipid keratopathy. In humans, hyperlipoproteinaemia may be an associated systemic factor and early onset corneal arcus is a recognised feature of certain primary hyperlipoproteinaemias and their secondary phenotypes. In dogs, corneal arcus is always associated with hyperlipoproteinaemia. Corneal vascularisation is a ubiquitous feature of lipid keratopathy in all species and both necrotic fibroblasts and foam cells are common in progressive lesions. The extent and position of lipid deposition and the evolution of lipid keratopathy can be related to local ocular disease and circulating lipids and lipoproteins. Many aspects of the pathogenesis of lipid keratopathy are similar to those of atherogenesis. Hyperlipoproteinaemia, especially hypercholesterolaemia is the commonest systemic abnormality. In crystalline stromal dystrophy (Schnyder's crystalline stromal dystrophy) of the cornea there is no inflammatory element and no vascularisation. The dystrophy is associated with accumulation of lipid within the corneal fibroblasts, but typical foam cells are absent, the crystalline opacity involves the coolest part of the cornea, correlates with local fibroblast death, and is always bilateral. Hyperlipoproteinaemia, may be present, but this is not universally so.The objective of this paper is to evaluate the factors that may influence ocular involvement in hyperlipoproteinaemia. A comparative approach, utilising information available from studies of both ocular and non-ocular tissues, aids elucidation of the complex pathogenesis.

Relationship between corneal arcus and hyperlipidaemia is clarified by studies in familial hypercholesterolaemia

In subjects with familial hypercholesterolaemia for whom integrated exposure to hyperlipoproteinaemia can be determined, arcus development correlates with age rather than extent or pattern of hyperlipoproteinaemia. This permissive effect whereby arcus development becomes progressively time-dependent rather than dose-dependent at increasing levels of hyperlipoproteinaemia may underlie difficulties in the interpretation of premature corneal arcus in less specific disorders. Arcus development is not apparently influenced by levels of high-density lipoprotein in plasma.

Lipid-protein constituents of human corneal arcus

Extracts of fresh senile human peripheral cornea with varying degrees of arcus were prepared by soaking minced tissue in buffered saline/EDTA. Apolipoprotein B was, at most, an occasional feature of these extracts; interactions involving glycosaminoglycans were not evident; and the lipid composition, particularly of the cholesterol ester fraction, was also not consistent with a recent origin from plasma components and particularly form low density lipoprotein. Assuming this origin, substantial secondary changes must follow insudation, involving protein loss and lipid reesterification, as is described for lipid deposits forming intracellularly at other sites. The manner of these changes in deposit forming extracellularly in the avascular peripheral cornea is not clear.

Presenile corneal arcus in healthy persons. A possible cardiovascular risk indicator in younger adults

The results of blood-lipid screening of 200 39--49-year-old participants with incidentally diagnosed corneal arcus from the Copenhagen City Heart Study are reported. A large sample of study-participants of the same age-group without arcus served as controls. In general, the arcus-group had higher se.-cholesterol than the control-group (P less than 0.01 in males and less than 0.02 in females). The se.-triglycerides in the two groups did not differ. A trend towards positive correlation between arcus-intensity and cholesterol-level was demonstrated by non-parametrical statistics. By use of the same statistics, an association between lipids and arcus-localisation was searched out. Dense arcus in the nasal/lower limbal regions occurred together with hypercholesterolemia more often than did a marked upper/outer arcus. Consequently, based on the present investigation, se.-cholesterol-screening of middle-aged persons with marked lower/nasal arcus seems justified, since hypercholesterolemia might will be an underlying cause. Finally, the importance of diagnosing and treating hypercholesterolemia is briefly discussed.

Spontaneous rupture of the Achilles tendon - a sign of hyperlipoproteinaemia (HLP) type II

In biopsies from spontaneously ruptured Achilles tendons a serum lipid and lipoprotein analysis was performed in fifty nine patients. In nine males considerable histological signs of lipid deposition were detectable. The tendon fibers were found to be partly desintegrated. Only in these cases LDL-cholesterol values were found to exceed the normal range indicative of type II hyperlipoproteinaemia (HLP). None of the fifty remaining patients presented biochemical or clinical signs of disorders of lipid metabolism. The observations demonstrate that a spontaneous rupture of Achilles tendom may indicate a primary type II HLP.