Significance of corneal arcus.

The corneal arcus consists of cholesterol, phospholipids and triglycerides. As serum triglyceride is one of the accurate of lipid metabolic state, greater importance was given, and it was found to be elevated in 72% of patients and a positive correlation with increasing age. This suggests a strong correlation between impairment of lipid metabolism and incidence of corneal arcus.

Corneal arcus or arcus senilis is deposition of lipid in the peripheral cornea and is generally considered a concomitant of normal ageing process and expected in the elderly patient. However, there are controversial reports regarding the association of lipid metabolism. We conducted a study at our institute to find out whether corneal arcus is an indicator of deranged lipid metabolism or only a consequence of normal ageing process.

Materials and Methods

Five hundred people above the age of 40 were screened for corneal arcus and were studied with regards to age, sex, diet habits, thickening of peripheral arteries (fundus examination), blood pressure and associated cataract and fundus pathology.

Fifty cases of dense corneal arcus were taken for blood analysis and followed tests were done. Blood sugar, urea, cholesterol, triglycerides, total lipids, and serum glutamic-oxaloacetic transaminase (SGOT).

Observation

Only 225 out of the 500 screened had corneal arcus (45%).

A distinct increase in the incidence of corneal arcus with age can be observed and more so above the age of 60 [Table 1].

Table 1

Age incidence

The above table shows that there was no correlation between corneal arcus with thickening of peripheral arteries, high diastolic pressure, and cataract or with exudates or sheathing in the fundus.

Blood sugar and blood urea were within normal limits in all 50 cases taken for blood analysis.

Serum cholesterol was above 250 mg/dl only 6% of the total cases.

A progressive increase in triglyceride levels with age was observed.

Only 12% had a raised blood lipid. Females had a higher level when compared to males.

Discussion

The corneal arcus consists of cholesterol, phospholipids and triglycerides. Tissue necrosis and atrophy are not present, and the entire process appears to be a deposition of lipid substances from the blood stream. Lipids are found extracellularly in the corneal stroma in an hourglass pattern.[1]

Of the 500 people screened only 45% had corneal arcus [Table 2]. Waltens had reported a 60% incidence in his study in the age group between 40 and 60 years whereas in our study the incidence was only 36%.[2] However, the presence of arcus was noted in 70% of patients above 60 years of age. The probable reason is the increased permeability of limbal vessels with age allowing low-density lipoproteins to pass through the cornea. There was no correlation between the thickening of the peripheral arteries or increased diastolic blood pressure with the incidence of arcus.[3] Thirty-nine percent of patients had associated cataract that was comparable to the control group which had 37% [Table 3].

Table 2

Sex incidence

Table 3

Correlation of associated factors in corneal arcus

Fifty patients with dense arcus where subjected to blood analysis and all of them had normal blood sugar and urea. Serum cholesterol was raised in only 6% of patients although up to 25% have been reported in the past [Table 4].

Table 4

Serum cholesterol level in relation to sex

As serum triglyceride is one of the accurate of lipid metabolic state, greater importance was given, and it was found to be elevated in 72% of patients and a positive correlation with increasing age [Table 5].[4]

Table 5

Serum triglyceride level in relation to age group

The amount of lipid that accumulate in the arterial wall is closely related to the serum lipid level and was found to be >500 mg/dl in only 12% of cases [Table 6]. Elevated SGOT levels were seen in 26% of the patients [Table 7].

Table 6

Serum lipid level and sex

Table 7

Serum glutamic-oxaloacetic transaminase level and age group

The correlation between the latter and the degree of corneal arcus was found to be poor. The thickening of peripheral arteries and sheathing of blood vessels closely follow total lipid level which was not found to be significant in patients with and without corneal arcus.

Conclusion

Corneal arcus was present only in 45% of the total 500 patients screened over 40 years of age. However it was present in >70% of cases over 60. Absence of corneal arcus in many geriatric patients and its presence in some individuals during third and fourth decade and no correlation with the incidence of cataract appears that it is associated with abnormal lipid metabolism. Fasting serum triglyceride, one of the accurate indices of functional status of lipid metabolism was raised in 72% of cases suggesting a strong correlation between impairment of lipid metabolism and incidence of corneal arcus.