Erythrocyte stearic to oleic acid ratio in patients with ocular melanoma.

The main characteristics of malignant cells include increased metabolism and capacity for division which are associated with high membrane fluidity. Membrane fluidity is in turn controlled by multiple factors which include the ratio of saturated to unsaturated fatty acids in the cell wall i.e. the Saturation Index (SI). The SI is known to be reduced in neoplastic cells as well as in the circulating erythrocytes of patients with some malignant tumours but not others. It has been suggested that the SI may be useful as a marker of malignancy.

Electrophoretic assessment of aqueous and serum neurone-specific enolase in retinoblastoma and ocular malignant melanoma.

The isoenzyme pattern of enolase was examined in the aqueous humour and serum of patients with retinoblastoma (10 aqueous, 8 sera), malignant melanoma (4 aqueous, 25 sera), and normal subjects undergoing cataract surgery (25 aqueous, 30 sera). The assay we used allowed assessment of all three major isoenzymes, including the gamma gamma isoenzyme (neurone-specific enolase). No enolase was detectable in normal aqueous; alpha alpha isoenzyme was present in the aqueous of one patient with malignant melanoma, while aqueous from all patients with retinoblastoma contained both alpha alpha and gamma gamma. Normal serum contained only an alpha alpha band, while serum from patients with retinoblastoma contained alpha alpha, alpha gamma, and gamma gamma bands (7 sera, 87.5%), or alpha alpha only (1 patient, 12.5%). All sera from patients with malignant melanoma contained the alpha alpha band, with low levels of gamma gamma in 16 (60%). In a single patient with Coats's disease alpha alpha was present in the serum, but no enolase was detected in aqueous. Increased amounts of gamma-containing isoenzymes of enolase are found in both serum and aqueous from patients with retinoblastoma. In malignant melanoma there is often an increase in serum gamma gamma enolase. The assessment of aqueous and serum enolase patterns may be of value in the diagnosis of retinoblastoma and malignant melanoma.

Lipid keratopathy and atheromatosis in an SPF laboratory rabbit colony attributable to diet.

Sporadic cases of corneal opacity occurred in an SPF rabbit colony fed on a diet containing 10% white fish-meal. Routine histological monitoring also revealed atheromatous lesions involving the intima of the aorta, coronary arteries and the arteries of other organs in 29 rabbits examined. Serum cholesterol levels above 10 mmol/l were found in 7 rabbits, including 4 affected with corneal lesions, which proved to be lipid keratopathy on histochemical and electron microscopical examination. The serum cholesterol level was found to be within normal range (below 2.27 mmol/l) in 10 rabbits reared entirely on a modified version of the diet, where the 10% fish-meal content was replaced with 10% grass-meal. No more ocular or atheromatous lesions have been found since the adoption of the new diet for the colony.

Familial lecithin:cholesterol acyltransferase deficiency. Biochemistry of the cornea.

Opacification of the cornea from lipid accumulation is an early and characteristic feature of familial lecithin:cholesterol acyltransferase (LCAT) deficiency. Visual impairment in a female age 48 years led to keratoplasty and the first detailed analysis of cornea in this disorder. Multilaminar figures were present, and total lipid extracts were enriched with phospholipid and cholesterol; cholesteryl esters were reduced, and accounted for about 12% of the cholesterol. Linoleate C18:2 was the predominant residue in the cholesteryl ester fatty acid fraction, with a C18:1/18:2 ratio of 1:6.5. This ratio differs from that in normal cornea, and from that in plasma and in other tissue deposits in LCAT deficiency. Various disorders of the HDL/LCAT system in plasma can lead to corneal lipid accumulation and opacification. These disorders may share general defects of lipid clearance from the cornea, but this study of LCAT cornea indicates that the character of the accumulating lipid is significantly influenced by active local metabolism, irrespective of the defect in the HDL/LCAT system also present.

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.

Problems with corneal arcus.

Corneal arcus presents many puzzling features. The correlation between its incidence and serum lipid levels is poor and, using immunoelectrophoresis, we have only been able to identify low-density lipoprotein inconsistently in corneae containing this deposition. Infrared thermography has shown us that arcus commences in the warmest regions of the cornea. We have considered the possible relevance of our biochemical and thermographic findings to other problems with corneal arcus such as its irreversibility, anatomical distribution, and clear zone.

Penetration of mercury from ophthalmic preservatives into the human eye.

Single corneas of nine patients about to undergo full-thickness corneal keratoplasty were exposed to thiomersal by application of a hydrophilic gel contact lens preserved with this mercurial agent. These lenses were removed at operation 4 h later, and the lenses, corneal buttons, and samples of aqueous were taken for determination of total mercury by wet digestion and flameless atomic absorption. The contact lenses contained little residual mercury, but mercury was readily detected in the corneal buttons and in the samples of aqueous over the range of 1--60 ng/ml. Five control samples of aqueous obtained without exposure to mercurial preservatives contained less than 1 ng/ml mercury. Although specific effects on ocular function are not described, the use of these preservatives is associated with penetration of mercury into the aqueous in concentration similar to those reported with systemic poisoning by organic mercurials.

Tear calcium levels and contact lens wear.

Hydrophilic contact lens spoliation can be associated with the deposition of calcium salts. The relationship between the concentration of calcium in tear fluid and contact lens use has been studied in healthy volunteers and in patients using various forms of hard and soft contact lenses, tear samples being collected with Schirmer strips and with lenses in situ. Methods are suggested for correcting data on calcium per strip to concentration when this cannot be directly determined. Further data were obtained by direct extraction of freshly removed soft contact lenses. The collected results indicate some variation in tear calcium concentrations, but values are unrelated to use of contact lens and type of lens fitted, and to the rates of tear flow with our procedures for collection. Local calcium concentrations are unlikely therefore to be a significant primary factor in soft contact lens spoliation, but the enlargement of the tear pool associated with the use of a soft contact lens does greatly increase the amount of calcium present, and this may be a factor in secondary deposition.