Tryptophan fluorescence enables earlier cataract diagnosis

Compiled by BioPhotonics staff

A widely used method of monitoring protein changes in biophysical research could become a clinically useful tool sensitive enough to diagnose cataracts before significant damage, light scattering, aggregation and visual impairment occur.

Cataracts are the leading cause of blindness worldwide, affecting 17 million people and resulting in 1.3 million operations annually in the US alone, according to the World Health Organization.

Researchers at Edinburgh Instruments (EI), NHS Princess Alexandra Eye Pavilion and Heriot-Watt University have explored the possibility of early cataract detection by using tryptophan fluorescence, which can detect protein folding, conformation and aggregation by virtue of shifts in the emission spectrum in different polar microenvironments.

Experiments with artificially created cataract lenses from pigs’ eyes – made by means of ultraviolet radiation – have shown that tryptophan fluorescence offers a sensitive method for monitoring very early changes in the lens structure that cannot be detected by the standard slit-lamp method. Spectral measurements were taken using an EI FLS920 spectrometer in a temperature-controlled 1-cm quartz cuvette in phosphate buffer solution at 22 °C, retaining uniform tissue viability over 16 hours.

Current methods for cataract detection are based on subjective observation of lens opacity by Rayleigh light scattering. This method does not provide the protein-level detail offered by tryptophan fluorescence, however, because of limitations of the scattering techniques, so it cannot reveal structural changes on a molecular level.

The new technique could help researchers establish the point at which the irreversible crystalline protein change that triggers the need for surgical intervention occurs. Clinical application of the method also will help in diagnosing early stages of metabolic disorders, such as diabetes, and in deciding on preventive treatment.

The study was published in the March 31, 2011, issue of the Journal of the Royal Society Interface (doi:10.1098/ rsif.2010.0608).