Comparison of specific blue and green fluorescence in cataractous versus normal human lens fractions

The authors compared the specific green and blue fluorescence levels in soluble and insoluble fractions (cortical and nuclear) extracted from cataractous lenses with those corresponding to clear lenses and tried to establish the nature of the role of extrinsic fluorophores in cataractogenesis.

Laser-induced fluorescence was measured with an optical-fiber sensor. The specific fluorescence was evaluated as the ratio of the fluorescence intensity to the protein concentration. Four brunescent, three pure nuclear, and four mixed nuclear-subcapsular cataractous lenses were investigated.

Specific blue fluorescence levels in cataractous fractions were similar to those in clear lens fractions, except for the insoluble nuclear fractions in which the levels were slightly lower. The specific green fluorescence in the soluble cataractous fractions showed marked increases compared with the clear lens fractions of similar ages. The insoluble cataractous fractions had similar (cortical fractions) or slightly lower (nuclear fractions) specific green fluorescence levels compared with the normal lens fractions.

The similarity in blue fluorescence levels suggests that the blue fluorophore(s), although increasing in concentration with age, are not indicators of cataractogenesis and may not play an active role in opacification. The levels of specific green fluorescence indicate either a dramatic increase in the fluorescence quantum efficiency and/or an increase in the number of fluorescent sites per protein unit. The green-to-blue ratios were greater by a factor of as much as six in all cataractous soluble fractions versus clear ones. This suggests an accelerated formation of the green fluorescent species in cataractous tissues.