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Light-scattering technique may pinpoint protein changes, early cataract risk
Arch Ophthalmol. 2008;126(12):1687-1693.
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A noninvasive imaging technique detected early protein changes associated with lens opacity and potential cataract in a National Eye Institute-NASA clinical trial.
Dynamic light scattering (DLS) identified decreases in alpha-crystallin, a protein that maintains lens transparency by preventing damaged lens proteins from binding and forming cataracts, the study authors said.
"Clinical detection of pre-cataractous lens damage in clinically clear lenses and identification of patients at high risk for cataracts would be useful for many reasons," they said. Early detection may provide ample warning and allow patients to minimize factors such as smoking and alcohol consumption.
The compact fiber-optic probe was based on a DLS device used to study the growth of protein crystals in space, according to a press release from the NEI and NASA.
The clinical trial included 380 eyes of 235 patients ranging in age from 7 years to 83 years with nuclear lens opacity grades of 0 (clear) to 3.8 (opaque). The primary outcome measure was the alpha-crystallin index (ACI), a measurement of unbound alpha-crystallin based on DLS testing.
Data showed a significant correlation between increased lens opacity grade and decreased ACI (P < .001). Mean ACI values decreased with age, even in clear lenses. The mean ACI in subjects younger than 22 years with clear lenses was 31%; the mean ACI in eyes with opacity grades of 2 or higher was 2%. DLS detected early protein changes even in clinically clear lenses with no visible signs of opacity, the authors said.
This study confirms that cataract formation (specifically nuclear sclerosis in this case) is a process that probably starts at birth. It has been apparent that the earliest known optically important changes in nuclear sclerosis is the formation of multilamellar bodies that create light scatter and are clinically noticed as glare even with excellent visual acuity. Tom Vandenberg has shown that light scattering is directly related to aging because of this phenomenon, and the present study shows that the loss of alpha-crystallin over time represents the loss of a key lens repair mechanism to help maintain clarity.
Tom Vandenberg invented the C-Quant as a clinical means of measuring light scatter in patients, and this could become an important and more objective tool to document clinical progression. It tells us much the same information as the study set-up, which I think will be used mainly for research and in clinical studies of proposed pharmaceutical treatments of nuclear sclerosis (yes, there are some proposed treatments out there). Both clinical instruments will better quantify glare, is my best guess, probably with similar findings. Might light scatter become a standard clinical measure of nuclear sclerosis? Possibly, but this will not supplant the need for clear clinical correlation and patient subjective symptomatic response to the cataract process in any decision for surgery.
– Randall J. Olson, MD
OSN Cataract Surgery Board Member