Device converts movement to measurement

Issue: August 25, 2016

Dynamic light scattering may be used to determine whether age-related nuclear cataracts are associated with loss of a critical protein in the crystalline lens.

In one study, the authors set out to corroborate a previous cross-sectional study showing that higher levels of unbound alpha-crystallin, a lens molecular chaperone protein, are associated with a reduced risk of cataract formation and that lower levels are associated with cataract formation and progression.

“What this implies is that since we are born with a fixed amount of alpha-crystallin, when we lose our supply, then we’re almost doomed to develop a cataract. So, we have to find a way to preserve this alpha-crystallin to prevent a cataract from developing,” Manuel B. Datiles III, MD, the corresponding author, said.

The dynamic light scattering (DLS) cataract detection device, designed by Rafat R. Ansari, PhD, of NASA, works on the principle of Brownian movement, the random motion of small particles suspended in a liquid or gas.

“When you shine a light on a viscous solution or just a plain solution, it’s almost like when you shine a light at night with a flashlight — you would see the dust particles moving about (Tyndall effect),” Datiles said. “The large particles move slowly while small particles move fast, so physicists have figured out a way to convert this Brownian movement into measurement of the size of the particles.”

The authors used the NASA-National Eye Institute DLS cataract device to estimate the unbound alpha-crystallin index (ACI) in the lens nucleus. They hypothesized that in vivo estimation of the ACI with the DLS device may be used to measure lens opacity risk of nuclear cataract in clinical studies in which cataract development may be influenced — caused or prevented — by a drug or device.

“This device, we found, could measure certain substances in the patient’s eyes in vivo. These lens proteins could never be measured before unless you ground up the lens and looked at it in the lab,” Datiles said.

Crystallins are clear proteins that allow the lens to focus light.

“The alpha-crystallin protein, we found out, has special properties that stabilize UV light- and oxidation-damaged lens proteins and thus prevent clouding that leads to cataract formation. These alphas are really key to studying the cause and formation of nuclear cataract, which is the most common age-related cataract in the world,” Datiles said.

In a study published in 2008 in Archives of Ophthalmology, Datiles and colleagues showed that nuclear cataracts developed as alpha-crystallin levels decreased.

The current longitudinal study, conducted in close collaboration with Walter Stark, MD,previous director of cataract and corneal diseases of the Wilmer Eye Institute of Johns Hopkins Hospital, was published in Ophthalmology. It included 66 eyes of 45 patients between the ages of 34 years and 79 years with nuclear lens grades of 0 to 3. Every 6 months, patients underwent a comprehensive dilated eye examination that included slit lamp grading of lens opacity using the Age-Related Eye Disease Study grading system. Mean follow-up was 19 months.

The DLS device was used to examine the lens for about 5 seconds, Datiles said.

Cataract progression was most rapid in lenses with the lowest baseline ACI. Progression was slower or non-existent in lenses with a higher baseline ACI. Higher rates of alpha-crystallin loss were associated with more rapid cataract progression than lower rates. – by Matt Hasson

References:
Datiles MB, et al. Arch Ophthalmol. 2008;doi:10.1001/archophthalmol.2008.507.
Datiles MB, et al. Ophthalmology. 2016;doi:10.1016/j.ophtha.2015.10.007.

For more information:
Manuel B. Datiles III, MD, can be reached at the Office of the Clinical Director, National Eye Institute, National Institutes of Health, 10 Center Drive, Building 10, Room 10N226, Bethesda, MD 20892-1860; email: datilesm@nei.nih.gov.

Disclosure: Datiles reports no relevant financial disclosures.