Fiberoptic probe detects eye diseases

A diagnostic probe for detecting early symptoms of cataracts and other eye diseases has been developed by Rafat Ansari, project scientist at NASA`s Lewis Research Center (Cleveland, OH). Ansari and postdoctoral student Kwang Suh designed a single-angle fiberoptic device that both characterizes crystalline agglomeration in the lens of the eye and creates a three-dimensional (3-D) map of the lens. The probe was originally developed for studying the growth phenomena of protein crystals in space, Ansari says.

Probe design

The probe is based on quasi-elastic light scattering (or dynamic light scattering), which is routinely used for studying submicron particle dispersions and typically requires a laboratory-sized room for all the equipment used in such measurements. Dynamic light scattering involves suspending particles in a fluid medium. A laser beam interacts with the Brownian motion of the particles causing them to react in a Doppler broadening motion. The scattering intensity fluctuates in time. From these fluctuations, a time-autocorrelation function is constructed, from which the diffusion coefficient of the scattering particles is determined. The particle size and size distribution is then calculated from this diffusion data if the viscosity, the refractive index of the host fluid, and temperature of the experiment is known.

Using fiberoptic cable and advances in optoelectronic devices such as miniaturized lasers and photodetectors, Ansari and Suh designed a single-angle single-mode fiberoptic device with a diameter less than 1 cm and a length less than 1.3 cm. A fiberoptic receiver collects the scattered light and carries it to a photodetector, which amplifies the signal and transforms it into electronic signals. These are sent to a laptop computer programmed to compute the particle size from the data.

Transferring knowledge

When his father contracted cataracts, Ansari and associates experimented with using the probe to analyze this problem as well. The eye is 65% water and 35% protein, which is the highest concentration of protein in the human body. The lens is also the only component in the body in which protein is so well arranged and is transparent.

When cataracts form, there is no medical treatment, except for surgical removal of the lens. More than 1.4 million Americans undergo this procedure annually, and 50 million people develop cataracts worldwide.

The light-scattering probe characterizes particles from one nanometer to a few microns in size. The probe also has the capacity to visualize macro particles (a few microns to a few millimeters) via a miniature microscope built into the device.

The lens of the human eye is the size of an aspirin tablet. The probe can detect tiny clusters or clumps of protein crystallines before they form into an obstruction, allowing time for pretreatment of the condition. When analyzing the eye, a laser emitting at 670 nm was used. A relatively low output power (50 µW) ensured no harm came to the eye. Each measurement was taken between 5 and 10 seconds.

"We can also do a 3-D analysis with the same probe creating a `mammogram` of the lens, or what I call a cataract-o-gram," says Ansari. NASA is collaborating with the National Institutes of Health, through the National Eye Institute (both Bethesda, MD), on further experiments testing the probe with other diseases of the eye as well as with diabetes-related problems.