A compact fiber-optic probe has been found to be useful for noncontact diagnosis of interior parts of eyes. The probe was originally developed for performing dynamic-light-scattering measurements to determine transport properties of submicron particles suspended in fluids in microgravity, and is an improved version of the probes described in "Dynamic Light Scattering With Improved Fiber-Optic Probes (LEW-15461)" NASA Tech Briefs, Vol. 19, No. 9 (September 1995), page 86.

The probe (see figure) includes a probe head that holds two monomode optical fibers, of which one carries light with a power of a few microwatts from a laser diode to illuminate the region to be probed. The other optical fiber carries light scattered from the probed region to an avalanche photodiode (APD) for detection. The tips of the optical fibers in the probe head are aligned with an off-axis gradient-index-of-refraction (GRIN) lens, which is positioned with a gap of up to 0.5 mm from the fiber tips to obtain a tightly focused spot in the probed region.

The Probe Makes No Contact with the eye. Dynamic light-scattering measurements taken with the probe yield information on submicron particles inside the eye.

In operation, the probe is positioned in front of an eye to illuminate the interior and measure light back-scattered from submicron particles in the interior. Because of Brownian motion of the particles, the back-scattered light forms a rapidly changing interference pattern (dynamic light scattering) that manifests itself as fluctuations in the output of the APD. Information about the sizes of particles and other aspects of the dynamics of the scattering medium can be extracted by processing the output of the APD through an amplifier/discriminator and a digital correlator to obtain a correlation function.

The correlation function gives information about the particles in the scattering volume. This information is useful for research and diagnosis of eye diseases and other diseases with ocular manifestations. For example:

  • Cholesterol and blood-sugar molecules occur in the aqueous humors of patients with heart-related diseases and diabetes, respectively.
  • Protein crystallines and possibly other particles in the lens have been conjectured to play a role in cataractogenesis. Research is needed to establish the exact causes of cataracts and to develop techniques for early diagnosis and treatment.
  • Changes in macromolecules in the vitreous humor can be used to identify diseases of the posterior chamber of the eye and complications of those diseases; e.g., posterior vitreous detachment and diabetic retinopathy.

Thus, further development along this line holds promise for compact fiber-optic probes as clinical ophthalmic instruments for routine use.

This work was done by Rafat R. Ansari and Kwang I. Suh of Lewis Research Center. For further information,access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Life Sciences category, or circle no. 128 on the TSP Order Card in this issue to receive a copy by mail ($5 charge).

Inquiries concerning rights for the commercial use of this invention should be addressed to

NASA Lewis Research Center
Commercial Technology Office
Attn: Tech Brief Patent Status
Mail Stop 7-3
21000 Brookpark Road
Cleveland
Ohio 44135.

Refer to LEW-16429.

NASA Tech Briefs Magazine

This article first appeared in the February, 1998 issue of NASA Tech Briefs Magazine.

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