Near Infrared Light Transmission of In Vitro Porcine Opaque Corneas

Abstract

Abstract: : Purpose: Dense opacities of the cornea are successfully treated by corneal transplantation. However, under certain circumstances, even repeated corneal transplantation fail. In these cases an artificial keratoprosthesis is considered. A German research consortium was set up in March 1999 to develop a concept named Intraocular Vision Aid (IOVA) to restore sight to those with an opaque or blurred cornea. The blind patient wears a tiny CMOS camera integrated into a spectacle frame. The detected images are processed digitally and then sent optically to the intraocular LED microdisplay. The display is implanted into the capsular bag of the removed natural lens and projects the replicated images onto the healthy retina (see: Alteheld, ARVO 2002). In order to determine a suitable wavelength for transmitting the data set through the opaque cornea, transmission spectras of artificially blurred corneas have been analyzed. Methods: An optical transmission measurement system was set up, basically consisting of a white light source, a monochromator, a photo detector, a lock-in amplifier, and a connected computer. Porcine corneas were excised by a trepan from recently enucleated eyes obtained from the slaughterhouse. Blurring was achieved by immersing the corneas into sulfuric acid (H₂S0₄), hydrochloric acid (HCL) and potassium hydroxide lye (KOH) for 90 seconds. Results: A whitish scattering occurred, reducing transparency to an estimated visual acuity of hand movements. The opaque porcine cornea showed a total transparency of below 3 percent. The absorption quotient was calculated. The computer chip is designed in standard CMOS technology. For realization an Optoelectronic Integrated Circuit (OEIC) is desired, which means the integration of all optoelectronic and electric components on one silicon substrate. The spectrum of absorption of silicon is up to a wavelength of 1000nm. Conclusions: With these tests suitable wavelengths could be found in a range from 800 nm to 1000 nm, which is in the range of commercially available silicon photo-diodes (850nm). Despite a total transmission of below 3% in the considered near infrared range a reliable detection could be observed. In cooperation with the IoVA group, sponsored by DFG He 840/8-1

Keywords: cornea: basic science • optical properties