To make specimens for the biological materials, especially the retina and palpebral conjunctiva, and to detect the elements and organic substances.

Twelve-week-old male Wistar Kyoto rats were used. Immediately after the eyes were enucleated under pentobarbital anesthesia, the eyeballs and eyelids were put into liquid nitrogen without any fixation and covered by O.C.T. compound (TISSUE-TEK, Miles Inc.). Semi-thin sections (5 μm) were cut with a cryomicrotome at −30 °C (Zeiss, Germany). Sections of the retina and palpebral conjunctiva were placed on siliconwafer plates 10 × 7 × 1 mm and air-dried for 30 min or freeze-dried for 8 hrs. A metal microscope (Leica- DMRBE) was used to confirm the morphological features of the unstained conjunctiva and retina on the siliconwafer plate prior to analysis with a TOF-SIMS microscope. Without coating, the specimens were examined with a TOF-SIMS microscope (TRIFID) (Physical Electronics, USA). Positive and negative ion images were examined with a Ga+ source at an acceleration voltage of 15 kV. Secondary ion acceleration voltage of 4.5 keV was used. The amount of trace elements was analyzed by Wincadence (Physical Electronics, USA) software.