A Study of the Vascular Network of the Iris Using Flat Preparation

PURPOSE: This study was performed to examine the vascular network of the human iris using flat preparation. METHODS: The ciliary body-iris structures were separated from human eyeballs, and a portion of the irises were treated with trypsin to remove the pigment granules. These iris tissues were unfolded and placed onto glass slides using flat preparation, and the vascular network of each iris was examined by fluorescein microscopy. The ciliary body-iris structures separated from the remaining eyes were stained with hematoxylin-eosin without trypsin treatment and were examined by light microscopy. RESULTS: The long posterior ciliary artery formed several branches before entering the iris root, and such branches formed the major arterial circle of the iris with diverse diameters in the vicinity of the iris root and the ciliary process. In the pupillary margin, the iris vasculature network formed a cone shape and then formed an arcade by connecting to adjacent vasculatures. In the vicinity of the collarette, the iris vasculature network formed the minor arterial circle of the iris with diverse diameters perpendicular to the arcade of the iris network located in the pupillary margin. In the pupillary margin, the capillaries were somewhat thick and connected to the irregular traveling iris vein. CONCLUSIONS: The above findings explain the human iris vascular network and provide a theoretical basis for the sectoral filling of the iris vasculature seen in fluorescein iris angiography.

Transitional Zone of the Corneal Endothelium: Flat Preparation and Ultrastructural Findings

PURPOSE: To evaluate the morphological characteristics of the transitional zone between the corneal endothelium and the trabecular meshwork by flat preparation and electron microscopy. METHODS: The materials comprised 12 eyes examined by the flat preparation and 7 eyes by the electron microscopy. The specimens were derived from the transitional tissue between the corneal endothelium and the trabecular meshwork. The specimens in the flat preparation were stained with hematoxylin-eosin and examined by light microscopy. The specimens for scanning electronic microscopy (SEM) and in transmission electronic microscopy (TEM) were examined through routine processes. RESULTS: In the specimens examined by the flat preparation, unlike peripheral corneal endothelial cells, the endothelial cell nuclei in the transitional zone were overlapped and morphologically oval. On SEM, unlike typical hexagonality and tight interdigitation of corneal endothelial cells, the endothelial cells in the transitional zone were partially successive, spaced intercellularly, and morphologically irregular. On TEM, the endothelial cells in the transitional zone were partially successive. CONCLUSIONS: The loss of cell-cell contact of endothelial cells in the transitional zone may lead to the potential proliferation capacity of endothelial cells in the transitional zone under specific conditions. Therefore, further studies on the proliferation capacity of endothelial cells in the transitional zone are needed together with more research on cell biology.

Morphological Characteristics and Intercellular Connections of Corneal Keratocytes

PURPOSE: To investigate the morphological characteristics of keratocytes and the interconnection of keratocytes with adjacent keratocytes using the flat preparation method and scanning electron microscopy with a frontal section of the human corneal stroma. METHODS: The thin, corneal collagen lamellae were carefully dissected from the cornea (n=7), which had been stained by the flat preparation method. The remaining tissue was fixed in 3% glutaraldehyde and observed by transmission electron microscopy following the frontal section. RESULTS: The flat preparation revealed the corneal fibroblasts between the lamellae of the collagen fibers and showed that the ramifying cellular processes of the keratocytes were in contact with the cytoplasmic processes or cell bodies of neighboring fibroblasts. Two types of discrete subpopulations of keratocytes were identified: a smaller, cellular type of keratocyte with spindle-shaped nucleus with heterochromatin, and a larger, cellular type with a large indented nucleus with relatively scanty cytoplasm. Collagen fibers ran parallel to each other toward the fenestration of the cytoplasmic wall of the keratocyte. CONCLUSIONS: These flat preparation method results showed that the keratocytes within the corneal stroma are interconnected with the adjacent keratocytes, which indicates the presence of a functional communicating network through the keratocyte circuits within the stroma. A smaller, cellular type of keratocyte with spindle-shaped nucleus was morphologically differentiated from a larger, cellular type with a large, indented nucleus by flat preparation and transmission electron microscopy.

Histological Changes of the Vitreous and Retina in Retinal Lattice Degeneration

PURPOSE: To investigate of the histological characteristics of the lattice degeneration of the human peripheral retina. METHODS: The histological characteristics of the lattice degeneration of the retina was checked by flat preparation and serial section of the lattice lesion in three eyes was investigated by transmission electron microscopy. RESULTS: Flat preparation showed lattice lesion with a hole at the lateral margin with overlying sclerotic vessel and pigment clumping within the lesion. The ultrastructural initial findings showed that the collagen filament in the vitreous cavity was continuous with Muller fiber of the retina with the defect of the inner retina. The full-thikness defect of the sensory retina leaded to the retinal hole. The vascular wall was replaced and occluded by fine fibrillar collagen. The glial cell proliferated into the neural tissue of the sensory retina. These glial cells may secrete long spacing collagen (LSC) and curvilinear material shown at the area of the sensory retinal defect and near the vitreoretinal interface. CONCLUSIONS: These results suggest that the thinning of the retina occurs from the inner retina leading to retinal hole as the lattice degeneration progresses. LSC and curvilinear material are suggestive of derivatives derived from the extracellular material secreted from the glial cell.

Flat Preparation and Scanning Electron Microscopic Findings of Corneal Guttata

PURPOSE: The corneas obtained from 38 donor eyeballs were examined whether corneal guttata was present or not by flat preparation(15 eyeballs) and scanning electron microscopy(23 eyeballs) in order to investigate the relationship between age and the incidence of corneal guttata. METHODS: The corneal endothelial cells with Descemet's membrane were prepared on slides flat and examined by light microscope. The surface of the corneal endothelial cells was examined by scanning electron microscopy. RESULTS: The endothelial excrescences with pigment deposit were shown at the corneal periphery near the trabecular meshwork. The oval to round shaped corneal warts were isolated or confluent in shape. The corneal endothelial cells were variable in size. The cytoplasmic processes were observed on the surface of the bare Descemet's membrane. The fibrillar structure of the degenerating cytoplasm of the corneal endothelial cells over the corneal warts was shown with central pit. The fibrillar excrescences over Descemet's membrane was in banded structures. CONCLUSIONS: In normal cornea, corneal guttata was observed by flat preparation in all cases over 43 years. The endothelial edema was noted in two eyes combined with corneal guttata with the degeneration or loss of corneal endothelial cell.

The Cellular Characteristics of the Secondary Pupillary Membrane

PURPOSE: This study was performed to investigate the cellular characteristics of the secondary pupillary membrane. METHODS: The secondary pupillary membrane was removed from the anterior lens surface during cataract extraction from 2 patients with cataract associated with uveitis. Specimen from one patient was stained with hematoxylin-eosin with flat preparation method. Specimen from the other patient cultured for 1 and 2 weeks was observed with transmission electron microscopy. RESULTS: The flat preparation showed the neovascular membrane with pigment-laden cells. The cultured cells consisted of the well preserved vascular components which had the vascular endothelial cells and pericyte and pigment-laden cells lined by basement membrane on first week of culture. The iris pigment epithelial cell which contained the pigment granules within cytoplasm and lined by basement membrane were observed on second week of culture. CONCLUSIONS: These results suggest that the secondary pupillary membrane consists of vascular membrane and pigment epithelial cell of iris which is a major component of secondary pupillary membrane and secrets extracellular matrix.