Regulation of the mechanical properties of tree shrew sclera by the visual environment.

Experiments in several species have shown that the axial elongation rate of the developing eye can be increased or decreased by manipulating the visual environment, indicating that a visually guided emmetropization mechanism controls the enlargement of the vertebrate eye during postnatal development. Previous studies in tree shrews (Tupaia glis belangeri) suggest that regulation of the mechanical properties of the sclera may be an important part of the mechanism that controls the axial elongation rate in this mammal. To learn whether the mechanical properties of the sclera change when the axial elongation rate is increased or decreased under visual control, uniaxial mechanical tests were performed on 3-mm wide strips of tree shrew sclera.

The effect of osmolality on the shedding rate of the corneal epithelium.

It has been stated that in dry eye hyperosmolality damages the epithelium of the ocular surface by increasing the rate at which cells are shed. To test this hypothesis, paired excised rabbit corneas were superfused with balanced salt solutions in which all conditions were held constant except the osmolality in contact with the epithelium. For a period of 400 min the epithelium of one of the corneas was exposed to one of seven test osmolalities (200-425 mOsm/kg), whereas the other cornea was used as a control (305 mOsm/kg).

Levels of crystallin fragments and identification of their origin in water soluble high molecular weight (HMW) proteins of human lenses.

Purpose: The aims of this study were to determine in the human lens water soluble-high molecular weight (WS-HMW)-proteins: (a) the levels of degraded polypeptides (crystallin fragments), and (b) the in vivo cleavage sites in the parent crystallins to produce the major fragments.

Methods: The WS-HMW proteins (Mr > 15 x 10(6) daltons) were isolated as a void volume peak from homogenates of lenses of donors of different ages using Agarose A 15m gel-filtration chromatography. The degraded polypeptides (Mr < 18 kDa), present in the WS-HMW proteins, were separated by a preparative SDS-PAGE method and quantified as a percent of total WS-HMW proteins.

Corneal epithelial fluorescein staining.

Background: There is some difference of opinion in the literature about the nature of fluorescein staining of the epithelial surface. Most authors support the view that fluorescein staining is due to drop out of cells and pooling of fluorescein in the footprint. Others believe that fluorescein fills intercellular spaces.

Animal models of emmetropization: matching axial length to the focal plane.

Background: It has long been recognized that more people are emmetropic than would be expected from a random combination of the refractive and axial components of the eye. However, it has been difficult to determine whether this is the result of an active emmetropization mechanism.

Methods: This paper reviews some of the studies in animals that have been conducted during the past 20 years.

Reduced extracellular matrix in mammalian sclera with induced myopia.

The purpose of this study was to learn whether visual form deprivation, which produces myopia in the deprived eye, alters the scleral extracellular matrix in tree shrew, a mammal closely related to primates. Axial myopia was induced in 10 tree shrews by monocular deprivation imposed with a translucent diffuser. The other eye in each animal was an untreated control.

The effect of hypoxia on the shedding rate of the corneal epithelium.

The reason a cell leaves the corneal epithelial surface at a particular time is not understood. It is likely that a cell must depend on metabolic energy to accomplish this task successfully and with minimal disruption to the epithelial surface and barrier. The hypothesis under test is that the epithelium is directly dependent on atmospheric oxygen to maintain a normal cell shedding rate.

Covalent modification at the C-terminal end of a 9 kDa gamma D-crystallin fragment in human lenses.

The presence of a 9-kDa gamma D-crystallin fragment among water-soluble (WS) and water-insoluble (WI) proteins of human lenses was investigated using individual site specific antibodies to the N- and C-terminal regions of the molecule. The polyclonal antibodies were raised against nonapeptides corresponding to the N- and C-terminal ends and are referred to as anti-9-kDa-N and anti-9-kDa-C antibodies respectively. On Western blot analysis of WS and WI proteins from lenses of donors of different ages, the WS9-kDa species showed immunoreactivity to both the anti-9-kDa-N and anti-9-kDa-C antibodies whereas WI 9 kDa species showed immunoreactivity to only the anti-9-kDa-N antibody.

Lid-suture myopia in tree shrews with retinal ganglion cell blockade.

To determine whether central communication of retinal signals is necessary for the development of an experimentally induced myopia, tree shrews were exposed to monocular deprivation (MD) while the action potentials of retinal cells in the deprived eye were blocked with intravitreally injected tetrodotoxin (TTX-MD animals). TTX injections (0.6 microgram in 3 microL) and MD began about 15 days after eye opening, at the start of the susceptible period for the development of lid-suture myopia.