Specimen preparation for quantitative microradiography

Wound healing response in the presence of stromal irregularities after excimer laser treatment

PURPOSE

To trace the fate of stromal irregularities after excimer laser treatment and to increase our knowledge of the reasons why surface irregularities in the ablation bed cause inferior postoperative results.

METHODS

Twelve New Zealand White rabbits received a transepithelial photoablation to a preset depth of 60 microm. An electron microscopy specimen grid was then placed on the denuded stroma and another 20 microm ablation was applied in order to produce surface irregularities. Another six rabbits received a plano transepithelial photoablation to a preset depth of 80 microm. The treated corneas were harvested at various timepoints and differentially further processed for microradiography, hematoxylin-eosin -, hyaluronan (HA)- and leukocyte protein L1 staining.

RESULTS

In the grid treated corneas the subepithelial mesh pattern is clearly discernible after 1 week, and after 4 weeks it is replaced by a subepithelial layer containing HA and water. The thinning of this layer between 1 and 12 weeks is statistically significant (p<0.05). After 4 and 8 week the plano treated corneas only exhibit some subepithelial HA- and water accumulation. After 1 day the grid treated corneas show an extensive stromal infiltration of leukocytes. In the plano treated corneas the leukocytes mainly remain on the surface.

CONCLUSIONS

During the healing process stromal irregularities are flattened, leaving a homogeneous zone with increased water content. This subepithelial layer is rarefying as new subepithelial tissue is forming. Postablational irregularities induce a more pronounced healing reaction when compared to a smooth ablation surface. Leukocyte infiltration seems to play a role in this process.

Age-related changes in local water and protein content of human eye lenses measured by Raman microspectroscopy

The Raman microspectroscopic method was used to determine the local water and protein content in human lenses. In 18 lenses of varying age position-defined water/protein content measurements were carried out along the visual and the equatorial axis. A main characteristic of the human lens is its constant and relatively low protein content. In addition this constant nuclear value is reached within a short distance from the capsular surface. For statistical analysis of age-related changes the data points in individual lenses were piecewise linearized. (1) The mean nuclear water content was calculated from the data points in the inner 80% of the visual axis. (2) The steep drop in water content was linearized using a least-squares linear regression approach. The distance between lenticular surface and the intersection of the regression line with the line representing the nuclear mean was denominated as surface layer width. It proved that: (i) the mean nuclear water content significantly increased with age, (ii) the width of the surface layer was age independent in the anterior and posterior poles of the visual axis, and (iii) in the equatorial axis the surface layer width significantly decreased with age. Seven human lenses with small opaque spots were also investigated. The opaque spots proved to have a normal-for-site water content and some of them were flanked at their capsular side by a zone with a high-for-site water content.(ABSTRACT TRUNCATED AT 250 WORDS)

Corneal alkali wound healing in the monkey

Healing of a corneal alkali wound was followed in the monkey eye (Macaca fascicularis) for 4 months. A corneal alkali wound was inflicted in one eye in each of 30 monkeys under general anesthesia. A round filter paper, 5.5 mm in diameter, soaked in 1 N NaOH was put centrally on the cornea for 60 seconds. The alkali wounded all layers in the cornea underlying the filter paper, including the endothelium. Epithelial and endothelial healing was assessed morphometrically from photographs and micrographs, respectively. Stromal healing was documented using quantitative microradiography. During the observation period the wounds regained complete transparency. The epithelium showed few complications after primary healing during the first three days. The stroma regained normal thickness and dry mass content within one week. The endothelium resurfaced within one week and then remained intact. The role of the endothelial healing behaviour for the wound healing process is emphasized.

Hyaluronate in healing of corneal alkali wound in the rabbit

The effect of topically applied 1% and 2% sodium hyaluronate was studied on the healing of a standardized rabbit corneal alkali wound. The healing of the epithelium, the stroma, and the endothelium was evaluated separately by applying quantitative methods. The healing was followed for 8 weeks. Both 1% and 2% sodium hyaluronate have a statistically significant positive influence on the epithelial re-surfacing, especially during the late healing phase. Furthermore, sodium hyaluronate has a positive healing influence on the stromal healing at a certain time interval during the observation period. This was reflected as a better maintained stromal dry mass level compared to control. The stromal healing was parallel to a faster re-surfacing of the endothelium.

Nuclear cataract--a microradiographic study

Nuclear cataract is a common type of senile cataract characterized by an increased turbidity and often a yellow to brown pigmentation of the nucleus. Twenty-one human lenses with different degrees of nuclear turbidity were, after intracapsular cataract extraction, examined by a quantitative microradiographic technique. The dry mass concentration was determined along the lens axis, and revealed an overall distribution similar to the normal lens. The concentration increased from the poles towards the center of the lens, to reach a mean level of 0.47 g.cm-3 (range 0.38-0.55). Though the appearance of the nucleus as well as the dry mass were relatively uniform. In addition, different types of formations with reduced or increased dry mass were found in the nucleus. The location of these formations are described and their nature discussed.

Dry mass and water content in the corneal epithelium and superficial stroma during healing of corneal alkali wounds

The dry mass contents of the rabbit corneal epithelium and of the superficial stroma were determined during healing of a standardized corneal alkali wound. Quantitative microradiography was applied to freeze-sectioned corneal specimens. This method allows a morphological resolution of the order of 1 micron and quantitative dry mass determinations in volumes down to about 100 microns 3. For comparison, the epithelial morphology was studied using Toluidine Blue stained sections. Flat epithelial cells covered the wound surface during the first day, the dry mass content being equivalent to that of the normal wing cells. The dry mass content in the epithelium and, indirectly, the water content, followed the hydration state of the superficial stroma. A progressive thickening of the epithelium and a varying morphological picture were found during the first 2 months following initial damage. Normal thickness and cytoarchitecture were found after 6 months. Generally, the dry mass content of the epithelium was reduced compared with physiological values for 2 months. Later, the cells close to the stroma regained normal values. Cells in the middle zone and the superficial zone reached normal values after 6 months. The significance of the endothelial damage for the hydration state of the epithelium was discussed.

Stromal reaction and repair after corneal alkali wound in the rabbit: a quantitative microradiographic study

The corneal stromal reaction and repair were studied after alkali wound in the rabbit. The wound was followed for 6 months. The size and opacity of the wound were followed in the slit lamp and photographically. Morphology and dry mass or water content were studied using quantitative microradiography. The size of the wound opacity diminished throughout the observation period. The density of the opacity varied with the stromal water content. An increased water content as well as large variation in water content caused increased opacity. The corneal edema, determined already after 1 hr, was not detectable by 1 week using quantitative microradiography. Subsequently, an extensive edema developed, water accumulation being most marked in the posterior part of the cornea. After 8 weeks, an increase in interlamellar dry mass content could be determined as a sign of a stromal healing process. Stromal thickness and dry mass content had returned to normal values by 6 months.