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A Thaer

Publications and source records attributed to A Thaer.

9 recordsLinked to original sources
PubMed1998

Confocal microscopy reveals persisting stromal changes after myopic photorefractive keratectomy in zero haze corneas.

AIMS: Micromorphological examination of the central cornea in myopic patients 8-43 months after excimer laser photorefractive keratectomy (PRK), using the slit scanning confocal microscope. METHODS: Patients were selected from a larger cohort of individuals on the basis of full corneal clarity (haze grading 0 to +1; mean 0.3) and their willingness to participate in the study. 15 eyes of 10 patients with myopic PRK (-4 to -11 D; mean 6.7) and an uneventful postoperative interval of 8-43 months (mean 26) were examined. Contact lenses had been worn by eight of the 10 patients for 4-11 years (mean 6.7) before surgery. Controls included the five untreated fellow eyes of PRK patients, 10 healthy, age matched volunteers without a history of ocular inflammation or contact lens wear, and 20 patients who had worn rigid gas permeable (n = 10) or soft contact lenses (n = 10) for 2-11 years. Subjects were examined with a real time flying slit, scanning confocal microscope using x25 and x50 objectives. RESULTS: In PRK treated patients and contact lens wearers, basal layer epithelial cells sporadically displayed enhanced reflectivity. The subepithelial nerve plexus was observed in all individuals, but was usually less well contrasted in the PRK group, owing to the presence of a very discrete layer of subepithelial scar tissue, which patchily enhanced background reflectivity. Within all layers of the stroma, two distinct types of abnormal reflective bodies were observed in all PRK treated eyes, but in none of the controls. One had the appearance of long (> = 50 microns), slender (2-8 microns in diameter) dimly reflective rods, which sometimes contained bright, punctate, crystal-like inclusions, arranged linearly and at irregular intervals. The other was shorter (< 25 microns), more slender in form (< 1 micron in diameter), and highly reflective; these so called needles were composed of crystal-like granules in linear array, with an individual appearance similar to the bright punctate inclusions seen in rods, but densely packed. Both of these unusual structures were confined, laterally, to the ablated area, but were otherwise distributed throughout all stromal layers, with a clear predominance in the anterior ones. These rods and needles were observed in all PRK treated corneas, irrespective of previous contact lens wear. On the basis of qualitative inspection, the incidence of rods and needles did not appear to correlate with either the volume of tissue ablated or the length of the postoperative interval. In contact lens wearing controls, highly reflective granules, reminiscent of those from which the needles were composed, were found scattered as isolated entities throughout the entire depth and lateral extent of the corneal stroma, but rods and needles were never encountered. The corneal endothelium exhibited no obvious abnormalities. CONCLUSION: Confocal microscopy 8-43 months after PRK revealed belated changes in the corneal stroma. These were manifested as two distinct types of abnormal reflective bodies, which had persisted beyond the stage when acute wound healing would have been expected to be complete. The clinical significance of these findings in the context of contrast visual acuity and long term status of the cornea is, as yet, unknown.

Adult↗
PubMed1997

[Confocal microscopy of the corneal after photorefractive keratectomy with the excimer laser].

BACKGROUND: In photorefractive keratectomy (PRK) procedures, a variable superficial central corneal scar formation ("haze") can be observed following removal of corneal stromal tissue. Today, a near to normal slit lamp finding is observed one year postoperatively in most patients. We employed the slit scanning confocal microscope to study the corneal morphology years after PRK. METHODS: We selected 5 patients, who had been subjected to unilateral photorefractive surgery 1-3 years earlier and who had no corneal haze upon slit lamp examination. As controls we investigated the non-treated corneas of these patients, 5 healthy controls and 5 contact lens wearers. The confocal microscopic investigation was performed with 25x, 40x and 50x water immersion objectives. The video signal was synconized with the slit scan and stored on S-VHS video tape. By reviewing the videos in the single frame mode, all corneal layers could be qualitatively evaluated. RESULTS: Some minor abnormalities were observed in the epithelium of all PRK-treated eyes. In the epithelial basal cell layer some round structures of about the size of a cell with high reflectivity were observed. These changes were only occasionally found in contact lens wearers, but not in non-treated or normal control eyes. Bowman's layer was absent in the PRK treated eyes, instead, a fine layer of collagen tissue of increased reflectivity was found. The subepithelial corneal nerve plexus was normal in all non-treated eyes, whereas in the PRK-treated corneas nerve shape and branching pattern were changed to quite an extent. In the anterior stroma the keratocyte nucleus patterns indicated an increased cell density and irregular spacing, whereas a normal keratocyte pattern was found in the deeper stromal layers. A significant finding was the observation of rod and needle shaped highly reflective structures, which were limited to the area of the excimer laser keratectomy with a predominance in the anterior stroma. These longitudinal structures themselves consisted of linearly arranged highly reflective granules, which sometimes also were found as isolated dots within keratocyte processes. In long term contact lens wearers a comparable granule type, however with a singular and scattered arrangement, was variably found in all corneal regions and layers. In normal controls none of these findings were present. In contact lens wearers and PRK patients with a contact lens history, the corneal endothelium showed some degree of polymegathisms but no other specific findings. DISCUSSION: Up to now, refractive surgery with the excimer laser has been reported to elicit no other stromal changes but a mild fibroblast activation with subsequent scar tissue formation. In clinically clear corneas after PRK, we have described a new type of stromal deposit observed 1-3 years after surgery. As acute wound healing responses might have been expected to have passed at this point, this highly reflective stromal deposit can be assumed to consist of linear keratocyte processes filled with some highly reflective (degenerative?) matter as well as a corresponding extracellular stromal deposit arranged parallel to the stromal collagen bundles. Possibly, these stromal deposits represent the result of an inflammatory or degenerative stromal response resulting in the formation of stromal lipofuscein deposits. Visual acuity was not impaired in the patients investigated in this study. As these stromal deposits appear to be persisting years after surgery and possibly are irreversible in nature, a long term effect on the corneal physiology and function should carefully be monitored.

Adult↗
PubMed1994

[Examination of the cornea of intact donor eyes with confocal slit-scanning video microscopy].

The specular microscopic examination of the endothelium of intact donor eyes can be rendered difficult or even impossible due to light scattering of stromal edema. We have been able to visualize large areas of the corneal endothelium of a donor eye with advanced stromal edema--stored for over 32 h. in a moist chamber--with a confocal slit-scanning video microscope. Furthermore, this optical arrangement enables the examination of very thin tissue sections with high resolution and a remarkably enhanced contrast of the corneal micromorphology (epithelial cells, Bowman's membrane, nerve fibers, keratocytes, endothelial cells).

Alcoholism↗
PubMed1985

[Microscopic study of the corneal epithelium based on intracellular turnover of fluorogenic substrates].

The methods presently available for examination of the corneal epithelium by use of the ophthalmic slit lamp are more or less restricted to the detection and diagnosis of significant lesions and the morphological results of pathologic processes in the epithelial layer at relatively low magnification and optical resolution. There is an increasing demand, however, for early detection of initial damaging effects to the corneal epithelium by testing simple specific reactions at cell level. Fluorescein microscopy of the intracellular turnover of fluorogenic substrates may become a valuable methodological basis for such an examination of the corneal epithelium. Orienting experimental investigations into the uptake and turnover of fluorescein-di-acetate (FDA) by the epithelial cells of the rabbit cornea after its exposure to isotonic 10(-5) molar FDA solution, using an endothelial specular microscope and an image intensifier TV camera, demonstrate that this principle permits a superior microscopic presentation not only of the cellular epithelial structure in general, but also of locally damaged areas of the epithelium immediately after their exposure to damaging chemical agents, in particular to substances affecting cell membranes.

Animals↗
PubMed1978

[Specular microscopy of the corneal endothelium (author's transl)].

Specular microscopy enables the examination of the endothelium of the isolated and perfused cornea. It is of great help in evaluating donor material in an Eye Bank. The in vivo observation and microphotography of the corneal endothelium makes it possible to detect early degenerative, traumatic surgical and other pathological changes of the monolayer.

Adult↗
PubMed1975

Microscope fluorometric investigations on the reticulocytic maturation distribution as diagnostic criterion of disordered erythropoiesis.

A microscope fluorometric technique is described which permits not only the visual identification of reticulocytes under the fluorescence microscope but also the determination of their relative stage of maturation to normocytes. The technique is based on a specific staining procedure which results in a fluorescent complex between the reticulocytic RNA and acridine orange. Thus, the relative mass of RNA in the individual reticulocytes can be measured by means of mciroscope fluorometry. As the reticulocytic RNA content decreases and finally disappears during the final maturation process of reticulocytes after their release into the peripheral blood stream, the fluorescence signal indicates the relative degree of this maturation. A characteristic frequency distribution of this parameter can be obtained for a given blood sample by microscope fluorometry measuring 200 to 300 reticulocytes. The preliminary use of this technique for following up the course of two cases of hemolytic anemia and one of pernicious megaloblastic anemia during their treatment demonstrates the potential diagnostic value of this technique of identifying the change of the reticulocyte maturation distribution in addition to the reticulocyte count. Satisfactory agreement between the microscope fluorometric results and those obtained by counting separately the four reticulocytic maturation stages according to Heilmeyer and Wesbäuser has been achieved. The possibility of obtaining quantitative and comparable results by use of this method may be considered a general advantage and a promising basis for the development of an automated technique.

Acridines↗