PubMed · 3450697
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C O Peckar. 1987. Recent developments in Endovid.. https://doi.org/10.3109/17453058709150309
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Plasma formation with nanosecond and picosecond Nd:YAG laser pulses was investigated as a function of laser pulse energy to find possibilities for a spatial reduction of the laser effects. The threshold for plasma formation (optical breakdown) in distilled water is 200 microJ for ns pulses and 15 microJ for ps pulses. At a pulse energy of 1 mJ, the plasma length is 80 microns for ns pulses and 250 microns for ps pulses. For the same pulse energy, ps plasmas are on average three times larger than ns plasmas. The plasma length is approximately proportional to the cube root of the laser pulse energy for both ns and ps laser pulses. The decrease in the breakdown threshold achieved by using ps pulses renders photodisruption with a smaller pulse energy (in the microJ range) possible, and therefore a reduction in the side effects. The results are compared with the "moving breakdown" model.
The ultra-microstructure of the human corneal endothelium was examined by scanning and transmission electron microscopy. The samples were corneas of 26 human eyes taken from fetuses of 5-22 weeks gestation and a newborn 10 months after birth. Corneal endothelium appeared at the seventh or eighth week after gestation. Initially, they formed an irregular structure of two to three layers. From the 17th week of gestation they formed a single layer, and assumed the form of a cuboidal epithelium. Scanning and transmission electron microscopy showed numerous microvilli protruding towards the anterior chamber. Within the microvilli uniform microtubules were observed. By the 20th week, these microvilli disappeared, and subsequently, a single long narrow cilium appeared in the center of each cell. Each cilium had an axial filament complex structure. This cilium involuted as development progressed, and was barely visible by the 10th month after birth. The significance of this cilium is not clear.
We identified all patients who had undergone penetrating keratoplasty for keratoconus and were being observed longitudinally (N = 174). During the follow-up period, 57 of 174 patients (33%) showed evidence of an allograft rejection episode, which occurred at an average of eight months after the operation. We analyzed specular photographs of the corneal endothelium, taken before and after the first allograft rejection episode. A significant decrease in endothelial cell density was observed (11.8%, P less than .0001). As a control, we analyzed all available specular photographs from patients with keratoconus who showed no evidence of allograft rejection after penetrating keratoplasty. The observed endothelial cell density decrease (11.8%) in patients with keratoconus undergoing allograft rejection exceeded that found in the control subjects (6.8%) during a comparable time period (P = .06). Severe allograft rejection episodes resulted in a decrease in endothelial cell density that exceeded expected loss significantly (14.8% compared with 6.9%, P = .01), whereas mild allograft rejection episodes were not associated with a loss in endothelial cell density exceeding that expected (1.8% compared with 6.5%, P = .34).