Effect of neodymium: YAG laser on sodium hyaluronate in vitro as a model for postcapsulotomy intraocular pressure change.

PURPOSE: To define one possible etiology for the rise in intraocular pressure (IOP) after neodymium: YAG (Nd:YAG) laser capsulotomy and provide information for the continued investigation of this process. SETTING: Laser Center, Eye and Ear Institute, Pittsburgh, Pennsylvania. METHODS: Samples of 1% sodium hyaluronate or balanced salt solution (BSS) (control) were placed in a closed system and exposed to varying amounts of Nd:YAG energy delivered by a Coherent YAG laser. This system was hydrostatically coupled to a pressure monitor, and changes in pressure were recorded as a function of time. RESULTS: Average pressure increase was 0.140 mm Hg/mJ of YAG energy in the sodium hyaluronate samples and 0.017 mm Hg/mJ in BSS (P < .01). The relationship between total energy delivered and maximum pressure recorded for both substances was nearly linear. Further analysis of treated sodium hyaluronate samples showed that Nd:YAG energy can produce structural alterations. CONCLUSIONS: Neodymium:YAG laser energy has a pronounced effect on sodium hyaluronate that exceeds the thermal effect seen with BSS when the pressure is monitored in a closed system. These structural changes might contribute to the IOP rise seen clinically.

Pharmacologic induction of posterior vitreous detachment in the rabbit.

OBJECTIVE: To assay the proteolytic activity of plasmin on the vitreoretinal junction and to assess a potential facilitating effect on posterior vitreous detachment. METHODS: We injected 1 U of plasmin into the vitreous of rabbits. Some eyes underwent vitrectomy after plasmin injection. Electroretinography and electron microscopy were performed. RESULTS: In plasmin-treated eyes, electroretinography displayed a transient (3 days) decreased b-wave amplitude. Histologic examination demonstrated posterior vitreous detachment in eyes that received intravitreal plasmin followed by vitrectomy. CONCLUSION: Plasmin may prove to be a useful biochemical adjunct to mechanical vitrectomy.

Effects of emulsification, purity, and fluorination of silicone oil on human retinal pigment epithelial cells.

When silicone oil is used as a vitreous substitute, reproliferation of vitreoretinal membranes beneath the oil occurs frequently. Nevertheless, the effects of various properties of silicone oils such as purity, viscosity, fluorination, or emulsification on cellular proliferation have not been established. Human retinal pigment epithelial (RPE) cells were grown to confluence on filters, and then covered with silicone oil. The cellular monolayers were fed from below. At 72 hr and 14 days a proliferation index was determined by measuring 3H-thymidine incorporation into the cells. An assay for the enzyme gamma-glutamyl-transpeptidase (gamma GTP) was also done to assess cell polarization under some oils. A total of 14 different oils were studied. At 72 hr, emulsified oil was associated with significantly less proliferation than unemulsified oil, a difference that disappeared at 2 weeks. Neither fluorination nor viscosity had a significant effect on RPE proliferation. In addition, RPE proliferation indices were not significantly different from one another when purified oils were compared with most commercial-grade oils. However, a very contaminated oil was associated with a significantly higher proliferation index compared with severe purified or medical-grade oils.

Tuberculin skin-test-induced uveitis in the absence of tuberculosis.

A 16-year-old Caucasian girl who showed no evidence of tuberculosis or other systemic disease developed acute panuveitis progressing to bilateral serous retinal detachments following purified protein derivative (PPD) skin testing on two separate occasions separated by an interval of 8 years. Both episodes responded rapidly to steroid therapy. Uveal hypersensitivity to PPD skin testing has been described in the presence of ocular or systemic tuberculosis, Eales' disease, and the Vogt-Koyanagi-Harada syndrome (VKH). Our case, however, suggests that profound uveitis may be precipitated by routine PPD skin testing alone.

Effects of silicone oil and hyaluronic acid on cultured human retinal pigment epithelium.

An experimental model was developed to evaluate the effects of several vitreous substitutes on human retinal pigment epithelial (RPE) cells. Cultured RPE cells were grown into confluent monolayers on semipermeable membranes and nourished from the basal side only, while the apical surface was directly and continuously exposed to preparations of hyaluronic acid and silicone oil for up to 4 weeks. In the silicone oil-treated group, multilayer sheets formed within 2 weeks of exposure and incorporation of 3H-thymidine was twice that of controls. Exposure of RPE cells to silicone oil and certain preparations of hyaluronic acid resulted in a three- to fourfold decrease in cellular polarity, as measured by assaying the cell-surface enzyme, gamma-glutamyl transpeptidase. These results suggest that a model using cultured RPE-cell monolayers is useful in identifying and understanding alterations in ocular tissues triggered by exposure to vitreous replacement materials.

Retinal pigment epithelium wound closure in vitro. Pharmacologic inhibition.

Early-passage bovine retinal pigment epithelium (RPE) cells were grown to confluence in 24-well plates, and a central defect was created mechanically in the monolayer within quadruplicate wells, sequentially over 9 days. Closure of the wounded area occurred by single-cell migration of elongated RPE cells from the edge of the wound and subsequent cell proliferation. Ten days after wounding, the cultures were fixed, stained, and photographed, and the residual wound area was quantified by computerized planimetry. Cell counts of unfixed cultures were determined with a Coulter counter. Wound closure was complete after 10 days. Using this technique, we assessed the response of RPE to various concentrations of 5-fluorouracil (5-Fu), colchicine (COL), and cytochalasin-B (CYT-B). 5-Fu (10 micrograms/ml) and COL (0.1 and 1 microgram/ml) inhibited migration and proliferation of RPE cells. CYT-B (5 micrograms/ml) inhibited migration. This model allows in vitro study of the response of RPE cells after loss of contact inhibition. The technique provides a quantitative model for assessing the dynamic capabilities of RPE cells in response to a localized mechanical defect and for assessing the pharmacologic modulation of these responses.