An orally bioavailable positive allosteric modulator of the mGlu4 receptor with efficacy in an animal model of motor dysfunction

A high-throughput screening campaign identified 4-((E)-styryl)-pyrimidin-2-ylamine (11) as a positive allosteric modulator of the metabotropic glutamate (mGlu) receptor subtype 4. An evaluation of the structure-activity relationships (SAR) of 11 is described and the efficacy of this compound in a haloperidol-induced catalepsy rat model following oral administration is presented.

Development of a high-throughput AlphaScreen assay measuring full-length LRRK2(G2019S) kinase activity using moesin protein substrate

Mutations within the LRRK2 (leucine-rich repeat kinase 2) gene predispose humans to develop late-onset Parkinson's disease (PD). The most prevalent of these mutations, G2019S, has been shown to increase LRRK2 kinase activity. Therefore, the discovery of small molecule inhibitors of LRRK2(G2019S) through high-throughput screening (HTS) may provide a novel therapeutic strategy for treating PD. Current biochemical assays monitoring the activity of LRRK2(G2019S) either are radioactive or use short peptidic substrates. Here we describe the development and optimization of a novel HTS AlphaScreen assay for measuring the catalytic activity of full-length LRRK2(G2019S) using its putative physiological protein substrate moesin. The high sensitivity of this optimized 384-well assay allowed the use of enzyme concentrations as low as 0.75nM. The estimated apparent K(m) value for adenosine triphosphate (6 microM) using the glutathione S-transferase-moesin substrate was much lower than the one previously reported using LRRKtide, a synthetic peptide derived from moesin. Testing of nonselective kinase inhibitors (staurosporine, H-1152, and Y-27632) generated potencies consistent with published data. Finally, robotic validation of the assay yielded an average Z' factor of 0.80. Overall, these results indicate that the present HTS AlphaScreen assay might provide a more relevant biochemical approach for the discovery of novel LRRK2(G2019S) inhibitors.

Retinotomy and silicone oil for detachments complicated by anterior inferior proliferative vitreoretinopathy

AIM

To describe a subset of patients with recurrent retinal detachments caused by anterior intraretinal and subretinal proliferative vitreoretinopathy (PVR), which required greater than 180 degrees retinotomy and silicone oil tamponade.

METHODS

Interventional case series. Forty-one patients underwent >180 degrees retinotomy, anterior retinectomy, removal of subretinal membranes, laser to the retinotomy edge and silicone oil tamponade. Risk factors for detachment, prior surgical history and PVR location were examined. Main outcomes included change in visual acuity, recurrent detachment and postoperative complications.

RESULTS

Cataract extraction (49%), high myopia (29%) and lattice degeneration (27%) were preoperative risk factors. The average number of prior procedures for retinal attachment was 2.3 (SD 0.9). The majority of detachments were inferior and related to anterior intraretinal and subretinal PVR. Twenty-four patients (59%) saw 20/200 or better. Eleven patients (27%) had poor vision (<20/400) at the end of follow-up. Thirty-seven retinas (90%) remained attached. Increased rates of postoperative corneal decompensation (p<0.0001) and silicone oil in the anterior chamber (p<0.0001) were statistically significant markers of poor visual outcome.

CONCLUSIONS

Patients with complex PVR requiring a large retinotomy often had similar presurgical conditions. A large inferior retinotomy effectively addressed proliferations where they most frequently occur, and silicone oil was beneficial.

Peptide Protein Binding Assay Using ImageFlashPlates or Imaging Beads

Imaging devices used for the measurement of radioligand-receptor binding assays are typically based on charge-coupled device (CCD) cameras, which are more sensitive for red-shifted scintillation. In the past, red-shifted scintillants had only been integrated into microspheres, referred to as scintillation proximity assay (SPA) Imaging Beads. More recently, ImageFlashPlates have been developed that emit light at 615 nm when exposed to beta-radiation. In this article, we report the establishment of peptide-protein binding assays using either streptavidin-coated ImageFlashPlates or Imaging Beads in a low volume 384-well format. In these assays, we employed a biotinylated peptide X and a [33P]-phosphorylated protein Y as the binding partner. The FlashPlates required a washing step, the bead-filled microtiter plates (MTPs) needed a centrifugation step for optimal performance in the scintillation measurements. Both the peptide X-loaded FlashPlates and the beads displayed saturable binding of [33P]-phosphorylated protein Y with a similar scintillation efficiency. A KD value of about 30 nmol/l was measured using the bead-based assay. Due to the washing step in the FlashPlate experiment, approximately two-thirds of the [33P]-phosphorylated protein Y were withdrawn from equilibrium binding. This resulted in correspondingly lower scintillation signals for the FlashPlate experiment. For this reason, the FlashPlate produced a Z' value of 0.64 that was lower than the Z' value of 0.87 for the beads. Using a reference inhibitor in a competition assay produced similar IC50 values for the bead-based assay as for the FlashPlate. Depending on the local automation environment either the centrifugation step for the beads or the washing step for the FlashPlates may be considered more or less of a challenge. Low volume 384-well high-throughput screening (HTS) applicable assay formats are achievable using either the ImageFlashPlates or the Imaging Beads.

Pharmacokinetics and pharmacodynamics of terbogrel, a combined thromboxane A2 receptor and synthase inhibitor, in healthy subjects

AIMS

To characterize the pharmacokinetics of terbogrel, a new combined thromboxane A2 (TxA2) receptor and synthase inhibitor, in healthy human subjects after single or multiple oral administration.

METHODS

Forty-eight healthy male subjects received a single oral dose (10, 25, 50, 100, 150 or 200 mg) of terbogrel or placebo and 32 different subjects received one of the following treatments twice daily for 7 days: 50, 100 or 150 mg terbogrel, placebo, or once-a-day 330 mg acetylsalicylic acid.

RESULTS

Terbogrel was well tolerated without obvious adverse effects following either a single oral dose or administration over 7 days. Plasma drug concentrations were dose-linear and there was no accumulation over 7 days. There was a dose-dependent blockade of TxA2 receptors and of inhibition of thromboxane synthase activity with values for IC50 of 12 ng ml(-1) and 6.7 ng ml(-1), respectively. At the highest dose tested (150 mg) there was almost complete inhibition of thomboxane synthase and thromboxane receptor occupancy. Even at trough concentrations, receptor occupancy remained above 80% and thromboxane synthase was still completely inhibited. These two activities were associated with a dose-dependent inhibition of platelet aggregation (>80% at the 150 mg dose of terbogrel) and enhanced prostacyclin production.

CONCLUSIONS

Terbogrel is a potent agent having two distinct, complimentary pharmacodynamic actions, namely inhibition of thromboxane synthase and antagonism of the TxA2 receptor. The antithrombotic effect of terbogrel was dose-dependent and was associated with enhanced prostacyclin production. Terbogrel is an attractive candidate for long-term antithrombotic therapy.

Automated high throughput screening for serine kinase inhibitors using a LEADseeker scintillation proximity assay in the 1536-well format

High-throughput screening in the 1536-well format has been largely restricted to solution-based and cell-based screens. In this article, we show the feasibility of a completely automated, robust scintillation proximity assay in the 1536-well format that is suitable to identify inhibitors for a serine/threonine kinase from a compound library. The introduction of [(33)P]phosphate into a biotinylated peptide substrate mirrors the activity of the kinase. The peptide is immobilized on streptavidin-coated LEADseeker imaging beads and [(33)P]phosphate incorporation is detected with the LEADseeker imaging system of Amersham Pharmacia Biotech. To improve the liquid handling procedures for imaging bead suspensions in the low microliter range, we developed a novel trough with an integrated stirring function. A comparison of the 1536-well assay to a 384-well assay revealed a comparable assay quality with Z' factors of about 0.7 for the 384-well format and 0.6 for the 1536-well format. In an automated screen of a random compound collection, 94.4% of the inhibitory compounds could be identified with both assay formats. Dose-response curves were performed for a selection of identified kinase inhibitors and revealed similar IC(50) values for both assay formats.

Ocular manifestations of systemic hypertension

Recent population-based studies suggest that the fundus lesions of hypertension also occur in people without hypertension. In experimental studies, hypertensive lesions, which used to be the backbone of older classifications of the severity of hypertension, did not correlate sufficiently with severity to allow reliable grading. Hypertensive retinopathy, choroidopathy, and optic neuropathy are independent processes. Vascular narrowing appears to occur early in the disease process, whereas retinal hemorrhages and retinal lipid may occur later. Branch vein occlusion is a complication of hypertension, whereas open-angle glaucoma may not be. Choroidal neovascularization in the fellow eyes of patients with macular degeneration is associated with high blood pressure. Laser treatment for this disorder is less effective in patients with high blood pressure than it is in normotensive individuals, which suggests that choroidal neovascularization may be an expression of chronic hypertensive choroidopathy. Hypertensive optic neuropathy, a variant of ischemic optic neuropathy, has delayed onset compared with retinopathy and, in experimental studies, has not been linked to the severity of hypertension. Given these findings, it may be better to describe than to grade fundus lesions. In either event, it is important to take blood pressures accurately. Fundus lesions suggest high blood pressure. Sphygmomanometry is more specific and reliable than funduscopy in making that diagnosis.

Macular holes: migratory gaps and vitreous as obstacles to glial closure

PURPOSE

Retinal glia may play an important role in the closure of macular holes. This in vitro study examines whether and how the specific pathoanatomy, including foveal eversion and foveal vitreous, may interfere with glial closure of macular holes.

METHODS

Culture dishes used to grow glial cells were modified by the placement of slopes, vertical steps, and gaps to mimic the in vivo migratory surface in and surrounding macular holes. In separate experiments, defects were made in a rodent glial monolayer. These defects were exposed to hyaluronic acid (HA) and to rabbit (RV) and bovine (BV) vitreous gel. The migratory behavior and completeness of closure of defects were compared to controls.

RESULTS

As expected, glial cells migrated further and in greater numbers on a smooth surface. Slopes and steps were moderate obstacles to migration; gaps in the surface were absolute obstacles. HA modified the pattern of adhesion of cells at the bottom of defects. Defects in the glial monolayer were repaired in 5-7 days. Compared to these controls, repair was inhibited by 11% (n.s.), 28% (P = 0.02), and 58% (P = 0.004) after direct exposure of defects to HA, RV and BV, respectively.

CONCLUSION

The elevated and everted margins of macular holes represent slope, step, and gap-like obstacles to the migration of glial cells and hence to the healing of defects. The defect allows extension of extracellular matrix into it and the subretinal space. Our results indicate that gaps in the migratory surface caused and aggravated by eversion and the presence of vitreous present obstacles to glial migration and closure of macular holes.

Postsurgical hypotony: relationship to fistulization, inflammation, chorioretinal lesions, and the vitreous

Hypotony is a natural occurrence, symptom, and complication of surgical treatment. With more sophisticated and aggressive techniques, postsurgical hypotony recently has been given increased attention as an obstacle to success of surgery for glaucoma and retinal detachment. Whereas two standard deviations below normal pressure (15.9-5.8 = 10.1 mm Hg) can be called hypotonous, most eyes, depending on scleral rigidity, lid pressure, eye rubbing, or corneal or retinal edema, will be symptomatic at < 5 mm Hg. Hypotony can be defined as the low pressure (whether acute, transient, chronic or permanent) which, in an individual eye, leads to functional changes (whether asymptomatic or symptomatic) and structural changes (whether reversible or irreversible). Depending on its duration and degree, postsurgical hypotony produces characteristic tissue changes that often are modified by, but separate from, the tissue changes caused by an underlying disease or its surgical treatment. This review summarizes the situations, variably associated with hypotony, that occur after such interventions as cataract extraction, filtering surgery, cyclodialysis, cyclodestruction, and vitreoretinal surgery, in addition to the reported pathomechanisms of hypotony and its proposed treatments.

Endoscopy and biopsy of the orbit

Flexible endoscopes produce high-quality images, are small in size, and can deliver microsurgical instruments or laser probes. Early attempts at orbital endoscopy were limited by the relatively large size and poor visualization of rigid endoscopes. We performed endoscopic orbital exploration using the Olympus HYF flexible endoscope in four live dog orbits. We achieved excellent visualization of orbital structures including the globe, blood vessels, extraocular muscles, intermuscular septa, optic nerve, and fat. Visualization, hemostasis, and dissection were aided by the use of hyaluronic acid infused through the endoscope. We biopsied fat and extraocular muscle without complication using Olympus endoscopic cup biopsy forceps (confirmed by histopathologic examination). Our experience indicates that orbital endoscopy aided by viscoelastic hydrodissection may permit a less invasive approach to optic nerve sheath fenestration, tumor biopsy and treatment, and the removal of foreign bodies.

Schisis-like rhegmatogenous retinal detachment associated with choroidal colobomas

BACKGROUND

The breaks that cause retinal detachments in colobomatous eyes are often hidden within the lesion and difficult to find.

METHOD

To elucidate the pathoanatomy and possible pathomechanism of such detachments, histological sections of eight choroidal colobomas were reviewed.

RESULTS

Sections of the margin showed central continuation of the inner neuroblastic layer (the intercalary membrane) and eversion and separation of the outer neuroblastic layer. The opposite direction of continuity of the neuroblastic layers created a schisis-like configuration between the intercalary membrane and the everted outer retina. The zone of duplication was a point of retinal adhesion, but also a locus minoris resistentiae due to vitreous attachments and variable glial support at the margin.

CONCLUSION

The subset of coloboma-associated retinal detachments requires both a central break in the inner layer and a break in the outer layer at the margin of the coloboma. The inner layer break may be precipitated by retinovascular ischemia or scleral stretching; that in the outer layer may be caused by vitreous traction on the margin of the coloboma or extension of the formerly isolated detachment through the outer marginal zone of decreased glial support.

Cytologically proven seronegative Lyme choroiditis and vitritis

PURPOSE

To report on a vitreous specimen in a 53-year-old patient with unilateral choroiditis and vitritis of unknown cause.

METHODS

Cytologic examination of a vitreous aspirate stained by the Papanicolaou method.

RESULTS

Intravitreal spirochetes consistent with Borrelia burgdorferi were found in this seronegative patient.

CONCLUSION

Vitreous specimens of patients with choroiditis and vitritis of unknown cause should be examined cytologically, particularly when serologic results do not corroborate the clinical findings of Lyme disease.

Postvitrectomy hypotonia: the role of the vitreous and retinochoroidal lesions

The pathomechanisms of hypotonia after vitrectomy remain obscure. To examine the possible escape of intraocular fluid through the ocular wall, hydraulic fluid conductivity was measured across preparations of retina, pigmented epithelium, and choroid isolated from rabbit eyes 1, 3, 5, or 7 weeks after the production of laser or cryopexy lesions. The hydraulic conductivity measured in a modified Fischbarg-Bourguet chamber, was 0 in controls. At 1 and 3 weeks after transpupillary diode laser coagulation of the equatorial retina, hydraulic conductivity was measurable. However, the conductivity of these preparations returned to 0 by 5 weeks. After transscleral cryopexy, conductivity remained elevated for 7 weeks. Break-up of residual cortical vitreous with hyaluronidase increased the conductivity of "mature" cryopexy lesions to the values obtained 1 week after injury. These results suggest that there is escape of fluid across retinochoroidal lesions; fluid conductance typically decreases over time; an intact cortical gel can hinder conductance and seal the retinochoroidal leak. Thus, the risk factors for hypotonia appear to include extensive retinochoroidal lesions and the absence of a normal cortical vitreous in aphakia and/or after aggressive vitrectomy.

Neurilemmoma of the anterior ethmoidal nerve encroaching upon the nasolacrimal duct

The clinical, light microscopic, ultrastructural, and immunohistologic findings of a neurilemmoma encroaching upon the nasolacrimal duct are presented. This is the first reported case of this rare tumour of the nasolacrimal duct where the diagnosis has been confirmed by electron microscopy and immunohistochemical techniques.

Quantitative CW Nd:YAG pars plana transscleral photocoagulation in postmortem eyes

The effect of different types of burns and numbers of lesions on, and the role of initial pressure head in, the rate of aqueous outflow was studied in enucleated human and porcine eyes. Noncontact and contact CW Nd:YAG laser applied to human eyes 3 mm posterior to the limbus produced a 34% and 51% increase, respectively, in outflow as compared with controls (P = .01). In porcine eyes, outflow increased directly with the number of noncontact burns as well as with the amount of perfusion pressure. Our results suggest that intraocular pressure and outflow are functions of both the intensity of irradiation and the surface area treated, and that each individual pressure head may require an optimal pars plana area of treatment of therapeutic degree to lower pressure and yet prevent overfiltration and phthisis. Our results also suggest that there may be a passive transneuroepithelial and transscleral outflow component in clinical laser cycloablation and, therefore, a need to grade laser treatments in order to prevent visual loss through unnecessary injury.

Changes in aqueous outflow after in vitro neodymium: yttrium aluminum garnet laser cyclophotocoagulation

To examine the possible role of transscleral outflow routes, enucleated human and porcine eyes underwent noncontact neodymium:yttrium aluminum garnet (Nd:YAG) laser cyclophotocoagulation 3 mm posterior to the limbus. Pars plana lesions were verified histologically. The eyes were perfused with saline solution at 50 mm Hg perfusion pressure, placing the tip of the needle into the hyaloid orbicular space. The outflow facility was 0.072 microliter/min/mm Hg in paired controls and 0.105 microliter/min/mm Hg in human lasered eyes, a difference of 31%. In porcine eyes the difference was 43%. Since concepts of aqueous production, impaired circulation, and inflammation do not apply to enucleated eyes, the increase may be related to pars plana transscleral flow facilitated by disruption of the neuroepithelial barrier.

Intraocular pressure after peripheral retinal cryopexy in normotensive human eyes

Intraocular pressure (IOP) was measured before and after peripheral retinal cryopexy given for lattice degeneration and small retinal breaks. During the period of observation the IOP of treated eyes decreased, suggesting that freezing of areas remote from the ciliary body may lower IOP through mediation and/or transscleral outflow.

Noncontact and contact pars plana transscleral neodymium: YAG laser cyclophotocoagulation in postmortem eyes

Transscleral neodymium:YAG (Nd:YAG) laser energy (5 J), noncontact at 20 msec and contact at 0.5 sec exposure time, was applied to enucleated porcine and human eyes 3 mm posterior to the limbus. Coagulative pars plana lesions were noted in all cases. Related to focus and exposure time, noncontact lesions were larger, more homogeneous, and affected primarily the pigment epithelium, whereas contact lesions showed more full-thickness thermal effects, including sclera. Because the corona ciliaris was unharmed when laser applications were made 3 mm from the limbus, this commonly used clinical focus raises questions about cyclo "destruction." Future clinical research will have to show which phenotype of pars plana lesion correlates best with long-term lowering of pressure.

The role of inflammation in CW Nd:YAG contact transscleral photocoagulation and cryopexy

Cyclodestructive modalities in humans have been shown to be effective when applied 3.5 mm or more posterior to the limbus. Therefore, CW Nd:YAG contact transscleral laser and cryopexy were applied 6 mm posterior to the limbus of pigmented rabbits. The intraocular pressure (IOP), flare, iritis, cells and conjunctival hyperemia were monitored clinically up to 3 weeks. The pressure lowering effect was -7.5 +/- 7.7 mm Hg for laser retinopexy and -14.2 +/- 6.0 mm Hg for retinocryopexy at 3 weeks and was comparable to application of the same modalities directly over the ciliary body. Similarly, induction of intraocular inflammation by injecting 10 micrograms of endotoxin intravitreally lowered IOP significantly. These findings suggest that hypotension may not be directly due to cyclodestruction but may be related to the ocular irritative response and extent of neuroepithelial defect, irrespective of its distance from the limbus.

A comparison of CW Nd:YAG contact transscleral cyclophotocoagulation with cyclocryopexy

The cyclodestructive and inflammatory effects of CW Nd:YAG contact laser were compared to those of conventional cryopexy. CW Nd:YAG light transmitted by fiber optic cable and sapphire crystal was applied transsclerally to the ciliary body of pigmented and albino rabbits. Cyclocryopexy was given to a comparable second group. The intraocular pressure (IOP), flare, iritis, cells and conjunctival hyperemia were monitored clinically up to 3 weeks. The breakdown of the blood-aqueous barrier and time course of ocular inflammation was similar for both modalities and IOP was -12.2 +/- 4.2 mm Hg for laser cyclopexy and -15.1 +/- 5.4 mm Hg for cyclocryopexy at 3 weeks. Ciliary body lesions were noted in both groups. Overall, albino rabbits showed less histological damage and faster recovery of IOP. Contact cyclophotocoagulation and cyclocryopexy can be considered models of ocular injury. The similarities in ocular irritative response suggest a similar pathophysiologic mechanism underlying the pressure behavior in both thermal mode injuries.

Contact transscleral retinopexy using a sapphire crystal probe

To examine the laser-tissue interactions for contact transscleral irradiation, argon and CW Nd:YAG light was delivered through a synthetic sapphire crystal which was held in direct conjunctival contact perpendicular to the peripheral retina. The threshold for retinal whitening was 0.5 J in the rabbit, 1.0-1.5 J in the monkey, and 1.0-4.0 J in human eyes. Histologic examination of the acute injury and at 2 days, 1, 3, 6, and 12 weeks, showed coagulative lesions centered around the pigmented layers in the rabbit. While severe chorioretinal disruption and hemorrhage did occur depending on species, energy level, and probe location, no scleral perforation was noted at any setting. These preliminary studies suggest that transscleral contact lasers may be used safely in clinical situations where selective ablation of the peripheral retina or pigmented tissues is the primary objective.

Complications associated with the use of silicone oil in 150 eyes after retina-vitreous surgery

Complicated retinal detachments (RDs) were successfully managed in 150 eyes of 170 consecutive patients by one surgeon (JLF) using silicone oil in conjunction with modern pars plana vitrectomy. Long-term postoperative complications were observed between 6 months and 5 years of follow-up. Cataracts developed in all phakic eyes and all corneas with oil-endothelial touch showed band keratopathy within 6 months. Recurrent detachments were noted in 22% of eyes during silicone oil tamponade and occurred in 13% of eyes after the oil had been removed. Other complications associated with the use of oil for vitreous surgery included pupillary block glaucoma (3%), closure of the inferior iridectomy (14%), fibrous epiretinal and subretinal proliferations (15%), pain (5%), and subconjunctival deposits of oil (3%). Without exception, within a period of 1 year the intraocular silicone oil showed some degree of emulsification, suggesting that the physicochemical characteristics of the oil injected may be an important variable in long-term complications.

Pigmentary epitheliopathy, disc edema, and lead intoxication

A 52-year-old lead-exposed worker presented with disc edema, nerve fiber layer infarcts, and an acute bilateral pigment epitheliopathy that phenotypically resembled APMPPE. The patient had definite laboratory evidence of increased total body lead burden. The simultaneous involvement of retina, disc, and choriocapillaris suggests that what has been reported as the spectrum of APMPPE may represent a nonspecific vascular response to multiple injurious stimuli, including lead.

Vitreoretinal changes associated with rise in intraocular pressure after Nd:YAG capsulotomy

In a chart review of 100 consecutive Nd:YAG laser capsulotomies, six presumed risk factors of the rise in intraocular pressure (IOP) after capsulotomy were identified. A group of 15 patients in which the pressure rose to at least 10 mmHg above baseline postoperatively showed a significant (P less than or equal to 0.01) association with myopia, vitreoretinal disease, and vitreous prolapse into the anterior chamber. The previously known association of high pressures with glaucoma, a large capsular opening, or absence of a posterior chamber lens were also confirmed. There was no correlation between the energy used and IOP. These retrospective findings are suggestively consistent with the concept that injury to a liquefied vitreous may contribute to the IOP rise after capsulotomy.

A history of intraocular pressure rise with reference to the Nd:YAG laser

The rise in intraocular pressure after Nd:YAG laser capsulotomy is presently thought to be due to laser specific shockwaves and debris. Glaucoma has also been a frequent complication of mechanical discission as shown by a review of 84 cases from 1865-1932. Most authors have ascribed the pressure rise to vitreous or a quality of vitreous. Focusing on the disruption of the barrier between aqueous and vitreous as a common link between knife and laser discission, an attempt is made to combine the historical and recent views. It appears that apart from radiation effects, the Nd:YAG laser functions as a sharp knife and therefore shares the complications of mechanical discission, namely, glaucoma, injury to the vitreous and retinal detachment.

Interaction of ultraviolet laser light with the cornea

The effect of pulsed ultraviolet (UV) laser light on the cornea depends on wavelength (photon energy), irradiance (photon flux), and pulse firing rate. At the available excimer laser wavelengths of 193, 249, 308, and 351 nanometers, the authors have varied the irradiance per pulse (10 to 2000 mj/cm2) as well a pulse frequency (1, 10, 25 Hz) and determined the thresholds for coagulation and ablation of the corneal stroma. The latter ablative action creates a groove resembling an incision and was present at all wavelengths studied. The threshold for ablation increased for longer wavelengths and lower pulse frequencies, except for 193-nm exposure, which was characterized by a constant threshold independent of laser pulse rate. The grooves at 193 nm were both biomicroscopically and histologically smooth and no coagulation effects were noted. Some degree of coagulation of adjacent tissues was noted at 249, 308, and 351 nm.

The role of the vitreous in the intraocular pressure rise after neodymium-YAG laser capsulotomy

Autologous liquid vitreous injected into the anterior chamber of the phakic owl monkey eye leads to markedly increased intraocular pressure (IOP) peaking at one to two hours. In contrast, neodymium-YAG laser shock waves focused in the center of the anterior chamber of the same animal led to a mild decrease in IOP. Debris produced by laser pulses focused on the residual cortex of owl monkey eyes that had undergone extracapsular surgery failed to increase the IOP. Similarly, injection of dialyzed vitreous did not have any significant influence on IOP. We conclude that the disruption of the integrity of the anterior cortical gel and the subsequent release of a dialyzable intravitreal substance with a molecular weight of less than 10,000 daltons into the anterior chamber may contribute to the IOP rise after surgical discission, including neodymium-YAG laser posterior capsulotomy.

Excimer laser radial keratotomy

The central corneal flattening obtained by radial diamond knife incisions has been duplicated by radial laser incisions in 18 enucleated human eyes. The incisions, made by 193 nm far-ultraviolet light radiation emitted by the excimer laser, produced corneal flattening ranging from 0.12 to 5.35 diopters. Both the depth of the corneal incisions and the degree of central corneal flattening correlated with the laser energy applied. Histopathology revealed the remarkably smooth edges of the laser incisions.

Exogenous Na-hyaluronate in the anterior chamber of the owl monkey and its effect on the intraocular pressure

Exogenous, ultrapure (sterile, pyrogen-free), non-inflammatory fraction of Na-hyaluronate (NIF-NaHA) was introduced into the anterior chamber of owl monkeys (Aotus trivirgatus), replacing approximately 48% or 77% of the aqueous humor and creating post-injection intraocular pressures (IOPs) below normal (5-10 mmHg) or above normal (40-60 mmHg), respectively. Five different molecular weight samples (MW 1.7, 3.4, 3.7, 4.5 and 4.9 X 10(6)) were used. All solutions contained 1% NIF-NaHA and, because of the varying molecular weights, the viscosities of the solutions ranged between 10 000 and 930 000 cSt. The IOP and the rate of export of the exogenous NIF-NaHA from the anterior chamber were measured. All solutions caused an increase in the IOP, and the maximum level occurred at 4 hr after injection. In all cases, the IOP returned to normal 24 hr after injection. The highest and most persistent increase in IOP was observed after the injection of the solution with the lowest viscosity (10 000 cSt). The smallest increases in IOP over the post-operative value were observed after replacement of the aqueous humor using those samples with viscosities of 10 0000 to 300 000 cSt. The turnover (export rate) of injected NIF-NaHA depends for the most part on the viscosity of the injected solution. With increasing viscosity the rate constant, and therefore the half-life, of the injected NIF-NaHA decreases. The volume fraction of the viscous solution replacing the aqueous humor is also a determining factor in establishing the turnover rate. The molecular weight of the injected NIF-NaHA did not change during that time (48 hr) in which a sufficient amount of sample for analysis could be obtained. No evidence was found for the presence of any kind of hyaluronic acid-degrading agent in the anterior chamber.

Endothelial repair following Nd:YAG laser injury

Effects of different energy levels (1.2, 2.0, 2.8, 4.0 mj) of a mode-locked Nd:YAG laser beam focused directly on the corneal endothelium were evaluated in rabbit, cat, and owl monkey. The endothelial lesion observed by specular microscopy at 10 min; 8, 16, and 24 hr; 3, 5, 7, and 21 days measured up to 0.8 mM in diameter. It showed focal destruction of Descemet's membrane and a larger area of endothelial denudation corresponding probably to the shock wave generated by the plasma. The size of the defect correlated with the amount of energy delivered. Even though healing was characterized by a phase of rapid endothelial migration during the first 24 hr, only about one-half of the defect was covered after 1 week in all animals. This lesion persisted with minimal endothelial proliferation for 3 weeks in the rabbit and for 3 months in the cat. The monkey was followed for only 1 week. Our findings indicate that the laser-tissue interaction is different from mechanical or thermal modes of injury and interferes with the specific endothelial functions in repair.