In vitro flow properties of glaucoma implant devices.

PURPOSE: To develop a protocol for testing glaucoma implant devices and to use this protocol to characterize devices currently available. METHODS: The following devices were obtained: Ahmed Glaucoma Valve Implant, Baerveldt Implant, Krupin Eye Valve, Joseph Valve, and OptiMed Glaucoma Pressure Regulator. Pressure per unit time was measured in real-time during ramped pressure perfusion of the implant devices with an open-manometer system. Each device was measured during a 10 minute interval while a constant flow of fluid was pumped into the system. The open manometer allowed the resistance of the devices to generate a pressure head which was monitored by computer. Four independent runs were averaged for each device. RESULTS: The Ahmed devices demonstrated reliable valve performance with a mean opening pressure of 13.65 mm Hg, a facility flow of 1.2 microL/min/mm Hg and a closing pressure of 6.1 mm Hg. The Baerveldt devices had a mean facility flow of 7.56 microL/min/mm Hg. The Joseph devices had the most variable performance, opening from 2.05 to 6.21 mm Hg. Two of 4 Joseph devices had high facility of flow (5 microL/min/mm Hg). The Krupin devices had a mean opening pressure of 6.25 mm Hg in 3 of 4 devices. The remaining Krupin device did not exhibit valve behavior. The OptiMed device did not reveal an opening pressure, and had a mean facility of flow of 7.08 microL/min/mm Hg for high flow and 6.20 microL/min/mm Hg for low flow. CONCLUSION: An objective test protocol for glaucoma implant devices was demonstrated. All implant devices had high facility of flow compared to the normal eye and can be grouped into very high facility (Baerveldt and OptiMed), and high facility (Ahmed, Joseph and Krupin). Only the Ahmed device had consistent valve behavior. None of the devices created enough resistance to explain long-term clinical failure of glaucoma drainage device surgery.

A preliminary risk-benefit assessment of latanoprost and unoprostone in open-angle glaucoma and ocular hypertension.

Latanoprost and unoprostone (isopropyl unoprostone) represent the first commercially available prostaglandin analogues to be used for the treatment of glaucoma. Both compounds reduce intraocular pressure by enhancing uveoscleral outflow. Latanoprost, when used once daily in the evening, produces a greater reduction in pressure than timolol. Latanoprost produces mild conjunctival hyperaemia compared with timolol in some patients. Darkening of the irides has been reported, especially in green-brown, yellow-brown and blue/grey-brown irides. Hypertrichosis and hyperpigmentation of the eyelashes have also been demonstrated. Although latanoprost has not been proven to cause uveitis or cystoid macular oedema, case reports of an association exist. Latanoprost does not produce systemic adverse effects nor does it alter routine blood analyses. Unoprostone, when given twice daily, produces less of a reduction in intraocular pressure than timolol or latanoprost. Three times daily use may be required to approach the effectiveness of timolol. Unoprostone may have a similar adverse effect profile to latanoprost, but may to cause more corneal epithelial problems. Unoprostone is also not known to cause systemic adverse effects. Both agents are welcome additions to the treatment of glaucoma. However, additional studies and more experience are needed with each agents.

Tonometry in adults and children. A manometric evaluation of pneumatonometry, applanation, and TonoPen in vitro and in vivo.

OBJECTIVE: The purpose of the study was to determine the accuracy of applanation tonometry, pneumatonometry, and TonoPen tonometry in adults and children and the effect of age on tonometer error. DESIGN: The design was divided into four parts: part 1 was prospective and cross-sectional, and parts 2 through 4 were prospective, cross-sectional, and masked. PARTICIPANTS: This study contained 72 patients representing 74 data points. INTERVENTION: Tonometry with simultaneous manometry was performed. MAIN OUTCOME MEASURES: Intraocular pressure (i.o.p.) and the tonometric estimate of IOP were obtained. RESULTS: The normal pediatric IOP follows the line Ta = 0.71 age(years) + 10 up to age 10. Applanation tonometry under anesthesia differs from pneumatonometry by an average of -8.6 mmHg and is age related by the equation Ta = Tpn + 2.6 log(age) - 10.3. The TonoPen was the most accurate instrument for enucleated eyes, and the pneumatonometer was the most accurate in anesthetized living eyes. CONCLUSIONS: Applanation tonometry markedly underestimated IOP in young eyes. TonoPen tonometry performed well with enucleated eyes but was not adequately accurate for clinical use. The pneumatonometer performed the best clinically and the best overall.

Erbium: YAG laser trabecular ablation with a sapphire optical fiber.

The purpose of the study was to evaluate the effect of erbium (Er): yttrium aluminum garnet (YAG) laser trabecular ablation with a sapphire optical fiber on outflow facility. After obtaining baseline outflow facility using a computerized differential pressure perfusion system, human cadaver eyes were subjected to Er: YAG laser trabecular ablation using a sapphire optical fiber. Single pulses at varying energy levels (10 to 20 mJ pulse-1) were applied in a nearly contiguous fashion over four clock hours of meshwork. Post-laser outflow facility was then determined utilizing the same perfusion system and histopathologic analysis performed. Of the ten eyes, nine were perfused to steady baseline facility. One eye was excluded from the study because of a leak in our system during the initial perfusion. The mean baseline facility was 0.283+/-0.08 microl min-1 mmHg-1. There was a significant increase in outflow facility after trabecular ablation, with a mean post-laser facility of 0.62+/-0.15 microl min-1 mmHg-1 (P=0.01). Eyes which received a sham treatment showed no increase or a minimal increase in facility. Histopathologic analysis revealed ablation into Schlemm's canal with some thermal damage to the outer wall at all energy levels. Er: YAG laser trabecular ablation with a sapphire fiber is capable of increasing outflow facility in human cadaver eyes.

Erbium:YAG laser sclerectomy with a sapphire optical fiber.

BACKGROUND AND OBJECTIVE: Laser sclerectomy may offer advantages to conventional glaucoma filtering surgery by minimizing conjunctival manipulation and subsequent subconjunctival scarring and by providing easier access to difficult locations. It has been theorized that minimizing collateral thermal damage may enhance the success rate and reduce complications associated with laser sclerectomy. The thermal damage induced by the pulsed erbium:yttrium aluminum garnet (Er:YAG) laser is notably less than that of other laser modalities, including neodymium:YAG (1.06 microns), Er:YSGG (2.79 microns), holmium: YAG (2.10 microns), and holmium: YSGG (2.10 microns). A major obstacle to the clinical use of the Er:YAG laser has been the lack of an efficient and reliable delivery system. The single-crystal sapphire optical fiber has an acceptable attenuation rate and favorable characteristics for delivery of the Er:YAG wave-length in a clinical setting. MATERIALS AND METHODS: An Er:YAG laser (2.94 microns) focused into a 300-micron, single-crystal sapphire fiber was used to create ab-externo sclerectomies with varying energy levels and pulse rates in each eye of six anesthetized rabbits and six human cadaver eyes. Specimens then underwent histopathologic analysis and determination of the thermal damage zone. RESULTS: For the rabbit sclerectomies, there was a significant positive correlation between energy per pulse and the diameter of the thermal damage zone, which averaged 22.0 +/- 12.7 microns for all energy levels. For the human sclerectomies, a positive correlation existed between the total energy delivered (mJ/pulse x total pulses) and the thermal damage zone, with the mean thermal damage zone, being 25.0 +/- 9.0 microns. CONCLUSION: The Er:YAG laser with a sapphire optical fiber delivery system is an effective means of creating ab-externo sclerectomies with minimal thermal damage.

Radial keratotomy increases outflow facility in the porcine eye in vitro.

PURPOSE: To investigate the biomechanical effect induced by radial keratotomy on outflow facility in paired, enucleated whole porcine eyes. METHODS: Freshly enucleated porcine eyes were perfused at a constant pressure of 10 mm Hg. Radial keratotomy (RK), with a 3.5 mm central clear zone and eight radial incisions, was performed using a diamond knife with the blade length set at 100% of the paracentral corneal thickness, as measured by pachymetry. The fellow eye of each pair received sham RK as a control. RESULTS: Seven pairs of eyes were perfused (RK group n = 7, control n = 7). There was no significant difference in the mean baseline of outflow facility between the paired experimental and control eyes preoperatively (p = 0.5). After RK, outflow facility increased by 46% (p < 0.001) in the treatment group, compared to a 7% (p < 0.04) increase in the control group, resulting in a 39% increase in outflow facility attributed to RK (p < 0.001). CONCLUSIONS: Radial keratotomy produced a statistically significant acute increase in outflow facility in freshly enucleated porcine eyes. We believe that this increase results from steepening of the peripheral corneal curvature and the concomitant stretching of the iridocorneal angle. Further studies are needed to evaluate this effect in human eyes and in vivo.

Leukemic glaucoma: the effects on outflow facility of chronic lymphocytic leukemia lymphocytes.

The purpose of this study was to investigate the mechanisms of the leukemic glaucoma. We established a cell culture from leukemic cells collected from the aqueous humor of a living patient with chronic lymphocytic leukemia (CLL) and glaucoma secondary to the leukemia. We then perfused 16 pairs of fresh cadaver normal human eyes at a constant pressure of 10 mmHg at 37 degrees C. We delivered as a bolus either cultured CLL cells or cultured normal lymphocytes, using 3 x 10(2), 3 x 10(3), 3 x 10(4) or 3 x 10(5) cells in Bárány's solution, into one eye of each pair. The other eye of the pair served as a control, receiving a sham bolus of Bárány's solution alone. In addition, CLL and normal lymphocytes were perfused through 0.2, 0.6, 2, and 3 microns millipore filters. Following perfusion, the tissue and the filters were examined histopathologically by light, transmission and scanning electron microscopy. Cultured leukemic lymphocytes perfused into normal cadaver eyes caused a significantly more profound reduction in outflow facility than normal lymphocytes (P < 0.05); however, there was no significant difference in the effect on outflow facility between leukemic and normal lymphocytes when they were perfused through the millipore filters. Histopathology confirmed the presence of lymphocytes in the trabecular meshwork and Schlemm's canal, deforming on passage through the inner wall. Our results suggest that leukemic lymphocytes in CLL may reduce outflow facility by means of a biological interaction with the tissues of the outflow pathways, rather than by mechanical obstruction due to a lack of distensibility. Questions remain as to the nature of this biological interaction.