Michael E. Yablonski

Trabeculectomy with internal tube shunt: a novel glaucoma surgery.

Purpose:To describe a pilot study that evaluates the efficacy and mechanism of action of a new glaucoma operation, trabeculectomy with internal tube shunt. Methods:Twenty-three patients underwent the new operation in one eye for open angle glaucoma. Under a scleral flap, a deep sclerectomy was performed, resulting in an intrascleral lake. Laterally, on both sides, a small silicone tube was placed between the intrascleral lake and the suprachoroidal space. A trabeculectomy stoma and a peripheral iridectomy permitted easy access of aqueous to the tube. Postoperative and preoperative results were analyzed and also compared with results of 45 eyes that underwent a conventional trabeculectomy. Results:After a mean follow-up time of 324 days, the mean postoperative IOP was 13.8 mm Hg compared with a preoperative value of 25.4 mm Hg. The mean number of postoperative medications was only 1.1 compared with a preoperative value of 3.0. No significant change in outflow facility was seen. The bleb size was very small. In comparison, in conventional trabeculectomy eyes, the outflow facility and bleb size were significantly larger. Conclusion:Trabeculectomy with internal tube shunt is very effective in lowering IOP. It is postulated to work, to a large extent, by allowing access of the aqueous humor to the suprachoroidal space where the protein colloid osmotic pressure of uveal blood causes its absorption. This new procedure offers many advantages over other filter procedures and tube shunts.

Effects on aqueous flow of dorzolamide combined with either timolol or acetazolamide.

Purpose:To determine the effect on aqueous flow of topical dorzolamide 2%, topical timolol 0.5%, or oral acetazolamide 250 mg when used alone or when dorzolamide is combined with either timolol or acetazolamide. Methods:In 30 patients with ocular hypertension, aqueous flow and intraocular pressure (IOP) were determined at baseline and on the following combinations of drugs in a crossover design: (1) vehicle alone, (2) dorzolamide alone, (3) acetazolamide alone, (4) timolol alone, (5) dorzolamide + acetazolamide, and (6) dorzolamide + timolol. Treated eyes were compared with control eyes and comparisons were made between treatments. Results:Compared with baseline, significant (P < 0.04) IOP reductions in the order of efficacy were: dorzolamide + timolol > dorzolamide + acetazolamide = acetazolamide = timolol > dorzolamide. Aqueous flow was reduced more by dorzolamide + timolol than by each drug alone (P < 0.04) and more by dorzolamide + acetazolamide than by dorzolamide alone (P < 0.04). Conclusion:The combination of dorzolamide and timolol demonstrated significant aqueous flow additivity and had greater IOP efficacy than the combination of dorzolamide and acetazolamide.

Effects of multiple dosing of epinephrine on aqueous humor dynamics in human eyes.

Numerous studies have provided conflicting evidence to explain the ocular hypotensive mechanism of action of epinephrine. Although epinephrine has been shown consistently to increase outflow facility, its effects on aqueous flow and uveoscleral outflow are not as clear. The purpose of this study was to clarify the effects of multiple doses of topical epinephrine on aqueous humor dynamics in human eyes. This was done by evaluating the four main parameters that determine steady state intraocular pressure. These parameters were assessed at baseline and after a week of twice-daily treatment of epinephrine hydrochloride 2% to one eye. Twenty-six human volunteers were enrolled in the study. Intraocular pressure was measured by pneumatonometry, aqueous flow and trabecular outflow facility by fluorophotometry, episcleral venous pressure by venomanometry and uveoscleral outflow by mathematical calculation. In epinephrine-treated eyes compared to baseline, intraocular pressure and aqueous flow were reduced from 21.2 +/- 0.3 to 17.1 +/- 0.2 mmHg (19%, p = .01) and 3.3 +/- 0.2 to 2.9 +/- 0.2 microl/min (12%, p = .03), respectively. Trabecular outflow facility obtained by fluorophotometry was increased from 0.18 +/- 0.02 to 0.26 +/- 0.03 microl/min/mmHg (44%, p = .02). Topical epinephrine did not significantly affect uveoscleral outflow or episcleral venous pressure. In conclusion, multiple topical doses of epinephrine lowered intraocular pressure in human volunteers by reducing aqueous humor formation and increasing trabecular outflow facility. The increase in uveoscleral outflow suggested by other studies was not observed.

The effect of colchicine on aqueous humor dynamics

Abstract The plant alkaloid, colchicine, which binds specifically to tubulin, was studied for its effect on aqueous humor dynamics in the rabbit. Topical application of either 50 or 100 μg of colchicine resulted in a significant lowering of intraocular pressure after 24 hr. Colchicine significantly increases the rate of aqueous humor outflow while having no effect on aqueous inflow. Intraocular pressure returns to baseline despite continued administration of colchicine, which results in severe ocular toxicity. This study suggests that the aqueous outflow system contains microtubules or membrane-associated tubulin, the integrity of which is necessary for the maintenance of intraocular pressure.

Acute effects of insulin on aqueous humor flow in patients with type 1 diabetes

PURPOSEnPrevious studies reported reduced aqueous humor flow through the anterior segment of the eye in patients with type 1 diabetes. This study investigates whether reduced flow is the result of the diabetic state or of alterations in glucose or insulin concentrations.nnnMETHODSnA cross-sectional study, involving patients with type 1 diabetes and healthy controls, measured aqueous flow at different insulin concentrations. Eleven patients with type 1 diabetes (hemoglobin A1C = 7.0 +/- 0.3% [mean +/- SEM], normal < 6.5) with no microvascular complications and 17 controls were prospectively studied. Controls were studied fasting and during a hyperinsulinemic-euglycemic clamp (insulin 2 mU/kg per minute). Patients with type 1 diabetes were similarly studied during two euglycemic clamp procedures (insulin 0.5 and 2.0 mU/kg per minute). Aqueous flow was measured by fluorophotometry. Pulsatile ocular blood flow and intraocular pressure were measured with a Langham flow probe.nnnRESULTSnControl subjects had no change in aqueous flow during fasting and hyperinsulinemic conditions (3.0 +/- 0.1 vs 2.8 +/- 0.1 microl per minute). In the patients with type 1 diabetes, aqueous flow was not decreased with hyperinsulinemia, compared with the low insulin state (P =.7). Compared with control subjects, patients with type 1 diabetes had lower aqueous flow during hyperinsulinemia (2.4 +/- 0.1 microl per minute, P =.03) and at lower insulin conditions (2.6 +/- 0.1 microl per minute, P <.05). No differences in intraocular pressure or pulsatile ocular blood flow were noted between groups or between insulin states within groups.nnnCONCLUSIONSnAqueous flow is decreased in patients with type 1 diabetes under euglycemic conditions of high and relatively low insulin concentrations, despite the absence of microvascular complications.

A new fundus lens ophthalmodynamometer.

I devised a new ophthalmodynamometer by means of which a measured force is applied to a fundus lens, while the disk vessels are viewed at the slit-lamp microscope. In my hands, the new device was superior to the Bailliart ophthalmodynamometer when tested in normal volunteers. With the fundus lens ophthalmodynamometer, the diastolic end point differed between the two eyes by a mean of 2.3%, compared to 6.4% with the Bailliart. The new device showed a better correlation with systemic diastolic blood pressure than did the Bailliart instrument. The effect of intraocular pressure on the reading with the fundus lens device was significant, although variable.

A New Portable Applanation Tonometer

A portable applanation tonometer consisted of a Goldmann applanation doubling prism mounted on a dynamometer. Results obtained on 100 consecutive eyes showed a good correlation with the standard slit-lamp mounted applanation tonometer. This portable tonometer is small and easy to use, utilizing the same end point as the standard Goldmann tonometer. In addition, the patient may assume almost any position.