Orna Geyer

Nitric oxide synthase activity in tissues of the bovine eye

Abstract• Background: Nitric oxide synthase (NOS) is present in many ocular tissues where it may have different physiological functions. This warrants a thorough characterization of NOS activity in the eye. • Methods: NOS distribution and its biochemical properties were determined in the retina, choroid, ciliary processes (CP), and trabecular meshwork (TM). • Results: Retinal NOS required NADPH (diphenyleneiodonium, a flavoprotein inhibitor, which inhibited enzyme activity with an IC50 of 0.36 μM, FAD (40 μM), FMN (40 μM), and BH4 (4 μM) as cofactors for optimal activity. Ocular NOS appeared to be regulated by free divalent cations, since its activity was inhibited by EDTA (slopes >3.0 and IC50 values of 12.8, 19.7, and 53 μM, respectively). Ocular NOS required calmodulin, since NOS activity was inhibited by trifluoperazine (calmodulin inhibitor, IC50=41 μM). NOS activity is widely distributed in the eye, (choroid >reinta >CP >TM) and is mainly cytosolic (70–95%).l-Arginine analogs inhibited NOS in the retina, choroid, and TM. In all three tissues,NG-methyl-l,-arginine displayed the highest affinity for inhibition (IC50=0.2–0.7 μM) followed by canavanine (IC50=13–33 μM), while aminoguanidine only weakly inhibited NOS (IC50=93–179 μM). • Conclusion: In all tissues, the order of potency of inhibition points to the presence of constitutive rather than inducible NOS. Moreover, it is possible that TM contains more than a single form of NOS.

Management of large, leaking, and inadvertent filtering blebs with the neodymium: YAG laser

OBJECTIVEnThe purpose of the study was to test the efficacy of the neodymium:YAG (Nd:YAG) laser for repairing filtering blebs.nnnDESIGNnThe study design was a prospective study.nnnPARTICIPANTSnFive eyes of five patients with leaking blebs (group 1), five eyes of five patients with large irritating blebs (group 2), and four eyes of four patients with inadvertent filtering blebs in the surgical wound after cataract surgery (group 3) were studied.nnnINTERVENTIONnThe thermal mode of the Lasag Microrupter II Nd:YAG laser was used to treat the filtering blebs. The area of the bleb targeted for treatment was painted with methylene blue and then exposed to Nd:YAG laser treatment with an energy level of 2.5 to 3.75 J in a grid pattern. The aiming beam was focused on the conjunctiva, but the laser beam was offset according to the height of the bleb (offset of 0.9-1.5 mm, 4-5 on the Lasag) to selectively treat the internal surface of the bleb.nnnMAIN OUTCOME MEASURESnSymptomatology, intraocular pressure (IOP), and complications were measured.nnnRESULTSnAfter the laser treatment, all the leaks in group 1 were healed, all the patients in group 2 reported relief of their symptoms, and all blebs in group 3 shrank considerably. The IOP increased significantly (P < 0.001) after laser treatment in all three groups. This elevation appeared to diminish over time, with the major increase in IOP being recorded within the first month after the laser treatment. However, satisfactory IOP control was maintained in nearly all patients (13 to 14) who received none or one antiglaucoma medication. The visual acuity of one patient decreased significantly because of cataract formation. Complications included transient pressure rise (1 eye), bleb failure (1 eye), pupillary retraction toward the bleb (6 eyes), iatrogenic bleb leak (6 eyes), and cataract (1 eye).nnnCONCLUSIONnThe continuous wave Nd:YAG laser is an effective tool for repairing bleb-related problems while maintaining successful filtration.

Retinal Lesions in Septicemia

We explored the association between septicemia and specific retinal lesions in a prospective controlled study. Hemorrhages, cotton-wool spots, or Roths spots were found in 24 of 101 septicemic patients (24%), compared to four of 99 age- and gender-matched control patients (4%) (P = .0002). There was no significant association between types of organisms or focus of infection and the presence of specific lesions. Histologic examination of affected eyes disclosed cytoid bodies in the nerve fiber layer without inflammation. A definite association between septicemia and retinal lesions was found and indicates the need for routine ophthalmoscopy in septicemic patients.

Effectiveness of sub-Tenon’s versus peribulbar anesthesia in extracapsular cataract surgery ☆

PURPOSEnTo compare the effectiveness of sub-Tenons versus peribulbar anesthesia in extracapsular cataract surgery.nnnSETTINGnDepartment of Ophthalmology and the Maccabi Eye Institute, Tel Aviv, Israel.nnnMETHODSnSixty-four consecutive patients who had extracapsular cataract surgery were randomized to have sub-Tenons or peribulbar anesthesia. Intraocular pressure (IOP) was measured before and 1 and 10 minutes after injection. The motility of the rectus muscles was evaluated before and 20 minutes after the injection, and the patients anxiety level was recorded immediately after the injection. Pain was assessed intraoperatively and 1 and 24 hours postoperatively by patient self-grading.nnnRESULTSnOne minute after the injection, IOP increased significantly in the peribulbar group (mean 7.97 mm Hg +/- 8.80 [SD]) (P < .05). There was no significant increase in the sub-Tenons injection group (mean 0.12 +/- 3.09 mm Hg). In both groups, IOP returned to preinjection levels by 10 minutes postoperatively. Patients with peribulbar anesthesia reported a significantly higher level of anxiety than those who had sub-Tenons anesthesia (P < .05). Although the intraoperative pain levels were the same, the sub-Tenons group reported significantly higher levels of pain 1 and 24 hours postoperatively; 16% in the sub-Tenons group and none in the peribulbar group reported moderate pain 24 hours after anesthesia. Ocular motility was the same except for the inferior rectus muscle, which was less motile on average in the peribulbar group.nnnCONCLUSIONnSub-Tenons anesthesia led to less IOP elevation than peribulbar anesthesia and provided similarly good globe immobilization and approximately the same pain levels intraoperatively.

Clonidine provides an allergy-free alternative in glaucoma patients with proven allergy to apraclonidine

Abstractu2002· Purpose: The aim of this study was to determine allergic responses to clonidine hydrochloride 0.25% in glaucoma patients with proven allergic reaction to apraclonidine 0.5%.u2002· Methods: Fifteen consecutive glaucoma patients with allergic reaction to apraclonidine were prospectively challenged with clonidine hydrochloride 0.25% and evaluated for recurrence of allergic reactions and efficacy of treatment. Intraocular pressure (IOP), conjunctival hyperemia, blood pressure and resting pulse rate were determined at baseline and after 1, 3, 6 and 12 months.u2002· Results: None of the patients developed ocular allergic reaction during 12 months on clonidine therapy. Blood pressure and pulse rate did not change significantly with clonidine treatment. Clonidine caused a significant reduction of IOP from baseline. In one patient, topical clonidine caused fatigue, dizziness and dry mouth.u2002· Conclusion: Clonidine did not cause allergic reaction in patients with proven allergy to apraclonidine, indicating that there is no cross-reactivity with apraclonidine. Due to the small series, however, we cannot assume that allergy will not occur with clonidine 0.25% given time and a larger number of patients.

Capsular bag distension associated with sulcus implantation of intraocular lenses

Abstract Capsular bag distension syndrome after endophacoemulsification and in‐the‐bag intraocular lens (IOL) implantation has been reported. We describe 2 cases in which sulcus implantation of a posterior chamber IOL caused marked capsular bag distension. Both cases resolved with conservative treatment or a neodymium:YAG posterior capsulotomy.

Vasomotor reactivity in the ophthalmic artery: different from or similar to intracerebral vessels?

OBJECTIVEnIn order to evaluate hemodynamic features of ophthalmic arteries in patients with severe carotid artery stenosis, we assessed and compared vasomotor reactivity in the middle cerebral and ophthalmic arteries.nnnMETHODSnSixty-five patients (25 symptomatic, 40 asymptomatic) with severe (70-99%) internal carotid artery stenosis were studied using transcranial Doppler and the Diamox test.nnnRESULTSnVasomotor reactivity was found to be similar in the middle cerebral and ophthalmic arteries on the side of severe carotid stenosis in both symptomatic and asymptomatic patients. In contrast, the vasomotor reactivity of the ophthalmic arteries was significantly different from that of the middle cerebral arteries on the side of the normal or the non-significantly stenotic side of the internal carotid artery.nnnCONCLUSIONSnThese data suggest a specific autoregulative response of the ophthalmic artery compared to that of the middle cerebral artery and may shed light on the role of the ophthalmic artery in oculovascular hemodynamics.

The effect if divalent cations on bovine retinal NOS activity

The divalent cation requirements of NOS activity in bovine retina homogenate supernatant were investigated. Supernatants were assayed under standard conditions (in mM: EDTA 0.45, Ca2+ 0.25, Mg2+ 4.0). In order to investigate the enzymes dependence on divalent cations, the tissue homogenate was depleted of di- and trivalent cations by passing it over a cation-exchange column (Chelex 100). Surprisingly, NOS activity was 50-100% higher in this preparation. However, addition of either EDTA (33 μM) or EGTA (1 mM) almost fully inhibited NOS activity, suggesting a requirement for residual divalent metal cation(s). Phenanthroline or iminodiacetic acid at low concentrations had little effect on activity, suggesting no requirement for Fe2+, Zn2+ or Cu2+. Ca2+ had a moderate stimulatory effect, with an optimum activity around 0.01 mM. Mg2+ or Mn2+ had little effect at concentrations < 0.25 mM. However, in the presence of EDTA, Mn2+ or Ca2+ markedly stimulated NOS activity with the optimum at 0.1 mM. At high concentrations (> 0.1-0.2 mM), all divalent cations tested (Ba2+, Zn2+, Co2+, Mn2+, Mg2+, Ca2+), as well as La3+, dose-dependently inhibited NOS activity. We propose that retinal NOS requires low concentrations of naturally occurring divalent metal ions, most probably Ca2+, for optimal activity and is inhibited by high di- and trivalent metal concentrations, probably by competition with Ca2+.

Effect of oral nifedipine on ocular blood flow in patients with low tension glaucoma

AIMnTo investigate the effect of oral nifedipine on ocular blood flow in patients with low tension glaucoma (LTG).nnnMETHODSnIn this prospective study we examined the effects of 3 weeks of treatment with oral nifedipine 30 mg/day in 11 patients with LTG, by using colour Doppler ultrasound imaging to measure haemodynamic variables in the central retinal (CRA), short posterior ciliary (SPCA), and ophthalmic (OA) arteries. Intraocular pressure (IOP) and blood pressures were also evaluated.nnnRESULTSnNifedipine failed to alter IOP nor did it change peak systolic velocity, end diastolic velocity,or the resistance index in any of the three ocular vessels studied (p > 0.05). However systolic and diastolic systemic arterial blood pressure measurements varied significantly after nifedipine treatment compared with baseline (p < 0.05).nnnCONCLUSIONnOur study failed to demonstrate a significant effect of nifedipine on retrobulbar circulation of patients with LTG.