Monitoring the effect of mild ischemia with a built-in light-emitting diode contact lens electrode and a low-cost custom-made apparatus.

Electroretinography (ERG) is widely used in clinical work and research to assess the retinal function. We evaluated an easy to build ERG setup adapted for small animals comprising two contact lens electrodes with a built-in light-emitting diode and a custom-made amplification system. The system's sensitivity was tested by monitoring ERG in albino rat eyes subjected to mild ischemia. Flash ERG was recorded by two contact lens electrodes positioned on the rat's corneas and used alternately as test or reference. The a- and b-wave amplitudes, a-wave latency, b-wave implicit time and oscillatory potentials (OPs) were analyzed. Ischemia was achieved by elevating the intraocular pressure in the eye's anterior chamber. ERG was recorded on post-ischemia (PI) days -1, 1, 3 and 7. Morphological changes were analyzed on hematoxylin/eosin stained 5 µm sections of control 7d PI retinas. In control eyes, ERG exhibited a pattern similar to a standard recording. Retinas subjected to mild ischemia preserved ordered layered morphology, exhibiting approximately 30% loss of ganglion cells and no changes in gross morphology. By day 3 PI, ischemia caused an increase in the a-wave amplitude (from 34.9 ± 2.7 to 45.4 ± 4.3 µV), a decrease in the b-wave amplitude (from 248 ± 13 to 162 ± 8 µV), an increase in a-wave latency (from 11.1 ± 0.3 to 17.3 ± 1.4 ms) and b-wave implicit time (from 81.0 ± 1.6 to 90.0 ± 2.5 ms), and attenuation of OPs. The described setup proved sensitive and reliable for evaluating subtle changes in the retinal function in small animals.

Effect of sub-Tenon's and peribulbar anesthesia on intraocular pressure and ocular pulse amplitude.

PURPOSE: To compare the effect of peribulbar and sub-Tenon's anesthesia on intraocular pressure (IOP) and ocular pulse amplitude (OPA) in the injected eye and the fellow noninjected (control) eye. SETTING: Tel Aviv Medical Center, Tel Aviv, Israel. METHODS: This prospective study measured IOP and OPA at baseline and 1 and 10 minutes after administration of lidocaine anesthesia in 40 consecutive adult patients having elective cataract surgery. RESULTS: The IOP remained stable throughout the study with both modes of anesthesia. One minute after injection of the anesthetic agent, the OPA was significantly decreased in the injected eyes in both the sub-Tenon's (24%; P < .05) and peribulbar (25%; P < .05) groups. The decrease in the OPA in the sub-Tenon's group (14%; P < .05) was detectable after 10 minutes in the control eyes. In the peribulbar anesthesia group, the OPA in the control eyes increased significantly (9%; P < .05) 1 minute after injection of the anesthetic agent, returning to preinjection levels 10 minutes after the injection. CONCLUSIONS: The OPA in the eyes in which lidocaine was injected decreased significantly in both the sub-Tenon's and peribulbar groups. These findings have implications for the management of patients whose ocular circulation may be compromised.

Internal carotid artery hypoplasia presenting as anterior ischemic optic neuropathy.

PURPOSE: To describe the occurrence of anterior ischemic optic neuropathy in a young woman with internal carotid artery hypoplasia. METHODS: Case report with clinical and radiologic observations. RESULTS: A 38-year-old woman suffered from a sudden, painless loss of vision in her right eye. The diagnosis of anterior ischemic optic neuropathy was based on the clinical course and appearance of the fundus. Doppler evaluation of the carotid arteries, computed tomography (CT) scan, magnetic resonance imaging (MRI), and CT angiogram all demonstrated internal carotid artery hypoplasia on the same side. CONCLUSION: Although carotid artery disease (mainly atherosclerosis) is not a common predisposing factor for anterior ischemic optic neuropathy, our patient had an ipsilateral coexisting internal carotid artery hypoplasia and anterior ischemic optic neuropathy. We believe that the carotid artery anomaly might have contributed to the development of anterior ischemic optic neuropathy in this patient.

Acute effect of latanoprost on pulsatile ocular blood flow in normal eyes.

PURPOSE: To determine the effect of an acute dose of 0.005% latanoprost on intraocular pressure and pulsatile ocular blood flow in normal eyes. METHODS: Nineteen volunteers received a single dose (two drops) of latanoprost 0.005% in one eye and placebo in the fellow control eye, randomized and masked to the observer. Intraocular pressure, perfusion pressure, pulsatile ocular blood flow, and systemic circulatory parameters were measured before and 8 hours after dosing. RESULTS: The mean (+/- SE) intraocular pressure, perfusion pressure, and pulsatile ocular blood flow before treatment were 17 +/- 1 mm Hg, 46 +/- 3 mm Hg, and 13 +/- 1 microl per second, respectively, in both the treated and control eyes. The mean intraocular pressure reduction was 4.9 and 2.1 mm Hg (28% and 12%) in the treated and fellow eye, respectively. The mean perfusion pressure increase was 5.6 and 2.8 mm Hg (12% and 6%) in the treated and fellow eye, respectively. The mean pulsatile ocular blood flow increase was 2.7 and 0.2 microl per second (20% and 1%) in the treated and fellow eye, respectively. The treated eye change in pulsatile ocular blood flow was not correlated to the change in perfusion pressure. Simultaneous reduction of intraocular pressure and increase or no significant change in pulsatile ocular blood flow occurred in 15 of 19 (79%) of the treated eyes. The systemic blood pressure and pulse rates remained in normal ranges over the 8-hour period. CONCLUSION: In this study, topical latanoprost significantly reduces intraocular pressure and increases ocular blood flow in normal eyes 8 hours after dosing. These effects of latanoprost may be beneficial in the management of glaucoma patients.

[Retinal injury induced by laser pointers].

Laser pointers originally designed for use during presentations are ubiquitous and are even sold as toys (such as pens or on key chains) in drug stores. Though reported as safe, the laser pointers still carry the risk of potential damage to the eye. We report a 16-year-old boy with bilateral retinal injury caused by 20-30 seconds of exposure to a laser pointing-device. Immediately thereafter, vision was blurred bilaterally and he noted a central red scotoma in each eye. Symptoms resolved spontaneously within 2 days but the retinal scars remained all during the 10 months of follow-up. It is clear from our report and 3 other publications that retinal damage can develop from misusing laser pointers. Laser hazards and safety should be stressed for the general public. We recommend that laser-pointers should not be available as toys to children and teenagers.

[Causes of blindness in Israel].

Of the world population, 38 million are blind and another 110 million are visually impaired. Even in the developed countries there are 3.5 million who are blind. This study of blindness in Israel is based on the National Blind Registry. At the end of 1998, 15,937 were registered as blind, 0.3% of the total population; 776 (5%) of them were 18 years old or younger; 6,426 (40%) 18-65 years old; and 8,735 (55%) 65 years or older. The leading causes of blindness in Israel are glaucoma (2,074, 13%), macular degeneration (1,954, 12%) and diabetes mellitus (1,680, 11%). Since glaucoma and diabetes, and to a lesser extent glaucoma, respond to treatment, blindness could have been avoided in most cases. National screening programs for early diagnosis and treatment of these diseases would reduce prevalence of the newly blind.

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

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%. 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. 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. 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.

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

OBJECTIVE: In 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. METHODS: Sixty-five patients (25 symptomatic, 40 asymptomatic) with severe (70-99%) internal carotid artery stenosis were studied using transcranial Doppler and the Diamox test. RESULTS: Vasomotor 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. CONCLUSIONS: These 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.

Nonadrenergic, noncholinergic relaxation of bovine iris sphincter: role of endogenous nitric oxide.

PURPOSE: To investigate the role of endogenously generated nitric oxide (NO) in the relaxation of bovine iris sphincter. METHODS: Isolated bovine sphincters were mounted on an isometric tension apparatus. Contraction-relaxation response was elicited by electrical field stimulation (ES; 12 Hz, 50-msec duration, 70-80 V). Relaxation was arbitrarily defined as maximal decrease of tension below prestimulation baseline after cessation of ES. We also determined the tissue levels of cyclic guanosine monophosphate (cGMP) by radioimmunoassay. RESULTS: ES produced a biphasic response: contraction followed by relaxation. After cessation of ES, the muscle relaxed to below the initial baseline tension. Tetrodotoxin (TTX) abolished most of the contraction and all the relaxation response. Atropine blocked most of the contraction component, leaving the relaxation component unchanged. Prazosin and bupranolol (alpha1-adrenergic and beta-adrenergic antagonists, respectively) also did not affect the relaxation component of the response. Neither substance P nor its antagonist (N-acetyl-L-tryptophane 3,5-bis (trifluoromethyl)-benzyl ester; ATTB) inhibited or mimicked the response. The nitric oxide synthase (NOS) inhibitors Nomega-nitro-L-arginine methyl ester (L-NAME), Nomega-nitro-L-arginine (L-NNA), and aminoguanidine dose-dependently inhibited the relaxation response by 50% to 70%. The free radical scavenger 2-(4-carboxyphenyl) 4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (carboxy-PTIO) and the guanylyl cyclase inhibitor methylene blue also abrogated 70% and 45% of the relaxation response, respectively. ES caused an increase in muscle cGMP from 2.3+/-0.3 to 3.9+/-0.5 picomoles per muscle. L-NNA or L-NAME significantly decreased the tissue cGMP content (to 1.2+/-0.1 picomoles per muscle) and prevented the increase caused by ES. CONCLUSIONS: The relaxation component of the iris sphincter response to ES is a distinct nonadrenergic, noncholinergic, ES-induced event. Most of the relaxation is mediated by the endogenously generated NO-guanylyl cyclase-cGMP cascade.

The effect of 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 enzyme's 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 microM) 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+.

Pressure-volume relation for the living human eye.

PURPOSE: The pressure-volume relation for an eye is the mathematical equation that relates changes in intraocular pressure to changes in intraocular volume. This relation is useful for calculating outflow facility from tonography and pulsatile ocular blood flow from intraocular pressure pulsations. The present work develops a new relation by culling together all the published direct manometric rigidity measurements on living human eyes. METHODS: A total of 182 data items taken from 21 eyes are available in the 1958-62 literature of Ytteborg, Prijot, Eisenlohr, Langham and Maumenee. The approach was (i) to perform an error analysis based on the various experimental conditions, (ii) to assume general mathematical forms for the relation, (iii) to use least-squares analysis and statistical measures to find the optimal data representation, and (iv) to introduce the total volume of the eye into the formulation. RESULTS: A new formula for the pressure-volume relation for the living human eye is derived relating DeltaV, the change in volume, to P, the corresponding intraocular pressure: DeltaV = V (C + C(0) x ln P + C( 1) x P), where V is the volume of the eye, C, C(0) and C(1) are numerical parameters. This equation gives the most statistically significant fit to the experimental data. CONCLUSION: The new equation for the pressure-volume relation derived from all the currently available ocular rigidity data on the living human eye gives a larger volume increment for a given increment of pressure than Friedenwald's equation based on measurements performed on cadaver eyes.

Effectiveness of sub-Tenon's versus peribulbar anesthesia in extracapsular cataract surgery.

PURPOSE: To compare the effectiveness of sub-Tenon's versus peribulbar anesthesia in extracapsular cataract surgery. SETTING: Department of Ophthalmology and the Maccabi Eye Institute, Tel Aviv, Israel. METHODS: Sixty-four consecutive patients who had extracapsular cataract surgery were randomized to have sub-Tenon's 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 patient's anxiety level was recorded immediately after the injection. Pain was assessed intraoperatively and 1 and 24 hours postoperatively by patient self-grading. RESULTS: One 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-Tenon's 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-Tenon's anesthesia (P < .05). Although the intraoperative pain levels were the same, the sub-Tenon's group reported significantly higher levels of pain 1 and 24 hours postoperatively; 16% in the sub-Tenon's 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. CONCLUSION: Sub-Tenon's anesthesia led to less IOP elevation than peribulbar anesthesia and provided similarly good globe immobilization and approximately the same pain levels intraoperatively.

Pulsatile ocular blood flow in diabetic retinopathy.

PURPOSE: To assess circulatory properties of eyes with progressive stages of diabetic retinopathy. METHODS: The intraocular pressure, pulse amplitude (PA) and pulsatile ocular blood flow (POBF) were measured with a pneumatonometer (OBF Labs UK Ltd). The eyes were grouped: (a) normal control, n = 26, (b) diabetes with no observable diabetic retinopathy (NDR), n = 18, (c) mild to moderate non-proliferative diabetic retinopathy (NPDR), n = 20, and (d) very severe pre-proliferative and proliferative diabetic retinopathy (PPDR/PDR), n = 12. RESULTS: The PA and POBF values were lower than normal values in the earliest stage (NDR). The POBF increased but was still below normal levels at the NPDR stage, and then increased to an above normal level in the PPDR/PDR stage of diabetic retinopathy. The PA was at normal levels in these later two stages. CONCLUSION: An initial decrease in pulsatile ocular blood flow is present with the onset of diabetes where no diabetic retinopathy has yet occurred. Subsequently, the pulsatile ocular blood flow increases with the severity of the retinopathy.

"The disappearing lens": failure of CT to image the lens in traumatic intumescent cataract.

The CT scans of three patients whose eyes were lacerated by trauma failed to demonstrate the lens. A slit-lamp examination of those eyes clearly indicated that the lenses were present behind the iris but that they were swollen and opaque (intumescent cataract). Apparently, a shift of water into the injured lens had reduced the expected hyperdense CT image of the lens to a level that it was no longer discernible.

Elevated tear interleukin-6 levels in patients with Sjögren syndrome.

OBJECTIVE: The purpose of the study was to investigate interleukin-6 (IL-6) levels in the tear fluid and sera of patients with Sjögren syndrome (SS). PARTICIPANTS: Twelve patients with primary SS and 12 normal control subjects participated. INTERVENTION: Tear fluid and sera were obtained from the study and the control groups. Evaluation of tear fluid and sera IL-6 levels was done by using a quantitative enzyme-linked immunosorbent assay kit. All assays were carried out blindly with respect to diagnosis. MAIN OUTCOME MEASURES: Tear fluid IL-6 levels were measured. RESULTS: The mean concentration (+/- standard error) of IL-6 in the tears of patients with SS was elevated significantly compared to that of normal control subjects (88.6+/-16.2 vs. 42.1+/-10.6 pg/ml; P < 0.05). No significant differences were noted in the serum IL-6 levels between the two groups. A significant correlation (r = 0.742, P = 0.006) was found between tear fluid IL-6 levels and the focus score of lip biopsy specimens in patients with SS. CONCLUSION: Tear fluid IL-6 levels may serve as an important marker for tear gland involvement in SS.