ETa-receptor blockade, but not ACE inhibition, blunts retinal vessel response during isometric exercise.

Angiotensin II and endothelin-1 are potent vasoconstrictors that appear to play a role in retinal blood flow regulation. In the present study, we investigated the possible role of the angiotensin and the endothelin system in the regulation of retinal vessel diameters during isometric exercise in healthy humans. The study design was randomized, double-masked, placebo-controlled, and three-way cross over. Twelve healthy subjects performed squatting exercises for 6 min during infusion of either an angiotensin-converting enzyme inhibitor (enalapril), an ET(A)-receptor antagonist (BQ-123), or placebo. Retinal vessel diameters were measured continuously with the Zeiss retinal vessel analyzer. Systemic hemodynamics were assessed noninvasively, and intraocular pressure was measured with applanation tonometry. Squatting induced a significant increase in blood pressure and pulse rate, which was paralleled by a vasoconstriction in retinal arteries and veins. Intraocular pressure was only slightly increased during the squatting periods. BQ-123 significantly blunted the exercise-induced decrease in venous (P < 0.01) and arterial (P < 0.02, ANOVA) vessel diameters but had no effect on basal retinal diameters. By contrast, enalapril did neither influence vessel diameter at baseline conditions nor in response to isometric exercise. The data of the present study indicate that retinal vasoconstriction during isometric exercise is modified by ET(A)-receptor blockade, whereas it is not altered by angiotensin-converting enzyme inhibition. Hence, the present data indicate that endothelin-1, but not angiotensin II, is involved in retinal blood flow regulation during isometric exercise.

Biometry and refractive outcome of eyes filled with silicone oil by standardized echography and partial coherence interferometry.

BACKGROUND: We evaluated the validity of calculations for refractive outcome in cataract surgery in silicone oil-filled eyes. The retrosilicone space (RSS) was included in these calculations. METHODS: In a prospective study the axial length (AL) of silicone oil-filled eyes was measured. with standardized A-scan echography (SAE) and partial coherence interferometry (PCI). Meldrum's formula was used to transform the velocity of ultrasound within the vitreous cavity. To investigate whether refractive outcome can be calculated accurately, we assessed the difference between precalculated and final refractive outcome. Furthermore, we determined the advantages and disadvantages of SAE and PCI. A minor aim was to assess whether the AL of the two eyes differed significantly. RESULTS: In 85% of 117 eyes the difference between precalculated and postsurgical refraction was smaller than 1 diopter spherical and statistically not significant (p>0.2). The mean AL was 24.1 mm (range 20.0-31.4 mm). The difference in outcome between the two methods was without statistical significance: the AL difference was 0.4 (+/-2.6) mm on measurement with SAE and 0.04 (+/-0.46) mm with PCI. PCI has the advantage that it can be performed more easily, without contact, while echography is advantageous in the presence of advanced cataracts. In supine position an oil-free fluid space behind the silicone oil was detected with echography. The mean dimension of this space was 1.9 (+/-0.67) mm and it was taken into consideration for IOL calculation. The mean AL difference between the two eyes was 0.4 mm, but the difference was greater than 1 mm in 26% of the patients. CONCLUSION: The AL of eyes filled with silicone oil can be measured reliably with SAE and PCI. In supine position the RSS has to be considered to obtain more accurate IOL calculations.

Regulation of human retinal blood flow by endothelin-1.

There is evidence from in vitro and animal studies that endothelin is a major regulator of retinal blood flow. We set out to characterize the role of the endothelin-system in the blood flow control of the human retina. Two studies in healthy subjects were performed. The study design was randomized, placebo-controlled, double-masked, balanced, two-way crossover in protocol A and three way-way crossover in protocol B. In protocol A 18 healthy male subjects received intravenous endothelin-1 (ET-1) in a dose of 2.5 ng kg (-1)min(-1) for 30 min or placebo on two different study days and retinal vessel diameters were measured. In protocol B 12 healthy male subjects received ET-1 in stepwise increasing doses of 0, 1.25, 2.5 and 5 ng kg (-1)min(-1) (each infusion step over 20 min) in co-infusion with the specific ET(A)-receptor antagonist BQ123 (60 microg min (-1)) or placebo or BQ123 alone investigating retinal vessel diameters, retinal blood velocity and retinal blood flow. Measurements of retinal vessel size were done with the Zeiss retinal vessel analyzer. Measurements of blood velocities were done with bi-directional laser Doppler velocimetry. From these measurements retinal blood flow was calculated. In protocol A exogenous ET-1 tended to decrease retinal arterial diameter, but this effect was not significant versus placebo. No effect on retinal venous diameter was seen. In protocol B retinal venous blood velocity and retinal blood flow was significantly reduced after administration of exogenous ET-1. These effects were significantly blunted when BQ-123 was co-administered. By contrast, BQ-123 alone had no effect on retinal hemodynamic parameters. Concluding, BQ123 antagonizes the effects of exogenously administered ET-1 on retinal blood flow in healthy subjects. In addition, the results of the present study are compatible with the hypothesis that ET-1 exerts its vasoconstrictor effects in the retina mainly on the microvessels.

Ocular surface changes and tear film alterations associated with sun gazing during a solar eclipse.

PURPOSE: A solar eclipse occurred in central Europe on August 11th, 1999. Following the eclipse, patients with ocular symptoms were investigated. Gazing at the sun without protection is liable to damage the retina. Our attention was focused on changes of the ocular surface and the tear film. METHODS: Forty-three patients were investigated within one week after the solar eclipse as baseline. 33 of them were followed up one year later. Visual acuity and the central visual-field were measured, and the ocular surface and the fundus were examined using a slit lamp. The quality of the lacrimal tear film was examined using Schirmer's test for the aqueous layer, break-up time for the mucous layer and interference observation for the lipid layer, measured by a slit lamp and a tearoscope. RESULTS: At the baseline 19 patients had non-specific visual problems. Pathological alterations of the tear film were seen in all three tear-film layers: Schirmer's test was pathological in 87%, break-up time decreased in 85%, the interference pattern of the lipid layer changed in 67% and there were changes in 87% using the tearoscope. One year later the non specific visual disorders had disappeared. Schirmer's test did not reveal much change from the baseline: 51% pathological, 24% remained pathological in break-up-time and the lipid layer was normalized except in 9%. Using the tearoscope, lipids were better than grade 3 in all patients. CONCLUSION: After gazing at a solar eclipse the ocular surface and tear film changed. While the aqueous layer remained pathological in many patients, the lipid layer and the mucous layer recovered spontaneously.

Aqueous flare and macular edema in eyes with diabetic retinopathy.

BACKGROUND: The breakdown of the blood-retina barrier in diabetic patients is correlated with a dysfunction of the blood-aqueous barrier. In our study, we wanted to investigate the effect of grid photocoagulation in diabetic macular edema on the aqueous flare. METHODS: Modified grid pattern photocoagulation was performed on 20 patients with diabetic macular edema. The aqueous flare intensity was measured by the laser flare cell meter before and 4 months after laser treatment. RESULTS: The mean flare value was 9.8 +/- 4.7 photons/ms before laser treatment. After grid photocoagulation, the flare value was 7.1 +/- 3.6 photons/ms. Flare values were significantly decreased after laser treatment. CONCLUSION: Our results suggest a correlation between the effect of grid photocoagulation on the blood-retina barrier and the permeability of the blood-aqueous barrier. The laser flare intensity seems to be a quantitative indicator for the diabetic dysfunction of the blood-retina barrier.

Cataract surgery in patients with diabetic retinopathy: visual outcome, progression of diabetic retinopathy, and incidence of diabetic macular oedema.

BACKGROUND: Compared to non-diabetic patients, outcome after cataract surgery was reported to be worse in diabetic patients--especially in those with diabetic retinopathy. This prospective study was planned to evaluate visual outcome, progression of diabetic retinopathy, and incidence of clinically significant macular oedema (CSME) in a homogenous group of patients with non-proliferative diabetic retinopathy (NPDR) without CSME at baseline 1 year after cataract surgery. METHODS: Over a period of 18 months, all consecutive patients with mild-to-moderate diabetic retinopathy who had cataract surgery with phacoemulsification and posterior chamber lens implantation were prospectively followed up. Outcomes were assessed 1 year postoperatively and included visual acuity (VA), progression of retinopathy, and incidence of CSME. Progression of retinopathy and incidence of CSME were compared to the non-operated fellow eyes. RESULTS: Of 50 patients included, 42 completed the 1-year follow-up. VA improved in 85% of patients, and was better than 0,5 in 71%. Progression of retinopathy occurred in 12% of eyes after cataract surgery and in 10.8% of non-operated fellow eyes. No patient developed proliferative diabetic retinopathy in the operated eye. CSME occurred in 13 operated eyes (31%), five of them with retinal ischemia, and in five non-operated eyes (13.5%). Patients with ischemic macular oedema had the worst prognosis regarding VA. CONCLUSION: Modern cataract surgery seems to have no influence on the progression of diabetic retinopathy. A visual improvement is achieved in the majority of patients with NPDR, but poorer visual outcome is observed in patients developing macular oedema.

Effect of noradrenaline on retinal blood flow in healthy subjects.

PURPOSE: To gain insight into the role of circulating catecholamines on retinal blood flow in vivo. DESIGN: Nonrandomized, open, crossover design. PARTICIPANTS: In 10 healthy male subjects, tyramine and noradrenaline were administered in stepwise increasing doses. These doses were selected to induce comparable changes in systemic blood pressure. METHODS: During each infusion step, retinal vessel diameter and retinal venous blood speed were measured with the Zeiss retinal vessel analyzer (Zeiss, Jena, Germany) and laser Doppler velocimetry, respectively. MAIN OUTCOME MEASURES: Retinal blood flow through a major temporal vein was calculated. RESULTS: As expected, tyramine and noradrenaline induced a systemic hypertensive response. Tyramine caused a moderate increase in noradrenaline plasma levels, whereas exogenous noradrenaline increased noradrenaline plasma levels more than 10-fold. Nevertheless, neither tyramine nor noradrenaline induced any effect on retinal hemodynamic parameters. CONCLUSIONS: These data indicate that even high levels of circulating noradrenaline have little impact on retinal vascular tone and retinal blood flow. Hence, the adrenergic system appears not to play a major role in retinal blood flow regulation.

Is acupuncture an useful tool for pain-treatment in ophthalmology?

Pain that does not respond to conventional treatment procedures makes it necessary to look for alternative methods. Acupuncture is an ancient procedure with empirical effects on pain. Previous studies established the increased output of messengers at neuronal junctions in spinal cord and hypothalamic locations, especially of endorphins which inhibit the perception of pain. We treated several painful symptoms with acupuncture and evaluated the outcome of the treatment. Patients with various kinds of therapy-refractory pain and patients in whom conventional treatment methods could not be applied were included in the study. The diagnoses included glaucoma. Tolosa-Hunt-Syndrome, ophthalmic migraine, blepharospasm, and dry eyes. In one case acupuncture was used for analgesia during surgery. Acupuncture was performed with sterile disposable needles, at points known to have an empirical analgesic effect. The stimulation was adapted to the patient's individual needs. VAS assessments before and after acupuncture were compared. The t-test was used for statistical evaluation. Acupuncture had no side effects, but reduced pain to a variable extent. Especially in cases of severe pain and in surgery, very effective pain reduction was achieved. In general, pain was significantly reduced in all patients by the use of acupuncture. A statistically significant effect was noted (p < 0.05). Further studies should be conducted to demonstrate the specific effect in larger patient populations. Monitoring neurotransmitter activity will possibly help to illustrate the effect.