High-altitude retinopathy and retinal vascular dysregulation.

PURPOSE: (a) To show that high-altitude retinopathy (HAR) is common at high altitudes even in well-acclimatised climbers and that it should not be regarded as part of the spectrum of benign mountain sickness but rather as a clinical sign with a separate aetiology. (b) To test the hypothesis that HAR could be interpreted as a clinical expression of 'ocular vascular dysregulation'. METHODS: Both eyes of the 8 mountaineers of the First Vienna Himalayan Expedition in May/June 1996 were examined 2 weeks before departure to and 2 weeks after descent from a high altitude. Retinal blood flow was measured in the right eyes of 7 climbers, using the Heidelberg Retina Flowmeter (HRF). RESULTS: Two of the 8 climbers had bilateral retinal haemorrhage after the expedition. In 5 climbers chronic hypoxic exposure caused an increase in retinal blood flow between +18% and +96%, and in 2 climbers a decrease in retinal blood flow between -21% and -31%. The 2 climbers (climbers 1 and 2) with bilateral retinal haemorrhage showed a significant increase in HRF parameters. CONCLUSIONS: HAR may be a clinical sign of mountaineers with a tendency towards ocular vascular dysregulation. The pronounced increase in all haemodynamic parameters in the 2 climbers with retinal haemorrhage combined with a dilated epipapillary network 2 weeks after the exposure reflects a retinal vessel configuration, as might be expected at high altitudes under acute hypoxic stress. An inadequate autoregulatory response of the retinal circulation under conditions of chronic hypoxia may play an important part in the pathogenesis of HAR.

Long-term course of surgically induced astigmatism after a 5.0 mm sclerocorneal valve incision.

PURPOSE: To study surgically induced astigmatism (SIA) after a sutureless 5.0 mm sclerocorneal valve incision. SETTING: Department of Ophthalmology, University of Vienna, Vienna, Austria. METHODS: This study evaluated SIA in 34 cases of sutureless cataract surgery with a 5.0 mm superior sclerocorneal valve incision and implantation of a poly(methyl methacrylate) intraocular lens. Keratometry was measured with a Zeiss keratometer in all cases preoperatively, and 1 day, 1 week, 1 and 3 months, and 1 and 5 years postoperatively. RESULTS: Surgically induced astigmatism, calculated by Cravy's vector analysis, showed an initial mean with-the-rule shift of 0.35 diopter (D), followed by an against-the-rule shift to a mean of -0.30 D after 1 month. One year postoperatively, mean SIA was -0.46 D. Between 1 and 5 years postoperatively, there was a statistically significant increase in mean SIA calculated by Cravy's vector analysis; SIA increased from -0.46 D after 1 year to -0.76 D after 5 years postoperatively. CONCLUSIONS: A small, although statistically significant, amount of postoperatively induced astigmatism occurred 5 years after a sutureless 5.0 mm sclerocorneal valve incision.

Episcleral versus combined episcleral and intrascleral application of mitomycin-C in trabeculectomy.

BACKGROUND AND OBJECTIVE: To determine whether intrascleral exposure to mitomycin-C (MMC) improves the control of intraocular pressure (IOP), increases the incidence of complications, or both. PATIENTS AND METHODS: The authors retrospectively evaluated 38 eyes of 29 patients following the intraoperative application of MMC (0.2 mg/ml; 5 minutes). In 21 eyes the MMC-soaked sponge was applied to the intact episclera (episcleral group). In 17 eyes, two sponges, one episcleral and the other intrascleral (sandwich group), were applied. The median follow-up times were 19.0 (episcleral group) and 24.0 (sandwich group) months. Outcome measures were the IOP, the number of medications, success rates, and the incidence of complications. RESULTS: The only statistically significant difference between the two groups was the 2-week postoperative IOP, which was significantly lower in the episcleral group (P = .0314). CONCLUSION: Because there is no additional benefit, the authors recommend that the intrascleral application of MMC be avoided. However, they did not observe increased complication rates when MMC was applied in this way.

Phacotrabeculectomy with a small-optic PMMA implant: two-year functional and morphological results.

PURPOSE: Previous studies have documented good pressure control with combined cataract and filtering surgery. However, relatively high incidences of iridocapsular synechiae (ICS) and cell precipitates on the optic (CPO) were found. Corneal valve incisions preclude intraoperative chamber flattening and iris injury or prolapse. Rigid one-piece PMMA lenses with a small optic maintain a pronounced optic-iris clearance. In a prospective series, the effect of this approach was studied with special regard to the morphological results. METHODS: A temporary corneal lip was created in the clear cornea beneath the scleral flap to serve as a temporary valve during cataract extraction. The lip was then widened and a rigid one-piece 5-mm PMMA lens implanted. Lip and trabeculum were finally excised en bloc at a width of 3 mm. Two years' functional and morphological results were evaluated. RESULTS: Fifty-four eyes were available for evaluation. After the mean follow-up of 21 months, mean IOP had dropped from 21.6+/-3 mm Hg preoperatively to 13.9+/-2.4 mm Hg, with a mean pressure reduction of 7.7+/-3.4 mm Hg. IOP was 18 mm Hg or less in all cases. The mean medication index dropped from 2.7 to 1.0. Eyes with a preoperative IOP of 21 mm Hg or more showed a significantly greater IOP reduction than eyes with an IOP of 20 mm Hg or less (-9.2+/-3.0 vs. -6.1+/-2.9 mm Hg, p = 0.0003). Intraoperatively, the temporary valve effectively prevented chamber flattening and iris injury or prolapse. Postoperatively, 9 eyes or 6% showed hyphemas, 1 undergoing lavage. Two eyes developed a capsular hematoma, 1 requiring YAG capsulotomy. Ten eyes or 19% developed mild and 2 eyes severe but transient fibrin exudation following hypotony or iridoplasty. One eye showed grade I anterior chamber flattening, 1 developed a ciliolenticular block requiring surgery. Postoperative pressure spikes of 30-35 mm Hg were noted in 4 eyes. Three eyes showed prolonged hypotony associated with transient choroidal effusion. A pronounced optic-iris clearance was found in 87% of the eyes. Iris-optic touch developed in 1 eye with prolonged postoperative anterior chamber flattening and in 3 of the 4 eyes that had undergone intraoperative iridoplasty. Three of the latter developed extensive ICS followed by CPO. The mean optic-iris distance was 1.2 mm and the anterior chamber depth 4.2 mm. CONCLUSION: Apart from effectively lowering IOP, the surgical approach used significantly reduced the incidence of ICS and CPO.

Noninvasive investigations of the normal ocular circulation in humans.

PURPOSE: To compare the reproducibility of laser interferometric measurements of fundus pulsation, pneumatonometric measurement of pulse amplitude (PA) and pulsatile ocular blood flow (POBF), and Doppler ultrasonic measurements of blood flow velocity in the ophthalmic artery (OA) and the posterior ciliary arteries (PCAs) and to investigate the association of the results obtained with these methods and to characterize ocular hemodynamics during Valsalva maneuver and isometric handgrip. METHODS: All studies were performed in healthy subjects. Fundus pulsation (n = 48), POBF (n = 24), and blood flow velocities (n = 24) were measured at baseline and during the Valsalva maneuver and isometric handgrip. Intraclass correlation coefficients were calculated for test/retest variability, for short-term variability, and for interobserver variability. RESULTS: Intraclass correlation coefficients were between 0.95 and 0.98 for fundus pulsation measurements, between 0.54 and 0.76 for pneumatonometric measurements, between 0.44 and 0.88 for Doppler sonographic measurements in the OA and between 0.32 and 0.60 in the PCAs. There was a high degree of association between pneumatonometric parameters and fundus pulsation amplitude. Valsalva maneuver significantly reduced fundus pulsations, PA, and POBF, whereas isometric handgripping did not change these parameters. CONCLUSIONS: The reproducibility of fundus pulsation measurements was excellent. Reproducibility of pneumatonometric parameters and ultrasonographic measurements in the OA was satisfactory. Reproducibility of ultrasonographic measurements in the PCAs was low. Data obtained during the autonomic stimuli experiments argue against the sole use of systems to measure pulsatile blood flow, if no additional data on flow pulsatility are available. At least in cases when changes in blood pressure are likely to occur the ratio of pulsatile to nonpulsatile blood flow might not be constant and POBF might not be an adequate measure of total ocular blood flow.

Age dependence of choroidal blood flow.

OBJECTIVE: To investigate the age dependence of choroidal blood flow. DESIGN: A cross-sectional study. SETTING: Department of Clinical Pharmacology, Vienna University. PARTICIPANTS: A total of 130 healthy volunteers between the ages of 19 and 83 years. MEASUREMENTS: Fundus pulsation amplitude (FPA) with a recently developed laser interferometric method, mean arterial pressure (MAP) with an automated oscillometric device, intraocular pressure (IOP) with an applanation tonometer, and ocular perfusion pressure (OPP) as calculated from MAP and IOP. RESULTS: There was a significant correlation of FPA with age r = -0.242 (P = .005). MAP, IOP, and OPP showed a significant positive correlation with age. Multiple regression analysis showed that FPA is associated with age but not with MAP, IOP, or OPP. CONCLUSION: Choroidal blood flow is reduced in older subjects, which argues in favor of an increase in ocular vascular resistance with age. This may be a risk factor in the development of common ocular diseases such as age-related macular degeneration or glaucoma.

Reversal of endothelin-1-induced ocular hemodynamic effects by low-dose nifedipine in humans.

BACKGROUND AND PURPOSE: There is evidence that calcium channel blockers may be useful in patients with normal tension glaucoma and vasospastic reactions. We therefore hypothesized that calcium channel blockers may increase ocular blood flow and that there may be a functional antagonism between endothelin-1 (ET-1) and calcium channel blockers in the ocular vasculature. METHODS: This was a randomized, double-blind, three-way crossover study with respect to ET-1 infusions (placebo, 2 ng/kg/min ET-1, and 4 ng/kg/min ET-1) and a randomized double-blind study in two parallel groups with respect to nifedipine (placebo or 5 mg nifedipine). Ocular hemodynamics in the 12 healthy subjects participating in the study was assessed by laser interferometric measurement of fundus pulsation amplitude (FPA) in the optic disc and two-dimensional scanning laser Doppler flowmetry in the optic disc. RESULTS: ET-1 caused a dose-dependent decrease in FPA and flow. With a dose of 4 ng/kg/min a decrease of -18% +/- 5% (p < 0.001) and -17% +/- 5% (p = 0.023) on FPA and flow, respectively, were observed. This effect was completely reversed by nifedipine compared with placebo (FPA, p < 0.001; flow, p = 0.011). However, nifedipine did not affect ocular hemodynamics after placebo infusion. CONCLUSIONS: These results show that nifedipine does not increase optic nerve head blood flow during baseline conditions but reverses ET-1-induced constriction in ocular vasculature at doses that do not affect systemic hemodynamics. This supports the close relation of the therapeutic effect of calcium channel blockers in patients with normal tension glaucoma to the endothelin system. Moreover, the present study provides a strong rationale for a study of low dose nifedipine as a supplementary medication in glaucoma patients.

Short-term oral pentoxifylline use increases choroidal blood flow in patients with age-related macular degeneration.

OBJECTIVE: To study the ocular hemodynamic effects of a 3-month oral treatment with pentoxifylline in patients with nonexudative age-related macular degeneration. DESIGN: Double-blind, placebo-controlled, randomized, parallel group study. SETTING: Outpatient clinic of the Department of Ophthalmology, Vienna University, Vienna, Austria, that specializes in age-related macular degeneration. METHODS: Forty patients with age-related macular degeneration received pentoxifylline (400 mg 3 times a day orally, n=20) or placebo (n=20) for 3 months. Retinal blood flow was assessed by scanning laser Doppler flowmetry and pulsatile choroidal blood flow was assessed by laser interferometric measurement of fundus pulsation amplitude. MAIN OUTCOME MEASURES: Changes in retinal blood flow and fundus pulsation amplitude. RESULTS: Four patients receiving pentoxifylline and 3 patients receiving placebo discontinued medication because of nausea. In the remaining subjects, the use of pentoxifylline increased ocular fundus pulsation amplitude (P<.001 vs placebo and baseline). The maximum increase was 28% after 3 months. In contrast, retinal blood flow was not changed by the use of pentoxifylline. CONCLUSIONS: A 3-month course of oral pentoxifylline treatment increases choroidal but not retinal blood flow in patients with age-related macular degeneration. These data strongly support the concept that pentoxifylline might be useful in the treatment of age-related macular degeneration. Long-term clinical outcome trials are now warranted to test this hypothesis.

Ocular and systemic reactivity to isoprenaline in patients with insulin-dependent diabetes mellitus.

There is experimental evidence of decreased beta-adrenergic myocardial sensitivity in patients with insulin-dependent diabetes mellitus (IDDM). In the present study we hypothesized that the ocular response to isoprenaline, as a consequence of increased arterial vessel rigidity, might also be blunted in patients with IDDM. We therefore compared the correlation between systemic pulse pressure amplitude (PPA) and fundus pulsation amplitude (FPA) during intravenous isoprenaline administration in 11 otherwise healthy IDDM patients and 11 healthy control subjects. Ocular fundus pulsations were measured by a recently developed laser interferometric method. Isoprenaline increased PPA in both study groups in a dose-dependent way, but the response was significantly less in IDDM patients (at 0.8 microgram min-1: +38% in control subjects, +27% in IDDM patients, P < 0.05 between groups). Moreover, a dose-dependent increase in FPA was observed, which again was more pronounced in healthy subjects (at 0.8 microgram min-1: +45% in controls, +17% in IDDM patients, P < 0.005 between groups). The regression line between PPA and FPA was very close to the 45 degrees line in healthy subjects, whereas it was significantly flattened in IDDM patients. In conclusion, linear regression between PPA and FPA during isoprenaline suggests arterial stiffening in patients with IDDM. Hence, comparison of systemic PPA and FPA during isoprenaline provocation may be a useful method of estimating changes in arterial capacitance in patients with diabetes mellitus.

Renal and ocular hemodynamic effects of insulin.

There is evidence that the vasodilator action of insulin is mediated by the release of nitric oxide (NO). We hypothesized that euglycemic hyperinsulinemia might increase renal and ocular blood flow, and that the vasodilator capacity of insulin might be NO-dependent. Euglycemic insulin clamps were performed in 10 healthy subjects. Sixty minutes after the start of insulin administration, an intravenous coinfusion of N-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthase, or of norepinephrine (NE), an endothelium-independent vasoconstrictor, was started. Renal plasma flow was measured by para-aminohippurate (PAH) clearance method. Ocular hemodynamics were assessed by laser interferometric measurement of fundus pulsations and Doppler sonographic measurement of blood flow velocity in the ophthalmic artery. Renal plasma flow and ocular fundus pulsations were increased by insulin. L-NMMA almost completely abolished the vasodilative effects of insulin, whereas the effects of combined infusion of insulin and NE were approximately the sum of the hemodynamic changes induced by each agent alone. The results show that during euglycemic hyperinsulinemia, renal and ocular blood flow are increased, which may be mediated either by a local vasodilator effect or a systemic increase in flow. The hemodynamic effects of insulin in the kidney and the eye are at least partially dependent on NO synthesis. Because the insulin plasma levels we obtained are in the high physiological range, it may be assumed that insulin plays a role in renal and ocular blood flow regulation.

Effects of changes in intraocular pressure on human ocular haemodynamics.

PURPOSE: Myogenic autoregulation is the ability of a vascular bed to maintain blood flow despite changes in perfusion pressure. Ocular perfusion pressure is defined as the difference between ocular arterial pressure and ocular venous pressure, the latter dependent on intraocular pressure (IOP). The aim of the present study was to investigate the effect of moderate increases in IOP on ocular haemodynamics. METHODS: Changes in IOP (+ 10 mmHg, +20 mmHg) were induced by a suction cup in 10 healthy subjects. Ocular fundus pulsations in the macula and the optic disc were measured by laser interferometry; blood flow velocities in the central retinal artery (CRA) and in the ophthalmic artery (OA) were measured by Doppler sonography. RESULTS: Changes in IOP caused a significant reduction in fundus pulsations, which was more pronounced in the macula (at +10 mmHg: -9 +/- 2%, p < 0.01; at +20 mmHg: -19 +/- 3%, p < 0.001) than in the optic disc (at +10 mmHg: -5 +/- 2% (ns); at +20 mmHg: -9 +/- 3%, p < 0.01). Mean flow velocity in the CRA was reduced by -5 +/- 3% at +10 mmHg (ns) and by -14 +/- 5% at +20 mmHg (p < 0.005), resistive index was increased by +4 +/- 1% at +10 mmHg (p < 0.05) and by +6 +/- 2% at +20 mmHg (p < 0.01). In contrast, a rise in IOP did not affect blood flow parameters in the OA. CONCLUSIONS: Our results from fundus pulsation measurements indicate that choroidal blood flow decreases when IOP is increased. The Doppler sonographic findings in the CRA indicate reduced blood flow velocity in this artery during raised IOP.

Exhaled NO during graded changes in inhaled oxygen in man.

BACKGROUND: Nitric oxide (NO) is present in the exhaled air of animals and humans. In isolated animal lungs the amount of exhaled NO is decreased during hypoxia. A study was undertaken to determine whether changes in arterial oxygen tension affect levels of exhaled NO in humans. METHODS: Sixteen healthy subjects were randomised to inhale different gas mixtures of oxygen and nitrogen in a double blind crossover study. Eight gas mixtures of oxygen and nitrogen (fractional inspired oxygen concentration (FiO2) 0.1 to 1.0) were administered. Exhaled NO was measured with a chemiluminescence detector from end expiratory single breath exhalation. RESULTS: A dose-dependent change in exhaled NO during graded oxygen breathing was observed (p = 0.0012). The mean (SE) exhaled NO concentration was 31 (3) ppb at baseline, 39 (4) ppb at an FiO2 of 1.0, and 26 (3) ppb at an FiO2 of 0.1. CONCLUSIONS: The NO concentration in exhaled air in healthy humans is dependent on oxygen tension. Hyperoxia increases the level of exhaled NO, which indicates increased NO production. The mechanism behind this phenomenon remains to be elucidated.

Effects of endothelin-1 (ET-1) on ocular hemodynamics.

PURPOSE: There is evidence from in vitro and animal data that endothelin-1 (ET-1) plays an important role in ocular blood flow. The aim of the present study was to investigate the effect of systemic ET-1 administration on ocular circulation in healthy subjects. METHODS: In a double blind, placebo-controlled, randomized, 2-way cross over study in 10 healthy male subjects, we administered stepwise, increasing doses of ET-1 (0 (saline), 1.25, 2.5 and 5.0 ng/kg/minutes; 20 minutes per dose (level) or placebo. Blood flow velocity in the ophthalmic artery as well as ocular fundus pulsations in the macula and the optic disc, and systemic hemodynamic parameters were measured. RESULTS: ET-1 dose-dependently reduced fundus pulsations in the macula (maximum effect -12 +/- 2% versus baseline; p < 0.001 versus baseline and placebo) and the optic disc (maximum effect: -19 +/- 5% versus baseline; p < 0.001 versus baseline and placebo), but did not affect blood flow velocity in the ophthalmic artery or systemic hemodynamics. CONCLUSIONS: Endothelin-1 reduces pulsatile blood flow in the choroid and the optic disc at doses which do not affect systemic hemodynamics or flow velocity in the ophthalmic artery. These results indicate that ocular circulation is particularly sensitive to changes in local ET-1 concentration and confirms the hypothesis that ET-1 may play a role in ocular vascular diseases.

Nitric oxide synthase inhibition in the histamine headache model.

Histamine has been widely used experimentally to induce headache in healthy subjects and migraine in migraineurs. There is evidence that the vascular effects of histamine are at least partially mediated by nitric oxide (NO). Hence we hypothesized that subjective symptoms and hemodynamic effects of histamine could be reduced by systemic NO-synthase inhibition. We therefore studied the effect of pretreatment with N-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of NO-synthase, or placebo on headache, flush and discomfort scores during histamine infusion. Additionally, blood flow velocities in the middle cerebral and the ophthalmic artery and ocular fundus pulsations were measured. Whereas L-NMMA blunted the effect of histamine in the ophthalmic artery and the ocular circulation, NO-synthase inhibition did not mitigate subjective symptoms. Histamine did not affect mean blood flow velocities in the middle cerebral artery. Hence, we conclude that NO-synthase inhibition reduces the histamine-induced vascular effects in the ocular circulation, but is not sufficient to attenuate or abort the subjective symptoms provoked by histamine infusion.

Effects of antiglaucoma drugs on ocular hemodynamics in healthy volunteers.

BACKGROUND AND PURPOSE: There is evidence that ocular blood flow plays a critical role in the clinical course of glaucoma. Hence a reduction in ocular blood flow due to topical antiglaucoma treatment should be avoided. The purpose of this study was to characterize the effect of antiglaucoma drugs on ocular hemodynamics. METHODS: In a double-blind, placebo-controlled, randomized crossover study, we investigated the effects of single topical doses of five beta-blocking agents (befunolol, betaxolol, levobunolol, metipranolol, and timolol), two adrenergic agents (clonidine and dipivefrin [INN, dipivefrine]), and a parasympathomimetic agent (pilocarpine) on ocular and systemic hemodynamics in healthy subjects (n = 10). Fundus pulsation amplitudes in the macula and the optic disc were measured to characterize pulsatile choroidal and optic disc blood flow, respectively. Moreover, central retinal and ophthalmic artery blood flow velocities were measured by Doppler ultrasound. RESULTS: Befunolol, metipranolol, timolol, clonidine, and dipivefrin reduced fundus pulsations in the macula and the optic disc (-9% to -14% versus baseline). In contrast, betaxolol, levobunolol, and pilocarpine had no effect on fundus pulsations. Antiglaucoma drugs had no effect on either blood flow velocities in the central retinal or the ophthalmic artery or systemic hemodynamics. CONCLUSIONS: Our results indicate that befunolol, metipranolol, timolol, clonidine, and dipivefrin reduce choroidal and optic disc blood flow. This could be caused by drug diffusion to the choroid, which may cause vasoconstriction. Ocular blood flow reduction was not observed with betaxolol, levobunolol, or pilocarpine. The lack of effect of all drugs under study on central retinal blood flow velocity might partially be the result of autoregulative mechanisms. Because optic nerve head blood flow likely plays a critical role in the clinical course of glaucoma, the use of antiglaucoma drugs, which reduce blood flow, should be reconsidered.

Reproducibility and sensitivity of scanning laser Doppler flowmetry during graded changes in PO2.

AIMS/BACKGROUND: Recently a commercially available scanning laser Doppler flowmeter has been produced, which provides two dimensional maps of the retinal perfusion. The aim of the present study was to investigate the reproducibility and the sensitivity of these measurements. METHODS: 16 healthy subjects were randomised to inhale different gas mixtures of oxygen and nitrogen in a double blind crossover study. The following gas mixtures of oxygen and nitrogen were administered: 100% oxygen + 0% nitrogen, 80% oxygen + 20% nitrogen, 60% oxygen + 40% nitrogen, 40% oxygen + 60% nitrogen, 30% oxygen + 70% nitrogen, 20% oxygen + 80% nitrogen, 15% oxygen + 85% nitrogen, and 10% oxygen + 90% nitrogen. Retinal haemodynamic variables and systemic haemodynamics were measured during all inhalation periods. Recordings under resting conditions were performed three times to calculate intraclass coefficients. RESULTS: In two subjects we did not obtain technically adequate results. A dose dependent change in retinal blood flow during graded oxygen breathing was observed (p < 0.001). During 100% oxygen breathing blood flow decrease was between 29% and 33%, whereas blood flow increase was between 28% and 33% during inhalation of 10% oxygen + 90% nitrogen. CONCLUSIONS: Scanning laser Doppler flowmetry has an acceptable reproducibility and is appropriate for description of the effect of graded changes in PO2 on retinal haemodynamics. The main problems with the system are the large zero offset, the fixation during retinal scanning, and the neglect of blood flow changes during the cardiac cycle.

Surgically induced astigmatism following a 4.0 mm sclerocorneal valve incision.

PURPOSE: To determine whether sutureless small incision cataract surgery reduces induced astigmatism over the long term. SETTING: University Eye Hospital, Vienna, Austria. METHODS: In a prospective study, we investigated surgically induced astigmatism in 63 cases of no-stitch, small incision cataract surgery with a 4.0 mm square sclerocorneal tunnel and implantation of a flexible intraocular lens. Follow-up was 4 to 5 years. Keratometry was measured with a Zeiss keratometer preoperatively and after 1 day, 1 week, 1, 3, and 9 months, and a median of 4.4 years. In 21 nonoperated eyes, we investigated the natural course of astigmatism over 5 years. RESULTS: The mean keratometric cylinder stabilized at 0.8 diopter (D) after 1 week and slightly decreased to 1.0 D after 4 to 5 years. Cravy's vector analysis showed an immediate against-the-rule (ATR) shift of -0.2 D that remained relatively stable until 9 months. Between 9 months and 4.4 years postoperatively, there was a statistically significant increase in ATR induced astigmatism from -0.2 to -0.5 D. The natural course of astigmatism in the nonoperated eyes showed an ATR shift of -0.1 D for the same period. CONCLUSION: The result show a small, though statistically significant amount of postoperatively induced astigmatism 4 to 5 years after no-stitch, small incision cataract surgery.

Nitric oxide and ocular blood flow in patients with IDDM.

Endothelial dysfunction has been implicated in the pathogenesis of diabetic vascular disorders such as diabetic retinopathy. We hypothesized that either local endogenous nitric oxide (NO) synthesis or local reactivity to endogenous NO might be impaired in patients with IDDM and that this may contribute to the development of diabetic retinopathy. Ten otherwise healthy patients with long-standing IDDM and ten healthy control subjects were studied according to an open randomized two-way cross-over design. Subjects received intravenous infusions of either N(G)-monomethyl-L-arginine, an inhibitor of NO-synthase, or L-arginine, the precursor of NO synthesis, on two separate study days. Ocular hemodynamics were assessed by laser interferometric measurement of fundus pulsations and Doppler sonographic measurement of blood flow velocity in the ophthalmic artery. N(G)-monomethyl-L-arginine decreased fundus pulsations and blood flow velocity in the ophthalmic artery and increased blood pressure in healthy subjects. The responses to NO-synthase inhibition were significantly less in diabetic subjects. In contrast, L-arginine caused a comparable increase in fundus pulsations and decrease in blood pressure in both cohorts. These results indicate that systemic and ocular hemodynamic reactivity to NO-synthase inhibition is reduced in patients with long-standing IDDM, compared with healthy control subjects. Thus, this study indicates that either NO-synthase activity is increased or NO sensitivity is decreased in patients with IDDM and supports the concept of an involvement of the L-arginine-NO system in the pathophysiology of diabetic retinopathy.

Capsular bag shrinkage after implantation of an open-loop silicone lens and a poly(methyl methacrylate) capsule tension ring.

PURPOSE: To quantify the dynamics of capsular bag shrinkage after cataract surgery. SETTING: University Eye Hospital, Vienna, Austria. METHODS: Nineteen eyes in 13 patients had clear corneal cataract surgery with implantation of a foldable, open-loop, silicone posterior chamber intraocular lens (IOL) (AMO SI-30). At the same time, an open, poly(methyl methacrylate) capsule tension ring (Morcher type 14 or 14A) was inserted to allow measurement of capsular bag circumference and diameter. After surgery, capsular bag shrinkage was quantified by measuring anterior chamber depth (ACD), iris-lens distance (ILD), and distance between the eyelets of the capsule tension ring using optical methods. Capsular bag circumference (CBC) was deduced from these measurements, which were taken 1 day (baseline), 1 week, and 1 and 3 months postoperatively. RESULTS: Between 1 day and 3 months, all three parameters decreased significantly. During the first postoperative week, ACD and ILD did not change, while both parameters decreased between 1 week and 1 month. After 1 month, ACD did not decrease further; ILD continued to decrease. The CBC decreased during the entire postoperative period. CONCLUSION: Besides ACD and ILD, CBC significantly decreased during the first 3 months after cataract surgery with in-the-bag posterior chamber IOL implantation. The CBC can be calculated from the distance between the ends of the capsule tension ring, which can be measured gonioscopically. From this, the diameter of the capsular bag can be calculated in the living eye. The influence of the capsule tension ring itself on capsular bag shrinkage remains to be established.