Macular perfusion velocities in the ocular ischaemic syndrome.

PURPOSE: To assess retinal perfusion in eyes with unilateral ocular ischaemic syndrome (OIS) and to compare with control subjects. METHODS: Retrospective case series. Linear blood flow velocities in macular vessels were estimated using motion-contrast fundus photography in eight patients with unilateral OIS (eight OIS eyes, seven fellow eyes) and 12 control subjects. The diagnosis of OIS was supported by carotid artery Doppler ultrasonography and pneumoplethysmographic measurement of ocular systolic perfusion pressure. RESULTS: Macular arterial blood flow velocity (median, range) was 1.8 (1.4-2.7) mm/s in OIS eyes, 4.0 (2.9-5.3) mm/s in fellow eyes (p = 0.016) and 3.8 (2.3-5.1) mm/s in control eyes (p = 0.0004 and p = 0.67 versus OIS and fellow eyes, respectively). Macular venous blood flow velocity was 1.5 (1.0-2.1) mm/s in OIS eyes, 2.6 (2.0-2.9) mm/s in fellow eyes (p = 0.016) and 2.7 (1.8-3.5) mm/s in control eyes (p = 0.0007 and p = 0.64). Arterial velocities were below or equal to the lowest value observed in control subjects (≤2.3 mm/s) in seven of eight eyes with OIS. Visual acuity 0.7 or worse was found in two OIS eyes with arterial velocities below 1.7 mm/s and venous velocities below 1.3 mm/s and together with neovascular glaucoma or polycythemia vera (one eye each). CONCLUSION: Motion-contrast imaging revealed markedly reduced macular perfusion velocities in OIS eyes compared with unaffected fellow eyes and healthy control eyes. The method appears to provide a clinically meaningful quantitative measure of macular hypoperfusion.

Retinal angiographic blood flowmetry is reduced in the ocular ischaemic syndrome.

INTRODUCTION: The aim of this study was to examine the use of quantitative fluorescein angiographic analysis as a means of estimating rates of perfusion of the retina in eyes with a circulatory deficit secondary to carotid artery stenosis. MATERIAL AND METHODS: The study included 21 eyes with ocular ischaemic syndrome (OIS) and 20 control eyes from subjects with carotid artery stenosis but without signs of ocular ischaemia. Analyses of video fluorescein angiograms extracting time intervals for the time delay between specific phases of the angiogram were performed. Time delay was compared between groups and in relation to degree of carotid artery stenosis and ocular systolic blood pressure. RESULTS: Among the three flow indices of retinal perfusion (arteriovenous passage time 1 (AVP1), arteriovenous passage time 2 (AVP2) and venous filling time (VP)), those including the venous filling phase were significantly prolonged in the OIS group. Furthermore, AVP2 was delayed by 3 sec. in OIS eyes (16.6 sec. versus 13.6 sec. in controls). VP was 2.4 sec. longer in OIS eyes (11.5 sec. versus 9.1 sec.). We found a significant correlation between AVP2 and ocular perfusion pressure, but no correlation between the degree of carotid artery stenosis and any of the flow indices. CONCLUSION: In a patient population spanning a wide ocular systolic blood pressure range, angiography-based quantitative flowmetry demonstrated a difference between carotid artery stenosis patients with and without OIS and a correlation between flow and ocular perfusion pressure. While angiographic flowmetry proved effective in discriminating between groups of individuals, it can only be used to support the diagnosis of the ocular ischaemic syndrome in patients with extreme flow reduction.

Cone pathway function in relation to asymmetric carotid artery stenosis: correlation to blood pressure.

PURPOSE: To examine retinal function in relation to retinal perfusion pressure in patients with carotid artery stenosis. METHODS: Thirteen patients with carotid artery stenosis without clinical eye disease underwent assessment of ophthalmic artery systolic blood pressure (OSP) by ocular pneumoplethysmography, carotid artery obstructive disease by ultrasonography, intraocular pressure by applanation tonometry, retinal perfusion by fluorescein angiography and retinal function by multifocal electroretinography (mfERG). Data analysis compared the eye on the most stenotic side with the fellow eye in the same patient. RESULTS: Ophthalmic systolic pressure was 95.8 ± 13.1 mmHg on the side with the highest degree of carotid artery stenosis (mean 94.0%) and 111.7 ± 10.3 mmHg in the fellow eyes on the side with the lesser degree of stenosis (mean 33.9%). Summed mfERG implicit times (N1 and P1) were 3.4% and 2.0% longer (p = 0.013 and 0.021), and N1 and P1 amplitudes were 18.0% and 16.0% (p = 0.0041 and 0.020) lower in eyes on the side with the higher stenosis compared with the contralateral eyes. Shorter implicit times and higher amplitudes were correlated with higher brachial systolic arterial blood pressure (p = 0.0028, 0.011, 0.041 for N1, P1, N2 implicit times, respectively, and p = 0.0086, 0.016, 0.040 for N1, P1, N2 for amplitudes, respectively, corrected for OSP). CONCLUSION: Cone function deviation was observed in clinically healthy eyes on the side with highest degree of carotid artery stenosis and was found correlated to arterial blood pressure.

Delayed response of the retina after hyperbaric oxygen exposure.

PURPOSE: To examine retinal electrophysiological function and retinal thickness in healthy eyes before and after hyperbaric oxygen (HBO) exposure. METHODS: The healthy eye in each of six subjects who underwent experimental HBO treatment for branch retinal vein occlusion in the fellow eye was examined using multifocal electroretinography (mfERG) and optical coherence tomography (OCT) at baseline and following a course of five consecutive daily sessions of exposure to HBO at 2.4 atmospheres of absolute pressure lasting 90 min each. RESULTS: After HBO, P1 implicit times of the mfERG were significantly shorter than at baseline. The response was delayed, being undetectable on the day treatment concluded, whereas a 2.65% reduction in implicit time was seen 1 week later (p = 0.032). The P1 implicit time remained 2.49% shorter than at baseline 1 month after the end of the HBO sessions (p = 0.020). The bulk of the response to HBO was found in the foveal and parafoveal regions. No detectable change was seen in mfERG amplitudes or in the volume or thickness of the retina. CONCLUSION: A mfERG component related to bipolar and Müller cell function was accelerated by a short intermittent exposure to HBO. The response developed after the end of the HBO exposure and lasted for at least 3 weeks, suggesting that it was prompted by the withdrawal of HBO rather than the onset and subsequent brief exposure to HBO.

Scotopic electrophysiology of the retina during transient hyperglycemia in type 2 diabetes.

PURPOSE: To examine dark-adapted retinal function in subjects with type 2 diabetes during transient hyperglycemia. METHODS: Twenty-four subjects with type 2 diabetes and minimal diabetic retinopathy were randomized to an oral glucose tolerance test (OGTT) or a fasting regimen. One study eye was kept in the dark-adapted state at all times. Full-field electroretinography (ffERG) and blood glucose measurements were performed at baseline and after 20, 80, 140, and 200 minutes. RESULTS: Mean capillary glucose had increased 162% from the fasting baseline value when the concentration peaked in the OGTT group after 80 minutes (P < 0.0001). Concomitantly, rod b-wave amplitude had increased by 34% (P = 0.0007), whereas the a- and b-wave amplitudes of the standard combined rod-cone response had increased by 17% (P = 0.0013 and P = 0.0064). The dark-adapted 30-Hz flicker response was unaffected by hyperglycemia. The scotopic ffERG amplitudes rose and fell in phase with the glycemia. Implicit times did not change with the rise and fall in glycemia. CONCLUSIONS: The change in scotopic signaling amplitude in the outer and middle layers of retina in subjects with diabetes was proportional to the change in capillary glucose. Cone amplitude was not influenced by hyperglycemia in this study.

Prolonged multifocal electroretinographic implicit times in the ocular ischemic syndrome.

Purpose. To examine retinal function in chronic ocular ischemia using multifocal electroretinography (mfERG). Methods. Thirteen patients with unilateral ocular ischemic syndrome (OIS) underwent assessment of ophthalmic systolic blood pressure by ocular pneumoplethysmography, carotid artery patency by ultrasonography, intraocular pressure (IOP) by applanation tonometry, retinal perfusion by fluorescein angiography, and retinal function by mfERG. Results. Ophthalmic systolic blood pressure was 67.0 +/- 11.6 mm Hg in eyes with OIS and 106.1 +/- 18.0 mm Hg in fellow eyes, whereas IOP was 13.8 +/- 3.2 and 14.4 +/- 1.7 mm Hg, respectively. Summed mfERG implicit times (N1, P1, N2) were prolonged in eyes with OIS, by 7.6%, 6.2%, and 7.5%, respectively, compared with fellow eyes (P < or = 0.0048). The retardation of retinal function was significant outside the macula, whereas the assessment of responses from the central retina was limited by high variance. Second-order kernel (first slice) summed implicit times (N1, P1, N2) were also prolonged in OIS, by 6.6%, 7.3%, and 6.8%, respectively (P < or = 0.0058). Of the amplitudes, only the second-order N2 amplitude was significantly abnormal, being reduced by 23.2% in OIS (P = 0.011). Conclusions. The function of the outer and middle layers of the retina was found to be suppressed in chronic ocular hypoperfusion. The moderate delay in retinal function does not appear to explain the prominent photopic symptom of diffuse glare in bright light, and the delay could be evidence of a functional adaptation that serves to maintain and optimize signaling under conditions of compromised perfusion. (ClinicalTrials.gov number, NCT00403195.).

Profound retinal ischaemia after ranibizumab administration in an eye with ocular ischaemic syndrome.

PURPOSE: To report the result of ranibizumab administration in an eye with ocular ischaemic syndrome. METHODS: Fluorescein angiography, ocular pneumoplethysmography and retinal vessel calibre measurement. RESULTS: An 85-year-old man with ocular ischaemic syndrome demonstrated vision loss, retinal vessel calibre constriction and profound retinal ischaemia after intravitreal ranibizumab. CONCLUSION: We advise against the use of intravitreal vascular endothelial growth factor inhibitors in eyes with ocular ischaemic syndrome.

Lens autofluorescence is not increased at high altitude.

PURPOSE: To study the relation between ambient environmental ultraviolet radiation exposure and lens fluorescence. METHODS: Non-invasive lens fluorometry measurements were compared in healthy Bolivian and Danish subjects. Background ultraviolet radiation was 4.5 times higher in Bolivia than in Denmark. RESULTS: No significant differences in lens fluorescence or transmittance were found between Bolivian and Danish volunteers. CONCLUSION: Age-corrected lens fluorescence and transmittance were comparable for healthy participants living at high altitude near the equator and healthy volunteers living at sea level at 55 degrees northern latitude. These results suggest that lens ageing, as assessed by lens autofluorometry, is independent of exposure to ultraviolet radiation.

Retinal vessel diameters in relation to hematocrit variation during acclimatization of highlanders to sea level altitude.

PURPOSE: To examine variations in retinal vessel diameters during acclimatization of native highlanders to normobaric normoxia at sea level. METHODS: Fifteen healthy residents of the greater La Paz region in Bolivia (3600 m above sea level) were examined thrice over a 72-day period, after having traveled by airplane to Copenhagen, Denmark, near sea level. RESULTS: In the study subjects, hematocrit decreased from 49.6% (day 2) to 45.9% (P = 0.0066, day 23) and 41.7% (P < 0.0001, day 72); from days 2 to 23, retinal vein diameter increased by 2.68% (P = 0.0079); whereas retinal artery and vein diameters were indistinguishable from baseline after 72 days. No funduscopic signs of retinopathy were observed. Arterial blood pressure remained stable throughout the study. CONCLUSIONS: Although a 16% reduction in hematocrit occurred between days 2 and 72 after arrival at sea level, the only significant excursion observed was that the diameter of the veins was larger at day 23 than at days 2 and 72. Retinal vessel diameters demonstrated a wide homeostatic range during acclimatization-driven hematocrit variation.

The effect of high- to low-altitude adaptation on the multifocal electroretinogram.

PURPOSE: To examine variations in retinal electrophysiology assessed by multifocal electroretinogram (mfERG) during acclimatization of native highlanders to normobaric normoxia at sea level. METHODS: Eight healthy residents of the greater La Paz area in Bolivia (3600 m above sea level) were examined over 72 days after arriving in Copenhagen, Denmark (sea level). A control group of eight healthy lowlanders was used for comparison. RESULTS: During the period of observation, hemoglobin decreased from 16.7 to 15.0 g/dL (P = 0.0031), erythrocytes decreased from 5.3 to 4.6 trillion cells/L (P = 0.0006), and hematocrit decreased from 49.4% to 42.2% (P = 0.0008). At baseline, day 2 after arrival, the amplitudes (N1, P1, and N2) of the mfERG were 43.1% to 59.9% higher in the highlanders than in the lowlanders (P < 0.017). During acclimatization, the mfERG amplitudes increased 16.9% to 20.4% (P < 0.028) to a level of 73.2% to 87.0% higher in the highlanders than in the lowlanders (P < 0.0008). The increase in numerical amplitudes was proportional to the decrease in erythrocyte concentration (P = 0.023, 0.053, and 0.12 for N1, P1, and N2, respectively). CONCLUSIONS: On arrival at sea level, the highlanders had markedly supernormal multifocal electroretinographic amplitudes that continued to increase during the 72-day period of observation where the highlanders' hematocrit normalized. The results suggest that acclimatization after a change in altitude and hence in ambient oxygen tension involves intrinsic retinal mechanisms and that acclimatization was not complete by the end of the study.

[Interobserver variation in ultrasonographic scanning of carotid stenosis]. / Interobservatørvariation ved UL-scanning af carotisstenose.

INTRODUCTION: Ultrasonic carotid interna scanning is today the gold standard for diagnosing carotid stenosis in patients with stroke or transient ischemic attack. The procedure of ultrasonic carotid interna scanning is not a well-defined procedure. Knowledge of the reproducibility of the method used in own department is important in order to evaluate its usefulness. MATERIAL AND METHODS: Interobserver variability of ultrasonic, duplex carotid artery scanning was examined in 68 carotid arteries in 35 patients by two experienced technologists. The two observers were compared using the kappa (kappa) statistics to analyse the agreement beyond chance. RESULTS: kappa was 0.70 (CI: 0.56-0.83) when the stenoses were categorised in the intervals 0-14%, 15-49%, 50-69%, 70-79%, 80-99% and occlusion. Categorising the stenosis in the clinically relevant intervals 0-69%, 70-79% and occlusion which are used to determine if the patient is a candidate or not to carotid endarterectomy yielded a kappa = 0.92 (CI: 0.81-1.00). DISCUSSION: Low level stenosis accounted for most variability. If state-of-the-art ultrasonic equipment and experienced technologists are used a high level of reproducibility can be achieved.