Pulsatile ocular blood flow study: decreases in exudative age related macular degeneration

Understanding the Impact of the Sirtuin 1 (SIRT1) Gene on Age-related Macular Degeneration: A Comprehensive Study

Age-related macular degeneration (AMD) is a prevalent and incurable condition affecting the central retina and posing a significant risk to vision, particularly in individuals over the age of 60. As the global population ages, the prevalence of AMD is expected to rise, leading to substantial socioeconomic impacts and increased healthcare costs. The disease manifests primarily in two forms, neovascular and non-neovascular, with genetic, environmental and lifestyle factors playing a pivotal role in disease susceptibility and progression. This review article involved conducting an extensive search across various databases, including Google Scholar, PubMed, Web of Science, ScienceDirect, Scopus and EMBASE, to compile relevant case-control studies and literature reviews from online published articles extracted using search terms related to the work. SIRT1, a key member of the sirtuin family, influences cellular processes such as ageing, metabolism, DNA repair and stress response. Its dysregulation is linked to retinal ageing and ocular conditions like AMD. This review discusses the role of SIRT1 in AMD pathology, its association with genetic variants and its potential as a biomarker, paving the way for targeted interventions and personalised treatment strategies. In addition, it highlights the findings of case-control studies investigating the relationship between SIRT1 gene polymorphisms and AMD risk. These studies collectively revealed a significant association between certain SIRT1 gene variants and AMD risk. Further studies with larger sample sizes are required to validate these findings. As the prevalence of AMD grows, understanding the role of SIRT1 and other biomarkers becomes increasingly vital for improving diagnosis, treatment and, ultimately, patient outcomes.

Imaging-based Assessment of Choriocapillaris: A Comprehensive Review

PURPOSE

Over the past two decades, advancements in imaging modalities have significantly evolved the diagnosis and management of retinal diseases. Through these novel platforms, we have developed a deeper understanding of the anatomy of the choroidal vasculature and the choriocapillaris. The recently developed tools such as optical coherence tomography (OCT) and OCT angiography (OCTA) have helped elucidate the pathological mechanisms of several posterior segment diseases. In this review, we have explained the anatomy of the choriocapillaris and its close relationship to the outer retina and retinal pigment epithelium.

METHODS

A comprehensive search of medical literature was performed through the Medline/PubMed database using search terms: choriocapillaris, choroid, quantification, biomarkers, diabetic retinopathy, age-related macular degeneration, choroidal blood flow, mean blur rate, flow deficit, optical coherence tomography, optical coherence tomography angiography, fluorescein angiography, indocyanine green angiography, OCTA, Doppler imaging, uveitis, choroiditis, white dot syndrome, tubercular serpiginous-like choroiditis, choroidal granuloma, pachychoroid, toxoplasmosis, central serous chorioretinopathy, multifocal choroiditis, choroidal neovascularization, choroidal thickness, choroidal vascularity index, choroidal vascular density, and choroidal blood supply. The search terms were used either independently or combined with choriocapillaris/choroid.

RESULTS

The imaging techniques which are used to qualitatively and quantitatively analyze choriocapillaris are described. The pathological alterations in the choriocapillaris in an array of conditions such as diabetes mellitus, age-related macular degeneration, pachychoroid spectrum of diseases, and inflammatory disorders have been comprehensively reviewed. The future directions in the study of choriocapillaris have also been discussed.

CONCLUSION

The development of imaging tools such as OCT and OCTA has dramatically improved the assessment of choriocapillaris in health and disease. The choriocapillaris can be delineated from the stromal choroid using the OCT and quantified by manual or automated methods. However, these techniques have inherent limitations due to the lack of an anatomical distinction between the choriocapillaris and the stromal choroid, which can be overcome with the use of predefined segmentation slabs on OCT and OCTA. These segmentation slabs help in standardizing the choriocapillaris imaging and obtain repeatable measurements in various conditions such as diabetic retinopathy, age-related macular degeneration, pachychoroid spectrum, and ocular inflammations. Additionally, Doppler imaging has also been effectively used to evaluate the choroidal blood flow and quantifying the choriocapillaris and establishing its role in the pathogenesis of various retinochoroidal diseases. As tremendous technological advancements such as wide-field and ultra-wide field imaging take place, there will be a significant improvement in the ease and accuracy of quantifying the choriocapillaris.

Age-related macular degeneration: Epidemiology, genetics, pathophysiology, diagnosis, and targeted therapy

Age-related macular degeneration (AMD) is a complex eye disorder and is the leading cause of incurable blindness worldwide in the elderly. Clinically, AMD initially affects the central area of retina known as the macula and it is classified as early stage to late stage (advanced AMD). The advanced AMD is classified into the nonexudative or atrophic form (dry AMD) and the exudative or neovascular form (wet AMD). More severe vision loss is typically associated with the wet form. Multiple genetic factors, lipid metabolism, oxidative stress and aging, play a role in the etiology of AMD. Dysregulation in genetic to AMD is established to 46%-71% of disease contribution, with CFH and ARMS2/HTRA1 to be the two most notable risk loci among the 103 identified AMD associated loci so far. Chronic cigarette smoking is the most proven consistently risk living habits for AMD. Deep learning algorithm has been developed based on image recognition to distinguish wet AMD and normal macula with high accuracy. Currently, anti-vascular endothelial growth factor (VEGF) therapy is highly effective at treating wet AMD. Several new generation AMD drugs and iPSC-derived RPE cell therapy are in the clinical trial stage and are promising to improve AMD treatment in the near future.

Relationship Between the Parameters of Corneal and Fundus Pulse Signals Acquired With a Combined Ultrasound and Laser Interferometry Technique

Purpose

To estimate the relationship between the characteristics of the corneal pulse (CP) signal and those of the fundus pulse (FP) signal measured with a combined noncontact ultrasonic and laser interferometry technique in healthy subjects.

Methods

Twenty-two healthy subjects participated in experiments that included measurements of intraocular pressure, ocular pulse amplitude, ocular biometry, blood pressure, and heart rate. Additionally, simultaneous recordings of CP and FP signals were acquired with a noncontact ultrasonic device combined with laser interferometry. Subsequently, ocular perfusion pressure (OPP) and the time and spectral parameters of CP and FP signals were computed. A system model was proposed to relate the FP signal to the CP signal.

Results

The system model revealed that the eye globe transfers information between signals of the posterior and anterior eye, relatively amplifying higher spectral harmonics. The amplitude of the second CP harmonic is predicted by FP_RMS and OPP (R² = 0.468, P = 0.002). Partial correlation analysis showed that the CP signal parameters are statistically significantly correlated with those of the FP signal and OPP, after correcting for age and sex.

Conclusions

The eye globe can be viewed as a high pass filter, in which the CP characteristic changes in relation to the fundus pulsation. The FP signal and OPP have an impact on the variations of the CP signal morphology.

Translational Relevance

Investigation of differences between the characteristics of the anterior and posterior tissue movements is a promising method for evaluating the role of circulatory and biomechanical components in the pathophysiology of ocular diseases.

Choroidal vascular changes in age-related macular degeneration

PURPOSE

To assess the choroidal vascular changes using choroidal vascularity index (CVI) in patients with age-related macular degeneration (AMD) compared to controls.

METHODS

Enhanced depth imaging (EDI) optical coherence tomography (OCT) scans of 64 patients with unilateral or bilateral AMD were obtained. Images with a poorly demarcated choroidal-scleral interface (CSI) were excluded from the analysis. Foveal scans of 63 AMD eyes and 35 'normal fellow' eyes were analysed. Images of 30 eyes from 18 age-matched healthy subjects were included as controls. Choroidal vascularity index (CVI) was derived from binarization of EDI OCT images, using fiji software.

RESULTS

The mean age was 56.50 ± 5.50 years for AMD patients and 52.25 ± 6.75 years for controls. All patients were treatment naïve. Subfoveal choroidal thickness (SFCT) in AMD, 'normal fellow' eyes and controls was 314.02 ± 78.80 μm, 300.88 ± 53.85 μm and 278.5 ± 65.31 μm, respectively. Choroidal vascularity index (CVI) in AMD, 'normal fellow' eyes and controls was 64.04 ± 2.43%, 64.66 ± 2.25% and 66.07 ± 1.72%, respectively. Choroidal vascularity index (CVI) of both AMD and 'normal fellow' eyes was significantly lower compared to controls (p < 0.0001 and p = 0.007). The SFCT of AMD eye was not found to be significantly different from 'normal fellow eyes' (p = 0.45).

CONCLUSION

There was no statistical difference in SFCT, but CVI was significantly lower in patients with AMD. Choroidal vascularity index (CVI) was also lower in 'normal fellow' AMD eyes as compared to controls. This suggests possible reduction in choroidal vascularity in eyes with AMD and also to a certain extent in the 'normal fellow' eyes without phenotypical manifestations and may suggest underlying choroidal morphological change leading to wet AMD.

Choroidal Blood Flow Change in Eyes with High Myopia

Purpose

To evaluate choroidal blood flow changes in eyes with high myopia according to the pulsatile components of ocular blood flow analysis.

Methods

A total of 104 subjects (52 males and 52 females) were included in this study. One eye of each participant was randomly selected and assigned to one of four refractive groups, designated as, hyperopes (n = 20; refractive error, ≥+1.00 diopter [D]), emmetropes (n = 28; refractive error, ±0.75 D), lower myopes (n = 33; refractive error, -1.00 to -4.75 D), and high myopes (n = 23; refractive error, ≤-5.00 D). Components of pulse amplitude (OBFa), pulse volume (OBFv), pulse rate (OBFr), and pulsatile ocular blood flow (POBF) were analyzed using a blood flow analyzer. Intraocular pressure and axial length were measured.

Results

Pulsatile components of OBFa, OBFv, and POBF showed positive correlations with refractive error and showed negative correlations with axial length (r = 0.729, r = 0.772, r = 0.781, respectively, all p < 0.001; r = -0.727, r = -0.762, r = -0.771, respectively, all p < 0.001). The correlations of refractive error and axial length with OBFr were irrelevant (r = -0.157, p = 0.113; r = 0.123, p = 0.213). High myopes showed significantly lower OBFa, OBFv, and POBF than the other groups (all p < 0.001).

Conclusions

Axial length changes in high myopes potentially influence choroidal blood flow, assuming the changes are caused by narrowing of the choroidal vessel diameter and increasing rigidity of the choroidal vessel wall. These finding explains the influence of axial length on OBFa, OBFv, and POBF, but not on OBFr. Thus, changes in axial length and the possible influence of these changes on the physical properties of choroidal vessels is the mechanism believed to be responsible for putting high myopes at risk for ocular vascular diseases.

Neurocardiovascular instability may modulate end-organ damage: A review of this hypothesis investigating the eye and manifestations of NCVI

Neurocardiovascular instability (NCVI) represents age-related changes in blood pressure and heart rate behaviour. It has been associated with increased leukoaraiosis in the brain and also conditions which are likely to be are related to cerebral end-organ damage, such as stroke and falls. The eye is a 'window' into the brain and cardiovascular (CV) system, changes in retinal microvasculature being independently predictive of cardiovascular events. The eye is highly vascular, having two circulatory systems and as such the ideal target end-organ to investigate NCVI and early end-organ damage. The retinal and choroidal circulations of the eye would be vulnerable to NCVI if ocular vasoregulation becomes impaired with age, particularly given the high metabolic activity of the retina. The choroid is predominantly extrinsically regulated by the autonomic nervous system. In patients with NCVI, autonomic dysfunction is more common and thus impairment of the tightly regulated ocular microcirculation may indeed be compromised. We review the evidence for the hypothesis that NCVI may modulate end-organ cardiovascular pathology and that the eye is the ideal target organ to monitor this.

Corneal thickness of eyes with unilateral age-related macular degeneration

PURPOSE

To compare the central corneal thicknesses (CCT), peripheral corneal thicknesses, and corneal volumes (CV) of the 2 eyes of patients with unilateral age-related macular degeneration (AMD).

METHODS

Twenty patients who were diagnosed with unilateral AMD were included in this prospective study for the purpose of making comparison between the diseased and healthy eyes. Optical coherence tomography and fundus fluorescein angiography imaging were applied to all patients in order to confirm and reveal the presence of unilateral AMD. Then, the measurements of CCT, peripheral corneal thickness measured 4 mm distant from the center of the cornea (4 mm CT), and CV of each eye of these patients were obtained through the rotating Scheimpflug corneal topographer.

RESULTS

Wilcoxon signed-rank test did not demonstrate a statistically significant difference between the 2 eyes of patients with unilateral AMD when we compared the CCT and CV of diseased and healthy eyes (p>0.05). However, 4 mm CT of the diseased eyes of these patients were statistically significantly thicker than the healthy eyes (p<0.05).

CONCLUSIONS

The significant difference in terms of 4 mm CT between the diseased and healthy eyes of patients with unilateral AMD may demonstrate the possible effect of peripheral corneal thickness on the development of AMD.

Retinal vascular abnormalities in neovascular age-related macular degeneration

PURPOSE

To determine the prevalence of retinal vascular abnormalities (RVA) in neovascular age-related macular degeneration (AMD).

METHODS

A post hoc subanalysis of images acquired during a Phase III randomized controlled trial was undertaken, selecting images from participants with untreated, neovascular AMD in at least one eye. Protocol mandated fundus photographs and fluorescein angiograms were acquired at baseline and Year 2, from 107 sham-treated study eyes with neovascular AMD and 107 untreated fellow eyes. Images were reanalyzed by an independent reading center for the presence of RVA, defined as at least one of the following: microaneurysms, vessel staining or leakage, dilated or tortuous vessels, intraretinal hemorrhage, vessel sheathing or narrowing, capillary nonperfusion, or capillary infarcts.

RESULTS

The baseline prevalence of RVA in the sham-treated study eyes was 14.4% (15 of 104 gradable images) versus 8.3% (5 of 60) in the fellow eyes with dry AMD. The baseline prevalence of individual RVAs in study eyes was: microaneurysms (6.7%), vessel staining or leakage (6.7%), dilated or tortuous vessels (4.8%), intraretinal hemorrhage (4.8%), vessel sheathing or narrowing (2.9%), capillary nonperfusion (0%), and capillary infarcts (0%). Results were similar at 24 months.

CONCLUSION

Compared with several studies that relied solely on fundus photographs, this study included fluorescein angiography and found a higher prevalence of RVAs occurring in eyes with neovascular AMD.

Ocular pulse amplitude and retinal vessel caliber changes after intravitreal ranibizumab

The purpose of the present study was to examine the effects of intravitreal ranibizumab on ocular pulse amplitude (OPA) and retinal vessel caliber (RVC) in wet age-related macular degeneration (AMD). Thirty-two eyes of 32 wet AMD patients were included in this case series. Three consecutive monthly injections of ranibizumab were performed. The OPA was measured with the Pascal dynamic contour tonometer. RVC measurements were taken with spectral-domain optical coherence tomography. Pre-injection mean OPA value was 2.55 ± 0.76 mmHg and post-injections mean OPA value was 2.79 ± 0.88 mmHg at the last visit (p = 0.10). Pre-injection mean arteriole and venule RVC were 96.7 ± 9.4 and 125.9 ± 8.4 µm; while post-injections arteriole and venule RVC were 96.0 ± 8.7 and 125.6 ± 8.9 µm, respectively (p > 0.05). OPA and RVC are unchanged after triple intravitreal ranibizumab injections, indicating that this treatment does not significantly alter gross retina-choroidal vasculature and hemodynamics.

Delayed patchy choroidal filling in the Comparison of Age-Related Macular Degeneration Treatments Trials (CATT)

PURPOSE

To determine the relationship between delayed patchy choroidal filling and morphologic and functional outcomes among eyes treated with ranibizumab or bevacizumab.

DESIGN

Cohort study.

METHODS

Comparison of Age-related Macular Degeneration Treatment Trials participants were assigned randomly to ranibizumab or bevacizumab on a monthly or as-needed schedule. Presence of delayed patchy choroidal filling and morphologic and functional outcomes were evaluated among eyes with gradable fluorescein angiography at baseline (n = 973) and at 1 year (n = 860) eyes.

RESULTS

Delayed filling was present in 75 (7.7%) of 973 eyes at baseline. Eyes with incident delayed filling at 1 year (23 [2.9%] of 798) showed a mean decrease of 1.7 letters in visual acuity, whereas eyes without incident delayed filling had a mean improvement of 8.1 letters (difference [Δ], -9.8; 95% confidence interval [CI] , -15.8 to -3.9; P < .01). Eyes with incident delayed filling had a larger increase in mean total lesion area of choroidal neovascularization (3.00 mm(2)) than eyes without incident delayed filling (0.56 mm(2); Δ , 2.4; 95% CI, 0.4 to 4.4; P = .02). The proportion with incident delayed filling at 1 year was similar among eyes treated with ranibizumab (10 [2.4%] of 413) or bevacizumab (13 [3.3%] of 385; P = .53) and among eyes treated monthly (12 [3.1%] of 388) or as needed (11 [2.7%] of 410; P = .83).

CONCLUSIONS

Delayed patchy choroidal filling was uncommon at baseline. Although only a small percentage of eyes demonstrated delayed filling during the first year of anti-vascular endothelial growth factor treatment, these eyes had worse visual acuity and a larger increase in total lesion area of choroidal neovascularization.

Smoking and choroidal thickness in patients over 65 with early-atrophic age-related macular degeneration and normals

OBJECTIVE

To compare macular choroidal thickness between cigarette smokers, those with a history of smoking, and nonsmokers in patients over 65 years of age with early-atrophic age-related macular degeneration (AMD) and normals.

METHODS

Prospective, consecutive, observational case series. Enhanced depth imaging spectral domain optical coherence tomography 12-line radial scans were performed and choroidal thickness manually quantified at 84 points in the central 3 mm of the macula. Data of normals, soft drusen alone, and soft drusen with additional features of early AMD were compared. A multivariate analysis of variance (MANOVA) model, controlling for age, was constructed to evaluate the effect of smoking history and AMD features on choroidal thickness.

RESULTS

A history of smoking was significantly associated with a thinner choroid across all patients via logistic regression (P=0.004; O.R.=12.4). Mean macular choroidal thickness was thinner for smokers (148±63 μm) than for nonsmokers (181±65 μm) among all diagnosis categories (P=0.003). Subgroup analysis of patients with AMD features revealed a similar decreased choroidal thickness in smokers (121±41 μm) compared with nonsmokers (146±46 μm, P=0.006). Bivariate analysis revealed an association between increased pack-years of smoking and a thin choroid across all patients (P<0.001) and among patients with features of early AMD (P<0.001). Both the presence of features of macular degeneration (P<0.001) and a history of smoking (P=0.024) were associated with decreased choroidal thickness in a MANOVA model.

CONCLUSION

Chronic cigarette smoke exposure may be associated with decreased choroidal thickness. There may be an anatomic sequelae to chronic tobacco smoke exposure that underlies previously reported AMD risk.

Does fundus fluorescein angiography procedure affect ocular pulse amplitude?

Purpose. This study examines the effects of fundus fluorescein angiography (FFA) procedure on ocular pulse amplitude (OPA) and intraocular pressure (IOP). Materials and Methods. Sixty eyes of 30 nonproliferative diabetic retinopathy patients (15 males, 15 females) were included in this cross-sectional case series. IOP and OPA were measured with the Pascal dynamic contour tonometer before and after 5 minutes of intravenous fluorescein dye injection. Results. Pre-FFA mean OPA value was 3.05 ± 1.36 mmHg and post-FFA mean OPA value was 2.93 ± 1.28 mmHg (P = 0.071). Pre-FFA mean IOP value was 17.97 ± 1.99 mmHg and post-FFA mean IOP value was 17.81 ± 2.22 mmHg (P = 0.407). Conclusion. Although both mean OPA and IOP values were decreased after FFA procedure, the difference was not statistically significant. This clinical trial is registered with Australian New Zealand Clinical Trials Registry number ACTRN12613000433707.

Evaluation of retrobulbar blood flow by color doppler ultrasonography after intravitreal ranibizumab injection in patients with neovascular age-related macular degeneration

PURPOSE

This study aimed to evaluate the changes in retrobulbar blood flow by using color Doppler sonography in patients who had undergone intravitreal ranibizumab injection for neovascular age-related macular degeneration (AMD).

METHODS

The study comprised 37 AMD patients who had undergone intravitreal 0.5 mg ranibizumab injection. The ophthalmic artery, central retinal artery, and short lateral posterior ciliary artery of both eyes of patients were evaluated by color Doppler sonography. Peak systolic velocity, end-diastolic velocity, and resistance index were calculated before injection, and after injection on day 7 and day 30. The pre- and postinjection values were compared using Wilcoxon signed rank test.

RESULTS

In a comparison with the preinjection values of peak systolic velocity, end-diastolic velocity, and resistance index, the postinjection values at both day 7 and day 30 showed no statistically significant difference in ophthalmic artery, lateral posterior ciliary artery, and central retinal artery (p > 0.05). Similarly, for the same parameters, pre- and postinjection values in the uninjected fellow eye showed no statistically significant difference (P > 0.05).

CONCLUSIONS

Intravitreal ranibizumab injection for neovascular AMD does not cause a significant change in the retrobulbar blood flow in either the injected eye or the fellow eye.

Relationship between choroidal thickness and choroidal circulation in healthy young subjects

PURPOSE

To investigate the relationship between the choroidal thickness and choroidal blood flow in healthy young subjects.

DESIGN

Retrospective, cross-sectional study.

METHODS

We examined 25 eyes of 25 healthy young Japanese subjects. The subfoveal choroidal thickness was measured by enhanced depth imaging optical coherence tomography (EDI-OCT). The total choroidal blood flow and subfoveal choroidal blood flow were evaluated by pulsatile ocular blood flow using Langham OBF computerized tonometry and the choroidal blood flow using laser Doppler flowmetry. The refractive error, intraocular pressure, and axial length were also measured.

RESULTS

The mean refractive error was -3.4 ± 3.1 diopters, mean intraocular pressure 15.3 ± 1.7 mm Hg, and axial length 25.4 ± 2.0 mm. The subfoveal choroidal thickness was correlated positively (r = 0.785, P < .01) with the refractive error and negatively (r = -0.735, P < .001) with the axial length. No significant correlation was found between the subfoveal choroidal thickness and the pulsatile ocular blood flow or choroidal blood flow.

CONCLUSION

Our results suggested that there were no significant correlations between the subfoveal choroidal thickness and the total choroidal blood flow and the subfoveal choroidal blood flow in healthy young subjects; however, decreased subfoveal choroidal thickness was associated with decreased refractive error and axial length.

Cellular and physiological mechanisms underlying blood flow regulation in the retina and choroid in health and disease

We review the cellular and physiological mechanisms responsible for the regulation of blood flow in the retina and choroid in health and disease. Due to the intrinsic light sensitivity of the retina and the direct visual accessibility of fundus blood vessels, the eye offers unique opportunities for the non-invasive investigation of mechanisms of blood flow regulation. The ability of the retinal vasculature to regulate its blood flow is contrasted with the far more restricted ability of the choroidal circulation to regulate its blood flow by virtue of the absence of glial cells, the markedly reduced pericyte ensheathment of the choroidal vasculature, and the lack of intermediate filaments in choroidal pericytes. We review the cellular and molecular components of the neurovascular unit in the retina and choroid, techniques for monitoring retinal and choroidal blood flow, responses of the retinal and choroidal circulation to light stimulation, the role of capillaries, astrocytes and pericytes in regulating blood flow, putative signaling mechanisms mediating neurovascular coupling in the retina, and changes that occur in the retinal and choroidal circulation during diabetic retinopathy, age-related macular degeneration, glaucoma, and Alzheimer's disease. We close by discussing issues that remain to be explored.

The ocular pulse amplitude at different intraocular pressure: a prospective study

PURPOSE

To investigate changes in ocular pulse amplitude (OPA) during a short-term increase in intraocular pressure (IOP) and to assess possible influences of biometrical properties of the eye, including central corneal thickness (CCT) and axial length.

METHODS

In a prospective, single centre study, OPA and IOP as measured by dynamic contour tonometry (DCT) were taken before baseline- and post-OPA (delta) intravitreal injection of 0.05 ml anti-vascular endothelial growth factor agents. Analysis was performed employing linear regression with baseline- and post (delta)-OPA differences as the dependent and post-IOP as well as delta IOP as the independent variable. A multilinear regression analysis with delta OPA as the dependent variable and baseline IOP, post-IOP, CCT and axial length as independent variables was conducted.

RESULTS

Forty eyes of 40 patients were included. IOP and OPA increased significantly after injection (IOP mean increase ± SD: 17.83 ± 9.83 mmHg, p < 0.001; OPA mean increase ± SD: 1.39 ± 1.16 mmHg, p < 0.001). For every mmHg increase in IOP, the OPA showed a linear increase of 0.05 mmHg (slope 0.05, 95% CI: 0.02-0.09, p = 0.003, r(2) = 0.20). Multiple regression analysis with delta OPA as the dependent variable revealed a partial correlation coefficient of 0.47 (p = 0.003) for post-IOP as the only significant contribution.

CONCLUSION

A clear positive relationship between OPA measurements and IOP levels was shown in a clinical routine setting using DCT focusing on baseline and postinterventional comparisons of OPA values after intravitreal injections in patients with exudative age related macular degeneration. When considering the OPA for diagnostic purposes, we recommend indication of corresponding IOP values.

Effects of corneal thickness and axial length on intraocular pressure and ocular pulse amplitude before and after cataract surgery

OBJECTIVE

To investigate the relationship between the biophysical properties of the cornea and eye on the intraocular pressure (IOP) and ocular pulse amplitude (OPA) before and after cataract surgery.

DESIGN

Intervention study.

PARTICIPANTS

The left eyes of 311 patients.

METHODS

The left eyes of 338 patients undergoing cataract surgery without other eye pathology were studied. IOP and OPA were recorded by dynamic contour tonometry (DCT) 1 week before and 14 weeks after cataract surgery. The axial length, corneal curvature, central corneal thickness, anterior chamber depth, and anterior chamber angle were measured 1 week before cataract surgery. Multiple regression analyses of these factors to the preoperative OPA were performed. The difference between the pre- and postoperative IOP and OPA were investigated by paired t tests.

RESULTS

Three hundred and eleven of 338 eyes were analyzed. The preoperative OPA was negatively correlated with axial length (β = -0.24, p < 0.0001) and positively correlated with the preoperative IOP (β = 0.13, p < 0.0001). The average OPA was significantly decreased after cataract surgery (p < 0.0001). The mean change in postoperative OPA was -0.45 ± 0.63 mm Hg (95% CI -0.52 to -0.38 mm Hg).

CONCLUSIONS

The preoperative OPA was negatively correlated with axial length as reported. A significant decrease in OPA was observed after the cataract surgery.

The effect of intravitreal bevacizumab (Avastin) injection on retinal blood flow velocity in patients with choroidal neovascularization

Purpose

To study the short-term effects of intravitreal bevacizumab (Avastin) on retinal blood flow velocity and compare them to clinical outcomes assessed by optical coherence tomography (OCT) and tests of visual acuity.

Methods

The Retinal Function Imager (RFI) was used noninvasively and quantitatively to measure retinal blood flow velocity. Eight patients receiving intravitreal injection of Avastin for choroidal neovascularization (CNV) were included in this study. All were imaged by the RFI preinjection and 1 and 7 days postinjection. Visual acuity (VA) and OCT were recorded preinjection and 1 month postinjection. Comparisons were performed using paired Student t test and correlation using Spearman rank test.

Results

A good correlation was found between the 1-month change in VA and OCT measurements and the short-term change induced in blood flow velocity. Arterial and venous velocity changes 1 day after the injection correlated with the VA change (p<0.05). The 1-day arterial velocity changes correlated with total macular volume (p=0.02) and venous velocity changes correlated to central macular thickness (p=0.04).

Conclusions

The RFI provides a noninvasive technique to assess early hemodynamic responses to intravitreal injection of Avastin. These early changes may prove important for better understanding of the mechanism underlying this treatment and serve as a quantitative marker for treatment optimization.

The effect of intravitreal bevacizumab (Avastin) on ocular pulse amplitude in neovascular age-related macular degeneration

PURPOSE

To evaluate the effect of intravitreal (IVT) bevacizumab in neovascular age-related macular degeneration (AMD) on global choroidal hemodynamics, as measured by ocular pulse amplitude (OPA).

METHODS

This was a two-center prospective study (Sheba Medical Center, Israel, and University Hospitals Leuven, Belgium). AMD patients who required IVT bevacizumab (1.25 mg/0.05 mL; first or repeated) were examined three times: at days 0 (prior to injection), 7 (±3), and 28 (±7) postinjection. At each visit, OPAs of both eyes were measured using the Pascal dynamic contour tonometer (DCT). A paired t-test between preoperative and postoperative OPA was conducted. Pearson correlation was used to evaluate the influence of various measured parameters on DCT-OPA.

RESULTS

A total of 38 neovascular AMD patients were recruited, and 30 patients were included in the final analysis (18 females and 12 males; age 78.8 ± 5.82 years [mean ± standard deviation]). A good correlation was found throughout the study between the DCT-intraocular pressure (IOP) and Goldmann IOP and between DCT-IOP and DCT-OPA. No change in OPA of bevacizumab-treated eyes was found between the visits (2.24 ± 0.73, 2.2 ± 0.86, and 2.23 ± 0.73 mm Hg at visits 1, 2, and 3, respectively; paired t-test: P = 0.77 between visits 1 and 2, P = 0.98 between visits 1 and 3). No correlations were found between DCT-OPA and age, heart rate, systemic blood pressure, axial length, keratometry readings, and central corneal thickness.

CONCLUSIONS

OPA, an indirect measure of global choroidal hemodynamics, remains unchanged following IVT off-label bevacizumab. This finding adds to the growing evidence regarding the safety profile of bevacizumab in AMD treatment.

Choriocapillaris vascular dropout related to density of drusen in human eyes with early age-related macular degeneration

PURPOSE

Age-related macular degeneration (AMD) is a common, potentially blinding disease characterized by the presence of extracellular deposits beneath the retinal pigment epithelium (RPE). Choroidal vascular changes have also been noted in AMD. This study examined the relationship between the choroidal vasculature and extent of drusen and other sub-RPE deposits, the key pathologic landmarks of AMD.

METHODS

Sections of the maculas of 45 human eyes (21 early AMD and 24 age-matched control) were evaluated morphometrically. The cross-sectional area of sub-RPE deposits, vascular density, number of CD45+ leukocytes, and number of "ghost vessels" were determined in a masked fashion and evaluated by regression analysis. In addition, the extramacular vascular density either directly beneath drusen or adjacent to drusen was evaluated in a separate set of donor eyes.

RESULTS

The vascular density of the choriocapillaris showed a trend toward decreasing in association with AMD status. By linear regression analysis, vascular density was inversely associated with sub-RPE deposit density (r(2) = 0.22, P < 0.01). The number of ghost vessels was negatively correlated with vascular density (r(2) = 0.55, P < 0.001) and positively correlated with sub-RPE deposit density (r(2) = 0.57, P < 0.001). In morphologic studies of extramacular solitary drusen, vascular density beneath drusen was found to be 45% lower than adjacent to drusen (P < 0.01).

CONCLUSIONS

These findings support the concept that microvascular changes are related to the pathogenesis of AMD and suggest that vascular endothelial cell loss occurs in association with sub-RPE deposit formation. Whether microvascular events are a cause or consequence of drusen or other deposit formation remains to be determined.

A study comparing ocular pressure pulse and ocular fundus pulse in dependence of axial eye length and ocular volume

PURPOSE

There is a long-standing discussion about whether myopia is associated with decreased choroidal blood flow, as suggested by pneumotonometric measurements of pulsatile ocular blood flow (POBF). However, it has been noted previously that calculations of POBF depend on intraocular volume.

METHODS

In the present study we investigated this volume dependence through the comparison of ocular pressure pulse and ocular fundus pulse. Fifty-one healthy participants with different refractive errors participated in the study. Pulse amplitude (PA) and POBF were measured using pneumotonometry. Fundus pulsation amplitude (FPA) was measured with laser interferometry. Axial eye length (AEL) was measured with partial coherence interferometry. A mathematical model was used to calculate choroidal volume changes based on FPA. The ocular pressure pulse was converted into pulse volume (PV) according to the standard procedure used for pneumotonometry.

RESULTS

PA and POBF were found to decrease with increasing axial length (r = -0.55, p < 0.001 and r = -0.57, p < 0.001, respectively). A similar relationship existed for PV (r = -0.57, p < 0.001) and FPA (r = -0.46, p = 0.001). In addition, there was a significant association between PV and choroidal volume change during the cardiac cycle (r = 0.61, p < 0.001).

CONCLUSION

The present study confirms experimentally that PA, FPA and POBF are dependent on ocular volume and indicates that the pulsatile component of ocular blood flow is not reduced in myopic patients. Accordingly, the relationship between AEL and POBF described previously appears to be a consequence of different ocular volumes. Our findings have important implications for studies using PA or POBF.

Metabolic physiology in age related macular degeneration

Ischemia and hypoxia have been implicated in the pathophysiology of age related macular degeneration (AMD). This has mostly been based on studies on choroidal perfusion, which is not the only contributor to retinal hypoxia found in AMD eyes. Other features of AMD may also interfere with retinal oxygen metabolism including confluent drusen, serous or hemorrhagic retinal detachment, retinal edema and vitreoretinal adhesion. Each of these features contributes to retinal hypoxia: the drusen and retinal elevation by increasing the distance between the choriocapillaris and retina; vitreoretinal adhesion by reducing diffusion and convection of oxygen towards and vascular endothelial growth factor (VEGF) away from hypoxic retinal areas. Hypoxia-inducible-factor is known to exist in subretinal neovascularization and hypoxia is the main stimulus for the production of VEGF. Each feature may not by itself create enough hypoxia and VEGF accumulation to stimulate wet AMD, but they may combine to do so. Choroidal ischemia in AMD has been demonstrated by many researchers, using different technologies. Choroidal ischemia obviously decreases oxygen delivery to the outer retina. Confluent drusen, thickening of Bruch's membrane and any detachment of retina or retinal pigment epithelium, increases the distance between the choriocapillaris and the retina and thereby reduces the oxygen flux from the choroid to the outer retina according to Fick's law of diffusion. Retinal elevation and choroidal ischemia may combine forces to reduce choroidal oxygen delivery to the outer retina, produce retinal hypoxia. Hypoxia leads to production of VEGF leading to neovascularization and tissue edema. A vicious cycle may develop, where VEGF production increases effusion, retinal detachment and edema, further increasing hypoxia and VEGF production. Adhesion of the viscous posterior vitreous cortex to the retina maintains a barrier to diffusion and convection currents in the vitreous cavity according to the laws of Fick's, Stokes-Einstein and Hagen-Poiseuille. If the vitreous is detached from the surface of the retina, the low viscosity fluid transports oxygen and nutrients towards an ischemic area of the retina, and cytokines away from the retina, at a faster rate than through attached vitreous gel. Vitreoretinal adhesion can exacerbate retinal hypoxia and accumulation of cytokines, such as VEGF. Vitreoretinal traction can also cause hypoxia by retinal elevation. Conceivably, the basic features of AMD, drusen, choroidal ischemia, and vitreoretinal adhesion are independently determined by genetics and environment and may combine in variable proportions. If the resulting hypoxia and consequent VEGF accumulation crosses a threshold, this will trigger effusion and neovascularization.

Changes in central retinal artery blood flow after ocular warming and cooling in healthy subjects

Context:

Retinal perfusion variability impacts ocular disease and physiology.

Aim:

To evaluate the response of central retinal artery (CRA) blood flow to temperature alterations in 20 healthy volunteers.

Setting and Design:

Non-interventional experimental human study.

Materials and Methods:

Baseline data recorded: Ocular surface temperature (OST) in °C (thermo-anemometer), CRA peak systolic velocity (PSV) and end diastolic velocity (EDV) in cm/s using Color Doppler. Ocular laterality and temperature alteration (warming by electric lamp/cooling by ice-gel pack) were randomly assigned. Primary outcomes recorded were: OST and intraocular pressure (IOP) immediately after warming or cooling and ten minutes later; CRA-PSV and EDV at three, six and nine minutes warming or cooling.

Statistical Analysis:

Repeated measures ANOVA.

Results:

(n = 20; μ ± SD): Pre-warming values were; OST: 34.5 ± 1.02°C, CRA-PSV: 9.3 ± 2.33 cm/s, CRA-EDV: 4.6 ± 1.27 cm/s. OST significantly increased by 1.96°C (95% CI: 1.54 to 2.37) after warming, but returned to baseline ten minutes later. Only at three minutes, the PSV significantly rose by 1.21 cm/s (95% CI: 0.51to1.91). Pre-cooling values were: OST: 34.5 ± 0.96°C, CRA-PSV: 9.7 ± 2.45 cm/s, CRA-EDV: 4.7 ± 1.12 cm/s. OST significantly decreased by 2.81°C (95% CI: −2.30 to −3.37) after cooling, and returned to baseline at ten minutes. There was a significant drop in CRA-PSV by 1.10cm/s (95% CI: −2.05 to −0.15) and CRA-EDV by 0.81 (95% CI: −1.47 to −0.14) at three minutes. At six minutes both PSV (95% CI: −1.38 to −0.03) and EDV (95% CI: −1.26 to −0.02) were significantly lower. All values at ten minutes were comparable to baseline. The IOP showed insignificant alteration on warming (95% CI of difference: −0.17 to 1.57mmHg), but was significantly lower after cooling (95% CI: −2.95 to −4.30mmHg). After ten minutes, IOP had returned to baseline.

Conclusion:

This study confirms that CRA flow significantly increases on warming and decreases on cooling, the latter despite a significant lowering of IOP.

Blood velocity measurement in the posterior segment of the rabbit eye using combined spectral Doppler and power Doppler ultrasound

BACKGROUND

It is challenging for the current Doppler imaging to detect blood flow in small retinal vessels. Power Doppler, with its high sensitivity to detect minimal blood flow, can be used with spectral Doppler to measure blood velocity in small vessels of the eye and orbit.

METHODS

Sixteen eyes of twelve normal pigmented rabbits were studied, using a dedicated small animal, high-resolution imaging unit (Vevo 770) and 17.6 MHz ultrasound probe. Spectral Doppler (ISPPA = 67.1 W/cm(2), ISPTA = 483.7 mW/cm(2), MI = 0.5) was combined with power Doppler (ISPPA = 137.7 W/cm(2), ISPTA = 83.1 mW/cm(2), MI = 0.77) to measure the blood velocity over each identified vessel, including the central retinal artery and vein, branch retinal artery and vein, choroidal vein, and the long and short posterior ciliary artery. Three readings from each vessel were averaged to reduce measurement error. Three indices were calculated from the arterial blood velocity readings: the resistive index, the pulsatility index and the A/B ratio.

RESULTS

The highest arterial blood velocity was measured over the long posterior ciliary artery; peak systolic velocity was 18.29 cm/s and end diastolic velocity was 16.63 cm/s, while the lowest arterial blood velocity was measured over the branch retinal artery; peak systolic velocity was 5.08 cm/s and end diastolic velocity was 3.25 cm/s. On the other hand, the highest venous blood velocity was measured over the choroidal veins (7.0 cm/s), and the lowest venous blood velocity was measured over the branch retinal vein (2.88 cm/s). No statistically significant difference was observed between the nasal and temporal retinal arterial blood velocity. Combining power Doppler with spectral Doppler imaging caused no damage and is a safe technique to measure blood velocity.

CONCLUSION

A combination of spectral Doppler and power Doppler ultrasound can be used as a noninvasive and efficient tool for reproducible measurement of the blood velocity in the posterior segment.

Ocular haemodynamic changes after single treatment with photodynamic therapy assessed with non-invasive techniques

PURPOSE

To investigate in patients with neovascular age-related macular degeneration (ARMD) the changes in ocular perfusion caused by single treatment with photodynamic therapy (PDT) by different non-invasive methods; to evaluate correlations between relative changes of ocular haemodynamic parameters after PDT among each other and compared to morphological parameters; and to assess this in relation to early changes of visual acuity.

METHODS

STUDY POPULATION

17 consecutive patients with subfoveal choroidal neovascularization (CNV) caused by ARMD scheduled for PDT without previous PDT treatment (four patients with predominantly classic CNV and 13 patients with occult CNV).

OBSERVATION PROCEDURES

best-corrected visual acuity (before PDT, 6 and 8 weeks after PDT), fundus photography, fluorescein angiography, haemodynamic measurements with laser Doppler flowmetry (LDF), laser interferometry and ocular blood flow (OBF) tonometry (baseline and 1, 2, 6 and 8 weeks after treatment).

MAIN OUTCOME MEASURES

choroidal blood flow (CHBF), fundus pulsation amplitude (FPA), pulsatile ocular blood flow (POBF), visual acuity. Changes smaller than 20% were considered clinically irrelevant.

RESULTS

Ocular haemodynamic parameters did not change significantly in the follow-up period. Changes of haemodynamic parameters showed no correlation to treatment spot, morphological changes or visual acuity. Changes of visual acuity were comparable to results of earlier studies.

CONCLUSION

Single treatment with PDT did not modify ocular blood flow parameters above 20% as assessed with different non-invasive methods.

Age-related macular degeneration and the aging eye

Age-related macular degeneration (AMD) is an ocular disease that causes damage to the retinal macula, mostly in the elderly. Normal aging processes can lead to structural and blood flow changes that can predispose patients to AMD, although advanced age does not inevitably cause AMD. In this review, we describe changes that occur in the macular structure, such as the retinal pigment epithelium and Bruch's membrane, with advancing age and in AMD. The role of genetics in AMD and age-related changes in ocular blood flow that may play a role in the pathogenesis of AMD are also discussed. Understanding the pathophysiology of AMD development can help guide future research to further comprehend this disease and to develop better treatments to prevent its irreversible central vision loss in the elderly.

Ocular blood flow in diabetes and age-related macular degeneration

The 2 leading causes of blindness in adults in the industrialized nations, diabetic retinopathy and age-related macular degeneration, have been investigated thoroughly with respect to their pathogenesis. In recent years, it has been discovered that dysfunctional ocular microcirculation appears to play a part in the development of both diseases. In diabetic retinopathy, it has been shown that the disease is associated with early retinal vascular dysregulation. In the later states of the disease, retinal tissue hypoxia is a major trigger of sight-threatening neovascularization. In age-related macular degeneration, there is increasing evidence that reduced blood flow in the choroid is associated with the development and progression of the disease. Knowledge of the pathophysiological vascular states underlying these diseases is essential for the assessment and development of future therapies.

Foveolar choroidal circulation and choroidal neovascularization in age-related macular degeneration

PURPOSE

To investigate in a longitudinal study whether foveolar choroidal blood flow changes are associated with the development of choroidal neovascularization (CNV) in AMD.

METHODS

Relative foveolar choroidal blood velocity (ChBVel), volume (ChBVol), and flow (ChBFlow) were assessed in 135 patients with AMD, at baseline and then annually with laser Doppler flowmetry. All study eyes had visual acuity of 20/40 or better and no CNV at the time of enrollment. Comparison of foveolar choroidal circulatory measurements at baseline and their change before the development of CNV was made between eyes that had CNV and those that did not.

RESULTS

CNV developed in 28 eyes during the study. Baseline average foveolar ChBVol and ChBFlow in these eyes were 24% (P < 0.0001) and 20% (P = 0.0007) lower than that observed in the 165 eyes in which CNV did not develop. In the eyes with CNV, foveolar ChBVol and ChBFlow decreased by 9.6% and 11.5% before the formation of CNV, whereas in the eyes that did not, they increased by 6.7% (P = 0.006) and 2.8% (P = 0.004), respectively. Eyes with lower baseline foveolar ChBFlow were more likely (risk ratio = 3.47, 95% CI: 1.24-8.70) to show visual loss of three or more lines than were eyes with a higher baseline ChBFlow (P = 0.005).

CONCLUSIONS

The development of CNV and visual loss are associated with lower choroidal circulatory parameters at baseline. In addition, the results suggest that decreases in the foveolar choroidal circulation precede the development of CNV in AMD and may play some role in its development.

The clinical utility of dynamic contour tonometry and ocular pulse amplitude

PURPOSE

To determine if ocular pulse amplitude (OPA) as measured by dynamic contour tonometry (DCT) is related to severity of glaucoma, and if intraocular pressure (IOP) as measured by DCT is related to central corneal thickness (CCT).

METHODS

Patients were selected from the Duke Eye Center glaucoma clinic. Fifty-five eyes of 32 patients were included; right and left eyes were analyzed separately. CCT, OPA, DCT IOP, Goldmann applanation tonometry (GAT), Tonopen applanation tonometry (TAT), and systemic blood pressure were measured. Advanced Glaucoma Intervention Study score and mean deviation of visual field, and vertical and horizontal cup-disc ratios were recorded in a masked manner. Descriptive statistics were obtained, and OPA, DCT IOP, GAT, and TAT underwent univariate analyses to assess for relationships with predictor variables.

RESULTS

OPA, DCT IOP, GAT, and TAT were positively associated with CCT and with having no surgical intervention for right and left eyes, and were negatively associated with vertical and horizontal cup-disc ratios.

CONCLUSIONS

Increased OPA seems to correlate with less severe glaucoma and with increased CCT. DCT IOP seems to be affected by CCT along with GAT and TAT.

[Ocular pulse amplitude: a new biometrical parameter for the diagnose of glaucoma?]

BACKGROUND

Dynamic contour tonometry (DCT) enables accurate transcorneal measurements of the intraocular pressure and ocular pulse amplitude (OPA). In this study, we investigated whether this new biometrical parameter can characterize different glaucoma types and serve as a helpful tool in the diagnosis and therapy of the disease.

PATIENTS AND METHODS

A total of 441 eyes of 222 patients were included. Pressure measurements were performed with contour and applanation tonometry.

RESULTS

Mean OPA was 3.1+/-1.4 mmHg. Eyes with ocular hypertension showed significantly higher OPA values (3.6+/-1.3 mmHg) than healthy eyes (3.1+/-1.4 mmHg) and eyes with low-tension glaucoma (2.9+/-1.4 mmHg). After trabeculectomy, the values were significantly lower (2.4+/-1.3 mmHg) than in healthy eyes.

CONCLUSION

The size of the OPA seems to be characteristic for different types of glaucoma and directly dependent on intraocular pressure levels. Further investigation is indicated to clarify its diagnostic usefulness.

Technical note: How many readings are required for an acceptable accuracy in pulsatile ocular blood flow assessment?

PURPOSE

Pulsatile ocular blood flow (POBF) assessment aids the diagnosis of ocular diseases with defective ocular haemodynamics, such as glaucoma. Although each successful POBF measure given by the instrument represents five 'repeatable' pulses, there has been no study verifying how repeatable they are. There is also no report on the minimal number of measurements for an acceptable accuracy.

METHODS

Forty-three healthy young subjects were recruited and each subject had five consecutive POBF measurements obtained from one randomly selected eye. The coefficient of variation was calculated from the raw data of the five 'repeatable' pulses. The average from five consecutive measurements was considered as the standard for comparison with the first, average of the first two, the first three and the first four measurements. The 95% limits of agreement were determined using the Bland and Altman approach.

RESULTS

The coefficient of variation was greater than the manufacturer's claim of within 10%. The mean (+/-S.D.) POBF calculated from five consecutive measures was 732.5 +/- 243.2 microL min(-1). The mean (+/-S.D.) difference between the standard POBF and the first, average of the first two, the first three and the first four measurements was (in microL min(-1)): 12.5 +/- 59.8, 7.8 +/- 42.1, 9.6 +/- 32.5 and 3.7 +/- 19.6 respectively. The corresponding 95% limits of agreement were (in microL min(-1)): +/-117.2, +/-82.6, +/-63.8 and +/-38.4 respectively.

CONCLUSIONS

As the five 'repeatable' pulses were not as repeatable as the manufacturer claims, practitioners should not rely on one single POBF measure. An average of three consecutive measurements will be adequate to detect the minimum reported difference in POBF between glaucoma and normal patients.

The Relationship Between Retrobulbar and Choroidal Hemodynamics in Non-Neovascular Age-Related Macular Degeneration

BACKGROUND AND OBJECTIVE

To evaluate the relationship between retrobulbar and choroidal hemodynamics in non-neovascular age-related macular degeneration.

PATIENTS AND METHODS

Thirteen patients with age-related macular degeneration were assessed by both color Doppler imaging and scanning laser ophthalmoscope indocyanine green (ICG) angiography. Color Doppler imaging was used to measure peak systolic and end diastolic velocity (from which the resistance index, a measure of the resistance to flow downstream, was calculated) in the retrobulbar vessels. Scanning laser ophthalmoscope ICG angiograms were analyzed by area dilution analysis for quantitative choroidal fluorescence intensity assessment. Color Doppler imaging parameters were correlated with scanning laser ophthalmoscope ICG area dilution analysis parameters.

RESULTS

A good correlation was found between the posterior ciliary arteries resistance index and scanning laser ophthalmoscope ICG area dilution analysis fluorescence duration.

CONCLUSIONS

Scanning laser ophthalmoscope ICG area dilution analysis "duration" may serve as an alternative to color Doppler imaging in assessing the resistance to blood flow in the posterior ciliary arteries.

[Dynamic contour tonometry]

Dynamic contour tonometry (DCT) is a new technology for noninvasive and direct measurement of intraocular pressure (IOP); its results are thought to be influenced less than those of other methods by structural characteristics of the eye. The curvature of the pressure sensing device is concave and only slightly flatter than that of the human cornea. The cornea adapts to the curvature of the transducer head, and the sensor in the centre of the adapted area measures the pressure on the other side of the cornea in the force-free range. Studies published so far suggest that DCT is less heavily dependent than applanation tonometry on the biomechanical properties of the cornea . A further advantage of DCT over other forms of tonometry is the capability of dynamic measurements over time. It is also possible to measure both the diastolic and the systolic IOD and determine the difference between the two, i.e. the ocular pulse amplitude (OPA). OPA is an indirect indicator of choroidal perfusion and reflects the condition of the arterial vascular system and the action of the heart. It could be important in the diagnosis and treatment of glaucoma.

CUTTING THE ENCIRCLING BAND

PURPOSE

To report the effect of cutting the encircling band on ocular blood flow.

METHODS

In an interventional case series of 27 eyes with an encircling band, the ocular pulse amplitude (OPA) was measured and pulsatile ocular blood flow (POBF) derived and compared with fellow eyes. The bands were cut in 11 eyes and the POBF measured at 1 month, 3 months, and 1 year. Changes in POBF, buckle height, and visual acuity were determined.

RESULTS

The presence of the encircling band reduced the POBF to a mean of 43% (P < 0.001) of the fellow eye. Cutting the band resulted in a mean recovery to 85.6%. No retina detached after cutting, buckle height was only slightly diminished, and the visual acuity was unaffected.

CONCLUSION

An encircling band diminishes the POBF. Cutting the band restores significant flow.

Comparison of pulsatile ocular blood flow in Indians and Europeans

PURPOSE

To compare pulsatile ocular blood flow (POBF) in Europeans and Indians and provide reference values for a group of healthy Indians.

PATIENTS AND METHODS

Measurement with the POBF Tonograph was performed on healthy Indian subjects in India (n=252). A further 80 subjects (40 of Indian descent and 40 Europeans) underwent measurements in Cambridge, England. The instrument used for measurement was the same for both the studies.

RESULTS

The mean POBF in the Indians in India was found to be 1176 microl/min. The mean POBF value in the Europeans was found to be 1033 microl/min and that for Indians in England was 1061 microl/min. The difference between the POBF within groups was significant (one-way ANOVA P<0.05) with the POBF of Indians in India being higher than Europeans and Indians in the UK. The difference between the Europeans and Indians in the UK did not reach statistical significance.

CONCLUSIONS

POBF values in Indians living in India were found to be considerably higher than the previously published normal value of 650 microl/min in European studies and other studies for other racial groups. The reason for this apparent difference may be instrument-related rather than genetic because such a large difference was not observed when a comparison was performed in the UK. In addition, the results for both groups in our comparative study were still considerably higher than reported in previous studies. The POBF of Indians in India is slightly higher than the POBF of people of Indian ethnic origin in England.

Ocular rigidity in patients with age-related macular degeneration

PURPOSE

To compare the ocular rigidity in vivo measurements of patients with age-related macular degeneration (AMD) and control subjects.

DESIGN

Prospective comparative clinical study.

METHODS

The pressure-volume relation and the ocular rigidity coefficient were compared among 32 patients with AMD (AMD group: 16 with neovascular and 16 with nonneovascular AMD) and 44 age-matched control patients (control group) who underwent operation for cataract. This was achieved by an injection of 200 microl of a balanced salt solution (in steps of 4.5 microl) through the limbus in the anterior chamber, while the intraocular pressure was monitored continually with a transducer, up to the limit of 30 mm Hg.

RESULTS

The mean age (AMD group: 69.89 +/- 15.92 years vs control group: 65.28 +/- 12.34 years; P = .195), gender (AMD group: 13 female vs control group: 17 female; P = .513), eye's axial length (AMD group: 23.14 +/- 0.75 mm vs control group: 23.04 +/- 1.16 mm; P = .725) of patients with AMD and the healthy control subjects were comparable. No statistically significant difference in ocular rigidity measurements between patients with AMD and control subjects (AMD group: 0.0142 +/- 0.0077 microl(-1) vs control group: 0.0125 +/- 0.0049 microl(-1); P = .255) was found. When we examined separately the two subgroups of patients with AMD (neovascular and nonneovascular AMD), the average ocular rigidity measurements were higher in patients with neovascular AMD vs both control subjects and patients with nonneovascular AMD (neovascular AMD group: 0.0186 +/- 0.0078 microl(-1) vs control group: 0.0125 +/- 0.0048 microl(-1) [P = .014] vs nonneovascular AMD group: 0.0104 +/- 0.0053 microl(-1) [P = .004]).

CONCLUSIONS

Despite the limitations placed by the small sample of the examined cases, patients with neovascular AMD who are treated (with photodynamic therapy) have increased ocular rigidity measurements compared with patients with nonneovascular AMD and control patients.

Pulsatile ocular blood flow in asymmetric age-related macular degeneration

PURPOSE

Ocular perfusion abnormalities have been proposed in the pathogenesis of age-related macular degeneration (AMD) with differences in pulsatile ocular blood flow (POBF) in eyes with asymmetric AMD in Japanese and Taiwanese patients. The purpose of our study was to observe POBF difference in the fellow eyes of Caucasians with asymmetric AMD.

METHODS

This was a cross-sectional study comparing POBF in three groups of patients with asymmetric AMD in the fellow eyes: Group 1 (n=21) with drusen and active choroidal neovascularisation (CNV); Group 2 (n=18) with drusen and disciform scar; Group 3 (n=8) with CNV and disciform scar. The POBF was adjusted for intraocular pressure (IOP), pulse rate (PR), and axial length using multiple regression analysis. Generalised estimation equation model was used to include both eyes in each group.

RESULTS

The geometric mean (95% confidence interval) POBF values were as follows: Group 1 with drusen 1097.9 microl/min (957.0, 1259.7) in one eye and the fellow eye with CNV 1090.1 microl/min (932.3, 1274.7); Group 2 with drusen 946.0 microl/min (794.2, 1126.7) and disciform scar 966.2 microll/min (780.3, 1196.4); Group 3 with CNV 877.1 microl/min (628.3, 1224.6) and disciform scar 767.2 microl/min (530.5, 1109.7). Adjusting for differences in axial length, pulse rate and intraocular pressure, no statistically significant difference in POBF was found between fellow eyes in the same subject.

CONCLUSIONS

POBF is not different between fellow eyes of Caucasian patients with asymmetric AMD.

Refraction, axial length and age-related maculopathy

PURPOSE

To study the relationship between age-related maculopathy (ARM)/age-related macular degeneration (AMD) and phakic refraction and between ARM/AMD and axial length.

METHODS

The study was a point prevalence study that included 663 randomly selected persons aged over 65 years. We measured axial length and refraction. Fundus images were graded for ARM according to a modified Wisconsin Age-related Maculopathy Grading System standard. Data from both eyes were available from most participants. We analysed the results for both individual eyes and pairs.

RESULTS

The mean axial length was 23.22 mm for right eyes and 23.21 mm for left eyes. Women had a 0.57-mm shorter mean axial length than men. The mean refraction was +1.0 dioptres (D) for right eyes and +0.9 D for left eyes. At 70 years of age women were more hypermetropic than men by 0.66 D. There was no significant difference in refraction or axial length among the groups with different ARM stages.

CONCLUSION

We found no statistically significant relationship between axial length/refraction and AMD/ARM. There was a statistically significant sex difference in axial length and refraction, where women had shorter axial lengths and were more hypermetropic than men.

Refraction, axial length and age-related maculopathy

PURPOSE

To study the relationship between age-related maculopathy (ARM)/age-related macular degeneration (AMD) and phakic refraction and between ARM/AMD and axial length.

METHODS

The study was a point prevalence study that included 663 randomly selected persons aged over 65 years. We measured axial length and refraction. Fundus images were graded for ARM according to a modified Wisconsin Age-related Maculopathy Grading System standard. Data from both eyes were available from most participants. We analysed the results for both individual eyes and pairs.

RESULTS

The mean axial length was 23.22 mm for right eyes and 23.21 mm for left eyes. Women had a 0.57-mm shorter mean axial length than men. The mean refraction was +1.0 dioptres (D) for right eyes and +0.9 D for left eyes. At 70 years of age women were more hypermetropic than men by 0.66 D. There was no significant difference in refraction or axial length among the groups with different ARM stages.

CONCLUSION

We found no statistically significant relationship between axial length/refraction and AMD/ARM. There was a statistically significant sex difference in axial length and refraction, where women had shorter axial lengths and were more hypermetropic than men.

Pulsatile ocular blood flow change after treatment with systemic steroid in patients with Graves' ophthalmopathy

PURPOSE

Our previous study has demonstrated an impairment of pulsatile ocular blood flow (POBF) in patients with Graves'ophthalmopathy (GO). Here we further evaluate the haemodynamic change in GO patients after systemic steroid.

METHODS

In a prospective, interventional, consecutive clinical case series, all patients with active and moderately severe GO who underwent systemic steroid treatment were evaluated. The change of POBF and the clinical activity and severity of the disease were assessed.

RESULTS

In total, 11 patients underwent intravenous methylprednisolone pulse therapy followed by 2-month oral prednisolone therapy. POBF improved from a mean value of 476.5 to 614.7 microl/min (P<0.001) after treatment. Likewise, the mean clinical activity score reduced from 4.8 to 1.6. However, systemic steroid had less effect on the severity of GO. It also revealed that there is a greater improvement of POBF in those with more clinical activity score (>4) at the onset.

CONCLUSIONS

Following treatment with systemic steroid we have demonstrated a significant improvement in POBF in patients with GO.

Topical dorzolamide increases pericentral visual function in age-related maculopathy: pilot study findings with short-wavelength automated perimetry

PURPOSE

Numerous studies have confirmed the enhancement of ocular circulation by carbonic anhydrase inhibitors (CAIs). Topical CAI treatment with dorzolamide averts the significant pericentral visual function loss accompanying retinal and choroidal vasoconstriction during acute hyperventilation-induced hypocapnia. This study was designed to discern whether dorzolamide might similarly enhance macular function in patients with age-related maculopathy (ARM).

METHODS

In a masked, placebo-controlled study, 40 patients with ARM and acuity > 20/50 were randomized to receive either dorzolamide or placebo for 12 weeks, thrice daily. After pre-study perimetric training, pericentral function (mean sensitivity) was quantified using Humphrey 10-2 short-wavelength automated perimetry (SWAP), before and after 12 weeks of topical therapy.

RESULTS

Dorzolamide-treated eyes demonstrated a significant increase in mean sensitivity of + 1.55 dB (p = 0.04); placebo-treated eyes showed no significant change (+ 0.58 dB; p = 0.10). Given the non-significant increase of mean sensitivity in the placebo-treated group, fewer than 100 subjects per group would be required to afford > 70% power to yield a significant direct comparative difference between treatment and placebo in a prospective, randomized study of equally short duration.

CONCLUSIONS

This study demonstrated a significant increase in short-wavelength sensitivity in ARM with dorzolamide and the lack thereof with placebo. These encouraging pilot study data suggest a potential role for topical CAIs in ARM patients, and establish objective parameters for prospective studies to further evaluate the effects of dorzolamide in ARM.