Guenther Weigert

Role of Adenosine in the Control of Choroidal Blood Flow during Changes in Ocular Perfusion Pressure

PURPOSE The purpose of the present study was to investigate whether the nucleoside adenosine is involved in the regulatory processes of choroidal blood flow (ChBF) during an experimental decrease in ocular perfusion pressure (OPP). METHODS In this randomized, double-masked, placebo-controlled, two-way crossover study, 14 subjects received either intravenous adenosine or placebo on two different study days. The suction cup method was used for a stepwise increase in intraocular pressure (IOP). Subfoveal ChBF was measured by laser Doppler flowmetry. Mean arterial pressure (MAP) and IOP were measured noninvasively. Ocular perfusion pressure was calculated as OPP = 2/3MAP - IOP. RESULTS Adenosine increased ChBF significantly versus placebo before application of the suction cup (P < 0.05). When the suction cup was applied, a significant decrease in OPP was observed. This effect was comparable on all study days. The decrease in OPP was paralleled by a significant decrease in ChBF (maximum between -43% and -52%) which was less pronounced than the decrease in OPP (maximum between -62% and -64%). Neither placebo nor adenosine influenced the ChBF increase during suction cup-induced changes in OPP. CONCLUSIONS The data of the present study confirm that the human choroid shows some regulatory capacity during a decrease in OPP. Adenosine influences basal vascular tone in the choroid but is not involved in the regulatory mechanisms during an increase in IOP. (ClinicalTrials.gov number, NCT00712764.).

Strategies for reducing variance in laser Doppler flowmetry measurements

BackgroundScattering of blood flow data as assessed with laser Doppler flowmetry (LDF) in humans is a problem in many studies using this technique. We set out to reduce variability in LDF data by eliminating the effect of the total returning light level (DC) on LDF parameters in the choroid through partial regression analysis.MethodsIn 20 healthy subjects, choroidal blood flow parameters were measured at different DC values using a portable confocal LDF device. We used two different strategies to reduce scattering of data eliminating the effect of yield, which is defined as DC/gain. On the one hand, we used a previously described method based on a third-order polynomial fit, which combines all obtained data. On the other hand, we applied a new method based on a linear fit for each individual subject.ResultsVariability of data during changes in DC is higher for LDF parameters volume and flow than for velocity. Both methods were successful in reducing scattering of LDF parameters with varying DC.ConclusionsThe present study indicates that both methods to correct for changes in yield were successful in reducing the variability of LDF measurements. When systematic changes in DC occur after an intervention, one needs to be careful in interpreting the obtained data and it remains to be shown if either of the two techniques is capable of correcting for this effect. The approach presented here may, however, represent an effective, easily applicable and valid approach to reduce scattering of data from using LDF to assess blood flow in the posterior pole of the human eye.

ROLE OF ADDITIONAL DEXAMETHASONE FOR THE MANAGEMENT OF PERSISTENT OR RECURRENT NEOVASCULAR AGE-RELATED MACULAR DEGENERATION UNDER RANIBIZUMAB TREATMENT.

Purpose: To assess the efficacy of a combination therapy of intravitreal ranibizumab together with a dexamethasone implant in comparison with ranibizumab monotherapy in neovascular age-related macular degeneration. Methods: Forty eyes of recurrent or persistent neovascular age-related macular degeneration were included in this prospective study. Patients were randomly assigned to two groups. Based on a pro re nata treatment regimen, the first group received intravitreal ranibizumab monotherapy (IVM). The second group received a combination of intravitreal dexamethasone implant and ranibizumab (intravitreal combination [IVC]) at baseline and was retreated with ranibizumab as needed. A second dexamethasone implant was allowed for retreatment after at least 6 months. Retreatment criteria included evidence of subretinal fluid, cystoid macular edema or new hemorrhage, and/or a visual acuity decrease of 5 Early Treatment Diabetic Retinopathy Study letters. Results: During 12 months, a mean of 7.95/5.5 (IVM/IVC; P = 0.042) retreatments were given. The median time until first retreatment differed significantly between the groups (P = 0.004). Functional variables could be maintained in both groups with no differences between them. Visual acuity changed from 62 letters at baseline to 67 at Month 12 in the IVM and remained stable at 68 letters in the IVC group (P = 0.68); macular sensitivity changed from 6.95 dB to 7.01 dB in IVM and from 7.24 dB to 7.12 dB in IVC (P = 0.4). Central retinal thickness decreased, however, with no difference between the groups (P = 0.38). In the IVM/IVC group, 11/12 (55/60%) patients were phakic at the time of study entry. One (9%) patient from the IVM and 4 (33%) from the IVC group were referred to cataract surgery after study completion (P = 0.4). Conclusion: This pilot study indicates combined therapy to delay retreatment in patients with persistent/recurrent neovascular age-related macular degeneration and an overall reduction in required ranibizumab retreatments compared with ranibizumab monotherapy with consistent functional outcomes.