Decreased Heidelberg Retina Flowmeter (HRF) parameter "flow" at the papilla shortly after smoking a cigarette.

PURPOSE: To investigate the effect of smoking a cigarette on the Heidelberg Retina Flowmeter (HRF) parameter "Flow" at the papilla of healthy young volunteers. METHODS: Three HRF measurements were taken over the papilla (20 x 5, 256 x 64 pixels) in fourteen occasional smokers and in 14 non-smokers. Ten minutes later three similar HRF measurements were again made. In between the two series of measurements occasional smokers were asked to smoke a cigarette (Marlboro, nicotine content 9 mg) and non-smokers not. RESULTS: In occasional smokers, the values (arbitrary units) of the HRF parameter "Flow", calculated at the papilla (50 x 50 pixels), significantly (P = 0.01) decreased (11.2 +/- 3.5%) after smoking a cigarette. In contrast, in non-smokers, the values of the HRF parameter "Flow" did not decrease significantly (2.9 +/- 2.2%) when measurements were repeated 10 minutes later. CONCLUSIONS: The results of the present study suggest that smoking a cigarette can affect the HRF-parameter "Flow" at the papilla. The clinical implication of such an observation needs further investigations.     

Modulation of Heidelberg Retinal Flowmeter Parameter Flow at the Papilla of Healthy Subjects: Effect of Carbogen,Oxygen, High Intraocular Pressure,and β-Blockers

The Heidelberg Retina Flowmeter (HRF) is intended to assess ocular blood flow by scanning laser doppler flowmetry. In the retina and possibly in the optic nerve head, carbogen increases blood flow, whereas pure oxygen or high intraocular pressure (IOP) decrease it. This study addresses whether at the papilla of healthy volunteers, the HRF parameter flow, is modulated by breathing 5 % carbogen (5 % carbon dioxide + 95 % oxygen) for 7 minutes, breathing 100% oxygen for 7 minutes, increasing IOP to 50 mm Hg with a suction cup, or decreasing IOP with a single topical ocular instillation of the β-blockers 0.5 % betaxolol (betoptic) or 0.5 % timolol (timoptic). At the papilla (20° × 5°, 256 × 64 pixels), values of HRF parameter, flow (50 × 50) pixels, increased after carbogen (N = 5, P < 0.05), but decreased after oxygen (N = 5, P < 0.05) or IOP increase (N = 5, P < 0.01). Although IOP values were significantly reduced by betaxolol (N = 9, P < 0.05) and timolol (N = 9, P < 0.01), HRF values were only significantly decreased (N = 9, P < 0.05) after timolol. In conclusion, at the papilla of healthy volunteers, a positive correlation exists between changes in values of the HRF-parameter, flow, and stimuli considered to modulate retinal and ONH blood flow. Furthermore, although of unkown clinical relevance, it appears that in contrast to betaxolol, values of the HRF parameter, flow, at the papilla of healthy volunteers are significantly decreased after a single instillation of timolol.     

Velocity model for Heidelberg retinal flowmetry

BACKGROUND: An application of scanning-laser ophthalmoscopic flowmetry, Heidelberg Retina Flowmetry (HRF) is reported to faithfully quantify retinal perfusion. Indeed, without convincing regard for the fact that the method produces numerical values for such so-called "VELOCITY" (and subsequently "calculates" "FLOW", and "VOLUME") with no physical units or proven real-life meaning, current clinical drug studies and patient care are being based on this method. To test the physical "fidelity" of the HRF method, the author hence devised a simple, reliable mechanical model to generate known velocities of movement of a test surface. MATERIALS AND METHODS: Movement of the circumferential surface of an 89 mm (3 1/2-inch) ? cylinder, belt-driven by a brass spindle with segments of increasing diameter, was "analyzed" with the HRF method. The true velocities (mm/sec) with which the surface passed the HRF's focal point were then determined using a stopwatch. A 10 degrees x 2.5 degrees measuring field and a 20 x 20-pixel analysis window were used. Measurements were made for horizontal, diagonal (45 degrees and 135 degrees), and vertical motion at all velocity settings of the model. RESULTS: The relationship between real velocities of cylinder-surface motion and the corresponding HRF-"VELOCITY" values was nonlinear, an effect which increased significantly for diagonal and vertical motion. CONCLUSIONS: Considering the dependency on orientation of motion and the non-linearity of the relationship between HRF results and true velocity, as well as several other weaknesses discussed herein, the question arises whether the validity of the HRF method should be reconsidered.     

Alterations of retinal capillary blood flow in preclinical retinopathy in subjects with type 2 diabetes

Background. To identify alterations of retinal capillary blood flow in the papillomacular area in preclinical diabetic retinopathy using the Heidelberg scanning laser Doppler flowmeter. Methods.Ten eyes from ten patients with type 2 diabetes and no lesions visible on fundus photography (level 10 of Wisconsin grading) and ten eyes from ten healthy subjects of similar age range were examined with the HRF. Intravisit reproducibility of retinal capillary blood flow measurements was assessed in normal subjects and in type 2 diabetic patients, comparing different measurement areas and different analysis procedures: (a) 10᎒ pixel box with original software, (b) 10᎒ pixel box with SLDF software, and (c) whole-scan analysis with SLDF software (automatic full-field perfusion image analysis). Results.Intravisit reproducibility for the whole-scan analysis in the papillomacular area was 3.52%, 4.81% and 4.60% for volume (VOL), flow (FLW) and velocity (VEL) respectively. Using this method, mean and SD values for retinal capillary blood-flow are 13.25DŽ.87, 214.58ᇋ.30 and 0.74ǂ.17, for VOL, FLW and VEL for healthy eyes, comparing with 19.85Lj.22, 360.87끦.70 and 1.20ǂ.48 in eyes with preclinical diabetic retinopathy (P<0.010, P<0.019 and P<0.015 respectively). Conclusions.The HRF shows acceptable reproducibility when using whole-scan analysis in the papillomacular area. Retinal capillary blood VOL, FLW and VEL were particularly increased in five of the ten diabetic eyes examined, with values over the mean + 2SD of the control population, suggesting that eyes showing increased retinal capillary blood flow may indicate risk of progression.     

Reproducibility of pixel‐by‐pixel analysis of Heidelberg retinal flowmetry images: the Thessaloniki Eye Study

Purpose: To identify the investigator effect in the analysis results of Heidelberg retinal flowmetry (HRF) images when pixel‐by‐pixel analysis is performed. Methods: Thirty‐two of 732 HRF images were randomly selected from a population‐based study. Pixel‐by‐pixel analysis was performed by two trained masked graders in the following way: a square window of 40 × 40 pixels or two windows of 30 × 30 pixels or four windows of 20 × 20 pixels free from blood vessels at the peripapillary retina were identified. Using a 1 × 1‐pixel window, the grader performed pointwise analysis according to a specific protocol. The analysis process was performed by each observer three times (A, B, C) at 1‐week intervals. The percentage of pixels with < 1 arbitrary unit of flow (zero flow), the 10th, 25th, 50th, 75th and 90th percentiles and mean flow values were calculated. The difference between the results of analyses B?A and C?A for all HRF parameters was estimated using the Wilcoxon signed rank test. Mixed‐effect regression models were also used after controlling for grader effect and correlation within subjects. Results: There was no statistically significant difference between the results of analyses B?A and C?A or for any parameter in the mixed‐effect regression models. Intraclass correlation was 0.9665 for the percentage of zero flow pixels. Conclusions: Pixel‐by‐pixel analysis of HRF images by trained graders remains a highly reproducible method. No grader effect was found. If a precise protocol is followed, the results are independent of the exact placement of the analysis windows and the pointwise analysis of the identified and mapped retinal tissue.     

Photodetector sensitivity level and heidelberg retina flowmeter measurements in humans

PURPOSE: In vitro models suggest that Heidelberg retina flowmeter (HRF) measurements are affected by changes in photodetector sensitivity. We measured blood flow in a single volume of human retinal tissue in vivo at various sensitivity (DC) levels. METHODS: The peripapillary retinal regions of 12 normal subjects were examined by HRF under five different sensitivity settings: (1) average DC range below 100; (2) average DC range below 125; (3) average DC range near 150 (normal sensitivity); (4) average DC range above 175; and (5) average DC range above 200 or extremely overexposed. The distributions of flow values were examined by pointwise analysis. All pixels from a common tissue location were analyzed, and the effect of their brightness on the flow measurement was evaluated by ANOVA with Fisher's protected least significant difference model. RESULTS: ANOVA analysis of image DC level showed that significantly different DC levels were achieved for each of the five sensitivity settings (P < 0.0001). Flow values decreased with increasing DC for each of the 25th percentile, 50th percentile (P: < 0.0001 for each), 75th percentile (P: = 0.0026), 90th percentile (P: = 0.0216), and mean (P: = 0.0004) flow values. The percentage of pixels with values of zero (avascular tissue) increased with increasing photodetector sensitivity (P< 0.0001). CONCLUSIONS: Improper sensitivity settings alter the detected percentage of avascular tissue and the blood flow measurements in tissue containing capillaries. Consistent assessment of retinal blood flow requires consistent photodetector sensitivity settings between longitudinal images.     

Reproducibility of circadian retinal and optic nerve head blood flow measurements by Heidelberg retina flowmetry

BACKGROUND/AIM: The Heidelberg retina flowmeter (HRF) is designed to measure retinal capillary blood flow. Previous studies however showed weak reproducibility of data. The intraindividual reproducibility of circadian HRF measurements was examined in healthy subjects in three locations of the retina. METHODS: 36 healthy volunteers (27.3 (SD 4.3) years) were examined by HRF seven times a day (t0-t6). Using a default window of 10 x 10 pixels, three consecutive measurements were performed in three precise focusing planes: superficial, intermediate and deep layer, peripapillary retina, neuroretinal rim and cup, respectively. Images of identical tissue locations identified by capillary landmarks of each layer were selected to quantify the retinal microcirculation of each volunteer. Means and standard deviations of all flow results of a given subject were calculated, at t0-t6 and the coefficients of variation as a measure of reproducibility. RESULTS: The coefficients of variation ranged between 8.4% and 41.0% in the superficial layer (mean 19.8% (SD 8.4%)), 10.6%, and 43.0% in the intermediate layer (mean 24.0% (SD 8.4%)), and 9.9% and 84.0% (mean 29.6% (SD 15.8%)) in the deep layer. CONCLUSIONS: These data show the best reproducibility of measurements in the superficial layer followed by the intermediate and the deep layer. Clinically, this is an unsatisfactory intraindividual reproducibility of flow values in each studied layer.     

New neuroretinal rim blood flow evaluation method combining Heidelberg retina flowmetry and tomography

AIM: Accurate Heidelberg retina flowmeter (HRF) measurements require correct manual setting of the HRF photodetector sensitivity. The neuroretinal rim produces a weak signal relative to the peripapillary retina. A newly developed HRF alignment and sensitivity protocol, capable of accurate rim measurement, was investigated. METHODS: 18 eyes of nine healthy volunteers were examined by HRF. Three images of each eye were taken using three different imaging methods. Method 1: a conventional image (optic nerve head centred image with photodetector sensitivity optimised for the strong signal from the peripapillary retina); method 2: the setting of method 1 with photodetector sensitivity optimised for the weak signal from the rim; and method 3: the setting of method 2 with the temporal rim margin tangent to the lateral image border to remove the overpowering signal from the temporal peripapillary retina. The neuroretinal rim was defined by the Heidelberg retina tomograph (HRT). Blood flow and reflectivity values (DC component) in the rim area were compared for the three methods using pointwise analysis. Coefficients of variation of repeated measurements in 12 subjects have been calculated for method 3. RESULTS: The neuroretinal rim area measured by method 1 had a significantly lower brightness compared with method 2 and 3 (p=0.0002 and p=0.0002, respectively). Method 2 provided proper sensitivity for the weak signals of the rim area based on rim tissue DC values; however, this sensitivity setting was too high for the strong signal from the peripapillary retina. Method 3 avoided the strong peripapillary signal with the proper signal from the rim and provided significantly higher flow values of the rim area at 75 and 90 percentile pixels (p=0.0065 and p=0.0038 respectively) compared with method 2. Interobserver repeatability ranged from 16.85% to 21.96% for the different parameters. CONCLUSIONS: Method 3 provides an accurate and reproducible flow measurement of the neuroretinal rim area through proper sensitivity for the weak rim signal, alignment, and removal of the strong temporal signal from the image. This new method is recommended to improve accuracy of blood flow measurement in the neuroretinal rim.     

Retinal blood flow measurements and neuroretinal rim damage in glaucoma

AIM: To assess retinal blood flow characteristics in subjects with normal tension glaucoma (NTG), primary open angle glaucoma (POAG), and a group of controls using the Heidelberg retina flowmeter (HRF). The vascular parameters were correlated against structural damage of the optic nerve head, assessed using the Heidelberg retina tomograph (HRT). METHODS: HRF images were obtained in 76 subjects with NTG, 58 with POAG, and 38 controls. Optic nerve head images, acquired using the HRT, were analysed with Moorfields Regression Analysis software. The HRF variables, measured adjacent to a rim segment identified as "abnormal," were compared with the vascular parameters of the "normal" rim segments. The HRF parameters of the segments identified as normal in glaucoma subjects were compared with matched control segments. RESULTS: The glaucoma subjects had significantly lower retinal haemodynamics than the control subjects. There were no significant differences in the HRF parameters between the NTG and POAG subjects. The discs that had been identified as having abnormal segments had lower HRF values than those with a corresponding normal segment. The glaucoma subjects with normal rim segments had statistically significant lower velocity, flow, and volume measurements than the controls for each location sampled. CONCLUSION: This study shows a relation between structural damage of the optic nerve head and the level of retinal blood flow. The changes in the circulation could indicate that it may be an early marker of the pathological process.     

Detector sensitivity influences blood flow sampling in scanning laser Doppler flowmetry

PURPOSE: To establish the effect of photodiode sensitivity on the DC (brightness) value and the resultant blood flow measurements of retina and rim tissue using a scanning laser Doppler flowmeter (SLDF). METHODS: The sample consisted of one eye of each of 15 healthy subjects (mean age 27.8 +/- 6.1 years). Using the Heidelberg Retina Flowmeter (HRF), three 10-deg images of the superior temporal retina and three further images of the superior temporal rim were acquired for each of five DC bands: band 1: 30-70; band 2: 70-110; band 3: 110-150; band 4 150-190; band 5: 190-230. Retinal blood volume, flow and velocity were determined for each image using a 10 x 10 pixel square grid located at a predetermined location on the retina and rim for each subject. Following image acquisition, the DC values corresponding to each pre-assigned retinal or rim location were determined. The mean and standard deviation were determined for the blood flow parameters within each DC band for each subject in both locations. Analysis of variance was used to identify significant change in the data as a function of the DC value (P<0.05). RESULTS: Analysis of variance revealed that retinal blood flow measures acquired within DC band 5 resulted in significantly lower measures of blood flow and velocity (P=0.035 and P=0.049 respectively) than at lower DC values. Band 5 values of flow, volume and velocity in the neuroretinal rim were also significantly low (P=0.016, P= 0.003 and P=0.026 respectively). Peak neuroretinal rim blood flow was recorded when the DC value was between 70 and 110. For blood flow measurement at the retina and neuroretinal rim the DC value should not exceed 190. CONCLUSION: Photodiode sensitivity as indicated by the DC value affects measurements of ocular blood flow using the HRF.     

Microvascular blood flow of the optic nerve head and peripapillary retina in unilateral exfoliation syndrome

PURPOSE: To measure microvascular blood flow in patients with unilateral exfoliation syndrome (XFS) without glaucoma or ocular hypertension and to compare the values in the eyes with clinically detected exfoliation, their nonexfoliative fellow eyes of the same patients and control eyes. METHODS: Twenty-two patients with clinically detected unilateral XFS and 30 age-matched healthy subjects were included in this study. Group 1 consisted of 22 eyes with clinical XFS, and the nonexfoliative fellow eyes of the same patients formed Group 2. The control group (Group 3) comprised te randomly selected eyes of 30 age-matched healthy subjects. Ocular blood flow values (volume, flow and velocity) were recorded from the opti nerve head (ONH) and peripapillary retina (PPR) using the Heidelberg retinal flowmeter (HRF). The difference between the three groups were compared statistically. RESULTS: The mean values of blood flow obtained from the ONH and PPR in eyes with clinically detected exfoliation (Group 1) and their nonexfoliative fellow eyes (Group 2) were both significantly lower than the values for the control eyes (Group 3). The differences in ocular blood flow between the eyes with exfoliation and the nonexfoliative fellow eyes were not statistically significant [one-way analysis of variance (ANOVA), Dunnett's T3 test, p >/= 0.05]. CONCLUSION: These findings suggest that the eyes with clinically detected unilateral XFS were associated with reduced blood flow values in both the ONH and the PPR. The nonexfoliative fellow eyes also have lower blood flow values than the control eyes.     

The capillary blood flow in ischaemic type central retinal vein occlusion: the effect of laser photocoagulation

PURPOSE: To determine the effect of photocoagulation on retinal blood flow (RBF) in eyes with ischaemic type central retinal vein occlusion (CRVO). PATIENTS AND METHODS: Retinal blood flow was measured in 12 eyes with CRVO, 12 fellow eyes and 12 eyes of 12 age-matched healthy subjects using the Heidelberg retinal flowmeter (HRF). Microvascular blood flow values (volume, flow, velocity) were recorded from the upper temporal retina and macula. Eyes were re-examined 1 month after photocoagulation. We investigated whether there was a difference in RBF measurements before and after photocoagulation treatment. RESULTS: In eyes with CRVO, mean RBF values (volume, flow and velocity) obtained from the upper temporal retina increased significantly after treatment (paired t-test, p < 0.05). In contrast, mean RBF values from the macula were unaffected by photocoagulation (paired t-test, p > 0.05). Retinal blood flow values from the upper temporal retina obtained from control subjects were significantly higher than the values in eyes with CRVO before and after photocoagulation (unpaired t-test, p < 0.05), but there was no significant difference between control subjects and CRVO patients in RBF values from the macula (unpaired t-test, p > 0.05). Mean RBF values were significantly higher in CRVO patients' fellow-eyes before photocoagulation in the eyes with CRVO (paired t-test, p < 0.05) but were lower than in age-matched healthy control eyes (unpaired t-test, p < 0.05). Macular blood flow did not differ between the eyes with CRVO and fellow eyes (paired t-test, p > 0.05). CONCLUSION: Laser photocoagulation increased retinal blood flow in eyes with CRVO, but RBF did not reach normal values. Photocoagulation was found to have no effect on RBF in the macular area.     

Hyperreflective foci as biomarkers for inflammation in diabetic macular edema: Retrospective analysis of treatment naïve eyes from south India

Purpose:The aim of this study was to analyze the factors associated with hyperreflective foci (HRF) in diabetic macular edema (DME) in treatment naïve eyes.Methods:This retrospective observational study included 131 eyes of 91 treatment naïve patients with DME. Details of ophthalmological examination with duration of vision loss and systemic parameters were noted. The spectral-domain optical coherence tomography (SD-OCT) images were analyzed for number and location of HRF and the associated imaging biomarkers.Results:Inner retinal (IR) HRF were seen in 88 eyes (67%), outer retinal (OR) in 28 (21%), and subretinal (SR) in 12 (9%). The IR had (7.1 ± 7) HRF, the OR (6.5 ± 4.8), and SR (3.9 ± 2.9). A greater proportion of eyes with HRF also had subretinal fluid (SRF), significantly higher blood pressure and lower serum triglycerides. Univariate linear regression analysis showed women (3 HRF greater vs. men, P = 0.04), eyes with cystoid spaces (2.95 more HRF vs. no cystoid spaces, P = 0.02), and SRF (2.96 more HRF vs. no SRF, P = 0.007) had more HRF, whereas higher triglycerides (1 HRF lesser per 50 mg lower TGL, P = 0.03) had lesser.Conclusion:Our study highlights the importance of HRF as an imaging biomarker in DME suggesting an inflammatory origin. Long-term observations of large cohorts with automated analysis can give more insights.     

Aerobic exercise reduces intraocular pressure and expands Schlemm’s canal dimensions in healthy and primary open-angle glaucoma eyes

Purpose:Aerobic exercise (AE) has been reported to decrease intraocular pressure (IOP) in healthy subjects and there are concomitant morphological changes in the anterior segment of the eye including the Schlemm’s canal (SC). However, its effects on IOP and SC morphology in glaucoma patients had not been studied before. We aim to investigate the effect of AE on the IOP and SC dimension in both healthy and primary open-angle glaucoma (POAG) eyes.Methods:The area and diameter of SC and IOP were measured in 35 primary open-angle glaucoma (POAG) patients (59 eyes) and 36 healthy subjects (72 eyes) before and after performing moderate intensity of AE by running on a treadmill for 30 min. SC was imaged by swept-source optical coherence tomography (SS-OCT) for evaluation.Results:In comparison with baseline values, mean IOP decreased significantly following AE in both POAG and healthy eyes (both P < 0.001), in which POAG eyes showed a greater degree of reduction compared to healthy eyes (P = 0.002). In comparison with baseline values, in both POAG and healthy eyes, the average cross-sectional area (POAG: 80.48 +/- 59.54 vs. 99.20 +/- 54.87 pixels; healthy: 151.84 +/- 52.76 vs. 198.23 +/- 53.70 pixels; both P < 0.001) and diameter (POAG: 3.73 +/- 1.69 vs. 4.33 +/- 1.74 pixels; healthy: 5.61 +/- 1.02 vs. 6.47 +/- 1.20 pixels; both P < 0.001) of SC significantly increased after AE. In POAG, both treated and untreated with IOP-lowering medications, a significant reduction in mean IOP and increase in SC dimensions following AE were observed (all P < 0.05), and there were no significant differences of such measurements between the two subgroups (all P > 0.05).Conclusion:AE-induced reduction in IOP and an increase in SC dimensions in POAG eyes as in healthy eyes. Further studies to evaluate the long-term effect of AE on IOP control and SC morphology in POAG seem warranted.     

Foveolar Choroidal Blood Flow in Idiopathic Macular Hole

Purpose: To measure choroidal blood flow from foveal region in the eyes with idiopathic macular hole. Methods: Thirteen patients with macular hole and 20 age-matched healthy subjects were included into the study. While group 1 consisted of 13 eyes of idiopathic stage 4 macular hole, seven fellow eyes of the same patients with stage 1a macular hole formed the group 2. The control group (group 3) comprised the randomly selected eye of 20 age-matched healthy subjects. Mean values of blood perfusion parameters that were composed of volume, flow and velocity, were recorded from foveal region of fundus using Heidelberg Retinal Flowmeter (HRF). The differences between the three groups were compared with unpaired t-test, Wilcoxon Signed Rank and Fisher’s Exact test using statistical package program. Results: The mean blood volume and velocity in the eyes with stage 4 macular hole (group 1) and in the eyes with stage 1a macular hole (group 2) were both significantly lower than the eyes in control eyes (group 3) ( p < 0.05, unpaired t-test). Although, the mean blood “flow” parameter of group 2 was significantly lower than group 3 ( p < 0.05, unpaired t-test), there was no statistical difference in the “flow” parameter between group 1 and group 3 ( p > 0.05, unpaired t-test). The comparison between group 1 and group 2 revealed no significant difference in any perfusion parameter ( p > 0.05, Wilcoxon Signed Rank Test). Conclusion: Although, it may be result of macular hole, not necessarily the cause of it, these findings suggest that the eyes with idiopathic macular hole are associated with reduced foveolar blood flow. The measurement of the foveolar blood flow from choriocapillaris may be useful for identifying the subjects who have increased risk of development of macular hole in future. The study showed the association of a decrease in foveolar choroidal blood flow in eyes with idiopathic macular hole using HRF. Authors suggested that quantitative measurement of foveolar choroidal blood flow may be helpful for identifying the subjects who have increased risk of development of idiopathic macular hole. This study was presented at XIII. Congress of European Society of Ophthalmology in Istanbul in June, 4, 2001.     

Effects of 0.005% latanoprost on optic nerve head and peripapillary retinal blood flow

Fifty-two eyes of 26 healthy volunteers were recruited for evaluating the effects of 0.005% latanoprost on optic nerve head (ONH) and peripapillary retinal blood flow. In a randomized double-blind design, one eye received one drop of 0.005% latanoprost and its fellow eye received one drop of a placebo eyedrop. Intraocular pressure (IOP), ONH and peripapillary retinal blood flow were measured with Heidelberg retinal flowmetry (HRF) before, 2 and 24 h after administration of eyedrops. IOP was decreased significantly in latanoprost-treated eyes at 2 and 24 h after administration (p < 0.05). In the volume, flow or velocity of ONH and peripapillary retina, there were no significant changes from the baseline values at 2 and 24 h after latanoprost administration in either latanoprost-treated eyes or their fellow eyes (p > 0.05). No significant differences were found in the measured quantities between latanoprost-treated eyes and their fellow eyes at each time point (p > 0.05). This result may suggest that 0.005% latanoprost in healthy subjects does not have any adverse effect on ONH and peripapillary retinal blood flow. Copyright Copyright 1999 S.Karger AG, Basel     

Necessary visual information for restoring reading with a retinal implant in a blind patients with massive retinal degeneration of photoreceptors]

DEFINITION OF THE PROBLEM: Our goal is to determine the minimum of information necessary for elementary reading, using a retinal implant. This concerns particularly the fragmentation (pixellisation) of the presented image and its position in the visual field. Fragmentation corresponds to the number of electrodes available, the position of the image in the visual field is equivalent to the site of the implant on the retina. MATERIAL AND METHODS: 10 degrees x 10 degrees windows, containing isolated words or letters, were presented to six healthy subjects on a computer screen. A coupling between the computer and an eye tracker stabilizes these images in an area of the visual field. This coupling constantly corrects the position of the image on the screen according to the direction of gaze. RESULTS: 1) A rapid decrease of the performance is observed at a certain threshold of pixellisation, dependent on the eccentricity of presentation of the images. 2) In central vision, about 400 pixels are sufficient to recognize 80% of the four-letters words. At 10 degrees of eccentricity, about 1225 pixels are needed. 3) An acceptable comprehension of a text (identification of four words out of five), is impossible at eccentricities higher than 10 degrees 4) About 50 pixels are sufficient for a satisfactory recognition of isolated letters, independently of their eccentricity. CONCLUSION: These data validate the method of investigation and provide valuable indications regarding minimal visual requirements in prosthetic vision.     

Retinal blood flow autoregulation after dynamic exercise in healthy young subjects

PURPOSE: To evaluate the retinal blood flow before and after the increase in systemic blood pressure to assess the autoregulation in healthy young subjects. METHODS: Twenty eyes of 20 healthy volunteers were examined. The retinal blood flow was assessed by a Heidelberg retina flowmeter (HRF), while the systemic pressure was assessed by a portable electronic sphygmomanometer. Furthermore intraocular pressure (IOP) was always measured by a Goldmann tonometer immediately after HRF assessments. All measurements of physiological and flow parameters were performed with the subjects seated at rest and then immediately after stair climbing. RESULTS: The IOP decreased significantly after dynamic exercise, while the heart rate and the systemic artery pressure increased significantly. At the baseline, the mean retinal blood flow was 276.8 +/- 80.7 arbitrary units (AU) in the superotemporal area, 243.4 +/- 63.68 AU in the superonasal area, 258.2 +/- 67.37 AU in the inferotemporal area and 243.9 +/- 72.24 AU in the inferonasal area. After dynamic exercise the mean retinal blood flow was 249.8 +/- 86.78 AU in the superotemporal area, 248.7 +/- 63.87 AU in the superonasal area, 245.4 +/- 83.85 AU in the inferotemporal area and 228.8 +/- 62.53 AU in the inferonasal area. No significant change in retinal blood flow was found. CONCLUSION: Our data support the hypothesis that in normal subjects autoregulation is sufficient to compensate the increase in blood pressure and maintain a stable retinal blood flow after exercise.     

Decreased blood flow at neuroretinal rim of optic nerve head corresponds with visual field deficit in eyes with normal tension glaucoma

PURPOSE: To determine the relationship between the blood flow parameters of the optic disc rim and the glaucomatous visual field changes. DESIGN: Observational cross-sectional study. METHODS: Tissue blood flow in the neuroretinal rim within the optic disc was determined with the Heidelberg retina flowmeter(HRF) in 54 eyes of 54 patients with normal tension glaucoma (NTG). Patients were selected whose visual field defects were confined to either the superior or inferior hemifield. Blood flow measurements were made in a 10 degrees x 2.5 degrees area of the superior and inferior neuroretinal rim within the optic disc. The mean blood flow (MBF) was calculated by the automatic full-field perfusion image analyzer program, and the ratio of the MBF in the superior to the inferior rim areas (the S/I ratio) was calculated from the same HRF image in order to minimize the variation of measurement condition. RESULTS: Inferior rim blood flow is less than superior rim blood flow in patients with superior hemifield defect, and superior rim blood flow is reduced compared to inferior in patients with inferior hemifield defect. The mean S/I ratios of the MBF in the patients with superior hemifield defect (1.46, n=37) was significantly higher than that in the patients with inferior hemifield defect (0.79, n=17; P<0.0001, Mann-Whitney U-test). CONCLUSIONS: The blood flow in the neuroretinal rim was found to correspond to the regional visual field defect in eyes with NTG. Reductions in flow were associated with reductions in function.     

The mechanical fundus perfusion model: blood flow velocity determined by ICG angiography and Heidelberg retina flowmetry]

BACKGROUND: Heidelberg Retina Flowmetry (HRF) is now popularly, perhaps even indiscriminately applied in eye research, without apparent concern for the fact that the results are given numerically, but without physical units. METHODS: 1) HRF: To challenge the HRF-device with known values of blood-flow velocity, a perfusion chamber with input and output connections was constructed of acrylic plastic. Three serial segments were milled to provide cross-sectional areas (1.93 mm2, 3.33 mm2, and 5.08 mm2) and accordingly decreasing, true, clinically representative flow-velocity values. Under a constant perfusion setting of a calibrated clinical infusion pump (Perfusor Secura FT, B. Braun Medical AG, Sempach, CH), heparinized human blood (P. H.) was pumped through the chamber, and the HRF-parameter, "VELOCITY" was measured within one image encompassing the three chamber segments, using a 20 degrees x 5 degrees-field and a 20 x 20-pixel measuring "window". 2) HRA: Immediately thereafter, our perfusion model was placed in front of the Heidelberg Retina Angiography device, the infusion pump started at the same constant level, and a 1 cc bolus of ICG dye was added to the blood. Digital ICG-angiography was then conducted, and the images analyzed on-screen. RESULTS: In the three segments of the perfusion chamber, flow velocities determined ICG-angiographically were 11.5 mm/s, 6.7 mm/s, and 4.4 mm/s, respectively. The corresponding values for HRF- "VELOCITY" were 5.3, 4.2, and 3.4, respectively (no units). CONCLUSIONS: Under identical perfusion conditions, the phenomenologically (ICG-angiographically) determined values of flow velocity in the 3 perfusion chamber segments ran similar to (but not numerically coincidental with) those determined for HRF-parameter "VELOCITY". Extrapolation of HRF-values to true physical units is, thus, feasible.