Influence of latanoprost on retinal microcirculation in glaucoma.

PURPOSE: To test whether latanoprost has an influence on ocular haemodynamics, considering the general reputation of prostaglandins which is frequently associated with vasoconstriction. The effect of latanoprost on the retinal blood supply of treatment-naïve glaucoma patients was tested. MATERIALS AND METHODOLOGY: 13 patients (7 male, 6 female) who had just recently been diagnosed with primary open-angle glaucoma (POAG) were treated with latanoprost (0.005%). The average age of our study group was 63.8 years (+/- 2.9 years). The drug's effect on retinal autoregulation was assessed by flicker test using the Dynamic Vessel Analyzer (DVA). Examinations took place before initializing treatment, after 4 weeks and once again after 4 to 6 months. RESULTS: In our group of POAG patients, the IOP under treatment was significantly reduced about 25%. No intraindividual differences in systemic blood pressure and heart rate were observed. In DVA measurements of glaucoma patients, the maximum flicker dilation of the arteries was significantly lower than reported for healthy volunteers. Beyond that, POAG patients did not show significant differences in vessel diameters, peak amplitudes as well as maximum dilations of retinal arteries and veins before and under treatment with latanoprost (0.005%). CONCLUSION: Latanoprost markedly lowered the IOP but it did not exert a significant effect on retinal haemodynamics. There was neither a tendency towards vasoconstriction nor towards vasodilation. Sustaining reperfusion damage after topical latanoprost therapy thus seems to be highly unlikely. Further studies must show if sole IOP lowering or a dual positive effect - IOP lowering and improvement of retinal vessel autoregulation - have a more positive impact on the long term follow-up of glaucoma patients.

[Temporal oscillations of retinal vessel diameter in healthy volunteers of different age]. / Zeitliche Schwingungen retinaler Gefässdurchmesser bei Gesunden unterschiedlichen Alters. Kreuz- und Autokorrelation für dynamische Gefässanalyse.

PURPOSE: We investigated whether temporal oscillations of the retinal vessel diameter, as measured with the dynamic vessel analyzer (DVA), undergo age-related changes. METHODS: Vessel diameters of retinal arterial and venous segments were examined with the DVA in 28 medically healthy volunteers divided into two age groups of 14 persons each: young subjects (21-32 years) and seniors (52-70 years). Continuous temporal records of vessel diameter were mathematically evaluated and divided into high-frequency (period <1.5 s) and low-frequency (period > or =1.5 s) oscillations. RESULTS: The phase difference between temporal arterial and venous vessel diameter records was higher in the young group [0.6 (0.1, 3.3)] s [median (1st quartile, 3rd quartile)] compared with the seniors [0.1 (-0.4, 0.3) s]. There was a difference in the periodicity in veins between the groups and, in seniors, between the arteries and the veins. CONCLUSIONS: High-frequency oscillations of vessel diameter correspond to the heartbeat. These were expressed more in seniors. Low-frequency oscillations were well expressed in young subjects. Our results show significant age-related alterations in retinal vessel regulation.

[Influence of two different cameras on the spectrometric measurement of oxygen saturation]. / Einfluss von unterschiedlichen Kameratypen auf die spektrometrische Messung der Sauerstoffsättigung.

OBJECTIVES: Oxygen saturation in retinal vessels can be measured by spectrometry. However, there are no studies on the influence of different camera chips on these measurements. The presented study reports the effect of two different camera chips ("1-CCD" vs. "3-CCD") on the spectrometric measurements in the same patients. METHODS: 61 eyes of 61 patients were included in this study. The study was approved by the local ethics commission. Patients were separated in 3 groups: the first group contained healthy volunteers, the second group patients with diabetes mellitus but without previous laser treatment, the third group included patients with diabetes mellitus and previous laser coagulation treatment. The oxygen saturation was calculated from the difference between wavelengths on and right next to the retinal vessel. This methodology uses the different absorption spectra of oxy- and deoxyhaemoglobin. RESULTS: All 3 groups demonstrated valid outcomes of the retinal oxygen saturation in arterial and venous vessels. No significant differences we found in the arterial-venous oxygen difference between the two different camera chips (group 1 p = 0.063, group 2 p = 0.204, group 3 p = 0.059). CONCLUSION: As no significant differences could be found between the two camera chips, the less expensive system should be used if the spectrometric measurement of oxygen saturation is added to an analysis system already established on the market.

Quantitative assessment of optic nerve head pallor.

Ischaemia, loss of neural tissue, glial cell activation and tissue remodelling are symptoms of anterior ischaemic as well as glaucomatous optic neuropathy leading to pallor of the optic nerve head. Here, we describe a simple method for the pallor measurement using a fundus camera equipped with a colour CCD camera and a special dual bandpass filter. The reproducibility of the determined mean pallor value was 11.7% (coefficient of variation for repeated measurements in the same subject); the variation over six healthy subjects was 14.8%. A significant difference between the mean pallor of an atrophic disc and that of the contralateral eye of the same individual was found. However, even the clinically unaffected eye showed a significantly increased pallor compared to the mean of the healthy control group. Thus, optic disc pallor measurement, as described here, may be helpful in the early detection and follow-up of optic neuropathy.

[Static vessel analysis in nonmydriatic and mydriatic images]. / Statische Gefässanalyse in nonmydriatischen und mydriatischen Bildern.

BACKGROUND: Static vessel analysis is a method to determine the diameter of retinal vessels in images of the ocular fundus. The suitability of non-mydriatic and mydriatic images for that method and the influence of mydriasis on the results were examined. MATERIALS AND METHODS: In the prospective study, 30 eyes of 15 patients (10 women, mean age 51.6 +/- 13.2 years) were examined. At first, 3 images were taken of each eye with the retinal camera Topcon NW 200 (magnification 1). After pupil dilation with tropicamid eye drops, 3 more images were taken using the Topcon and 3 others using the system Visualis (IMEDOS, Jena/Germany, FF450plus, 535-561 nm, 30 degrees image, 1840 x 1360 pixel). The vessel diameters were measured with the software Vesselmap2 (IMEDOS). The investigator assigned vessels to arteries or veins and their diameters were calculated automatically by the software. There is the possibility to define the vessel edge manually in cases of a poor image quality. The calculation of the central retinal arterial and venous equivalent (CRAE, CRVE) as well as the arterio-venous ratio (AVR) were made according to the formula of Parr-Hubbard. Furthermore, the nasal retinal vessels > 60 microm were examined to estimate the influence of tropicamid on the vessel diameter. RESULTS: Because of insufficient illumination and poor contrast in 21 % of the non-mydriatic images not all vessels could be detected automatically. Additionally, fewer vessels could be detected in 7 % of the non-mydriatic images compared to the mydriatic images. The average coefficient of variation of CRAE and AVR of each triplet of images was higher in non-mydriatic images (2.6 % and 3.2 %, respectively) than in mydriatic images of the Topcon (1.8 %; 2.3 %) and the FF 450 (1.7 %; 1.8 % ANOVA p < 0.05). No significant differences were found between the various examination methods for both the coefficient of variation of CRVE (1.9 %; 1.8 %; 1.7 %) and the average values of CRAE, CRVE and AVR. With regard to their diameters, the nasal retinal arteries and veins > 60 microm, were depicted sufficiently in all images, and only differed insignificantly between the three methods. CONCLUSION: The quality of non-mydriatic images is often lower than that of mydriatic images. This fact can account for the high variance of measured parameters in the non-mydriatic images. The depiction of all relevant vessel segments is a precondition for the image-based analysis. An influence of the mydriasis caused by tropicamid on the retinal vessel diameters > 60 microm was not found.

Blood pressure effects on retinal vessel diameter and flicker response: a 1.5-year follow-up.

PURPOSE: The study examined the influence of individual blood pressure changes overtime on retinal vessel diameter and the latter's response to flicker light. METHODS: The diameter of a retinal arterial and venous segment was measured continuously on-line with a Dynamic Vessel Analyzer in 20 patients twice (mean interval between examinations of 24 months). Eleven patients had no cardiovascular disease. Nine patients had arterial hypertension and were untreated at the time of the first measurement; at the time of the second measurement they were undergoing various antihypertensive therapies. Each test consisted of a 50-s baseline plus three 20-s periods of flicker stimulation followed by an 80-s period of observation. During the examinations the blood pressure was measured at 1-minute intervals. RESULTS: In the hypertension group changes in the mean arterial blood pressure (MAP) correlated significantly with changes in the arterial baseline diameter (y = -0.1 - 0.37x, r =0.74, p (increase) <0.03). A comparison of the two measurements showed no such relationship in the group of cardiovascularly healthy subjects. The venous baseline and the arterial and venous flicker response did not change significantly in either group between the two measurements and showed no relationship to blood pressure changes. CONCLUSIONS: In hypertensive subjects, long-term therapy-related changes in blood pressure induced a change in the arterial baseline by approximately +3.7 microm/-10 mmHg MAP. An influence of lowering MAP to the arterial flicker response could not be detected.

[Variance of retinal vessel diameter response to flicker light. A methodical clinical study]. / Varianz der Netzhautgefässreaktion auf Flickerlicht. Eine klinisch-methodische Studie.

AIM: The study investigated the variance of the retinal vessel response to flicker light between the right and left eyes and after a short and a medium-length time interval. METHODS: The prospective study included 28 volunteers. In the first exam both eyes were examined. One eye selected randomly was measured again after 1 h and after 1 month. The diameter response of an arterial and venous vessel segment was measured continuously by a Dynamic Vessel Analyzer (DVA, IMEDOS, Jena). Each examination consisted of 50 s baseline measurement and three periods of 20-s flicker light provocation followed by 80 s observation. The mean of three provocational cycles was calculated as dynamic vessel response. RESULTS: A significant correlation of the flicker response parameters between the right and left eyes was found. Arterial and venous baseline diameter, flicker light dilation, AVDQ, and BP did not change significantly between the first and follow-up examinations. There was no correlation between changes of BP and changes of vessel diameter parameters in the follow-up exams. CONCLUSION: Flicker-evoked dilation of retinal arterioles measured by the DVA is characterized under similar conditions by small variance after short and medium-length time periods. Therefore, this parameter is suitable as a functional parameter of the regulation ability of retinal arteries.

[Haemodynamics and diabetic retinopathy]. / Hämodynamik und diabetische Retinopathie.

Diabetic retinopathy is the most common cause of blindness in adults in all industrialised countries. A much better pathophysiological understanding of the disease has been achieved during the last years. There is evidence that a functional deficit in haemodynamics proceeds the morphological changes of the retina. Modern technologies for measuring haemodynamic parameters and their correlation to pathophysiology in diabetic retinopathy are discussed. In the near future it will be possible to use these parameters as an early sign of worsening before morphological changes occur. Measurement of the therapeutic success, e. g., in laser coagulation would seem to be possible.

[Comparison of diameter response of retinal arteries and veins to flickering light. A clinical study with healthy people]. / Vergleich der Durchmesserreaktion retinaler Arterien und Venen auf Flickerlicht. Eine klinische Studie an Gesunden.

PURPOSE: The aim of this study was to compare the diameter response of retinal arteries and veins after provocation with flickering light regarding the amplitude and temporal course. METHODS: The study included 26 healthy volunteers. The vessel diameter was automatically and continuously measured by the retinal vessel analyzer. The examination consisted of a baseline measurement (100 s) followed by five periods of 20-s flicker light provocation and 80-s follow-up observation. RESULTS: A diameter dilation was observed immediately after the end of the flicker period in arteries (6.9+/-2.8%) and veins (6.5+/-2.8%, difference n.s.). The quotient of arterial and venous dilation (AVDQ) was 1.25+/-0.69 (range: 0.2-2.8). A significant correlation of age and arterial or venous dilation or the AVDQ was not observed. The arterial diameter reduced faster than the venous and reached a minimum of -2.7+/-1.4% at 25.9+/-10.8 s after the end of the flicker phase. The veins were dilated by 0.5+/-1.3% at the time of the maximal individual arterial constriction (p<0.0001). CONCLUSIONS: Flicker-evoked response of retinal arteries and veins did not differ in the dilative amplitude but in the temporal course of the abatement of the dilation.

Flicker observation light induces diameter response in retinal arterioles: a clinical methodological study.

AIM: To investigate diameter changes in retinal arterioles in response to flicker variations of the examination light. METHODS: One randomised eye of five healthy subjects (mean age 33.8 (SD 1.6) years) was examined. The arterial diameter response to flicker light (12.5 Hz, 530-600 nm, duration 20 seconds) was automatically and continuously measured online three times by retinal vessel analyser (RVA) and once offline from flash images using the VesselMap program. RESULTS: An arterial diameter response to flicker light was found both by RVA and by analysis of flash images (p<0.001). The maximum induced dilation reached at the end of the flicker period was +7.4% (SD 2.4%) in the RVA measurements and +3.5% (0.8%) in the photographs (p = 0.01). In both techniques the vascular diameter overshot the baseline approximately 10 seconds. In the RVA measurements a minimum of -4.6% (1.9%) (p = 0.01) was measured 22 (4.7) seconds after the end of flicker exposure. CONCLUSION: Flicker evoked response for retinal arterioles was found both by RVA and by analysis of flash images. The authors believe that the method is suitable for the quantitative investigation of retinal vasosclerosis, especially in association with arteriosclerotic and hypertensive systemic disease.

Retinal Vessel Analyzer (RVA)--design and function.

The Retinal Vessel Analyzer (RVA) is a measuring device for online measurement of the diameter of retinal vessels in relation to time and locations along the vessel. It is furthermore provided with several tools for analyzing the measured data. The fundamental components consist of a fundus camera with CCD measuring camera attached and an advanced image-processing unit. The measurement range is from 90 microns, temporal resolution is 40 ms and measurement resolution is less than 1 micron. Systematic error of non-linearity is S < or = 1.6%, reproducibility is given by variation coefficient: short term vcs = 1.5%, long term vcl = 2.8%.

Retinal Vessel Analysis--new possibilities.

Retinal Vessel Analysis is a new technique to assess behavior of large retinal vessels based on diameter measurements. The Retinal Vessel Analyzer (RVA) measures continuously on-line obtaining data in relation to time and local position. Possible analysis tools include (a) Time Course Analysis of physiological, pathological, or therapy induced changes; (b) Local Course Analysis to recognize local narrow or wide vessel segments along the vessel; (c) Vasomotoric Analysis to determine vasomotions and blood pressure related diameter changes; (d) Functional Analysis to examine dynamic behavior e.g. the ability to autoregulate and (e) Functional Imaging to visualize functional parameters of vessels in single vessel segments. RVA is thus able to recognize and study different autoregulation mechanisms.

Functional analysis of retinal vessel diameter reaction to artificially raised intraocular pressure in glaucoma patients with and without dorzolamide therapy.

BACKGROUND: Examination of the influence of dorzolamide on the autoregulation of retinal vessel diameter in glaucoma patients. PATIENTS AND METHODS: Eleven patients with primary open angle glaucoma (age 60 +/- 11) without medication and four weeks after starting therapy with dorzolamid eye drops three times daily were examined in the study. Short-time rise of intraocular pressure (IOP) was obtained via suction-cup. Functional reaction of the diameter of a segment of a retinal artery and corresponding vein were assessed by retinal vessel analyzer. RESULTS: Dorzolamid lowered the IOP from 23.3 +/- 1.3 to 17.6 +/- 2.2 mmHg (p = 0.004). Therapy did not influence the absolute diameter of retinal vessels regarding maximal dilatation caused by the pressure rising provocation. In eyes with treatment the diameter decreased faster to baseline values (arteries 100 sec, veins 220 sec) compared to those without treatment (arteries 350 sec, veins 480 sec). CONCLUSION: Dorzolamid might possibly be able to accelerate autoregulation of retinal vessels in response to short term artificial IOP increase.

[Measurement of the diameter of segments of retinal branch vessels in digital fundus images - An experimental study of the method and reproducibility]. / Durchmesserbestimmung von Netzhautgefässabschnitten in digitalen Fundusfotografien - Eine klinische Studie zur Methodik und Reproduzierbarkeit.

PURPOSE: The aim of this study was the evaluation of new algorithms to measure diameter of segments of retinal branch vessels offline in local dependence and independent by observer. Methods 360 flashed fundus images (camera FF 450 ZEISS Germany, Visualis IMEDOS GmbH Weimar/Germany) of 12 eyes of healthy volunteers (10 independent sessions containing 3 images for every eye) were analysed. Algorithms detect the vessel diameter along the vessel course automatically. Corresponding segments of a retinal artery and vein were examined (mean length of the segment 2.5 mm) in every image of one eye. Results The marked arterial segment was detected automatically in 359 pictures and the venous segment in all pictures. The mean vessel diameter was detected in single pictures with a mean coefficient of variation (CV) for arteries of 3.4 % and for veins of 2.7 %. The differences of arterial and venous diameter between images were not significant. Analyzing sessions the CV of the mean vessel diameter were reduced for arteries to 2.7 % and for veins to 2.5 %. The standard deviation of the mean vessel diameter was independent of the vessel diameter (branch vessels with diameter of 120 to 200 micrometer). The mean CV of the vessel diameter at single locations were 5.7 % for arteries and 3.8 % for veins. Conclusions The new algorithms are useful for retinal vessel analysis, if there are no questions concerning the dynamic of vessel behaviour.

Retinal vessel reaction to short-term IOP elevation in ocular hypertensive and glaucoma patients.

PURPOSE: Regulation of ocular blood flow might be impaired in glaucoma patients. We compared the reaction of retinal vessels to a short-term increase of intraocular pressure (IOP), using a retinal vessel analyzer (RVA), in normal volunteers, ocular hypertensive patients (OH) and primary open angle glaucoma patients (POAG). METHODS: Ten healthy subjects (56+/-8 years, IOP 13.7+/-1.6 mmHg), 10 OH patients (55+/-12 years, IOD 23.4+/-4.1 mmHg) and 11 POAG patients (60+/-11 years, IOP 23.3+/-1.95 mmHg) were evaluated. Arterial and venous retinal vessel diameter was measured continuously before, during and after raising IOP to suprasystolic values by the suction cup method, described as ocular oscillo-dynamography. RESULTS: The change in vessel diameter after the IOP rise differed in its temporal sequence and in absolute values depending on the group examined. In the retinal branch veins the reduction of vessel diameter during the IOP rise was significantly different in POAG (0%+/-6.7) and volunteers (-6.7%+/-8.5; p = 0.06) and in POAG and OH (-6.7%+/-7.0; p = 0.04). At 70-130 sec after IOP increase a dilatation occurred, again differing significantly in POAG (+5.8%+/-3.9) and volunteers (+9.7%+/-4.3; p = 0.03). Systemic blood pressure did not show any significant differences between groups or during the course of the examination. DISCUSSION: At short-term rise in IOP leads to less retinal vessel reaction in POAG patients than in volunteers and OH. This might be due to impaired autoregulation to ocular perfusion changes in POAG patients.

[Retinal vessel reaction to 100% O2-breathing--functional imaging using the retinal vessel analyzer with 10 volunteers]. / Reaktion retinaler Gefässdurchmesser auf 100% O2-Atmung--funktionelle Messung mit dem Retinal Vessel Analyzer an 10 Probanden.

BACKGROUND: Retinal vessel diameter assessment is complicated by various components among them dynamic changes due to vasomotoric effects. Measurement of these diameters was usually obtained from fundus photographs. Functional diameter changes induced by external stimuli were difficult to evaluate because of their dynamic nature. The Retinal Vessel Analyzer (RVA) allows continuous on-line measurement of those dynamic changes. Whether functional changes due to 100% O2 breathing can be assessed by RVA is investigated in this study. MATERIALS AND METHODS: Continuous on-line registration of retinal arterial and venous branch vessels was obtained in 10 healthy volunteers. A baseline was taken during the first minute. Then for 5 minutes 100% O2 was delivered by mask. Further recording ensued for 4 minutes, while breathing room air. Vessel diameter change in percent to baseline was calculated for each individual and for a mean of the group. RESULTS: Each individual demonstrated vasoconstriction. The mean diameter reduction for the group was 6.5% for arteries and 15% for veins. CONCLUSIONS: RVA allows assessment of functional retinal branch vessel reactions. Retinal branch vessels diameters are denominators for capillary perfusion. RVA might be able to demonstrate an individual vessel's regulation potential by purposeful stimulation to constrict and dilate. This property could be helpful in understanding pathophysiologic processes as well as improving diagnosis and therapeutic effects in diseases influencing ocular perfusion such as diabetes, retinal vessel occlusion or even glaucoma. Further evaluation of effects of systemic diseases might be an additional application of functional retinal vessel diameter assessment by RVA.

[Dilatation of large retinal vessels after increased intraocular pressure]. / Dilatation grosser Netzhautgefässe nach Intraokulardrucksteigerung.

PURPOSE: To measure dilation of large retinal branch vessels. METHODS: Diameters of a vessel section of a branch artery and vein were examined by the retinal vessel analyzer. Intraocular pressure (IOP) was increased briefly by an oculo-oscillo-dynamograph. The examination was repeated after 2 weeks. RESULTS: A vessel reaction was found in all volunteers. The mean venous diameter decreased 9.9 +/- 9.4% during the suprasystolic phase of intraocular pressure. A maximal dilation was found in arteries (7.0 +/- 6.2%) and veins (9.3 +/- 5.2%) 1 min after lowering of IOP. The results were reproduced in the second examination for veins in all phases of the examination and for arteries in the middle phase after lowering IOP (4 min). Various changes in mean systolic blood pressure did not significantly affect reproducibility of the vessel reaction. CONCLUSION: The vessel reaction caused by rise in IOP can be measured for single vessel sections. The venous reaction is well reproducible in healthy volunteers. Further research should examine the benefit of this method in the diagnosis and follow-up of glaucoma.

Noninvasive measurement of the Bayliss effect in retinal autoregulation.

PURPOSE: The Bayliss effect describes the reaction of smooth muscle cells in the arterial wall to changes in blood pressure. A rise in mean arterial blood pressure (MAP) causes an autoregulatory myogenic vessel constriction by smooth muscle cells in the arterial wall. The responsiveness of retinal vessels to changes in MAP were analyzed using the Retinal Vessel Analyzer (RVA). METHODS: Continuous measurement of retinal arterial vessels was performed in 40 healthy volunteers (age 18-56 years.) over a 9-min period. After a 3-min baseline measurement (phase I), isometric exercise caused a rise in MAP over the next 3 min (phase II). During the last 3 min (phase III) recovery was observed. Blood pressure and ECG were documented simultaneously throughout the experiment. RESULTS: Exercise caused a significant rise of 22.8 (+/-6.0) mm Hg in MAP (phase II vs. phase I: P<0.001). Retinal arterioles showed 5.5% (+/-2.8%) vasoconstriction (P<0.001). During phase III vessel diameters returned to normal, with no difference from phase I (P = 0.179). CONCLUSION: Noninvasive measurement and quantitative analysis of the Bayliss effect in human retinal vessels by means of the RVA is possible. Analysis of retinal arterial autoregulation may provide valuable insight into pathologic conditions such as diabetic or hypertensive retinopathy.

[Online measurement of retinal artery branches in type II diabetic patients. Initial clinical trials before and after laser coagulation]. / Online-Messung retinaler Arterienäste bei Typ-II-Diabetikern. Erste klinische Versuche vor und nach fokaler Laserkoagulation.

UNLABELLED: By the use of a new online measuring system the effect of argon-laser coagulation in diabetics on the diameters of retinal arteries was measured. METHOD: The vessel diameter of retinal branch arteries were measured in patients with type-II diabetes before and after (0.5 h) argon-laser coagulation. Ten patients without previous laser treatment were included in this study. Measurements were taken in all four quadrants by the use of a new automatic online measuring system. RESULTS: The new technique allowed measurements to be made within an acceptable period of time and with little strain on patients. After argon-laser coagulation 56.7% of retinal arteries showed a significant vasodilation. No significant changes in vessel diameter were found in 18.9% of these arteries, whereas 24.3% showed significant vasoconstriction. CONCLUSION: The new online measuring system is able to measure the effects of photocoagulation on an individual basis with a noninvasive technique. The first findings presented here confirm previous studies of larger groups, with a considerable reduction in efforts required.

Remittance spectroscopy of human skin in vivo.

BACKGROUND/AIMS: The skin is an easily accessible organ on which non-invasive examination methods can be applied. Recently spectroscopic methods have been introduced in characterization of skin under physiological and pathological conditions. To examine remittance spectroscopic qualities of human skin in vivo and to clarify the influence of selected test conditions, a single-beam spectrometer MCS 410 (Carl Zeiss, Jena, Germany) has been used. METHODS: Remittance spectra readings were performed in 35 volunteers. Wavelength ranged from 362 nm to 780 nm. Individual remittance values and their standard deviations were obtained from 20 readings under standardized test conditions. The effect of pressure, rubbing, cooling, washing, greasing and degreasing on average remittance values was investigated. Statistical analysis was done with paired Student's f-test and Fisher's test. RESULTS: Pressure increased remittance values over a wide range of wavelength, peaking at 518 nm. Greasing and degreasing modified spectral remittance of shorter wavelength peaking around 362 nm. Rubbing and cooling did not induce significant variations of spectral remittance of skin. CONCLUSION: Spectral remittance provides an individual profile in human skin, which may be influenced by pressure and greasing/ degreasing. To establish standardized test conditions with a narrow range of intra-individual variation these items have to be kept constant.