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At least 829 records · Page 46Linked to original sources
PubMed1995

[Surgical results of vitrectomy for idiopathic macular hole--factors affecting postoperative visual prognosis].

Pars plana vitrectomy was performed on 19 eyes with idiopathic full-thickness macular holes (6 eyes at stage 2, 8 eyes at stage 3, and 5 eyes at stage 4). Factors affecting postoperative visual prognosis were evaluated. Preoperatively a potential acuity meter (PAM) and laser interferometry were used to predict postoperative visual acuity. Resolution of the surrounding fluid cuff and flattening of the macular holes were obtained in 9 eyes (47%). Eight eyes (42%) gained an improvement in visual acuity of 2 lines or more. Most eyes with anatomical success showed functional improvement. Eyes with short duration of macular holes were considered to have better visual postoperative prognosis. The stage of macular holes, however, had no relationship with postoperative visual acuity. Preoperative measurement with laser interferometry was relatively well correlated with postoperative visual acuity (r = 0.54, p = 0.07), but the results of PAM and preoperative visual acuity had poor correlation.

Aged↗
PubMed2000

Effects of insulin on retinal and pulsatile choroidal blood flow in humans.

BACKGROUND: Insulin induces vasodilation in several tissues, including skeletal muscle and kidneys. OBJECTIVE: To investigate whether insulin may contribute to ocular blood flow regulation. METHODS: The study was performed in a balanced, randomized, placebo-controlled, single-masked, 3-way, crossover design in 9 healthy male subjects. Each subject received 2 doses of insulin (1.5 or 3 mU/kg per minute) or placebo on 3 different study days. Measurements of fundus pulsation amplitude with laser interferometry to assess pulsatile choroidal blood flow, of retinal blood flow with the blue-field entoptic technique, and of mean blood flow velocity in the ophthalmic artery with Doppler sonography were performed under euglycemic clamp conditions over 120 minutes. RESULTS: Hyperinsulinemia significantly increased fundus pulsation amplitude (1.5 mU/kg per minute: 8.7% +/- 1.1% vs baseline; 3 mU/kg per minute: 13.2% +/- 2.3% vs baseline; P<.001 vs placebo [analysis of variance]) and mean blood flow velocity (1.5 mU/kg per minute: 10.0% +/- 4.3% vs baseline; 3 mU/kg per minute: 6.6% +/- 3.5% vs baseline; P = .03 vs placebo). Retinal blood flow did not increase during administration of insulin (1.5 mU/kg per minute: 6.4% +/- 8.0% vs baseline; 3 mU/kg per minute: 8.0% +/- 5.1% vs baseline; P = .99 vs placebo). Neither the effect in the choroid nor that in the ophthalmic artery was dose-dependent. CONCLUSION: Hyperinsulinemia significantly increases choroidal blood flow and mean blood flow velocity in the ophthalmic artery. By contrast, retinal blood flow was not influenced by hyperinsulinemia. The maximum effective dose of insulin for ocular hemodynamics is likely to be within the physiological range.

Adult↗
PubMed2003

Short-term effect of dorzolamide hydrochloride on central corneal thickness in humans with cornea guttata.

OBJECTIVE: To investigate the short-term effect of dorzolamide hydrochloride, a topical carbonic anhydrase inhibitor, on central corneal thickness in patients with cornea guttata. DESIGN AND METHODS: In this randomized, placebo-controlled, double-masked, 3-drug crossover study, 20 patients with cornea guttata (mean endothelial cell count, 1321 cells/mm2) and 8 healthy control subjects (mean endothelial cell count, 2483 cells/mm2) were included. Study medications included 2% dorzolamide hydrochloride (Trusopt 2% eye drops; Merck & Co Inc, Whitehouse Station, NJ), 0.9% saline solution (saline placebo), and a solution identical to the carrier substance of dorzolamide in Trusopt (carrier placebo). The study drugs were applied 4 times per day for 1 day only. Central corneal thickness measurements were performed using partial coherence interferometry on every study day at baseline and after 24 hours of study medication treatment. MAIN OUTCOME MEASURES: Change in central corneal thickness. RESULTS: The mean thickening in central corneal thickness within 24 hours in eyes with cornea guttata treated with dorzolamide, saline placebo, and carrier placebo was 12.0 micro m (95% confidence interval [CI], 7.0-17.1 microm), 0.6 micro m (95% CI, -1.0 to 2.2 microm), and 1.3 micro m (95% CI, -0.1 to 2.6 microm), respectively. CONCLUSION: Application of dorzolamide for 1 day results in a slight but statistically significant thickening of central corneal thickness in patients with cornea guttata.

Administration, Topical↗
PubMed1996

Preparation of purified atactic polypropylene and polyvinyl methyl ether surfaces for thrombogenicity studies.

Commercial samples of atactic polypropylene (aPP) and polyvinyl methyl ether (PVME) were purified and spin-cast onto glass coverslips with a view to using these as model surfaces in thrombogenicity studies. These materials differ from polyvinyl alcohol (PVA) in a single functional group and are similarly amorphous: with the same backbone they have a hydroxyl, a methoxy, or a methyl group. The objective was to understand the role of the hydroxyl group in the platelet reactivity of PVA. Surface characterization showed that they were chemically pure (as determined by X-ray photoelectron spectroscopy) but not smooth (as determined by scanning electron microscopy or interferometry), presumably due to the difficulties of spin-casting optically clear films from hot solutions (aPP or polyethylene [PE]) or because of imperfect adhesion to the saline-treated substrate (PVME). PVME was also gamma-irradiated to insolubilize it. Fewer platelets adhered to PVA than to PVME or to aPP and PE, but roughness effects and limited data preclude definitive conclusions regarding the effect of functional groups. Less protein was found on PVA than on the hydrophobic surfaces, but the significance of this observation is unclear. Further studies with more sensitive protocols are called for to examine the extent of platelet activation and its relationship to surface chemistry.

Adsorption↗
PubMed2000

Surface morphology and wear mechanisms of four clinically relevant biomaterials after hip simulator testing.

The surfaces of worn components hold clues to the underlying wear mechanisms. Previous evidence suggested that the absolute wear rates of acetabular components in a hip simulator were related to mechanical behavior; we hypothesized that the surface morphology of the liners might also be sensitive to mechanical properties. A noncontact, three-dimensional surface topography measurement system based on white light interferometry was used to quantify the surface morphology of ultra-high molecular weight polyethylene, polytetrafluoroethylene, high-density polyethylene, and polyacetal liners, and their corresponding femoral heads, after 3 million cycles in a multi-directional hip simulator. Comparisons were made with the fatigue soaked and control (as machined) components. Statistically significant power law relationships were observed between the arithmetic mean surface roughness (R(a)) of the worn acetabular liners and the volumetric wear rate in the hip simulator (p < 0.01, r(2) = 0.52). Significant relationships were also observed between R(a) and the elastic and large deformation mechanical behavior of the liner materials, measured directly from the wear-tested liners using the small punch test (p < 0.01, r(2) = 0.54-0.81). The results support the hypothesis that wear mechanisms of acetabular liners during hip simulator testing are related to surface morphology in conjunction with the mechanical behavior of the polymeric materials.

Acetals↗
PubMed2005

A critical comparison of methods for the determination of the aging sensitivity in biomedical grade yttria-stabilized zirconia.

Since the recent failure events of two particular series of zirconia femoral heads for total hip replacement prosthesis, a large decrease in the use of zirconia ceramics for orthopaedic implants has been observed. In spite of the biomedical success of this material during the last 10 years, this decrease in use was required for safety reasons, until the cause of the failures is known. It has been shown that these failures were related to the low temperature hydrothermal degradation (also known as aging). Thus, it is crucial to better understand the aging behavior, in order to be able to assess its importance and then control it if required. In this study, various techniques relevant to assess the hydrothermal degradation sensitivity of biomedical grade yttria-stabilized zirconia are discussed and compared. The expected outputs of conventional methods, that is, X-ray diffraction and scanning electron microscopy are examined. More recent methods like optical interferometry and atomic force microscopy are presented, with their respective benefits and drawbacks. An up-to-date comparison of these different techniques is provided, and their use for ensuring the long-term reliability of a particular batch of zirconia in terms of aging degradation is demonstrated.

Biodegradation, Environmental↗
PubMed1994

Interferometric surface monitoring of biological tissue to study inertially confined ablation.

We present results from the application of laser interferometry to the study of short-pulsed laser ablation of biological tissue. The mechanical response of tissue to laser-induced stress is examined under subthreshold conditions to determine its role in initiating the ablation process. A theoretical model is developed to relate this surface displacement to the pressure within the tissue and the mechanical properties of the tissue. In the experiment, a 7.5 ns pulse of 355 nm light was used to irradiate bovine shank bone, human meniscus, and an aqueous dye solution. Interferometric monitoring of the tissue surface was used to determine its motion after laser irradiation. The surface movement of bone was qualitatively consistent with the theoretical predictions of the model. The movement of meniscus and an aqueous dye solution showed additional features that are consistent with the growth and collapse of cavitation bubbles.

Animals↗
PubMed1998

Ocular axial length and choroidal thickness in newly hatched chicks and one-year-old chickens fluctuate in a diurnal pattern that is influenced by visual experience and intraocular pressure changes.

Low coherence laser Doppler interferometry (LDI) allows high precision measurements of the axial length of the eye and of the thickness of the individual layers of the ocular fundus. Here, we used LDI to monitor diurnal changes in these dimensions in eyes of newly hatched chicks and one-year-old chickens with normal or altered visual input. In chicks and chickens with normal visual experience, axial eye length displays diurnal fluctuations increasing during the light phase. Choroidal thickness also exhibits a diurnal pattern, shrinking during the day and expanding during the night. Retinal thickness does not vary. Based on the pressure compliance of the enucleated chick eye, the diurnal intraocular pressure (IOP) fluctuation could contribute both to the increase in axial length and to daytime choroidal shrinkage. Following deprivation of form vision by unilateral goggle wear, occluded chick eyes demonstrate enhanced axial elongation. Diurnal fluctuations in axial length but not in choroidal thickness are temporarily disrupted. The retina of form deprived eyes thins approximately 10% in five days. In contralateral eyes, the diurnal patterns of both axial length and choroidal thickness fluctuations are also disrupted. Following occluder removal in chicks, choroidal thickness increases for several days during both the light and dark phase, leading to its overall expansion. Retinal thickness returns to baseline. When deprived of form vision for five days, the eyes of year-old chickens do not exhibit measurable axial elongation. Diurnal patterns of fluctuation in axial length and choroidal thickness are however disrupted. After goggle removal, axial length fluctuation is restored to normal, but the diurnal choroidal thickness pattern is inverted. In contralateral eyes, choroidal thickness exhibits normal diurnal fluctuations both during and after form vision deprivation. In conclusion, axial length and choroidal thickness fluctuations are influenced by visual experience in both newborn chicks and one-year-old chickens. In selected instances a binocular interaction regarding axial length and choroidal thickness changes is suggested, the effect weakening with age.

Animals↗
PubMed1988

Preoperative prediction of postoperative visual acuity in patients with cataracts: a quantitative review.

Many tests of visual function have been proposed as means of preoperatively evaluating cataract patients' surgical outcomes. It is impractical to compare all of these tests simultaneously on the same group of patients. Quantitative reviews apply quantitative methods to comparisons across studies. We compared the results of 52 reports in which cataract patients' postoperative acuity was predicted by means of visually evoked potential, laser interferometry, or projection tests (potential acuity meters-pinhole). The results of each study were summarized in a 2 x 2 contingency table. Summary statistics were compared by means of analysis of variance and post hoc tests. Despite difficulties in metaanalysis, we found the visually evoked potential a better predictor with dense opacities. We recommend standardization in a quest for more precise predictions of postoperative visual acuity.

Cataract Extraction↗
PubMed1992

Interferometer assessment of potential visual acuity before YAG capsulotomy: relative performance of three instruments.

The accuracy of white light and laser interferometers in predicting visual acuity after YAG laser capsulotomy was compared. 42 eyes of 41 patients were tested with both a Haag-Streit (Lotmar) white light interferometer and a Rodenstock laser interferometer, and 14 were also tested with a Site white light machine. The laser interferometer predicted a final visual acuity to within one line of that actually achieved in 93%, and to within two lines in 98%, whereas for the Haag-Streit these figures were 64% and 81%, and for the Site 77% and 92%. In patients with poor initial visual acuity, the difference in the relative performance of the two instruments was increased further. When interferometry was repeated after capsulotomy, the values obtained with all instruments agreed closely with Snellen acuity. This difference in predictive accuracy shows that capsular thickening causes a greater degree of optical degradation of the image produced by a white light interferometer than occurs when a laser interferometer is employed.

Adult↗
PubMed1994

Middle-ear development. IV. Umbo motion in neonatal mice.

Laser interferometry was used to measure umbo velocity in the developing BALB/c mouse middle ear at 133 pure-tone frequencies between 2.0 kHz and 40.0 kHz, all at a constant 100 dB sound pressure level. Umbo velocities increased with age across the entire frequency range, and reached adult-like levels by about 19 days between 2.0 and 22.0 kHz. Velocities at 28.0 and 34.0 kHz took 27 and 52 days respectively to reach adult-like levels. A simple middle-ear model utilizing compliance, resistance, and inertia elements matched the general trends of our velocity results and provided an indication of the anatomical basis for the growth in umbo velocity. The model suggested that velocity development at the lowest frequencies may be attributed to increases in tympanic membrane compliance. The model also indicated that both the frictional resistance of the middle ear and the inertia of the tympanic membrane and ossicles decreased during the growth period. At frequencies below 20.0 kHz, age-related increases in umbo velocity coincided with improvements in N1 thresholds recorded from the round window and evoked potential thresholds obtained from the cochlear nucleus. These results indicated that the functional development of the middle-ear plays a major role in the development of hearing in the mouse.

Acoustic Stimulation↗
PubMed1998

Effect of pituitary adenylate cyclase activating polypeptide 1-27 on ocular, cerebral and skin blood flow in humans.

The aim of the study was to assess the effects of a neuropeptide, pituitary adenylate cyclase activating polypeptide 1-27 (PACAP), on ocular, cerebral and skin blood flow in man. PACAP (0.01-10 pmol kg(-1) min(-1)) was administered intravenously to eight healthy male subjects in a placebo-controlled, double-blind dose escalation trial. Fundus pulsation amplitude was measured by laser interferometry, mean blood flow velocity in the ophthalmic artery and the middle cerebral artery measured by Doppler sonography, and regional blood flow of the skin was estimated by laser Doppler flowmetry. Infusion of PACAP at the highest dose of 10 pmol kg(-1) min(-1) induced a significant increase in fundus pulsation amplitude (+83.4%), mean flow velocity in the ophthalmic artery (+91.9%) and regional skin blood flow (+260.3%, P<0.01, ANOVA; each parameter). In contrast, PACAP did not cause any change in middle cerebral artery blood flow velocity or systemic hemodynamics. Our findings indicate that the vasculatures of the eye and the skin are particularly sensitive to PACAP and may implicate a potential role for this peptide in the regulation of blood flow in these vascular beds.

Adult↗
PubMed2004

[Dry eye. An update on epidemiology, diagnosis, therapy and new concepts].

Recent epidemiologic studies quote a prevalence of 5,2% to 63% for dry eye depending on definition. Many risk factors have been identified, among other things the female gender. Dry eye interferes significantly with quality of live. Measurement of the change in temperature and humidity during blinking turned out to be a reliable diagnostic tool. Videokeratoscopy explains well-known visual impairments related to dry eye and, along with lipid film interferometry, provides insight into tear film dynamics. The importance of tear film proteins is underestimated. Among therapeutics for symptomatic relief hyaluronic acid proved to be particularly useful but also the sequence of lid hygiene, warm compresses and lid massage is fundamentally important. The effectiveness of punctum plugs is ascribed considerably to a more efficient impact of essential tear film components. Topical cyclosporine A, INS365, 15(S)-HETE as well as topical androgens represent a whole new class of drugs for causal therapy of dry eye.

Blinking↗
PubMed2005

Rapid responses of the cupula in the lateral line of ruffe (Gymnocephalus cernuus).

Displacements of cupulae in the supraorbital lateral line canal in ruffe (Gymnocephalus cernuus) have been measured using laser interferometry and by applying transient as well as sinusoidal fluid stimuli in the lateral line canal. The cupular displacement in response to impulses of fluid velocity shows damped oscillations at approximately 120 Hz and a relaxation time-constant of 4.4 ms, commensurate with a quality factor of approximately 1.8. These values are in close agreement with the frequency characteristics determined via sinusoidal fluid stimuli, implying that the nonlinearity of cupular dynamics imposed by the gating apparatus of the sensory hair cells is limited in the range of cupular displacements and velocities measured (100-300 nm; 100-300 microm/s). The measurements also show that cupular displacement instantaneously follows the initial waveform of transient stimuli. The functional significance of the observed cupular dynamics is discussed.

Animal Structures↗
PubMed2000

Temperature dependency of cupular mechanics and hair cell frequency selectivity in the fish canal lateral line organ.

The mechanical frequency selectivity of the cupula located in the supraorbital lateral line canal and the frequency selectivity of the hair cells driven by the cupula were measured simultaneously in vivo. Laser interferometry was used to measure cupular mechanics and extracellular receptor potentials were recorded to determine hair cell frequency selectivity. Results were obtained from two teleost fish species, the ruffe (Acerina cernua L.), a European temperate zone freshwater fish, and the tropical African knife fish (Xenomiystus nigri). In both species cupular displacement grows with increasing frequency of canal fluid displacement, reaching a maximum at 115 Hz in the ruffe and at 460 Hz in the African knife fish. Cupular best frequencies were independent of temperature. Cut-off frequencies of hair cell frequency selectivity were found to depend on temperature with a Q10 of 1.75, ranging from 116 Hz (4 degrees C) to 290 Hz (20 degrees C), as established in the ruffe. At normal habitat temperatures of the two fish species (ruffe, 4 degrees C; African knife fish, 28 degrees C), this results in hair cell cut-off frequencies that match the two different cupular best frequencies remarkably well. This match suggests adjusted signal transfer in these two peripheral stages of canal lateral line transduction.

Animals↗
PubMed2002

Evaluation of pulsatile choroidal blood flow in branch retinal vein occlusion.

BACKGROUND: The present study was undertaken to compare pulsatile choroidal blood flow in patients with branch retinal vein occlusion (BRVO) with the values in normal controls. METHODS: The study included male and female patients with manifest BRVO (n=16) and a healthy sex- and age-matched control group (n=36). Fundus pulsation amplitude (FPA) was measured in the fovea by laser interferometry to assess pulsatile choroidal blood flow. RESULTS: The FPA in eyes with BRVO (4.4 microm) was significantly higher than in the fellow eye (3.8 microm; P<0.0005). There was also a significant difference between the affected eye of the patients and the healthy control group (3.3 microm; P<0.0009). CONCLUSION: The increase in FPA indicates increased choroidal blood flow resulting from some local mechanisms compensating for the decrease in retinal blood flow.

Aged↗
PubMed2003

Experimental evaluation of online optical coherence pachymetry for corneal refractive surgery.

PURPOSE: Online optical coherence pachymetry (OCP) allows to monitor central changes of the corneal cross section intraoperatively. In this experimental evaluation the validity of the optical measurements for corneal refractive surgery was assessed. METHODS: Online OCP based on low-coherence interferometry with a wavelength of 1310 nm and a measurement frequency of 74 Hz was directly integrated in a clinical excimer laser. In 16 patients the central corneal thickness was measured with online OCP and ultrasound pachymetry (US). Furthermore, the ablation characteristics were assessed in corneoscleral discs unsuitable for transplantation (n=12) and PMMA samples (n=18). RESULTS: Online OCP was possible in all patients and materials studied. The mean central corneal thickness was 537+/-31 microm (OCP) and 546+/-33 microm (US). The corneal reproducibility was +/-4.3 microm (coefficient of variation [CV] 0.8%) with online OCP and +/-3.7 microm (CV 0.68%) with US. The reproducibility in PMMA samples was +/-1.0 microm (CV 0.16%). There was a significant correlation between online OCP and US measurements (r=0.93, P<0.001). The mean difference was 9.1 microm or 1.69% (P=0.01), and the limits of agreement (95% CI) ranged from -15 microm to 33 microm. There was a significant linear relationship (r=0,95; P<0.001) between the calculated and the optically determined ablation depth with online OCP. Also ablation depth measurements in PMMA correlated positively with spectrophotometric values (r=0.98; P<0.001). CONCLUSION: In this experimental evaluation, online OCP revealed to be a precise and reproducible method to assess the central corneal thickness and its changes intraoperatively. This could be important to monitor incisional and excimer laser-based corneal refractive procedures, such as PRK or LASIK.

Anatomy, Cross-Sectional↗
PubMed2005

Relationship between the retinal thickness of the macula and the difference in axial length.

PURPOSE: The purpose of this study was to evaluate the relationship between the retinal thickness of the macula and the difference in axial length with A-scan ultrasonography (UD-6000) and partial coherence interferometry (IOLMaster). METHODS: In 38 eyes of 26 patients with macular edema (ME), we measured axial length using both instruments and the retinal thickness of the macula using optical coherence tomography (OCT). To compare the difference in axial length between both methods, the Wilcoxon signed-ranks test was used. In addition, the relationship between macula thickness and axial length difference was analyzed by Spearman's correlation coefficient. RESULTS: There was a significant difference between axial-length measurements (p<0.001). In addition, the retinal thickness of the macula and the difference in axial-length measurements were positively correlated (correlation coefficient = 0.55, p=0.003). CONCLUSIONS: The difference in axial length obtained by both methods was considered to be the difference in optical and acoustic reflection site. This study may suggest that IOLMaster is sufficient for measuring axial length in eyes with macular edema and reducing postoperative refractive errors.

Biometry↗