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PubMed1979

Measurement of visual resolution at high luminance levels in patients with possible demyelinating disease.

An interferometric acuity device (Takata) has been used to study visual resolution in individuals with possible demyelinating disease. The instrument employed provides a large field with a continuous range of grid or fringe frequencies and a relatively intense (10(5) mean photopic trolands) stimulus. After a brief period of time with eyes closed, resolution thresholds of patient are repeatedly determined during a five minute period. In all individuals suspected of having a demyelinating disease tested to date, a fall off in resolution capability has been found in time when using this intense stimulus display. This occurs whether eye signs have been present, are present or have not yet been observed. Normal observers do not exhibit comparable decrements. The fall off in resolution capability may or may not occur at lower stimulus levels, and is often not revealed when testing routine Snellen acuity. Outer and inner retinal pathology (division based on vascular support) do not cause a comparable fall off in resolution in time. The interferometric acuity test is a non-invasive, easily applied test.

Adult↗
PubMed1985

Determination of correction factors of 3H-beta-self-absorption for quantitative evaluation of grain number in autoradiographic studies. Interferometric studies of different cell types in the mouse brain.

Deparaffinized and Feulgen-stained sagittal sections of the mouse brain were studied interferometrically in order to measure optical path differences of euchromatin and heterochromatin of various cell types. Furthermore, the ratio eu-: heterochromatin of each cell type was determined. From these data mass densities of karyoplasm and, finally, correction factors of 3H-beta-self-absorption were calculated for comparing grain numbers of different cell types in quantitative autoradiographic studies after application of tritium-labelled substances. Remarkable differences of correction factors up to a factor of 2.18 were found. Furthermore, the actual section thickness was determined interferometrically. A reduction to about 0.60 of the microtome setting was measured in two different areas of the brain. Using mass densities together with actual section thickness correction factors for a thickness of 1 micron were calculated. This was done also for cell types outside the brain the data of which were taken from literature. Thus, differences in correction factors up to about a factor of 4 were found pointing out the importance of considering 3H-beta-self-absorption in quantitative autoradiographic studies.

Animals↗
PubMed1995

Observations of chemical processing in the circumstellar environment.

High resolution interferometer and single-dish observations of young, deeply embedded stellar systems reveal a complex chemistry in the circumstellar environments of low to intermediate mass stars. Depletions of gas-phase molecules, grain mantle evaporation, and shock interactions actively drive chemical processes in different regions around young stars. We present results for two systems, IRAS 05338-0624 and NCG 1333 IRAS 4, to illustrate the behavior found and to examine the physical processes at work.

Astronomical Phenomena↗
PubMed1990

Medical treatment of senile cataract: clinical investigation of bendazac-lysine using objective and subjective methods.

A modified Zeiss slit lamp coupled with a digital image-processing system was used to evaluate objectively changes in lens transparency over 1 year at 4-month intervals in 150 eyes of 92 patients affected by early senile cataract. A total of 59 patients were treated daily with 1.5 g bendazac-lysine, and 33 patients constituted the control group. At follow-up, visual acuity was also tested using Snellen letter charts at variable contrast to provide an additional parameter closer to traditional methods. Results indicate that the minimal angle of resolution at 10% contrast (MAR10) and the mean gray-level value of the lens image obtained by retroillumination (MLR) are sensitive to early changes in lens transparency. Using MAR10 as a parameter, the control group showed a significant, progressive worsening of the lens status over 12 months, whereas the treated group exhibited no significant changes. MRL indicated the same behaviour as MAR10, although lens damage was detected later in the control group. The results show that bendazac-lysine may delay the formation of lens opacities.

Aged↗
PubMed1984

Interferometric analysis of intrasection and intersection thickness variability associated with cryostat microtomy.

Mach-Zehnder interferometric measurements were used to assess the extent of section thickness variability (inter- and intrasection) associated with cryostat microtomy of adrenal sections over a typical working range of 10-20 micron. Sections were obtained using a Bright's Cambridge rocking type and a Damon rotary type cryostat microtome to allow comparative analyses. The effective thickness of tissue sections after being mounted onto slides by flash drying was reduced by 90% relative to microtome section thickness setting. A linear relationship between measured thickness and microtome setting was obtained with both instruments. Thickness variability between replicate sections over the range of microtome settings approximated 11% for the rocking microtome and 5% with the rotary microtome. Average intrasection variability was found to be 7% for rocking microtome sections and 4% for sections obtained with the rotary microtome. However, this variability is a negligible source of error in cytophotometric analyses, providing replicate sections are used and an adequate number of measurements are made on mask-delimited individual cells or tissue specimen areas.

Adrenal Glands↗
PubMed1977

Photoelectric device for contact-free recording of the diameters of exposed arteries in situ.

A photoelctric device is described which permits contact-free recording of the diameter of an in situ exposed artery. The light emitted by the filament of a bulb (6 W) is collimated by a projection lens (1:2.8, 50 mm) and directed onto the surface of a silicone photocell (12.6X6.2 mm) covered by a neutral light filter. The voltage drop caused by the photocell current flowing through an adjustable load resistor represents the signal voltage which is fed into the input of an instrumentation amplifer. The artery under investigation is positioned above the photocell parallel to its short axis. The signal voltage decreases linearly with increasing area of the shadow cast by the artery on the photocell and thus the output voltage of the amplifier is linearly proportional to the diameter of the artery. The combined frequency response of photocell and amplifier was examined by sinusoidally modulated light emitted by a luminescent diode. The amplitude ratio was constant up to 200 Hz and the time lag was about 0.2 ms. The device was used on the canine carotid and femoral arteries. An example is shown.

Amplifiers, Electronic↗
PubMed1977

Corneal topography.

This paper explores the many aspects of the nature and measurement of the corneal surface. Its structure and the factors that influence it are described. The traditional techniques of keratometry are summarized and there is an emphasis on new experimental methods of determining corneal topography including moiré, holographic interferometric and profile techniques. The advantages and disadvantages of these procedures are considered.

Adult↗
PubMed1997

Fundus pulsation measurements in diabetic retinopathy.

BACKGROUND: There is experimental evidence that retinal blood flow is impaired in patients with diabetes mellitus. Much less attention has been paid to choroidal blood flow. Hence it was the aim of the present study to investigate choroidal blood flow in diabetic retinopathy. METHODS: A new non-invasive laser interferometric technique was used to measure fundus pulsations in the macula. The fundus pulsation amplitude, which is the maximum distance change between cornea and retina during the cardiac cycle, is a measure of local pulsatile blood flow. The eyes (n = 214) were divided into four groups according to the modified Airlie House classification: (1) no retinopathy (control group), (2) background retinopathy, (3) moderate to severe preproliferative retinopathy, (4) proliferative retinopathy. In 83 eyes of different group fundus pulsation measurements were repeated after 1-6 weeks. RESULTS: Fundus pulsation amplitudes were significantly smaller in group 4 than in the control group (P < 0.027). The reproducibility of the measurements was high and did not differ among the study groups. CONCLUSIONS: Local fundus pulsations in the macula are reduced in proliferative diabetic retinopathy, which is compatible with previous findings of reduced choroidal blood flow in late stages of the disease. Laser interferometric measurement of fundus pulsations is non-contactile, assures optimal comfort for the patient and could be used for the long-term observation of patients with diabetes mellitus.

Adult↗
PubMed1986

Retinal visual acuity with pattern VEP normal subjects and reproducibility.

Retinal visual acuity was determined using an objective method by means of VEP. Sixty subjects with subjective visual acuity ranging from 20/25 to 20/12 were measured with a computer-controlled laser interferometer, using interference fringes modulated in counterphase as pattern-reversal stimulus. Steady-state VEPs taken at different spatial frequencies were evaluated by Fourier analysis and linear regression. Objective retinal acuity was calculated as the intersection between the linear regression line and the linear scaled spatial frequency axis. In 68% of all cases, the difference between objective and subjective visual acuity was less than +/- 5.1 cycles per degree (c/d) (+/- 15.4% referred to subjective acuity); in 86%, the difference was less than +/- 7.7 c/d (+/- 23.1%).

Evoked Potentials, Visual↗
PubMed1987

A comparative study between the PAM and the laser interferometer in cataracts.

We conducted a prospective study on 35 consecutive eyes undergoing cataract extraction to compare the Guyton-Minkowski Potential Acuity Meter (PAM) and the Laser Interferometer (LI) in determining potential visual acuity. The eyes were divided into: group A, which had good visualization of optic disc details, and group B, whose media allowed only disc outline or less to be seen. We found that in group A eyes, both instruments were reliable (with accuracies of 94% for the PAM and 88% for the LI). However, in group B eyes (advanced cataracts), both instruments were unreliable (accuracies of 33% for the PAM and 53% for the LI). Interestingly, in a subgroup of high myopes (axial length greater than 29 mm) with moderate cataracts and poor visual acuties, both instruments were very reliable and helpful in determining how much of the vision loss was due to the cataracts. We therefore strongly recommend potential acuity testing in high myopes with moderate cataracts and poor visual acuity.

Aged↗
PubMed1997

[Laser vibrometry. A middle ear and cochlear analyzer for noninvasive studies of middle and inner ear function disorders].

A complete battery of audiometric methods is required for the differential diagnosis of different hearing disabilities (including puretone audiometry, impedance, stapes reflex, speech audiometry, brainstam evoked response audiometry, otoacoustic emissions, etc.). In many cases, a comprehensive diagnosis is not possible. Here we describe a new technique based on a laser-Doppler vibrometer that has the potential for non-invasive diagnosis not only middle ear disease but also cochlear pathologies. Disturbance of cochlear function can be ascertained because the input impedance of the cochlea acts as a mechanical load on the middle ear and therefore influences motion of the umbo. In the present study vibration of the umbo and eardrum were measured with a commercially available laser-Doppler vibrometer coupled directly into a standard surgical microscope. The use of the microscope allowed non-invasive measurements of vibrations without having to introduce reflecting material onto the tympanic membrane. Sound pressure was measured with a calibrated probe microphone placed near the tympanic membrane. The displacement response and the specific acoustic impedance of the umbo were calculated from the velocity and sound pressure measured. For normal hearing subjects, the amplitude of the umbo's displacement for frequencies from 0.1 kHz to 1 kHz was 1 nm at 60 dB SPL and decreased with a slope of 6 dB/octave for frequencies between 1 and 5 kHz. A strong correlation was found between the specific acoustic impedance of the umbo and hearing thresholds for hearing-impaired subjects (having otosclerosis or sensorineural hearing losses). The frequency response of the umbo proved to be a means for evaluating the function of both the middle ear and the cochlea under pathological conditions. The measurement technique described is also suitable for intraoperative investigation of the frequency response of the opened middle ear, as well as for the in situ frequency response of partial and total ossicular replacement prostheses.

Acoustic Impedance Tests↗
PubMed2005

Label-free characterisation of oligonucleotide hybridisation using reflectometric interference spectroscopy.

The potential of a label-free detection method, reflectometric interference spectroscopy (RIfS), for temperature-dependent DNA hybridisation experiments (for example in single nucleotide polymorphism (SNP) analysis) is investigated. Hybridisations of DNA, peptide nucleic acid (PNA), and locked nucleic acid (LNA) to a single stranded DNA were measured for several temperatures, and the melting curves and temperatures were calculated from the changes in optical thickness obtained. These measurements were performed by hybridising surface-immobilised single stranded oligomers with their complementary ssDNA or with ssDNA containing SNPs at different temperatures. DNA was compared to its analogue oligomers PNA and LNA due to their stability against nuclease. A comparison of melting temperatures demonstrated the higher binding affinities of the DNA analogues. Moreover, a continuous melting curve was obtained by first hybridising the functionalised surface with its complementary DNA at room temperature and then heating up in-flow. Measurement of the continuous melting curve was only possible due to the insensitivity of the RIfS method towards temperature changes. This is an advantage over other label-free detection methods, which are based on determining the refractive index.

Base Sequence↗
PubMed2003

Observing bacterial activity interferometrically.

It is shown that bacterial activity, even of slowly growing species, can be detected by precise interferometric measurements of refractive index changes of the culture medium. The bacteria-containing sample is kept in an isothermal block together with a reference liquid without bacteria. The biological activity is obtained from the difference of the index changes of these samples. Experiments were performed with Bacilo Calmette-Guérin. The order of magnitude of the observed total refractive index change was compatible with theoretical estimates based on the amount of available oxygen. An unexpected positive index change during the lag phase was observed, which might permit fast diagnostics in medical applications. This technique may provide cheap and quick tests of bacterial susceptibility with respect to antibiotics.

Interferometry↗
PubMed2002

[Dynamic aberrometry during accommodation of phakic eyes and eyes with potentially accommodative intraocular lenses].

Since the introduction of potentially accommodative intraocular lenses (IOLs), it was hard to perform an objective evaluation of the accommodative amplitude in pseudophakic eyes. Laser interferometric measurements were performed to evaluate anterior chamber depth changes, which provides information on the functionality of potentially accommodative IOLs. By means of wavefront analysis, the dynamic behaviour of potentially accommodative IOLs can be determined. All measurements in this study were performed using a Hartmann-Shack aberrometer at a frequency of 7 Hz. Six to 8 weeks after implantation of potentially accommodative IOLs (CrystaLens AT-45, C&C Vision, 1CU, Humanoptics), 43 eyes were investigated using this dynamic wavefront analysis. Patients focussed at a distance target for 10 s, followed by focussing at a near target for 10 s and then again at a distance target for a further 10 s. During these 30 s, a total of 200 single measurements were performed. The same measurements were also conducted in healthy eyes of young persons as well as in eyes after implantation of standard IOLs for comparative purposes. The dynamic course of changes in low-order aberrations (defocus, astigmatism) as well as high-order (e.g., fourth-order spherical aberration) were analysed. Dynamic wavefront analysis allowed objective and observer-independent measurement of changes in accommodation in phakic and pseudophakic eyes. Dynamic aberrometry is capable of objectively quantifying the effect of any surgical option for the treatment of presbyopia. We recommend use of this technology in addition to the common psychophysical examinations to attain objective information on the efficacy of the treatment modality used.

Accommodation, Ocular↗
PubMed2002

Optical coherence tomography in the evaluation of incomplete visual acuity recovery after macula-off retinal detachments.

PURPOSE: To determine whether pre and/or postoperative optical coherence tomography (OCT) evaluation of the fovea is useful in explaining delayed or incomplete visual acuity recovery after successful surgery for shallow macula-off retinal detachments. METHODS: Prospective study of 16 patients (10 female, 6 male; mean age 53+/-4 years) with a spontaneous rhegmatogenous retinal detachment with peripheral breaks and a shallow elevation of the fovea. Patients were examined by OCT preoperatively and at 1, 6, and 10-12 months after surgery. At 1 month after surgery, fluorescein angiography was also performed. Mean follow-up was 11.0+/-1.0 months. RESULTS: Preoperative OCT images could be classified into four categories according to the extent of retinal edema and presence of foveal depression. The extent of retinal edema in the detached macula did not correlate with preoperative or postoperative vision. In 11 cases, OCT images at 1 month after surgery showed a foveal detachment with residual subretinal fluid that was not visible clinically or on angiography. Long-term persistence of this fluid could be observed in eight cases at 6 months and in one case at 12 months, and was associated with incomplete recovery of visual acuity. CONCLUSIONS: Preoperative OCT of the detached macula can demonstrate widespread retinal edema, the extent of which does not appear to influence final postoperative vision. Delayed and incomplete visual recovery after successful reattachment of the retina may, however, be due to persistent circumscribed subfoveal fluid accumulation that is visible only on OCT not clinically or on fluorescein angiography.

Adult↗
PubMed2002

Detecting the inner and outer borders of the retinal nerve fiber layer using optical coherence tomography.

BACKGROUND: The purpose of this study was to develop a new algorithm to detect the inner and outer borders of the retinal nerve fiber layer (RNFL) using optical coherence tomography (OCT). METHODS: A program featuring a new algorithm was developed using a commercially available software development environment. The algorithm searches for peaks on each sampling line instead of applying conventional thresholding techniques. All circular peripapillary OCT images obtained at the New York Eye and Ear Infirmary from October 1996 to December 2000 were analyzed using the new and the commercially available algorithms. RESULTS: Four hundred one images of 98 patients were analyzed. The detection error rate (defined as number of scans with five consecutive sampling lines with disrupted RNFL borders) was significantly lower with the new algorithm (25/401 images, 6.2%) than with the commercially available algorithm (70/401 images, 17.5%) (P=0.018, chi-square). CONCLUSION: The new algorithm improved the ability of OCT to detect the borders of the RNFL.

Adult↗
PubMed2002

Multiple retinal holes in the macular region: a case report.

PURPOSE: To describe the first case of multiple retinal holes in the macular region successfully treated with vitrectomy. METHOD: A single case report. A 44-year-old man was treated for impaired vision caused by multiple macular holes in the right eye. RESULTS: Fundus examinations detected six retinal holes in the right macula and a giant macular hole in the left eye. Optical coherence tomography disclosed multiple vitreoretinal adhesions in the right macula. We vitrectomized the right eye to produce posterior vitreous detachment and then tamponaded the vitreous cavity with 20% SF(6) gas, resulting in closure of holes and improvement of the vision. CONCLUSION: Multiple macular holes may be treated by surgical posterior detachment combined with gas tamponade. Vitreoretinal adhesions are a possible cause of these holes. Similar multiple holes may have coalesced into one giant hole in this patient's left eye.

Adult↗
PubMed2002

Histopathological correlation of corneal diseases with optical coherence tomography.

PURPOSE: To correlate the cross-sectional images of corneal diseases obtained by optical coherence tomography (OCT) with light microscopy (LM) to determine the corneal components represented in OCT images. METHODS: In a prospective comparative tissue study clinicopathological correlations of six patients with pseudophakic bullous keratopathy ( n=3), advanced keratoconus ( n=1), persistent epithelial defect with corneal thinning ( n=1), and retrocorneal membrane ( n=1) were included. Immediately before a planned penetrating keratoplasty (PKP) noncontact slitlamp-adapted OCT of the cornea was performed. After PKP and following standard histological processing the specimens were examined under LM to compare qualitatively the morphology, and quantitatively the morphometry at selected corneal locations. RESULTS: The cross-sectional optical-reflectivity profiles enabled the reproducible morphological evaluation of the corneal structures and changes. Layers of relative high reflectivity corresponded to the anterior corneal surface and internal stromal layers. In contrast, the deeper corneal epithelial layer demonstrated relative low reflectivity by OCT. An increase in light reflectivity corresponded to corneal scarring, irregularities of the corneal lamellae, and deposition of basal membrane material. Low signal intensity was particularly due to fluid accumulations and shadowing. The most prominent changes were caused by corneal scars or edematous tissue. The morphometric analysis with OCT revealed, in this study, thickness measurements ranging from 31 to 902 micro m. Although the mean OCT thickness values were up to 9% ( P=0.014) higher than those derived from LM, there was a significant positive correlation (r=0.94; P<0.001) between corneal OCT and the light-microscopic measurements. CONCLUSION: Noncontact slitlamp-adapted corneal OCT revealed a good correlation with histological sections. The differences noted were partly related to shrinking processes during preparation. Thus, with certain limitations, OCT allows a non-invasive optical biopsy of pathological structures in corneal diseases.

Aged↗