Two-photon microscopy in brain tissue: parameters influencing the imaging depth

Light scattering by tissue limits the imaging depth of two-photon microscopy and its use for functional brain imaging in vivo. We investigate the influence of scattering on both fluorescence excitation and collection, and identify tissue and instrument parameters that limit the imaging depth in the brain. (i) In brain slices, we measured that the scattering length at lambda=800 nm is a factor 2 higher in juvenile cortical tissue (P14-P18) than in adult tissue (P90). (ii) In a detection geometry typical for in vivo imaging, we show that the collected fraction of fluorescence drops at large depths, and that it is proportional to the square of the effective angular acceptance of the detection optics. Matching the angular acceptance of the microscope to that of the objective lens can result in a gain of approximately 3 in collection efficiency at large depths (>500 microm). A low-magnification (20x), high-numerical aperture objective (0.95) further increases fluorescence collection by a factor of approximately 10 compared with a standard 60x-63x objective without compromising the resolution. This improvement should allow fluorescence measurements related to neuronal or vascular brain activity at >100 microm deeper than with standard objectives.

Concepts for nanoscale resolution in fluorescence microscopy

Spatio-temporal visualization of cellular structures by fluorescence microscopy has become indispensable in biology. However, the resolution of conventional fluorescence microscopy is limited by diffraction to about 180 nm in the focal plane and to about 500 nm along the optic axis. Recently, concepts have emerged that overcome the diffraction resolution barrier fundamentally. Formed on the basis of reversible saturable optical transitions, these concepts might eventually allow us to investigate hitherto inaccessible details within live cells.

Spinning-disk confocal microscopy -- a cutting-edge tool for imaging of membrane traffic

Confocal laser scanning microscopy is experiencing a revolution in speed from the world of seconds to that of milliseconds. The spinning Nipkow disk method with microlenses has made this remarkable innovation possible. In combination with the ultrahigh-sensitivity, high-speed and high-resolution camera system based on avalanche multiplication of photoconduction, we are now able to observe the extremely dynamic movement of small vesicles in living cells in real time.

A generic camera model and calibration method for conventional, wide-angle, and fish-eye lenses

Fish-eye lenses are convenient in such applications where a very wide angle of view is needed, but their use for measurement purposes has been limited by the lack of an accurate, generic, and easy-to-use calibration procedure. We hence propose a generic camera model, which is suitable for fish-eye lens cameras as well as for conventional and wide-angle lens cameras, and a calibration method for estimating the parameters of the model. The achieved level of calibration accuracy is comparable to the previously reported state-of-the-art.

A system matrix for astigmatic optical systems: II. Corrected systems including an astigmatic eye

The 4 x 4 system matrix is applied to corrected astigmatic systems including a schematic eye in which each surface is astigmatic at a different axis. In addition to representing the eye, the 4 x 4 system generates 2 x 2 magnification matrices which describe the meridional magnifications that occur in the presence of astigmatism including the magnifications that occur with bitoric eikonic correcting lenses, or other meridional magnifying systems.

Do tinted lenses improve the reading performance of dyslexic children? A cohort study

The use of tinted lenses as a method to improve reading skills in children with dyslexia has been a controversial issue in recent years. The purpose of the present study was to determine if tinted lenses cause a measurable improvement in the reading performance of dyslexic children. Twenty-four children aged 8 to 12 years participated in the study. Dyslexia was diagnosed in all children by psychological evaluation, and these children underwent an ophthalmic evaluation for inclusion into the study. Participants were graded for speed and accuracy as they read through spectacle frames that contained red-, blue-, yellow-, and green-tinted lenses, a neutral-density lens, and empty frames. All lenses for each subject were of the same density level, with subjects alternately distributed to one of two densities tested (0.12 or 0.30 log units). Each child was asked to select the lens condition that subjectively improved reading ability at the conclusion of testing. One-way analysis of variance of reading performance showed neither improvement nor deterioration attributable to lens color or density when applied to error rates (F = 1.73, P = .14 for a density of 0.12; F = 0.28, P = .92 for a density of 0.30) or to reading rates (F = 0.98, P = .44 for a density of 0.12; F = 0.81, P = .55 for a density of 0.30). In addition, the lens condition that was subjectively preferred by each child did not correlate with actual reading performance (chi 2 = 3.83, not significant; 11.07 needed for significance at P = .05).

Effects of the Seidel aberrations on visual target discrimination

The effects of Seidel aberrations (primary defocus, spherical aberration, astigmatism, and coma) were simulated on four images using a digital image-processing system. The tolerances of the human visual system to different levels and combinations of the aberration types were determined by a forced-choice discrimination technique. The resulting threshold levels, expressed in units of wavelength, specify the changes in wave-front aberration that can be detected with some defined probability and represent just-noticeable differences (JND's) in image quality. The results are related to the corresponding Strehl intensity ratios and to the equivalent modulation transfer functions. The ultimate aim of the work is to link wave-front distortion to human visual discrimination, in order that meaningful methods of assessing visual image quality may be devised. The present investigation lays the foundations for further work, which, inter alia, will determine the effects of some higher-order aberrations.

Effect of orthoptics upon the ability of patients to adapt to prism-induced heterophoria

In a previous study we showed that subjects with abnormal binocular vision either lacked or had a deficient ability to adapt their oculomotor systems to a prism-induced heterophoria. In this study we report on the results of an experiment designed to establish whether the adaptation ability improves in patients who are successfully treated, by means of orthoptics, for convergence insufficiency. In all seven patients examined, we found an improved ability to adapt. Whereas at the beginning of the experiment only two patients fell within the 95% confidence limits of the norm, at the end five patients fell within these limits. These results demonstrate that the success of orthoptics in relieving symptoms is associated with an improved ability to adapt to prism-induced heterophoria.

Choosing objective lenses: the importance of numerical aperture and magnification in digital optical microscopy

Microscopic images are characterized by a number of microscope-specific parameters--numerical aperture (NA), magnification (M), and resolution (R)--and by parameters that also depend on the specimen--for example, contrast, signal-to-noise ratio, dynamic range, and integration time. In this article, issues associated with the microscope-specific parameters NA, M, and R are discussed with respect to both widefield and laser scanning confocal microscopies. Although most of the discussion points apply to optical microscopy in general, the main application considered is fluorescence microscopy.

Tissue culture methods for testing the toxicity of ocular plastic materials

A screening method using tissue culture techniques determined inertness of ocular alloplastics. Secondary rabbit kidney cells revealed the presence of toxic constituents by absence of growth or cytopathic changes, or both. The optical portions of the lenses studied were nontoxic, whereas the polyamide loops of one lens were toxic. A keratoprosthesis that had been in situ in a patient for two years was highly toxic in culture. A neutralized agar overlay technique was not sufficiently sensitive to screen anterior chamber implants. The tissue culture technique, in combination with chemical, optical, and animal experimentation, may be helpful in determining which implant systems are most suitable for in vivo use.

A highly sensitive opto-electronic system for the measurement of movements

An opto-electronic system has been developed to measure movements of insect appendages. It is made from a mirror-lens and a linear position-sensitive photodiode. The design of the mirror-lens has been exploited to axially mount a high intensity halogen light source in front of the mirror-lens. The system monitors a reflective marker which is attached to the moving object. Upon illumination by the light source the reflected light is picked up by the optical system and is focussed on the diode. The diode provides a voltage output proportional to the distribution of the light on it's surface. Since the marker is the brightest spot in the image the output of the system corresponds to the position of the marker. At a working distance of 80 cm appendage movements with amplitudes from 10 microm to 20 mm peak-peak amplitude can be recorded. The system accurately detects movements ranging from slow positional changes to 5 kHz oscillations. Currently it used to measure the stridulatory wing movements of crickets but may be applied to a variety of movement recordings.

A minimally invasive lens-free computational microendoscope

Ultra-miniaturized microendoscopes are vital for numerous biomedical applications. Such minimally invasive imagers allow for navigation into hard-to-reach regions and observation of deep brain activity in freely moving animals. Conventional solutions use distal microlenses. However, as lenses become smaller and less invasive, they develop greater aberrations and restricted fields of view. In addition, most of the imagers capable of variable focusing require mechanical actuation of the lens, increasing the distal complexity and weight. Here, we demonstrate a distal lens-free approach to microendoscopy enabled by computational image recovery. Our approach is entirely actuation free and uses a single pseudorandom spatial mask at the distal end of a multicore fiber. Experimentally, this lensless approach increases the space-bandwidth product, i.e., field of view divided by resolution, by threefold over a best-case lens-based system. In addition, the microendoscope demonstrates color resolved imaging and refocusing to 11 distinct depth planes from a single camera frame without any actuated parts.

Evaluation of a district-wide screening programme for diabetic retinopathy utilizing trained optometrists using slit-lamp and Volk lenses

BACKGROUND

Debate exists about the optimum way to screen for diabetic retinopathy. Cameras produce a permanent record, but offer patients less choice about when and where to be screened. Optometrists offer flexibility but sensitivity and specificity of schemes have varied considerably, perhaps because of variability in screening methodology and that there is frequently no quality assurance programme.

AIMS

To audit our district-wide (population 340000) screening programme for diabetic retinopathy against national targets: sensitivity > 80%, specificity > 95% and referral to review < 3 months.

METHODS

Trained optometrists performed slit-lamp examination with Volk lenses (78 dioptre) with standardized reporting. Audit was by ophthalmologist with slit-lamp and Volk lenses through dilated pupils.

RESULTS

We examined 872 eyes of 439 patients; 64% were normal, 29% background diabetic retinopathy, 7% sight-threatening eye disease (STED). Sixty-three percent of patients were seen within 6 months of the original screen. Of these, sensitivity for any retinopathy was 72%, specificity 77%, positive predictive value (PPV) 53%, negative predictive value (NPV) 88%. For STED, in this group, sensitivity was 87% and specificity 91%, PPV 30%, NPV 99%. Median interval referral to ophthalmological review was 11.5 weeks with 73% reviewed in under the 13-week target. Of those referred 25% received laser therapy. Eleven patients found to have referable eye disease at their initial screen were not referred to an ophthalmologist by their GP.

CONCLUSIONS

We conclude that effective district-wide screening for diabetic retinopathy by optometrists using slit-lamp and Volk lenses is possible; however, only 36% of identified people with diabetes in the district were screened over a 4-year period.

Reversed telescopes on visual efficiency scores in field-restricted patients

Low vision aids have not been successfully prescribed for many people with peripheral visual field loss. Visual field and visual acuity measurements for four field-restricted subjects were made with and without field-expanding reversed telescopes. The calculated visual efficiency was not significantly improved with such devices; therefore, their value remains in question.

Visual field expanders

Diminishing telescope systems designed to widen the field of view of patients with tunnel vision are described. Theoretical analysis suggests that telescope systems will greatly improve visual search times and diminish the difficulties of such patients. This can be considered quantitatively, and it is suggested that the optimum amount of minifying power can be calculated by applying established formulations on visual efficiency. The inadequacies of previous designs have inhibited development, and further improvements to bioptic systems may be necessary before the final assessment of the clinical value of these devices can be made.

An Evaluation of the Confoscan3 for Corneal Endothelial Morphology Analysis

PURPOSE

We evaluated the ConfoScan3 confocal microscope and its associated software that allows automated analysis of the corneal endothelial morphology.

METHODS

Images were taken on 30 normal subjects and 29 contact lens wearers with the Konan SP-9000 specular microscope and the ConfoScan3. The Konan images were analyzed with the KSS-300 software (center method). The Confoscan3 images were first analyzed with the automated method and then edited manually (semiautomated method). The agreement between methods was evaluated by calculating the difference between pairs of measurements, determining the mean and standard deviation of these differences, and the 95% limits of agreement.

RESULTS

For normal subjects, all methods gave similar density values. The agreement with the Konan system was slightly better for the semiautomated method than the automated method. The automated method overestimated the degree of polymegethism (p < 0.001) and pleomorphism (p < 0.001). The semiautomated method showed substantial improvement. For contact lens wearers, agreement with the Konan system was poor for both automated and semiautomated methods. The automated method overestimated the degree of pleomorphism (p < 0.001) and the semiautomated method showed only modest improvement (p < 0.1). Both methods overestimated pleomorphism (automated p < 0.001; semiautomated p < 0.025).

CONCLUSIONS

When using ConfoScan3 to evaluate the corneal endothelium of normal subjects, investigators should manually edit the processed images to achieve results comparable with the Konan system. When evaluating contact lens wearers, values from the ConfoScan3 are not interchangeable with those from the Konan system.

Contrast in confocal scanning microscopy with a finite detector

The optical properties of a general scanning microscope are determined within the framework of Fourier imaging theory. For a simple model optical system, with Gaussian lens and detector apertures, the contrast transfer function can be expressed in terms of elementary functions. The theory predicts that spatial resolution and depth discrimination vary continuously with detector aperture and that defocus phase contrast is present in transmission images obtained with a symmetric objective, collector lens confocal microscope.

Guidelines for standard photography in gross and clinical anatomy

Photography has a widespread usage in medicine and anatomy. In this review, authors focused on the usage of photography in gross and clinical anatomy. Photography in gross and clinical anatomy is not only essential for accurate documentation of morphological findings but also important in sharing knowledge and experience. Photographs of cadavers are supposed to demonstrate the required information clearly. Thus, photographs should be taken with certain techniques in order to obtain high quality and standardization. Camera, lens, lighting, background, and certain photographic techniques are among the factors to achieve precise images. A set of suggested guidelines for accomplishing these standards are given for anatomists.

Development of a fogless scope and its analysis using infrared radiation pyrometer

BACKGROUND

In laparoscopic surgery, fogging of the lens tip instantly degrades the quality of image and interrupts the flow of surgical maneuvers. External warming devices prevent fogging for a certain length of time, but use of them is troublesome at best. These problems prompted us to develop a fogless mechanism built into the scope so that the fogless image would be continuous and trouble-free. We then conducted several experiments that demonstrate the precise effect it has on the lens tip.

METHODS

The infrared radiation pyrometer was used to compare the temperature distribution as well as the temperature change against time of each lens tip of the fogless and ordinary laparoscopes.

RESULTS

The temperature of the lens tip of the ordinary scope did not change, but that of the fogless scope rose to 41 degrees C in 184-208 s.

CONCLUSIONS

The fogless mechanism effectively warms the lens tip to a safe temperature that prevents fogging in the intraabdominal environment.

Minimal movement zoom lens

We make a novel telescope design using a pair of Alvarez lenses. Previous examples using these types of lenses were single elements used just to provide a change in power. Consequently, the location of the object and/or image plane must move. In this effort, we combine two elements to form a telescope. In this manner, we can fix the location of the object and image plane and simply change magnification. We describe the shapes of the Alvarez lenses used, as well as the advantages, the disadvantages, and the differences between a telescope using Alvarez lenses and a traditional telescope.

Mechanism of fixation of two-loop iridocapsular lenses

I used seven eyes obtained postmortem to study the mechanism of fixation of a Binkhorst two-loop iridocapsular lens. During the first postoperative weeks, vitreous pressure and traction on the posterior lens capsule exerted by the zonular fibers pushed the loops of the iridocapsular lens against the iris. The zonular traction maintained the posterior capsule taut so that the vitreous pressure was distributed equally over the entire surface of the capsular diaphragm. Lens epithelial cells proliferated around the margin of the capsular breaks and defects and formed plaques or masses of spindle-shaped cells. This pseudofibrous tissue bridged and sealed capsular defects and caused adhesions between the anterior and posterior lens capsule and between the anterior capsule and the iris pigment epithelium. Fixation of the lenses may be reinforced by proliferation of the iris pigment epithlium and of the fibrous tissue arising from the iris stroma.