KEYWORDS: 3D modeling, Optical coherence tomography, Standards development, Performance modeling, Systems modeling, Animal model studies, Tissues, Eye models, In vitro testing, 3D imaging standards
Glaucoma is caused by a pathological rise in the intraocular pressure, which results in a progressive loss of vision by a damage to retinal cells and the optical nerve head. Early detection of pressure-induced damage is thus essential for the reduction of eye pressure and to prevent severe incapacity or blindness. Within the new European Project GALAHAD (Glaucoma Advanced, Label free High Resolution Automated OCT Diagnostics), we will develop a new low-cost and high-resolution OCT system for the early detection of glaucoma. The device is designed to improve diagnosis based on a new system of optical coherence tomography. Although OCT systems are at present available in ophthalmology centres, high-resolution devices are extremely expensive. The novelty of the new Galahad system is its super wideband light source to achieve high image resolution at a reasonable cost. Proof of concept experiments with cell and tissue Glaucoma test standards and animal models are planned for the test of the new optical components and new algorithms performance for the identification of Glaucoma associated cell and tissue structures. The intense training of the software systems with various samples should result in a increased sensitivity and specificity of the OCT software system.
The transmission properties of the human lens were studied in donor lenses from the age of 17 to 76 years. The
transmission of white light was measured using a fiber coupled tungsten halogen lamp. The light transmitted by the lens
was collected using an integrating sphere that was coupled to a spectrometer by an optical fiber. As expected, the
transmission of blue and green light decreased in older lenses. The transmission of the near infrared part of the spectrum
was above 90% even in old donor lenses.
Photobleaching of a 58 year old human donor lens was demonstrated using an infra-red, femtosecond Ti:Sapphire laser. Pulse duration was 300 femtoseconds, pulse energy was 0.1 μJ, and the focal spotsize of the laser was approximately 14 μm in diameter. The lens was treated in a 1x1 mm large area by scanning the laser beam. Significant photobleaching was seen after laser treatment. Light transmission increased by 7%. The greatest effect was seen in the blue-green part of the visible spectrum.
Ultrafast femtosecond lasers are used increasingly for a wide range of medical purposes. The immediate tissue response
to pulses above a certain threshold is optically or laser induced breakdown, which is often visible as gas-filled cavities
that persist for some time. In the present study, we attempted to define the cavitation threshold in the human lens in vitro
using multiphoton effects based on radiation from a femtosecond 800 nm Ti:Sapphire laser. Cavitations were observed
from pulse energy densities exceeding 16 mJ/cm2, but only after several minutes of exposure and not as a result of a
single laser pulse. This suggests that cavitations were caused by a process which differs from the single-pulse cavitations
observed at higher intensities. To evaluate whether the release of gas was caused by ionization and plasma formation or
by thermal effects, we introduced pauses into the pulse train, which did not change the total exposure time needed to
form a cavitation. This suggests that local heating did not play a significant role in producing the observed phenomenon,
suggesting that photochemical reactions may be involved. These results demonstrate that there are several types of
ultrafast laser effects in the lens that have a potential for therapeutic application and treatment of eye disease though
further studies are needed to shed light on the nature of the formation of delayed cavitations.
Purpose: Quantification of outer retinal layers in humans. Method: 11 eyes in healthy subjects and 3 eyes in patients
after resolution of central serous chorioretinopathy (CSCR). Multiple line scans were obtained using OCT Stratus and
scans were registered and averaged to enhance contrast. The distance from the inner-outer segment junction to the
posterior part of the retinal pigment epithelium (RPE-OScomplex) was calculated. In addition, the reflectance of the outer
photoreceptor layer in the foveal center was compared to that peripheral to the fovea. Results: Mean thickness of the
RPE-OScomplex in healthy subjects was 77.3 μm, in CSCR 52.9 μm. The thickness of the RPE-OScomplex was significantly
correlated to visual acuity (r=0.95, p<0.01). The ratio of reflectance (fovea/parafovea) was 1.06 in healthy subjects,
1.18 in CSCR eyes. Conclusion: The RPE-OScomplex thickness was markedly reduced in eyes after resolution of CSCR
and highly correlated to the visual acuity, the correlation to total foveal thickness was less. An increased backscatter
was seen in CSCR, probably due to photoreceptor disorganization and atrophy.
The application of Optical Coherence Tomography (OCT) within ophthalmology is today relative widespread, the reason being that it is a major help in revealing details of structural damage and retinal patho-physiology that otherwise can be difficult to detect. Yet, there is still space for improvement and the OCT systems continuously improve both their speed and resolution. Besides the possibility of upgrading the hardware there is however also a possibility for "bootstrapping" the present generation of commercial devices by adequate post-processing of the acquired signals. We present evidence that with an existing commercial system it is possible to improve the signal-to-noise ratio of the recorded images by fusing multiple scans of the same retinal region. In order to achieve this improvement it is necessary to align a number of noisy signals. We have explored a number of different techniques for achieving this goal. The improvement is sufficient to reveal details that are impossible or difficult to observe from the individual OCT recordings.
Type 2 diabetes mellitus is a global epidemic with the number of affected subjects exceeding 4% of the adult population world-wide. Undiagnosed and untreated, the disease results in long-term complications such as myocardial infarction, stroke, and blindness. Treatment reduces the number and severity of long-term complications but treatment is often delayed by a time-lag of 10 years or more from the onset of disease to diagnosis. Earlier diagnosis can be achieved by systematic screening programs but the potential time won is unknown. The aim of the present study was to develop a mathematical model estimating the prediagnostic duration of type 2 diabetes mellitus using lens autofluorescence as an indicator of lifetime glycemic load. Fluorometry of the human is lens a quantitative measurement which is attractive because of the ease by which it can be performed. It is our hope that lens fluorometry will prove useful in estimating the prediagnostic duration of type 2 diabetes mellitus in population studies, a property of profound clinical relevance that is difficult to estimate by any other currently available method.
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