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Rafat R Ansari

Publications and source records attributed to Rafat R Ansari.

8 recordsLinked to original sources
PubMed2006

Pharmacologic vitreolysis with microplasmin increases vitreous diffusion coefficients.

BACKGROUND: Pharmacologic vitreolysis is a new approach to improve vitreo-retinal surgery and ultimately to liquefy and detach the vitreous from the retina to eliminate the contribution of the vitreous to retinopathy. The mechanism of action of the agents being developed for pharmacologic vitreolysis remains unclear. The effect of microplasmin on vitreous diffusion coefficients was investigated using the non-invasive technique of dynamic light scattering (DLS). METHODS: Vitreous diffusion coefficients in 18 intact porcine eyes were measured in vitro with dynamic light scattering (DLS). DLS was performed on all specimens at 37 degrees C 30 min after injections of human recombinant microplasmin at doses ranging from 0.125 to 0.8 mg, with 20-nm tracer nanospheres. RESULTS: DLS findings in untreated porcine vitreous were similar to the previously described findings in bovine and human vitreous. Microplasmin increased porcine vitreous diffusion coefficients in a dose-dependent manner (correlation coefficient, r=0.93), with an 85% increase after a 30-min exposure to the maximum dose. CONCLUSIONS: Pharmacologic vitreolysis with human recombinant microplasmin increases vitreous diffusion coefficients in vitro. The results of these studies have implications for the dosing, route of administration, duration of action and methods of determining efficacy in future studies of pharmacologic vitreolysis to enhance vitreo-retinal surgery, as well as the design of clinical trials to induce prophylactic posterior vitreous detachment.

Animals↗
PubMed2006

Particle-size and velocity measurements in flowing conditions using dynamic light scattering.

The noninvasive optical technique of dynamic light scattering (DLS) is routinely used to characterize dilute and transparent submicrometer particle dispersions in laboratory environments. A variety of industrial and biological applications would, however, greatly benefit from on-line monitoring of dispersions under flowing conditions. We present a model experiment to study flowing dispersions of polystyrene latex particles of varying sizes under varying flow conditions by using a newly developed fiber-optic DLS probe. A modified correlation function proposed in an earlier study is applied to the analysis of extracting the size and velocity of laminar flowing particulate dispersions. The complementary technique of laser Doppler velocimetry is also used to measure the speed of moving particles to confirm the DLS findings.

Journal Article↗
PubMed2005

Aggregation of lens crystallins in an in vivo hyperbaric oxygen guinea pig model of nuclear cataract: dynamic light-scattering and HPLC analysis.

PURPOSE: The role of oxygen in the formation of lens high-molecular-weight (HMW) protein aggregates during the development of human nuclear cataract is not well understood. The purpose of this study was to investigate lens crystallin aggregate formation in hyperbaric oxygen (HBO)-treated guinea pigs by using in vivo and in vitro METHODS: methods. Guinea pigs were treated three times weekly for 7 months with HBO, and lens crystallin aggregation was investigated in vivo with the use of dynamic light-scattering (DLS) and in vitro by HPLC analysis of water-insoluble (WI) proteins. DLS measurements were made every 0.1 mm across the 4.5- to 5.0-mm optical axis of the guinea pig lens. RESULTS: The average apparent diameter of proteins in the nucleus (the central region) of lenses of HBO-treated animals was nearly twice that of the control animals (P < 0.001). Size distribution analysis conducted at one selected point in the nucleus and cortex (the outer periphery of the lens) after dividing the proteins into small-diameter and large-diameter groups, showed in the O2-treated nucleus a threefold increase in intensity (P < 0.001) and a doubling in apparent size (P = 0.03) of large-diameter aggregate proteins, compared with the same control group. No significant changes in apparent protein diameter were detected in the O2-treated cortex, compared with the control. The average diameter of protein aggregates at the single selected location in the O2-treated nucleus was estimated to be 150 nm, a size capable of scattering light and similar to the size of aggregates found in human nuclear cataracts. HPLC analysis indicated that one half of the experimental nuclear WI protein fraction (that had been dissolved in guanidine) consisted of disulfide cross-linked 150- to 1000-kDa aggregates, not present in the control. HPLC-isolated aggregates contained alphaA-, beta-, gamma-, and zeta-crystallins, but not alphaB-crystallin, which is devoid of -SH groups and thus does not participate in disulfide cross-linking. All zeta-crystallin present in the nuclear WI fraction appeared to be there as a result of disulfide cross-linking. CONCLUSIONS: The results indicate that molecular oxygen in vivo can induce the cross-linking of guinea pig lens nuclear crystallins into large disulfide-bonded aggregates capable of scattering light. A similar process may be involved in the formation of human nuclear cataract.

Animals↗
PubMed2002

A clinical study of the human lens with a dynamic light scattering device.

A study was conducted to determine the potential usefulness and repeatability of a new dynamic light scattering (DLS) device for clinical studies of the human lens and early cataract. Studies using the cold cataract model showed this new device to be more sensitive than the Scheimpflug cataract imaging system in detecting the earliest cataractous changes. A miniaturized clinical DLS device developed by NASA using fiber optic probes was mounted on a Keratoscope (Optikon 2000), which has a 3-dimensional aiming system for accurate repeated sampling of the same area of the lens. A test/retest study was then conducted on the nuclear region of the lenses of 12 normal eyes. After a full, dilated eye examination, DLS data were obtained using the new device on the same eyes twice, 30-60 min apart. Particle size distributions and mean log particle size data were obtained. The mean percent differences between the larger and smaller of the test--retest pairs was 6.4% (range 0.05--10.8%); the between-test S.D. was 0.116. Actual numerical margin of error was +/- 0.023. In addition, the mean coefficient of variation was 4.2% (range 0.3--7.3%). A useful clinical end point obtained from data produced by the device was the mean log particle size. These results suggest that the DLS will be useful in the detection and study of the beginning and earliest stages of cataract formation in humans.

Adolescent↗
PubMed2002

In vivo assessment of diabetic lenses using dynamic light scattering.

One of the most threatening aspects of diabetes mellitus is the development of visual impairment. For example, cataracts are 1.6 times more common in people with diabetes than in those without diabetes. Cataract extraction is the only treatment. In many cases, diabetes-related ocular pathologies go undiagnosed until visual function is compromised. This paper compares and contrasts the ocular changes observed using dynamic light scattering (DLS) and conventional ophthalmic techniques during long-term maintenance of the sand rat (Psammomys obesus) on a high caloric diet. P. obesus is a wild rodent in the subfamily Gerbillinae that inhabits the desert areas of the Middle East and Africa. This animal is unique in that it develops mild to moderate obesity, hyperglycemia, pancreatic atrophy, impaired renal function, ketoacidosis, vision loss, and other diabetic complications when it consumes a high caloric diet. In this study, five animals were fed Purina sand rat chow and thus served as normal control animals. Five animals were fed a commercially prepared rodent diet (Purina 5002) consisting of only 4-5% fiber and a grain-based rabbit supplement (BioServe Rabbit Stix Appetite Stimulant) consisting of 50% carbohydrate to provide a high caloric (diabetogenic) diet and thus induce diabetes. Blood samples for the biochemical analyses, DLS, and other optical examinations were obtained on alternate weeks. Our preliminary results have demonstrated subtle changes in the lens of the diabetic sand rats as early as 2 months on a diabetogenic diet. This is an ongoing joint project with Food and Drug Administration and the National Aeronautics and Space Administration. This technique is proving to be a practical, sensitive, noninvasive diagnostic tool useful for the early detection of ocular pathologies and understanding the mechanism of cataract formation.

Animals↗
PubMedDate not supplied

Ocular static and dynamic light scattering: a noninvasive diagnostic tool for eye research and clinical practice.

The noninvasive techniques of static and dynamic light scattering are emerging as valuable diagnostic tools for the early detection of ocular and systemic diseases. These include corneal abnormalities, pigmentary dispersion syndrome, glaucoma, cataract, diabetic vitreopathy, and possibly macular degeneration. Systemic conditions such as diabetes and possibly Alzheimer's disease can potentially be detected early via ocular tissues. The current state of development of these techniques for application to ophthalmic research and ultimately clinical practice is reviewed.

Diagnostic Techniques, Ophthalmological↗
PubMedDate not supplied

New optical scheme for a polarimetric-based glucose sensor.

A new optical scheme to detect glucose concentration in the aqueous humor of the eye is presented. The ultimate aim is to apply this technique in designing a new instrument for, routinely and frequently, noninvasively monitoring blood glucose levels in diabetic patients without contact (no index matching) between the eye and the instrument. The optical scheme exploits the Brewster reflection of circularly polarized light off of the lens of the eye. Theoretically, this reflected linearly polarized light on its way to the detector is expected to rotate its state of polarization, owing to the presence of glucose molecules in the aqueous humor of a patient's eye. An experimental laboratory setup based on this scheme was designed and tested by measuring a range of known concentrations of glucose solutions dissolved in water. (c) 2004 Society of Photo-Optical Instrumentation Engineers.

Aqueous Humor↗