Clinical photon correlation spectroscopy evaluation of human diabetic lenses

In vivo quasi-elastic light scattering detects molecular changes in the lenses of adolescents with Down syndrome

Down syndrome (DS) is the most common chromosomal disorder in humans. DS is associated with increased prevalence of several ocular sequelae, including characteristic blue-dot cerulean cataract. DS is accompanied by age-dependent accumulation of Alzheimer's disease (AD) amyloid-β (Aβ) peptides and amyloid pathology in the brain and comorbid early-onset Aβ amyloidopathy and colocalizing cataracts in the lens. Quasi-elastic light scattering (QLS) is an established optical technique that noninvasively measures changes in protein size distributions in the human lens in vivo. In this cross-sectional study, lenticular QLS correlation time was decreased in adolescent subjects with DS compared to age-matched control subjects. Clinical QLS was consistent with alterations in relative particle hydrodynamic radius in lenses of adolescents with DS. These correlative results suggest that noninvasive QLS can be used to evaluate molecular changes in the lenses of individuals with DS.

In Vivo Quasi-Elastic Light Scattering Eye Scanner Detects Molecular Aging in Humans

The absence of clinical tools to evaluate individual variation in the pace of aging represents a major impediment to understanding aging and maximizing health throughout life. The human lens is an ideal tissue for quantitative assessment of molecular aging in vivo. Long-lived proteins in lens fiber cells are expressed during fetal life, do not undergo turnover, accumulate molecular alterations throughout life, and are optically accessible in vivo. We used quasi-elastic light scattering (QLS) to measure age-dependent signals in lenses of healthy human subjects. Age-dependent QLS signal changes detected in vivo recapitulated time-dependent changes in hydrodynamic radius, protein polydispersity, and supramolecular order of human lens proteins during long-term incubation (~1 year) and in response to sustained oxidation (~2.5 months) in vitro. Our findings demonstrate that QLS analysis of human lens proteins provides a practical technique for noninvasive assessment of molecular aging in vivo.

Analysis of diabetic vitreopathy with dynamic light scattering spectroscopy--problems and solutions related to photon correlation

PURPOSE

To explore the molecular alterations of the vitreous by dynamic light scattering (DLS) spectroscopy (quasi-elastic light scattering spectroscopy, photon-correlation spectroscopy) in normals and in patients afflicted with various degrees of non-proliferative and with proliferative diabetic retinopathy.

METHODS

Dynamic light scattering spectroscopy was employed to analyze the vitreous of normals and of patients with diabetes non-invasively to estimate both the sizes and diffusion coefficients of mobile macromolecules and/or microparticles.

RESULTS

Abnormal molecular behaviour of vitreous molecules was observed in patients with diabetes afflicted with various degrees of diabetic vitreo-retinopathy. In the non-proliferative (background) retinopathy, both the diameters of the microparticles increase and the diffusion constants decrease significantly and progressively as the diabetic disease progresses. In the proliferative phase, a significant trend in the direction of smaller particles and greater diffusion constants is evident. These behaviours could also be interpreted as an increase in the viscosity of the intermolecular substance in the first case and as a decrease in the second.

CONCLUSIONS

The vitreous in normals and even more so in diabetics with diabetic vitreo-retinopathy is optically a highly non-isotropic, multidispersive structure, making an optical analysis difficult. Advanced, but available models and technology, however, permits a major step forward in the optical analysis of the normal and the diseased vitreous.

Protein-protein interactions and lens transparency

Past studies have identified posttranslational modifications of human lens proteins occurring during cataract formation, and have also demonstrated that protein-protein interactions exist between different lens crystallins. Based upon current theories of lens transparency, these posttranslational modifications and their possible effects upon crystallin interactions may be the key to understanding why the lens is able to transmit light, and why transmission is decreased during cataractogenesis. This review will summarize current knowledge of posttranslational modifications during human cataractogenesis, and will propose their possible role in protein-protein interactions that are thought to be necessary for lens transparency. Based upon this premise, model systems will be described that will test the validity of the theory.

Dynamic light scattering study on phase separation of a protein-water mixture: application on cold cataract development in the ocular lens

We present a detailed dynamic light scattering study of the phase separation in the ocular lens emerging during cold cataract development. Cold cataract is a phase separation effect that proceeds via spinodal decomposition of the lens cytoplasm with cooling. The intensity autocorrelation functions of the lens protein content are analyzed with the aid of two methods, providing information on the populations and dynamics of the scattering elements associated with cold cataract. It is found that the temperature dependence of many measurable parameters changes appreciably at the characteristic temperature approximately 16+/-1 degrees C which is associated with the onset of cold cataract. By extending the temperature range of this work to previously inaccessible regimes, i.e., well below the phase separation or coexistence curve at Tcc, we have been able to accurately determine the temperature dependence of the collective and self-diffusion coefficients of proteins near the spinodal. The analysis showed that the dynamics of proteins bears some resemblance to the dynamics of structural glasses, where the apparent activation energy for particle diffusion increases below Tcc, indicating a highly cooperative motion. Application of ideas developed for studying the critical dynamics of binary protein-solvent mixtures, as well as the use of a modified Arrhenius equation, enabled us to estimate the spinodal temperature Tsp of the lens nucleus. The applicability of dynamic light scattering as a noninvasive, early-diagnostic tool for ocular diseases is also demonstrated in light of the findings of the present paper.

The relationship between nuclear colour and opalescence on the LOCSIII scale and physical characteristics of cataract nuclei

PURPOSE

To evaluate the compression characteristics of the human lens nucleocortex in relation to its LOCSIII clinical grading.

METHODS

Sixteen subjects undergoing planned extracapsular cataract surgery had pre-operative slit-lamp examination and assessment of cataract LOCSIII grade followed by postoperative in vitro evaluation of the nucleus with measurement of 'linear compressibility' by a purpose-designed caliper incorporating a strain gauge, enabling the derivation of a graph of nuclear compression (D (mm) against applied force (F (N)).

RESULTS

Nuclear colour correlates with the force required to compress a lens to 75% of its original depth (F75) (R = 0.625, P = 0.017). Nuclear opalescence correlates with the force required to compress a lens to 75% of its original depth (R = 0.651, P = 0.012) and inversely with linear compressibility (DeltaD/DeltaF, the slope of the graph of nuclear compression against applied force) (R = -0.610, P = 0.014). F75 is a direct and linear compressibility is an inverse related parameter of lens nucleus 'hardness'.

CONCLUSION

A new instrument is described which allows measurement of 'hardness'-related compression characteristics of the human cataract in vitro. There is a relationship between the LOCSIII clinical classification of nuclear cataracts and mechanical compression characteristics of the cataractous lens. LOCSIII classification may aid the preoperative planning of an appropriate surgical approach to an individual cataract.

Use of dynamic light scattering and Scheimpflug imaging for the early detection of cataracts

Cataract is a leading cause of blindness. Diabetes and glycemic conditions enhance the chances of developing cataracts early. At clinical stage cataracts are detected and documented by slit-lamp biomicroscopy and Scheimpflug photography. A compact fiber optic probe, developed for space experiments, was mounted on a Scheimpflug imaging system. The probe detects and documents cataracts at pre-clinical stage noninvasively and quantitatively. The early detection at the molecular level may lead to medical treatment of cataracts, better control of glycemia, and diabetes mellitus.

Effect of diabetes associated increases in lens optical density on colour discrimination in insulin dependent diabetes

Optical density (OD) of the crystalline lens has been shown in non-diabetics to increase linearly with age over the first five decades and at an increased rate thereafter; in insulin dependent diabetic (IDDM) patients, lens OD increases with age and with duration of diabetes at a rate similar to that in non-diabetics over the age of 60 years. Recently, it has been established that colour discrimination is abnormal in a majority of young patients with uncomplicated IDDM and angiographically normal retinas. Colour discrimination loss was attributed to functional abnormalities in the retina or neural pathways; yet the possibility exists that increases in lens OD may account for part or all of the colour discrimination loss in IDDM. In the present study, colour discrimination was compared in aretinopathic IDDM patients and age-matched controls, and then in a group of aretinopathic IDDM patients individually matched to controls with respect to lens OD. Colour discrimination was significantly worse in diabetic patients than in age-matched controls, and was significantly worse when diabetic patients were compared with controls matched for OD. The magnitude of the difference in 100 hue error score between diabetic patients and OD matched controls was, however, considerably less than the difference between diabetic patients and age-matched controls. These data suggest that colour discrimination loss in aretinopathic IDDM patients cannot be explained solely on the basis of diabetes induced increases in lens OD, but must involve abnormalities of the retina or its neural connections.

The lens in diabetes

This paper reviews the changes which occur in the human lens in diabetes. They include refractive changes and cataract and age-related increases in thickness, curvatures, light scattering, autofluorescence and yellowing. The incidence of cataract is greatly increased over the age of 50 years, slightly more so in women, compared with non-diabetics. Experimental models of sugar cataract provide some evidence for the mechanism of the uncommon, but morphologically distinct, juvenile form of human diabetic cataract, where an osmotic mechanism due to sugar alcohol accumulation has been thoroughly studied in diabetic or galactose-fed rats. The discrepancy between the ready accumulation of sugar alcohol in the lens in model systems and the very slow kinetics of aldose reductase (AR) has not been satisfactorily explained and suggests that the mechanism of polyol formation is not yet fully understood in mammalian systems. The activity of AR in the human lens lies mainly in the epithelium and there appears to be a marginal expectation that sufficient sorbitol accumulates in cortical lens fibres to explain the lens swelling and cataract on an osmotic basis. This is even more so in the cataracts of adult diabetics, which resemble those of age-related non-diabetic cataracts in appearance. The very low levels of sorbitol in adult diabetic lenses make an osmotic mechanism for the increased risk of cataract even less likely. Other mechanisms, including glycation and oxidative stress, are discussed. The occurrence of cataract is a predictor for increased mortality in the diabetic.

Photon correlation spectroscopy of light scattered by eye lenses in in vivo conditions

The application of photon correlation spectroscopy on mammalian eye lenses in vivo is revisited. It is shown that the use of a short wavelength laser type and a logarithmic correlator improves the signal-to-noise ratio to such an extent that shorter measurement times are possible without impairing the information content of the correlation function. Experimental correlation functions obtained in vivo on a rabbit eye lens, are analyzed with several techniques. The histogram approach is most successful for the determination of the distribution function of relaxation processes in the correlation function and proposes four different populations of components in the lens. This result is comparable to that from in vitro measurements on highly concentrated solutions of alpha-crystallins and of fiber cell cytoplasm, the former proteins being the main scattering components both in vivo and in vitro in the eye lens system. Our results indicate that the application of photon correlation spectroscopy on eye lenses in vivo offers new perspectives to use this technique as a fast, noninvasive tool to study relaxation phenomena in normal and cataractous lenses. The sensitivity of the method allows it to be used as an important analytical technique in the study of prevention and treatment of cataract.