UV light and the ocular lens: a review of exposure models and resulting biomolecular changes.

UV light is known to cause damage to biomolecules in living tissue. Tissues of the eye that play highly specialised roles in forming our sense of sight are uniquely exposed to light of all wavelengths. While these tissues have evolved protective mechanisms to resist damage from UV wavelengths, prolonged exposure is thought to lead to pathological changes. In the lens, UV light exposure is a risk factor for the development of cataract, which is a condition that is characterised by opacity that impairs its function as a focusing element in the eye. Cataract can affect spatially distinct regions of the lens. Age-related nuclear cataract is the most prevalent form of cataract and is strongly associated with oxidative stress and a decrease in the antioxidant capacity of the central lens region. Since UV light can generate reactive oxygen species to induce oxidative stress, its effects on lens structure, transparency, and biochemistry have been extensively investigated in animal models in order to better understand human cataract aetiology. A review of the different light exposure models and the advances in mechanistic understanding gained from these models is presented.

The Synergistic Effects of Polyol Pathway-Induced Oxidative and Osmotic Stress in the Aetiology of Diabetic Cataracts.

Cataracts are the world's leading cause of blindness, and diabetes is the second leading risk factor for cataracts after old age. Despite this, no preventative treatment exists for cataracts. The altered metabolism of excess glucose during hyperglycaemia is known to be the underlying cause of diabetic cataractogenesis, resulting in localised disruptions to fibre cell morphology and cell swelling in the outer cortex of the lens. In rat models of diabetic cataracts, this damage has been shown to result from osmotic stress and oxidative stress due to the accumulation of intracellular sorbitol, the depletion of NADPH which is used to regenerate glutathione, and the generation of fructose metabolites via the polyol pathway. However, differences in lens physiology and the metabolism of glucose in the lenses of different species have prevented the translation of successful treatments in animal models into effective treatments in humans. Here, we review the stresses that arise from hyperglycaemic glucose metabolism and link these to the regionally distinct metabolic and physiological adaptations in the lens that are vulnerable to these stressors, highlighting the evidence that chronic oxidative stress together with osmotic stress underlies the aetiology of human diabetic cortical cataracts. With this information, we also highlight fundamental gaps in the knowledge that could help to inform new avenues of research if effective anti-diabetic cataract therapies are to be developed in the future.

Time of day differences in the regulation of glutathione levels in the rat lens.

Introduction: Evidence in non-ocular tissues indicate that the antioxidant glutathione (GSH) may be regulated in a circadian manner leading to the idea that GSH levels in the lens may also be controlled in a circadian manner to anticipate periods of oxidative stress. Methods: Male rat Wistar lenses (6 weeks) were collected every 4 hours over a 24-hour period at 6am, 10am, 2pm, 6pm, 10pm and 2am and quantitative-PCR, western blotting and immunohistochemistry performed to examine the expression of core clock genes and proteins (BMAL1, CLOCK, CRY1-2, PER 1-3) and their subcellular localisation over a 24-hour period. Western blotting of lenses was also performed to examine the expression of NRF2, a transcription factor involved in regulating genes involved in GSH homeostasis and GSH related enzymes (GCLC, GS and GR) over the 24-hour period. Finally, HLPC was used to measure GSH levels in the aqueous humour and lenses every 4 hours over a 24-hour period. Results: The rat lens contains the core molecular components of a circadian clock with the expression of core clock proteins, NRF2 and GSH related enzymes fluctuating over a 24-hour period. BMAL1 expression was highest during the day, with BMAL1 localised to the nuclei at 10am. NRF2 expression remained constant over the 24-hour period, although appeared to move in and out of the nuclei every 4 hours. GSH related enzyme expression tended to peak at the start of night which correlated with high levels of GSH in the lens and lower levels of GSH in the aqueous humour. Conclusion: The lens contains the key components of a circadian clock, and time-of-day differences exist in the expression of GSH and GSH related enzymes involved in maintaining GSH homeostasis. GSH levels in the rat lens were highest at the start of night which represents the active phase of the rat when high GSH levels may be required to counteract oxidative stress induced by cellular metabolism. Future work to directly link the clock to regulation of GSH levels in the lens will be important in determining whether the clock can be used to help restore GSH levels in the lens.

Connexin 50 Influences the Physiological Optics of the In Vivo Mouse Lens.

Purpose: The purpose of this study was to utilize multi-parametric magnetic resonance imaging (MRI) to investigate in vivo age-related changes in the physiology and optics of mouse lenses where Connexin 50 has been deleted (Cx50KO) or replaced by Connexin 46 (Cx50KI46). Methods: The lenses of transgenic Cx50KO and Cx50KI46 mice were imaged between 3 weeks and 6 months of age using a 7T MRI. Measurements of lens geometry, the T2 (water-bound protein ratios), the refractive index (n), and T1 (free water content) values were calculated by processing the acquired images. The lens power was calculated from an optical model that combined the geometry and the n. All transgenic mice were compared with control mice at the same age. Results: Cx50KO and Cx50KI46 mice developed smaller lenses compared with control mice. The lens thickness, volume, and surface radii of curvatures all increased with age but were limited to the size of the lenses. Cx50KO lenses exhibited higher lens power than Cx50KI46 lenses at all ages, and this was correlated with significantly lower water content in these lenses, which was probably modulated by the gap junction coupling. The refractive power tended to a steady state with age, similar to the control mice. Conclusions: The modification of Cx50 gap junctions significantly impacted lens growth and physiological optics as the mouse aged. The lenses showed delayed development growth, and altered optics governed by different lens physiology. This research provides new insights into how gap junctions regulate the development of the lens's physiological optics.

Ascorbic acid export from human donor lenses: Is the lens a source of ascorbic acid in the ocular humors?

In previous work, we have shown that the lens acts a reservoir of the antioxidant glutathione (GSH), capable of exporting this antioxidant into the ocular humors and potentially protecting the tissues of the eye that interface with these humors from oxidative stress. In this study, we have extended this work by examining whether the lens acts as a source of ascorbic acid (AsA) to maintain the high levels of AsA known to be present in the ocular humors either by the direct export of AsA into the humors and/or by functioning as a recycling site for AsA, via the direct uptake of oxidised ascorbate (DHA) from the humors, its regeneration to AsA in the lens and then its subsequent export back into the humors. To test this, human lenses of varying ages were cultured for 1 h under hypoxic conditions and AsA/DHA levels measured in the media and in the lens. Human lenses were also cultured in compartmentalised chambers to determine whether efflux of AsA/DHA occurs at the anterior or posterior surface. Immunohistochemistry was performed on human donor lenses and sections labelled with antibodies against GLUT1, a putative DHA uptake transporter. Vitreous humor was collected from patients undergoing vitrectomy who either had a natural clear lens, an artificial intraocular implant (IOL) or a cataractous lens, and AsA/DHA and GSH and oxidised GSH (GSSG) measured. We found that cultured human donor lenses released both AsA and DHA into the media. Culturing of lenses in a compartmentalised chamber revealed that AsA and DHA efflux occurs at both surfaces, with relatively equal amounts of AsA and DHA released from each surface. The posterior surface of the lens was shown to express the GLUT1 transporter. Analysis of vitreous samples from patients undergoing vitrectomy revealed that vitreous GSH and AsA levels were similar between the natural lens group, IOL and cataractous lens group. Taken together, while human donor lenses were shown to export AsA and DHA into the surrounding media, the amount of AsA and DHA released from donor lenses was low and not sufficient to sustain the high levels of total AsA normally present in the humors. This suggests that although the lens is not the main source for maintaining high levels of AsA in the ocular humors, the lens may help to support local AsA levels close to the lens.

Structure of the lens MP20 mediated adhesive junction.

Human lens fiber membrane intrinsic protein MP20 is the second most abundant membrane protein of the human eye lens. Despite decades of effort its structure and function remained elusive. Here, we determined the MicroED structure of full-length human MP20 in lipidic-cubic phase to a resolution of 3.5 Å. MP20 forms tetramers each of which contain 4 transmembrane α-helices that are packed against one another forming a helical bundle. Both the N- and C- termini of MP20 are cytoplasmic. We found that each MP20 tetramer formed adhesive interactions with an opposing tetramer in a head-to-head fashion. These interactions were mediated by the extracellular loops of the protein. The dimensions of the MP20 adhesive junctions are consistent with the 11 nm thin lens junctions. Investigation of MP20 localization in human lenses indicated that in young fiber cells MP20 was stored intracellularly in vesicles and upon fiber cell maturation MP20 inserted into the plasma membrane and restricted the extracellular space. Together these results suggest that MP20 forms lens thin junctions in vivo confirming its role as a structural protein in the human eye lens, essential for its optical transparency.

Laser induced temperature-jump time resolved IR spectroscopy of zeolites.

Combining pulsed laser heating and time-resolved infrared (TR-IR) absorption spectroscopy provides a means of initiating and studying thermally activated chemical reactions and diffusion processes in heterogeneous catalysts on timescales from nanoseconds to seconds. To this end, we investigated single pulse and burst laser heating in zeolite catalysts under realistic conditions using TR-IR spectroscopy. 1 ns, 70 µJ, 2.8 µm laser pulses from a Nd:YAG-pumped optical parametric oscillator were observed to induce temperature-jumps (T-jumps) in zeolite pellets in nanoseconds, with the sample cooling over 1-3 ms. By adopting a tightly focused beam geometry, T-jumps as large as 145 °C from the starting temperature were achieved, demonstrated through comparison of the TR-IR spectra with temperature dependent IR absorption spectra and three dimensional heat transfer modelling using realistic experimental parameters. The simulations provide a detailed understanding of the temperature distribution within the sample and its evolution over the cooling period, which we observe to be bi-exponential. These results provide foundations for determining the magnitude of a T-jump in a catalyst/adsorbate system from its absorption spectrum and physical properties, and for applying T-jump TR-IR spectroscopy to the study of reactive chemistry in heterogeneous catalysts.

Potential Dependent Reorientation Controlling Activity of a Molecular Electrocatalyst.

The activity of molecular electrocatalysts depends on the interplay of electrolyte composition near the electrode surface, the composition and morphology of the electrode surface, and the electric field at the electrode-electrolyte interface. This interplay is challenging to study and often overlooked when assessing molecular catalyst activity. Here, we use surface specific vibrational sum frequency generation (VSFG) spectroscopy to study the solvent and potential dependent activation of Mo(bpy)(CO)4, a CO2 reduction catalyst, at a polycrystalline Au electrode. We find that the parent complex undergoes potential dependent reorientation at the electrode surface when a small amount of N-methyl-2-pyrrolidone (NMP) is present. This preactivates the complex, resulting in greater yields at less negative potentials, of the active electrocatalyst for CO2 reduction.

The 2D-IR spectrum of hydrogen-bonded silanol groups in pyrogenic silica.

Pyrogenic silica is a form of amorphous silica with a high surface area and a heterogeneous distribution of silanol hydroxyl terminations and defects. In this work, the interesting and unusual form of the hydroxyl-stretch 2D-IR spectrum of pyrogenic silica is presented and explored in the deuterated (deuteroxyl) form. Transition dipole couplings between hydrogen-bonded and non-hydrogen-bonded silanol groups give a distinct cross-peak in the 2D-IR spectrum, displaying interstate coherence oscillations during the 2D-IR experimental waiting time. The strong asymmetry about the diagonal is proposed to be the result of both the relatively small transition dipole coupling strength and the extreme differences in the width of the hydrogen-bonded and non-hydrogen-bonded silanol bands. The resulting interference of negative and positive cross-peaks has minimal intensity in the below-diagonal ω3 < ω1 region of the spectrum. An additional strong positive cross-peak is observed at a position in the 2D-IR spectrum inconsistent with transition dipole coupling. An assignment as a fifth order effect is proposed.

Verification of the gene and protein expression of the aquaglyceroporin AQP3 in the mammalian lens.

Transport of water is critical for maintaining the transparency of the avascular lens, and the lens is known to express at least five distinctly different water channels from the Aquaporin (AQP) family of proteins. In this study we report on the identification of a sixth lens AQP, AQP3 an aquaglyceroporin, which in addition to water also transports glycerol and H2O2. AQP3 was identified at the transcript level and protein levels using RT-PCR and Western blotting, respectively, in the mouse, rat, bovine and human lens, showing that its expression is conserved in the mammalian lens. Western blotting showed AQP3 in the lens exists as 25 kDa non-glycosylated and 37 kDa glycosylated monomeric forms in all lens species. To identify the regions in the lens where AQP3 is expressed Western blotting was repeated using epithelial, outer cortical and inner cortical/core fractions isolated from the mouse lens. AQP3 was found in all lens regions, with the highest signal of non-glycosylated AQP3 being found in the epithelium. While in the inner cortex/core region AQP3 signal was not only lower but was predominately from the glycosylated form of AQP3. Immunolabelling of lens sections with AQP3 antibodies confirmed that AQP3 is found in all regions of the adult mouse, and also revealed that the subcellular distribution of AQP3 changes as a function of fiber cell differentiation. In epithelial and peripheral fiber cells of the outer cortex AQP3 labelling was predominately associated with membrane vesicles in the cytoplasm, but in the deeper regions of the lens AQP3 labelling was associated with the plasma membranes of fiber cells located in the inner cortex and core of the lens. To determine how this adult pattern of AQP3 subcellular distribution was established, immunolabelling for AQP3 was performed on embryonic and postnatal lenses. AQP3 expression was first detected on embryonic day (E) 11 in the membranes of primary fiber cells that have started to elongate and fill the lumen of the lens vesicle, while later at E16 the AQP3 labelling in the primary fiber cells had shifted to a predominately cytoplasmic location. In the following postnatal (P) stages of lens growth at P3 and P6, AQP3 labelling remained cytoplasmic across all regions of the lens and it was not until P15 when the pattern of localisation of AQP3 changed to an adult distribution with cytoplasmic labelling detected in the outer cortex and membrane localisation detected in the inner cortex and core of the lens. Comparison of the AQP3 labelling pattern to those obtained previously for AQP0 and AQP5 showed that the subcellular distribution was more similar to AQP5 than AQP0, but there were still significant differences that suggest AQP3 may have unique roles in the maintenance of lens transparency.

Alterations in Lens Free Water Distribution Are Associated with Shape Deformation in Accommodation.

Objective: To investigate whether a redistribution of water within the crystalline lens is associated with the shape deformation that occurs during accommodation. Design: Observational, cross sectional study. Subjects: Eleven young adults without presbyopia (aged 18-39 years) and 9 middle-aged adults with presbyopia (aged 40-55 years). Methods: Magnetic resonance imaging (MRI) scans of the lens were acquired on a 3 Tesla clinical MRI scanner, without and with the presentation of a 3 Diopter accommodative stimulus. The MRIs were postprocessed using established methods to extract the geometric dimensions and spatial maps of water distribution of the lens. Main Outcome Measures: Accommodative changes in the full 3-dimensional description of lens shape, the lens total-water distribution profile, and the lens free-water distribution profile. Results: Viewing of an accommodative stimulus by young subjects elicited an elastic shape deformation of the lens consistent with accommodation that was associated with an elevated, smoother free-water distribution, primarily in the anterior region of the lens. In contrast, viewing of an accommodative stimulus by presbyopic subjects produced an atypical shape deformation of the lens that was instead associated with a lowered free-water distribution, primarily in the anterior region of the lens. No discernible changes to the lens total-water distribution were observed in response to the accommodative stimulus in either subject cohort. Conclusions: The present study suggests that protein-mediated alterations in the free-water distribution of the anterior region of the lens influence the shape deformation in accommodation, presenting pharmacological modulation of free-water distribution as an attractive novel approach for treating presbyopia. Financial Disclosures: The authors have no proprietary or commercial interest in any materials discussed in this article.

Piezo1 channel causes lens sclerosis via transglutaminase 2 activation.

Presbyopia is caused by age-related lenticular hardening, resulting in near vision loss, and it occurs in almost every individual aged ≥50 years. The lens experiences mechanical pressure during for focal adjustment to change its thickness. As lenticular stiffening results in incomplete thickness changes, near vision is reduced, which is known as presbyopia. Piezo1 is a mechanosensitive channel that constantly senses pressure changes during the regulation of visual acuity, and changes in Piezo1 channel activity may contribute to presbyopia. However, no studies have reported on Piezo1 activation or the onset of presbyopia. To elucidate the relevance of Piezo1 activation and cross-linking in the development of presbyopia, we analysed the function of Piezo1 in the lens. The addition of Yoda1, a Piezo1 activator, induced an increase in transglutaminase 2 (TGM2) mRNA expression and activity through the extra-cellular signal-regulated kinase (ERK) 1/2 and c-Jun-NH2-terminal kinase1/2 pathways. In ex vivo lenses, Yoda1 treatment induced γ-crystallin cross-linking via TMG2 activation. Furthermore, Yoda1 eye-drops in mice led to lenticular hardening via TGM2 induction and activation in vivo, suggesting that Yoda1-treated animals could serve as a model for presbyopia. Our findings indicate that this presbyopia-animal model could be useful for screening drugs for lens-stiffening inhibition.

Regulation of water flow in the ocular lens: new roles for aquaporins.

The ocular lens is an important determinant of overall vision quality whose refractive and transparent properties change throughout life. The lens operates an internal microcirculation system that generates circulating fluxes of ions, water and nutrients that maintain the transparency and refractive properties of the lens. This flow of water generates a substantial hydrostatic pressure gradient which is regulated by a dual feedback system that uses the mechanosensitive channels TRPV1 and TRPV4 to sense decreases and increases, respectively, in the pressure gradient. This regulation of water flow (pressure) and hence overall lens water content, sets the two key parameters, lens geometry and the gradient of refractive index, which determine the refractive properties of the lens. Here we focus on the roles played by the aquaporin family of water channels in mediating lens water fluxes, with a specific focus on AQP5 as a regulated water channel in the lens. We show that in addition to regulating the activity of ion transporters, which generate local osmotic gradients that drive lens water flow, the TRPV1/4-mediated dual feedback system also modulates the membrane trafficking of AQP5 in the anterior influx pathway and equatorial efflux zone of the lens. Since both lens pressure and AQP5-mediated water permeability ( P H 2 O ${P_{{{\mathrm{H}}_{\mathrm{2}}}{\mathrm{O}}}}$ ) can be altered by changes in the tension applied to the lens surface via modulating ciliary muscle contraction we propose extrinsic modulation of lens water flow as a potential mechanism to alter the refractive properties of the lens to ensure light remains focused on the retina throughout life.

Correction: Time-resolved infra-red studies of photo-excited porphyrins in the presence of nucleic acids and in HeLa tumour cells: insights into binding site and electron transfer dynamics.

Correction for 'Time-resolved infra-red studies of photo-excited porphyrins in the presence of nucleic acids and in HeLa tumour cells: insights into binding site and electron transfer dynamics' by Páraic M. Keane et al., Phys. Chem. Chem. Phys., 2022, 24, 27524-27531, https://doi.org/10.1039/D2CP04604K.

Breaking Barriers in Ultrafast Spectroscopy and Imaging Using 100 kHz Amplified Yb-Laser Systems.

ConspectusUltrafast spectroscopy and imaging have become tools utilized by a broad range of scientists involved in materials, energy, biological, and chemical sciences. Commercialization of ultrafast spectrometers including transient absorption spectrometers, vibrational sum frequency generation spectrometers, and even multidimensional spectrometers have put these advanced spectroscopy measurements into the hands of practitioners originally outside the field of ultrafast spectroscopy. There is now a technology shift occurring in ultrafast spectroscopy, made possible by new Yb-based lasers, that is opening exciting new experiments in the chemical and physical sciences. Amplified Yb-based lasers are not only more compact and efficient than their predecessors but also, most importantly, operate at many times the repetition rate with improved noise characteristics in comparison to the previous generation of Ti:sapphire amplifier technologies. Taken together, these attributes are enabling new experiments, generating improvements to long-standing techniques, and affording the transformation of spectroscopies to microscopies. This Account aims to show that the shift to 100 kHz lasers is a transformative step in nonlinear spectroscopy and imaging, much like the dramatic expansion that occurred with the commercialization of Ti:sapphire laser systems in the 1990s. The impact of this technology will be felt across a great swath of scientific communities. We first describe the technology landscape of amplified Yb-based laser systems used in conjunction with 100 kHz spectrometers operating with shot-to-shot pulse shaping and detection. We also identify the range of different parametric conversion and supercontinuum techniques which now provide a path to making pulses of light optimal for ultrafast spectroscopy. Second, we describe specific instances from our laboratories of how the amplified Yb-based light sources and spectrometers are transformative. For multiple probe time-resolved infrared and transient 2D IR spectroscopy, the gain in temporal span and signal-to-noise enables dynamical spectroscopy measurements from femtoseconds to seconds. These gains widen the applicability of time-resolved infrared techniques across a range of topics in photochemistry, photocatalysis, and photobiology as well as lower the technical barriers to implementation in a laboratory. For 2D visible spectroscopy and microscopy with white light, as well as 2D IR imaging, the high repetition rates of these new Yb-based light sources allow one to spatially map 2D spectra while maintaining high signal-to-noise in the data. To illustrate the gains, we provide examples of imaging applications in the study of photovoltaic materials and spectroelectrochemistry.

Modulation of Membrane Trafficking of AQP5 in the Lens in Response to Changes in Zonular Tension Is Mediated by the Mechanosensitive Channel TRPV1.

In mice, the contraction of the ciliary muscle via the administration of pilocarpine reduces the zonular tension applied to the lens and activates the TRPV1-mediated arm of a dual feedback system that regulates the lens' hydrostatic pressure gradient. In the rat lens, this pilocarpine-induced reduction in zonular tension also causes the water channel AQP5 to be removed from the membranes of fiber cells located in the anterior influx and equatorial efflux zones. Here, we determined whether this pilocarpine-induced membrane trafficking of AQP5 is also regulated by the activation of TRPV1. Using microelectrode-based methods to measure surface pressure, we found that pilocarpine also increased pressure in the rat lenses via the activation of TRPV1, while pilocarpine-induced removal of AQP5 from the membrane observed using immunolabelling was abolished by pre-incubation of the lenses with a TRPV1 inhibitor. In contrast, mimicking the actions of pilocarpine by blocking TRPV4 and then activating TRPV1 resulted in sustained increase in pressure and the removal of AQP5 from the anterior influx and equatorial efflux zones. These results show that the removal of AQP5 in response to a decrease in zonular tension is mediated by TRPV1 and suggest that regional changes to PH2O contribute to lens hydrostatic pressure gradient regulation.

Age-Dependent Changes in the Water Content and Optical Power of the In Vivo Mouse Lens Revealed by Multi-Parametric MRI and Optical Modeling.

Purpose: The purpose of this study was to utilize in vivo magnetic resonance imaging (MRI) and optical modeling to investigate how changes in water transport, lens curvature, and gradient refractive index (GRIN) alter the power of the mouse lens as a function of age. Methods: Lenses of male C57BL/6 wild-type mice aged between 3 weeks and 12 months (N = 4 mice per age group) were imaged using a 7T MRI scanner. Measurements of lens shape and the distribution of T2 (water-bound protein ratios) and T1 (free water content) values were extracted from MRI images. T2 values were converted into the refractive index (n) using an age-corrected calibration equation to calculate the GRIN at different ages. GRIN maps and shape parameters were inputted into an optical model to determine ageing effects on lens power and spherical aberration. Results: The mouse lens showed two growth phases. From 3 weeks to 3 months, T2 decreased, GRIN increased, and T1 decreased. This was accompanied by increased lens thickness, volume, and surface radii of curvatures. The refractive power of the lens also increased significantly, and a negative spherical aberration was developed and maintained. Between 6 and 12 months of age, all physiological, geometrical, and optical parameters remained constant, although the lens continued to grow. Conclusions: In the first 3 months, the mouse lens power increased as a result of changes in shape and in the GRIN, the latter driven by the decreased water content of the lens nucleus. Further research into the mechanisms regulating this decrease in mouse lens water could improve our understanding of how lens power changes during emmetropization in the developing human lens.

Ultrafast 2D-IR spectroscopy of intensely optically scattering pelleted solid catalysts.

Solid, powdered samples are often prepared for infrared (IR) spectroscopy analysis in the form of compressed pellets. The intense scattering of incident light by such samples inhibits applications of more advanced IR spectroscopic techniques, such as two-dimensional (2D)-IR spectroscopy. We describe here an experimental approach that enables the measurement of high-quality 2D-IR spectra from scattering pellets of zeolites, titania, and fumed silica in the OD-stretching region of the spectrum under flowing gas and variable temperature up to ∼500 ◦C. In addition to known scatter suppression techniques, such as phase cycling and polarization control, we demonstrate how a bright probe laser beam comparable in strength with the pump beam provides effective scatter suppression. The possible nonlinear signals arising from this approach are discussed and shown to be limited in consequence. In the intense focus of 2D-IR laser beams, a free-standing solid pellet may become elevated in temperature compared with its surroundings. The effects of steady state and transient laser heating effects on practical applications are discussed.

Regulation of lens water content: Effects on the physiological optics of the lens.

The lens is an important determinant of overall vision quality whose refractive and transparent properties change throughout life. Alterations to the refractive properties of the lens contribute to the process of emmetropisation in early childhood, and then the gradual loss in lens power that occurs throughout adulthood. In parallel to these changes to lens refractive power, age-dependent increases in lens stiffness and light scattering result in presbyopia and cataract, respectively. In recent years it has been confirmed that the lens operates an internal microcirculation system that generates circulating fluxes of ions, water and nutrients that maintain the refractive properties and transparency of the lens. By actively regulating lens water content, the microcirculation system controls two key parameters, lens geometry and the gradient of refractive index, which together determine the refractive properties of the lens. Furthermore, by delivering nutrients and antioxidants to the lens nucleus, the microcirculation system maintains lens transparency by preventing crystallin aggregation. Interestingly, the solubility, intramolecular packing and refractive index increment of crystallin proteins can be modulated by the ability of crystallin proteins to dynamically bind water, a processed called syneresis. In a series of previous studies it has been shown that the application of external pressure to the lens can induce syneresis. Since it is now known that lens water transport generates a substantial internal hydrostatic pressure gradient, we speculate that the microcirculation is capable of regulating crystallin function by altering the amount of water bound to lens proteins in the nucleus, where the pressure gradient and protein concentrations are the highest. Here we present evidence for the links between lens transport, pressure, syneresis and protein function. Furthermore, because the lens pressure gradient can be regulated by intrinsic and extrinsic stimuli, we suggest mechanisms via which this integrative system can be used to effect the changes to the refractive and transparent properties of the lens that are observed across our lifetime.

Early onset of age-related changes in the retina of cystine/glutamate antiporter knockout mice.

To determine the role of the cystine/glutamate antiporter on retinal structure and function, retinas of C57Bl/6J wild-type and xCT knockout mice, lacking the xCT subunit of the cystine/glutamate antiporter were examined from 6 weeks to 12 months of age. Fundoscopy, optical coherence tomography (OCT), and whole mount retinal autofluorescence imaging were used to visualise age-related retinal spots. Glial fibrillary acidic protein (GFAP) immunolabelling was used to assess retinal stress. Retinal function was evaluated using full-field and focal electroretinograms. Examinations revealed retinal spots in both wild-type and xCT knockout mice with the number of spots greater at 9 months in the knockout compared to wild-type. OCT confirmed these discrete spots were located at the retinal pigment epithelium (RPE)-photoreceptor junction and did not label with drusen markers. Whole mount lambda scans of the 9 month xCT knockout retinas revealed that the photoreceptor autofluorescence matched the spots, suggesting these spots were retinal debris. GFAP labelling was increased in knockout retinas compared to wild-type indicative of retinal stress, and the discrete spots were associated with migration of microglia/macrophages to the RPE-retina intersection. OCT revealed that the superior retina was thinner at 9 months in knockout compared to wild-type mice due to changes to the outer nuclear and photoreceptor layers. While global retinal function was not affected by loss of xCT, focal changes in retinal function were detected in areas where spots were present. Tother these results suggest that the xCT KO mice exhibit features of accelerated ageing and suggests that this mouse model may be useful for studying the underlying cellular pathways in retinal ageing.