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Crystalline Lens (crystalline + lens)
Selected AbstractsTowards metabolic mapping of the human retinaMICROSCOPY RESEARCH AND TECHNIQUE, Issue 5 2007D. Schweitzer Abstract Functional alterations are first signs of a starting pathological process. A device that measures parameter for the characterization of the metabolism at the human eye-ground would be a helpful tool for early diagnostics in stages when alterations are yet reversible. Measurements of blood flow and of oxygen saturation are necessary but not sufficient. The new technique of auto-fluorescence lifetime measurement (FLIM) opens in combination with selected excitation and emission ranges the possibility for metabolic mapping. FLIM not only adds an additional discrimination parameter to distinguish different fluorophores but also resolves different quenching states of the same fluorophore. Because of its high sensitivity and high temporal resolution, its capability to resolve multi-exponential decay functions, and its easy combination with laser scanner ophthalmoscopy, multi-dimensional time-correlated single photon counting was used for fundus imaging. An optimized set up for in vivo lifetime measurements at the human eye-ground will be explained. In this, the fundus fluorescence is excited at 446 or 468 nm and the time-resolved autofluorescence is detected in two spectral ranges between 510 and 560 nm as well as between 560 and 700 nm simultaneously. Exciting the fundus at 446 nm, several fluorescence maxima of lifetime t1 were detected between 100 and 220 ps in lifetime histograms of 40° fundus images. In contrast, excitation at 468 nm results in a single maximum of lifetime t1 = 190 ± 16 ps. Several fundus layers contribute to the fluorescence intensity in the short-wave emission range 510,560 nm. In contrast, the fluorescence intensity in the long-wave emission range between 560 and 700 nm is dominated by the fluorescence of lipofuscin in the retinal pigment epithelium. Comparing the lateral distribution of parameters of a tri-exponential model function in lifetime images of the fundus with the layered anatomical fundus structure, the shortest component (t1 = 190 ps) originates from the retinal pigment epithelium and the second lifetime (t2 = 1,000 ps) from the neural retina. The lifetime t3 , 5.5 ns might be influenced by the long decay of the fluorescence in the crystalline lens. In vitro analysis of the spectral properties of expected fluorophores under the condition of the living eye lightens the interpretation of in vivo measurements. Taking into account the transmission of the ocular media, the excitation of NADH is unlikely at the fundus. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source] Compensation for light loss due to filtering by macular pigment: relation to hue cancellationOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 3 2007James M. Stringham Abstract Background:, A long-standing question in colour vision research is how the visual system is able to correct for the significant absorbance of short wave light by the crystalline lens and macular pigment (MP). Such compensation must be required in order to maintain colour constancy across the retina where MP levels are changing quickly and dramatically. Objective:, We studied this compensation mechanism by measuring MP spatial density profiles and hue cancellation functions across the central retina in a sample of six young healthy subjects. Method:, Yellow (Y, 575 nm)/blue (B, 440 nm) and red (R, 600 nm)/green (G, 501 nm) cancellation functions were obtained at 0, 1, 1.75, 3 and 7° eccentricity. The MP optical density at 460 nm was measured at these same eccentricities using heterochromatic flicker photometry. One subject was assessed repeatedly over a 4-month period during daily supplementation with 30 mg of lutein (L). Results:, Hue cancellation values for the Y/B system did not change across the retina (r = 0.09). In contrast, R/G sensitivity changed as a direct function of MP absorbance (r = 0.99). The Y/B values did not change in the one subject supplemented with 30 mg L daily, despite increases in MP of about 50% over 4 months. Conclusions:, Despite large variations in MP across the retina, hue cancellation values for the Y-B system across the central retina were constant. For example, one subject's MP density declined from a central peak of 0.99 to near zero at 7° (near 90% transmission difference) yet thresholds for the Y/B system were unaffected. In contrast, the G lobe of the R/G system was directly correlated with MP density. Taken together, these results confirm that the Y/B system compensates for MP density, but the R/G system does not. [source] Determination of pseudophakic accommodation with translation lenses using Purkinje image analysisOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 2 2005Achim Langenbucher Abstract Purpose:, To determine pseudophakic accommodation of an accommodating posterior chamber intraocular lens (translation lens) using Purkinje image analysis and linear matrix methods in the paraxial space. Methods:, A 2 × 2 system matrix was defined for each Purkinje image I to IV using refraction, translation and mirror matrices. Image size (m) and axial image position (z) was determined as an example for an off-axis object (a 0.2 m off-axis object located 0.5 m in front of the cornea.). First, our method was applied to the phakic relaxed (emmetropic) and accommodated (6.96 D) Le Grand eye. Secondly, for demonstration of the applicability of the calculation scheme to the pseudophakic eye, we provide a clinical example where we determine the accommodation amplitude of the translation lens (1 CU, HumanOptics, Erlangen, Germany) from photographed Purkinje images in the relaxed and accommodated state. From the biometric data: axial length 23.7 mm, corneal power 43.5, corneal thickness 550 microns, implanted intraocular lens (IOL) with a refractive power of 20.5 D (shape equi-biconvex, refractive index 1.46), and refractive indices of the cornea, aqueous and vitreous from the Le Grand model eye, we calculated the refractive state and the sizes of Purkinje images I and III initiated from two off-axis light sources. Results:, For the Le Grand model eye, Purkinje image II (z/m = 3.5850 mm/0.0064) is slightly smaller than and directly in front of image I (z/m = 3.8698 mm/0.0077). Purkinje image III (z/m = 10.6097 mm/0.0151) is nearly double the size of image I and during accommodation it moves from the vitreous into the crystalline lens. Purkinje IV (z/m = 4.3244 mm/,0.0059) is inverted, three quarters the size of image I, lies in the crystalline lens and moves slightly towards the retina. For the pseudophakic eye, pseudophakic accommodation of 1.10 D was calculated from the proportion of distances between both Purkinje images I and III in the relaxed (3.04) and accommodated (2.75) state, which is in contrast to the total subjective accommodation of 2.875 D evaluated with an accommodometer. Conclusions:, We present a straightforward mathematical strategy for calculation of the Purkinje images I,IV. Results of our model calculation resemble the values provided by Le Grand. In addition, this approach yields a simple en bloc scheme for determination of pseudophakic accommodation in pseudophakic eyes with accommodative lenses (translation lenses) using Purkinje image photography. [source] Polarization properties of the in vitro old human crystalline lensOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 2 2003Juan M. Bueno Abstract We have studied the spatially resolved polarization properties of the in vitro intact old human crystalline lens (from 56 to 88 years old) by using Mueller-matrix imaging polarimetry. Analysis was performed within an average of 54 h of death. Results show that the overall retardation is small (7° on average) and decreases from the centre of the lens to the periphery. Lenticular birefringence is linear but has a spatial dependence, reducing outwards along the radius. The distribution of azimuthal angle of the birefringent structure of the crystalline lens changes depending on each individual lens. Diattenuation and polarizance were found to be small, however, depolarization was about 35% for the set of lenses studied here. [source] 3421: Straylight and visionACTA OPHTHALMOLOGICA, Issue 2010TJTP VAN DEN BERG Purpose Straylight is considered an important source of patient complaints. They can be voiced like halos, glare, hazy vision and blinding at night. With visual acuity, contrast sensitivity and slit lamp examination little may be found. Yet increased large angle light scattering in the eye media not detected by common tests, may degrade the image projected on the retina, thus decreasing the quality of vision. Aging changes to the crystalline lens and cataract are the most common causes of increased straylight. This study aimed to quantify the importance of straylight for daily life on the basis of patient complaint scores. Methods In a duocenter setting questionnaires were administered before and after cataract surgery. The 37 questions VFQ as well as a self developed 5 question straylight questionnaire were used. A comparison was made between the importance of visual acuity and of straylight to explain the questionnaire outcomes. Results A total of 214 patients were included in the study. For the comparison correlation coefficients were calculated between a weighted average of the 2 functional measures visual acuity and straylight on the one hand, and the questionnaire outcomes on the other. In all 4 cases (2 questionnaires x 2 visits) correlation was lowest for both visual acuity and straylight used in isolation. When visual acuity and straylight were combined to one combined score, correlation improved. Maximum correlation was found when visual acuity and straylight were combined 1:1 (preop) to 2:1 (postop), for both questionnaires. Conclusion For cataract patients, straylight is of about equal importance compared to visual acuity for their appreciation of daily function. In this comparison both were quantified as logarithms (logMAR and log(s)). [source] 4241: Optical characterization of PCOACTA OPHTHALMOLOGICA, Issue 2010TJTP VAN DEN BERG Purpose Opacification of the posterior capsule (PCO) is known to degrade visual function on both counts: small angle resolution (visual acuity and contrast sensitivity) as well as large angle light scatter (straylight). No studies have been performed to delineate the optical characteristics of PCO as a basis for explanation of these visual function defects. Methods Preparations of IOL-capsule combinations were harvested from donor eyes after removal of the cornea. They were mounted submersed in saline in an optical set-up, used earlier to characterize the optics of the crystalline lens (van den Berg et al. VR 1999). Illuminated by monochromatic beams of light, the light spreading originating from different areas of the preparation was measured as function of wavelength for different angles. Based on physical optics theory, the optical characteristics of PCO was derived. The data will be presented translated into the straylight parameter, directly comparable to the figures obtained in vivo using the clinical straylight meter (C-Quant from Oculus). Results Twenty successful preparations were harvested with at least some PCO areas. PCO grades varied from severe to slight. Two physically different types of light spreading could be discriminated. One type corresponding to pearl-like appearance, characterized by little wavelenght dependence and smal angle dominance. The other type corresponding to diffuse scatter, characterized by strong wavelength dependence and large angle dominance. The scatter values measured corresponded to clinical measures of straylight in PCO patients using the C-Quant. Conclusion The light scattering characteristics of PCO show two types of optical disturbance: a refractile type, probably dominated by pearl-like structures, and a diffuse type of scattering of yet unclear origin. [source] 2334: The challenge of interpreting the histomorphology of human fetal lensesACTA OPHTHALMOLOGICA, Issue 2010KU LOEFFLER Purpose On histology, the crystalline lens is , especially in fetal and infant eyes - an organ susceptible to numerous artifacts. Nevertheless, evaluation of the lens is often of paramount importance in the classification of fetal syndromes or forensic questions. Thus, the aim of our study is to evaluate various factors that might have an impact on lens histomorphology. Methods Our collection of eyes by now comprises more than 500 specimens from fetuses with a gestational age between 8 and 38 weeks, including a variety of syndroms. Apart from induced fetocid, death occured due to spontaneous abortion or post-natally. Specimens were fixed in formalin, and in selected cases one eye was put into Karnovsky's solution for comparison. All systemic findings as well as data related to the termination procedure were recorded. - Some individual cases shall be presented to demonstrate the variability of histopathologic findings. Results Most of the eyes revealed lens features different from the descriptions available in textbooks. At all ages, there were various morphologic changes particularly of the subcapsular cortex, compatible with cataractous lenses in the adult, while the well-known phenomenon of an indentation at the posterior pole was seen especially in older fetuses. The difference in fixatives had only a moderate impact on structural alterations. Conclusion Alterations in fetal lens morphology are extremely frequent and variable. These can be due to delayed fixation, cutting artifacts and other variables and have to be carefully taken into account particularly when interpreting post-mortem findings. The diagnosis of a fetal cataract should therefore only be made with great caution and not without a careful macroscopic evaluation. [source] The crystalline lens higher fatty acids influence on the lens physical characteristicsACTA OPHTHALMOLOGICA, Issue 2009Y KUDRYAVTSEVA Purpose To study influence lipids of a crystalline lens on its physical characteristics. Methods 114 patients at the age from 55 till 78 years, with a cataract of various degree of a maturity are selected. Researches of a lens nucleus in vitro included: definition of mechanical hardness on the original device for research of mechanical hardness of a crystalline lens, research of composition of the higher fatty acids on the gas-liquid chromatograph. Results Influence of the higher fatty acids composition on mechanical hardness of a lens nucleus is revealed. Strong direct dependence between polyunsaturated fatty acids contents and hardness of a crystalline lens is found out. The correlation factor is equal 0.7 (? <0.05). Pentadecanic and stearic acids - the saturated fat acids have average correlation with hardness of lens - the correlation factor is accordingly equal -0.6 (? <0.05) and -0.6 (? <0.05), in spite of low contents in the lens. The palmitic acid contains in the cataract lens in concentration comparable to level polyunsaturated fatty acids, however, essential correlation with hardness has no - the correlation factor is equal 0.21 (p >0.05). The oleic, linolic and linolenic acids are contained in the cataract lens in low concentration and have average (v and linolic acids) - the correlation factor is accordingly equal -0.5 (? <0.05) and -0.57 (? <0.05) and weak correlation (linolenic acid) with hardness of a crystalline lens - the correlation factor is equal -0.22 (p> 0.05). Conclusion The polyunsaturated higher fatty acids which are a basis of membranes of a crystalline lens have the maximal influence on mechanical characteristics of the lens. [source] Hardness of a crystalline lens and accommodationACTA OPHTHALMOLOGICA, Issue 2009A CHUPROV Purpose to estimate influence of mechanical characteristics of a crystalline lens on accommodation possibility Methods At 56 patients with a various condition of a crystalline lens we defined amplitude of accommodation by a method of finding of the nearest and far points. Mechanical properties of a crystalline lens defined by the original ultrasonic method. At the heart of a method, use of the information which formed at distribution of a mechanical wave in non-uniform environments. Results We revealed the strong inverse negative relationship between volume of accommodation and hardness of a crystalline lens nucleus - the factor of correlation was equal -0,63 (? <0,01). Conclusion One of the reasons of the accommodation worsening is the increase of a crystalline lens mechanical hardness [source] Pre-receptoral spectral absorption, healthy ageing and pre-clinical indications of retinal diseaseACTA OPHTHALMOLOGICA, Issue 2009E KONSTANTAKOPOULOU Purpose The aim of this study was to investigate how chromatic sensitivity changes as a function of age and to establish the extent to which such changes can be attributed to pre-receptoral spectral absorption of short wavelength light and/or changes in retinal mechanisms caused by ageing. Methods The absorption of blue light by the macular pigment (MP) and the crystalline lens and the subjects' sensitivity to rapid flicker were measured using the Macula Assessment Profile (MAP) test. Red-green (RG) and yellow blue (YB) chromatic detection thresholds were measured at the fovea for young and older subjects using the Colour Assessment and Diagnosis (CAD) test at 2.6, 26 and 65 cd/m2. The variables of interest included the spectral absorption of the lens, the optical density of the MP, subject's age and retinal illuminance. Results The absorption of blue light by the lens increased with age. Absorption of blue light by pre-receptoral filters did not affect RG chromatic sensitivity at any of the light levels investigated but had an effect on YB thresholds. The considerably higher colour vision thresholds of some subjects and the subsequent worsening of their chromatic sensitivity at the lower light level may reflect changes in the retina brought about by accelerated aging effects. Conclusion The effect of pre-receptoral absorption of blue light on chromatic sensitivity is small. Ageing affects the amount and spectral composition of the light reaching the photoreceptors and the processing of retinal signals. As a result, flicker sensitivity declines and colour vision deteriorates. Such effects arise mostly from changes in the retina. The MAP and CAD tests help us to detect the effects of accelerated ageing and retinal disease. [source] Comparison of anterior chamber depth measurements taken with the Pentacam, Orbscan IIz and IOLMaster in myopic and emmetropic eyesACTA OPHTHALMOLOGICA, Issue 4 2009Canan Asli Utine Abstract. Purpose:, This study determined to assess the degree of agreement between anterior chamber depth (ACD) measurements obtained using three different devices and to analyse the relationship between ACD and spherical equivalent (SE) refraction. Methods:, In this cross-sectional study, 42 eyes of 42 patients with a mean SE of , 4.69 ± 4.61 D (range 0.00 D to , 14.88 D) were analysed. Measurements of ACD between the corneal epithelium and the anterior surface of the crystalline lens, obtained using the Pentacam, Orbscan IIz and IOLMaster, were compared. The relationships between SE and ACD measurements obtained with different devices were also investigated. The results were analysed using Bland,Altman analyses, single-sample t -test and Pearson's correlation test. Results:, Orbscan ACD measurements were an average of 0.05 mm less than Pentacam measurements (p = 0.01). IOLMaster measurements were an average of 0.06 mm less than Orbscan measurements (p < 0.001). None of the ACD values measured by any of the devices were correlated with increasing SE (p > 0.05 for all). There was a weak positive correlation between SE and the difference in ACD measurements with Pentacam and Orbscan (p = 0.04); however, the differences between Pentacam and IOLMaster ACD measurements and Orbscan and IOLMaster ACD measurements seemed to be independent of SE (p = 0.17 and p = 0.54, respectively). Conclusions:, The ACD in clinically normal eyes is measured differently by various non-ultrasonic devices. However, the observed mean error between these modalities is too small to create any noticeable difference in refractive outcome. No significant relationship was found between SE and ACD measurements obtained by Pentacam, Orbscan or IOLMaster. [source] The analysis of fundus autofluorescence patterns in retinal diseasesACTA OPHTHALMOLOGICA, Issue 2007P POPOVIC Purpose: Fundus autofluorescence (AF) imaging is a method that shows accumulation of lipofuscin in the retinal pigment epithelium cells in vivo. Fundus AF may be recorded in retinal diseases either by scanning laser ophthalmoscope or by fundus camera using the appropriate filter. The aim of this study was to analyze the AF pattern by both methods. Methods: 20 patients with different retinal diseases including retinitis pigmentosa, cone-rod dystrophy, Stargardt disease, Best macular dystrophy, central serous retinopathy and age-related macular degeneration were included in the study. AF images were obtained from each subject using a confocal scanning laser ophthalmosope and digital fundus camera. The distribution and amount of AF were compared by the use of both systems. Results: In all disease entities both instruments showed distinct pattern of AF typical for the disease. Areas of high intensity of AF recorded with HRA matched to areas of increased intensity of AF detected with fundus camera. The distribution of areas of low or absent AF also corresponded well in both systems. Images taken with conventional fundus camera were in general lower contrasted and therefore less sharp. This was particularly true for patients with even mild media opacity. The advantage of fundus camera was however a recording of AF of a greater field of view. Conclusions: AF imaging is a very useful noninvasive method for detecting RPE abnormalities. In clinical practice, when scanning laser ophthalmoscope for recording of AF is not available, conventional digital fundus camera can be used for screening of patients suspected to have retinal disease. Care should be taken in patients with nuclear cataract, as the AF image is influenced by the AF of the crystalline lens by a great amount. [source] Marius Tscherning (1854,1939): his life and work in optical physiologyACTA OPHTHALMOLOGICA, Issue 5 2004Mogens Norn Abstract. Background:,This article is based on Tscherning's papers, scientific protocols and letters and the many original instruments kept in the Medical History Museum in Copenhagen, Denmark. History:,In 1884, after his thesis concerning the frequency of myopia in Denmark, Tscherning became adjunct director of the ophthalmological laboratory at the Sorbonne University in Paris. He was called back to Denmark in 1910 and appointed professor of ophthalmology and head of the Eye Department, Rigshospitalet. He continued to work scientifically as emeritus from 1925. Achievements:,Tscherning published about 100 scientific papers, mainly concerning optical physiology (i.e. the aetiology of myopia, entoptic phenomena, Purkinje pictures, the polygonal pattern provoked by corneal rubbing, etc.). He studied the law of Listing and projections depending on torsion of the eye and invented the ophthalmophacometer, which measures the changes that occur in the front and back curvatures of the crystalline lens during accommodation. Tscherning also studied aberration and calculated and constructed forward bulging periscopic (punctal) spectacle lenses. In addition, he studied colour sense, dark vision and adaptation. [source] Post-traumatic Scedosporium inflatum endophthalmitisCLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 1 2002Alexandra Taylor MB BS Abstract This is the first documented case of post-traumatic Scedosporium inflatum endophthalmitis and only the second of S. inflatum endophthalmitis occurring in a non-immunocompromised individual, to the authors' knowledge. A case is reported of a 57-year-old woman who, while chopping wood, had a wood chip hit her in the right eye. This caused a penetrating corneal injury with uveal prolapse and damage to the crystalline lens. There were also vitreous and suprachoroidal haemorrhages. No detectable intraocular foreign material was retained. The clinical manifestation of infection was delayed, but once established, it was very destructive. The initially indolent endophthalmitis eventually led to loss of all light perception and panophthalmitis which required enucleation. The responsible strain of S. inflatum was found to be resistant to all antifungal medication in vitro. [source] | ||||||||||