Properties of fiber cell plasma membranes isolated from the cortex and nucleus of the porcine eye lens

The organization and physical properties of the lipid bilayer portion of intact cortical and nuclear fiber cell plasma membranes isolated from the eye lenses of two-year-old pigs were studied using electron paramagnetic resonance (EPR) spin-labeling. Membrane fluidity, hydrophobicity, and the oxygen transport parameter (OTP) were assessed from the EPR spectra of precisely positioned spin labels. Intact cortical and nuclear membranes, which include membrane proteins, were found to contain three distinct lipid environments. These lipid environments were termed the bulk lipid domain, boundary lipid domain, and trapped lipid domain (lipids in protein aggregates). The amount of boundary and trapped lipids was greater in intact nuclear membranes than in cortical membranes. The properties of intact membranes were compared with the organization and properties of lens lipid membranes made of the total lipid extracts from the lens cortex or nucleus. In cortical lens lipid membranes, only one homogenous environment was detected, which was designated as a bulk lipid domain (phospholipid bilayer saturated with cholesterol). Lens lipid membranes prepared from the lens nucleus possessed two domains, assigned as a bulk lipid domain and a cholesterol bilayer domain (CBD). In intact nuclear membranes, it was difficult to discriminate the CBD, which was clearly detected in nuclear lens lipid membranes, because the OTP measured in the CBD is the same as in the domain formed by trapped lipids. The two domains unique to intact membranes-namely, the domain formed by boundary lipids and the domain formed by trapped lipids-were most likely formed due to the presence of membrane proteins. It is concluded that formation of rigid and practically impermeable domains is enhanced in the lens nucleus, indicating changes in membrane composition that may help to maintain low oxygen concentration in this lens region.     

Effect of vibration on crystalline lens transparency]

It was demonstrated experimentally that the transparency of the eye lenses diminishes under the influence of a prolonged vibration. Investigations were performed in a group of rabbits which were subjected to a long-lasting exposition to mechanical vibration of 10 Hz throughout a period of 5 months. The transparency of the extracted lenses was evaluated by spectrophotometry and compared with lenses of 2 control groups. Group 1 consisted of rabbits which in the same period of 5 months were subjected to a continuous neon illumination of 1200 lx intensity as a cataractogenous factor. A second comparative group consisted of rabbits not exposed to any external factor. The authors detected a statistically significant decrease of transparency of lenses of the examined group in reference towards the second comparative group, it was however smaller than in the 1-st group.     

Manipulation of extraocular muscle afference has no effect on higher order perceptual judgments

Observers perceive targets as farther while performing the Jendrassik Maneuver (JM) suggesting that eye position is registered as more divergent. We examined the effects of the JM perturbation in three studies of perceptual judgment that rely on accurate registration of absolute distance: size constancy, stereoscopic depth, and the magnitude of the Pulfrich illusion. The data showed no significant differences between the JM and control conditions. The lack of an effect may be due to the fact that vergence is not a perfect cue to distance. Furthermore, the relative contribution of extraocular muscle afference to registered eye position may be less significant for higher order perceptual judgments.     

Changes in the refractive index of lens fibre membranes during maturation--impact on lens transparency

PURPOSE: Local variations in refractive index are the physical cause of light scattering in a material or tissue and also induce phase changes of propagating light waves. The goal of this study was to analyse local differences in refractive index by phase contrast microscopy of sections of human lenses. METHODS: Refractive index was estimated by immersion refractometry. Cryo-sections of quick-frozen human donor lenses were embedded in a graded series of bovine serum albumin solutions, and in immersion oil, ranging in refractive index from 1.34 to 1.52. RESULTS: Fibre membranes in the lens cortex prove to have a refractive index considerably above that of fibre cytoplasm at the same location. Fibre membranes in the lens nucleus have a refractive index approximately the same as that of fibre cytoplasm at the same location. CONCLUSION: In the lens cortex, transparency is obtained by a high spatial order of the lens fibre lattice to compensate for the light scattering caused by differences in refractive index between fibre membranes and cytoplasm. In the lens nucleus, high spatial order is less important, because the minor differences in the refractive index between fibre membranes and fibre cytoplasm lead only to minimal scattering.     

Effect of aspirin and vitamin E on phase separation in calf lens homogenate

Vitamin E (d-alpha-tocopherol) and aspirin were evaluated for their effects on the phase separation temperature, Tc, of calf lens cytoplasm. Vitamin E and aspirin were added to nuclear homogenate and the change in Tc was measured. Aspirin had no measurable effect on Tc. Vitamin E lowered Tc at a rate of -22 degrees C M-1 l-1. The results suggest that the effects of aspirin on cataract are unrelated to phase separation and that vitamin E may act on the phase separation in precataractous lens cells.     

Generation of transparency and cellular organization in lens explants

The lens grows via the proliferation and differentiation of lens epithelial cells into lens fibres. This differentiation process, thought to be controlled by factors present in the vitreous fluid, generates tightly-packed, parallel-aligned fibre cells that confer transparency to the lens. Using lens epithelial-cell explants we examined how explant orientation and growth factor treatment can affect cellular arrangement and explant transparency. Fibre cell differentiation was induced in lens explants by culturing cells with fibroblast growth factor (FGF) or bovine vitreous. Cell shape and arrangement was investigated using confocal microscopy, electron microscopy, immunofluorescence and in situ hybridization. Explant transparency was measured using light microscopy. Confocal microscopy demonstrated that explant orientation determined cellular arrangement, irrespective of the differentiation stimuli used. In explants where epithelial cells were confined between their normal basement membrane (the lens capsule) and the base of the culture dish, the cells became elongated, thin and parallel-aligned. In contrast, in explants cultured with cells directly exposed to the culture media the cells appeared to be shorter, globular and haphazardly arranged. FGF initiated the differentiation of most lens epithelial cells; however, abnormal cellular morphologies developed with subsequent culture of the cells. As a result, the transparency of these explants decreased with prolonged culture. Interestingly, explants cultured with vitreous (i) did not develop abnormal cellular morphologies, (ii) contained two distinct cell types (retained epithelial cells and newly differentiated fibre cells) and (iii) remained transparent throughout the lengthy culture period. In summary, we have developed a culture system that generates a transparent tissue with a cellular arrangement resembling that of the lens in vivo. We have shown that while FGF and vitreous initiate differentiation within this system, better maintenance of fibre cell integrity, more appropriate regulation of molecular events, and better maintenance of explant transparency was achieved in the presence of vitreous. This system offers an opportunity to further investigate the process of lens fibre cell differentiation as well as a means of better identifying the factors that contribute to the development of tissue transparency in vitro.     

The influence of sodium-calcium exchange inhibitors on rabbit lens ion balance and transparency

Calcium regulation is essential to the maintenance of lens transparency. To maintain cytoplasmic calcium concentration at the required low level the lens must export calcium continuously. Here, studies were conducted to test whether sodium-calcium exchanger (NCX) inhibitors disturb calcium balance in the rabbit lens. Intact lenses were incubated up to 48 h in the presence or absence of the NCX inhibitor bepridil. Lens sodium, potassium and calcium content were determined by atomic absorption spectrophotometry. Fluo-4 was used to measure epithelial cell cytoplasmic calcium concentration in an intact lens preparation. NCX1 protein expression in lens epithelium was examined by western blot. NCX1 band density was similar in central and equatorial epithelium samples. Lenses exposed to bepridil (30 microM) lost transparency at the anterior and exhibited significant changes in electrolyte and water content. After 48 h, lens calcium content more than doubled, sodium increased four fold and potassium was significantly reduced. In contrast, lenses exposed to inhibitors of reverse mode calcium transport by NCX (KBR7943 or SN-6) remained transparent and the electrolyte and water content of the lens remained unchanged. The ability of bepridil to cause significant changes in lens transparency and electrolyte content points to an important role for NCX-meditated calcium export in the lens.     

Investigations on lens transparency and its disturbances by microdensitometric analyses of Scheimpflug photographs

During the aging process, the lens is subjected to changes of its pertinent properties which condition the transmission of light of different wavelengths. Between the second and the third decade, for instance, wavelengths below 400 nm are almost completely absorbed. The increase in lens thickness, effected by the appositional growth during life, might be considered responsible for this phenomenon, if the newly developing lens fibers in the outer periphery would synthesize proteins which, with respect to light transmission, differ from those formed during the embryonic phase. For such a phenomenon, however, no indication was found either by clinical observations or biochemical research. -Microdensitometric analysis of Scheimpflug-photographs of the anterior eye segment allows measurements of lens transparency in the single lens which directly depend on the respective wavelengths used in the photographic procedure. Investigations performed with this method on a normal age-grouped population, show that the changes in light transmission are most evident in two of the lens segments. The lens nucleus shows a continuous increase in light scatter during aging. Also the anterior cortex - particularly in the deeper layers - shows changes in light transmission. With advancing age (beginning between 30 and 40 years of age), increased lens fluorescence is found in the region of the deeper anterior cortex, which can be excited by UV wavelengths of 330-380 nm. This phenomenon is not found in the lens nucleus. The localization of the changes within the lens clearly shows that they are due to age-related modifications of the protein properties earlier designated as posttranslational or postsynthetic molecular modifications.(ABSTRACT TRUNCATED AT 250 WORDS)     

Investigation of the effect of simulated lens yellowing, transparency loss and refractive error on in vivo resonance Raman spectroscopy

PURPOSE: To separately investigate the impact of simulated age-related lens yellowing, transparency loss and refractive error on measurements of macular pigment (MP) using resonance Raman spectroscopy. METHODS: Two healthy young subjects with clear media underwent Raman spectroscopy under the following conditions: age-related lens yellowing was simulated using seven broad-band yellow filters with transmittance at 488 nm ranging from 0.54 to 0.90; cataract was simulated using five white filters of increasing opacity (scatter filters), the transmittance of which ranged from 0.42 to 0.86, each of which reduced peak contrast sensitivity by approximately 0.1 log units over the previous filter. Refractive error up to +6.25 D was achieved using soft contact lenses. RESULTS: The Raman signal declined steadily to an average value of 43% of the starting value with the densest yellow filter in place. The white scatter filters produced a progressive linear reduction in signal resulting in almost complete signal loss with the densest filter. Refractive error resulted in an initial slight improvement in Raman count up to a value of +2.00 D followed by a decline thereafter. CONCLUSIONS: These results imply that lens yellowing and increasing scatter has an influence on the Raman signal and suggest that studies using this technology to estimate MP levels in older populations should carefully account for the status of the lens.     

丙烯酸酯人工晶状体囊袋内稳定性和囊膜透明性观察

目的 用Pentacam三维眼前节分析系统测量研究一片式软襻与三片式硬襻两种丙烯酸酯折叠型人工晶状体(IOL)在囊袋内的稳定性和囊膜的透明性.方法 采用前瞻性研究,对51例双眼年龄相关性白内障患者行超声乳化白内障吸除联合IOL植入术,一只眼植入一片式软襻折叠型丙烯酸酯IOL SA60AT,对侧眼植入三片式硬襻折叠型丙烯酸酯IOL MA60BM.采用Pentacam三维眼前节分析系统测量术后1 d和1、6、12及24个月时IOL的偏心值、倾斜度、前房深度值以及晶状体后囊膜的光密度值.对所得数据两组之间比较采用配对t检验,组内不同时间点之间的比较采用重复测量资料方差分析.结果 分别比较一片式SA60AT组在不同时期的偏心值(0.37±0.16,0.36±0.15,0.36±0.16,0.37±0.15,0.38±0.16)、倾斜度(3.59±0.91,3.64±0.92,3.61±0.90,3.63±0.90,3.70±0.89)与后囊膜光密度值(22.20±3.99,21.96±4.00,22.40±4.03,22.53±4.00,22.95±3.87),差异均无统计学意义(F=1.938,0.785,1.814;P＞0.05);比较三片式MA60BM组在不同时期的偏心值(0.34±0.14,0.33±0.14,0.34±0.14,0.35±0.14,0.36±0.14)、倾斜度(3.55±0.90,3.57±0.92,3.63±0.88,3.61±0.88,3.65±0.89),与后囊膜光密度值(21.14±3.88,20.98±3.87,21.23±3.83,21.59±3.82,21.65±3.87),差异均无统计学意义(F=1.004,0.525,1.963;P＞0.05).在术后1 d和1、6、12及24个月,分别比较两组IOL的平均偏心值(t=0.802,0.701,0.588,0.898,0.631)、平均倾斜度(t=0.199,0.337,0.094,0.121,0.248)与后囊膜光密度值(t=1.214,1.119,1.334,1.082,1.517),差异均无统计学意义(P＞0.05).一片式SA60AT组在不同时期的前房深度变化不大(3.90±0.99,3.88±1.07,3.91±1.01,3.90±1.02,3.92±1.02),差异无统计学意义(F=1.333,P＞0.05);而三片式MA60BM组术后第1天的前房深度(4.37±1.02,3.90±0.98,3.95±0.99,3.93±0.96,3.97±0.99)大于术后其他时期(F=92.757,P＜0.05),也大于一片式SA60AT组术后不同时期的值,差异有统计学意义(t=102.944,P＜0.05).结论 一片式软襻与三片式硬襻两种丙烯酸酯IOL都有着良好的囊袋内稳定性和囊膜透明性.但在术后早期,前者的眼内稳定性要好于后者.

Abstract：

Objective To compare the amounts of intraocular lens (IOL) decentration and tilt, the anterior chamber depth (ACD) and the degree of posterior capsule opacification (PCO) using the Pentacam Scheimpflug System after cataract surgery between eyes with 1-piece acrylic IOL and 3-piece acrylic IOL Methods It was a perspective study. Fifty-one patients with bilateral senile cataract had implantation of a 1-piece SA60AT IOL in one eye and a 3-piece MA60BM IOL in the contralateral eye. The amount of IOL decentration, tilt, the ACD, and the degree of PCO was measured using the Pentacam Scheimpflug System 1 day and 1,6, 12 and 24 months postoperatively. Results There were no significant changes during the 24 m follow-up period in the decentration ( 0. 37 ± 0. 16, 0. 36 ± 0. 15, 0. 36 ± 0. 16, 0. 37 ± 0. 15,0. 38 ± 0. 16), tilt (3.59±0.91,3.64 ±0.92,3.61 ±0.90,3.63 ±0.90,3.70 ±0. 89)or PCO(22. 20 ±3.99,21.96 ±4. 00,22.40 ± 4. 03,22. 53 ± 4. 00,22. 95 ± 3. 87 ) in the 1 -piece SA60AT group ( F = 1. 938,0. 785,1. 814;P ＞ 0. 05 ) or in the 3-piece MA60BM group (0. 34 ± 0. 14,0. 33 ± 0. 14,0. 34 ± 0. 14,0.35±0.14,0.36 ±0.14),(3.55 ±0.90,3.57 ±0.92,3.63 ±0.88,3.61 ±0.88,3.65 ±0.89),(21.14 ±3.88,20. 98 ±3. 87,21.23 ±3. 83,21.59 ±3. 82,21.65 ±3. 87) (F = 1. 004,0. 525,1. 963;P ＞0. 05). There was no significant difference between the two groups in IOL decentration (t = 0. 802,0. 701,0.588,0. 898,0.631), tilt (t =0. 199,0.337,0.094,0. 121,0.248) or PCO(t = 1.214,1. 119,1.334,1. 082,1. 517)at any time points (P ＞ 0. 05 ). The ACD did not change after the surgery in the 1-piece group (3.90 ±0. 99,3.88 ± 1.07,3.91 ± 1.01,3.90 ± 1.02,3.92 ± 1.02) (F= 1. 333,P ＞0. 05) but was significantly deeper in the 3-piece group ( 4. 37 ± 1.02,3.90 ± 0. 98,3.95 ± 0. 99,3.93 ± 0. 96,3.97 ± 0. 99 ) ( F = 92. 757, P ＜ 0. 05 ) one day after the operation. The ACD was more shallow in the 1-piece SA60AT group than in the 3-piece MA60BM group at all time points. However, the difference was statistically significant only at 1 day after surgery ( t = 102. 944, P ＜ 0. 05 ). Conclusions The degrees of IOL decentration, tilt, ACD and PCO in eyes with a 1-piece acrylic IOL with flexible haptics implanted in the capsular bag were similar to those in eyes with a 3-piece acrylic IOL with rigid PMMA haptics. But the 1 -piece acrylic IOL provides a better stability than the 3-piece acrylic IOL in the early stage postoperatively.     

丙烯酸酯人工晶状体囊袋内稳定性和囊膜透明性观察

Objective To compare the amounts of intraocular lens (IOL) decentration and tilt, the anterior chamber depth (ACD) and the degree of posterior capsule opacification (PCO) using the Pentacam Scheimpflug System after cataract surgery between eyes with 1-piece acrylic IOL and 3-piece acrylic IOL Methods It was a perspective study. Fifty-one patients with bilateral senile cataract had implantation of a 1-piece SA60AT IOL in one eye and a 3-piece MA60BM IOL in the contralateral eye. The amount of IOL decentration, tilt, the ACD, and the degree of PCO was measured using the Pentacam Scheimpflug System 1 day and 1,6, 12 and 24 months postoperatively. Results There were no significant changes during the 24 m follow-up period in the decentration ( 0. 37 ± 0. 16, 0. 36 ± 0. 15, 0. 36 ± 0. 16, 0. 37 ± 0. 15,0. 38 ± 0. 16), tilt (3.59±0.91,3.64 ±0.92,3.61 ±0.90,3.63 ±0.90,3.70 ±0. 89)or PCO(22. 20 ±3.99,21.96 ±4. 00,22.40 ± 4. 03,22. 53 ± 4. 00,22. 95 ± 3. 87 ) in the 1 -piece SA60AT group ( F = 1. 938,0. 785,1. 814;P ＞ 0. 05 ) or in the 3-piece MA60BM group (0. 34 ± 0. 14,0. 33 ± 0. 14,0. 34 ± 0. 14,0.35±0.14,0.36 ±0.14),(3.55 ±0.90,3.57 ±0.92,3.63 ±0.88,3.61 ±0.88,3.65 ±0.89),(21.14 ±3.88,20. 98 ±3. 87,21.23 ±3. 83,21.59 ±3. 82,21.65 ±3. 87) (F = 1. 004,0. 525,1. 963;P ＞0. 05). There was no significant difference between the two groups in IOL decentration (t = 0. 802,0. 701,0.588,0. 898,0.631), tilt (t =0. 199,0.337,0.094,0. 121,0.248) or PCO(t = 1.214,1. 119,1.334,1. 082,1. 517)at any time points (P ＞ 0. 05 ). The ACD did not change after the surgery in the 1-piece group (3.90 ±0. 99,3.88 ± 1.07,3.91 ± 1.01,3.90 ± 1.02,3.92 ± 1.02) (F= 1. 333,P ＞0. 05) but was significantly deeper in the 3-piece group ( 4. 37 ± 1.02,3.90 ± 0. 98,3.95 ± 0. 99,3.93 ± 0. 96,3.97 ± 0. 99 ) ( F = 92. 757, P ＜ 0. 05 ) one day after the operation. The ACD was more shallow in the 1-piece SA60AT group than in the 3-piece MA60BM group at all time points. However, the difference was statistically significant only at 1 day after surgery ( t = 102. 944, P ＜ 0. 05 ). Conclusions The degrees of IOL decentration, tilt, ACD and PCO in eyes with a 1-piece acrylic IOL with flexible haptics implanted in the capsular bag were similar to those in eyes with a 3-piece acrylic IOL with rigid PMMA haptics. But the 1 -piece acrylic IOL provides a better stability than the 3-piece acrylic IOL in the early stage postoperatively.     

丙烯酸酯人工晶状体囊袋内稳定性和囊膜透明性观察

Objective To compare the amounts of intraocular lens (IOL) decentration and tilt, the anterior chamber depth (ACD) and the degree of posterior capsule opacification (PCO) using the Pentacam Scheimpflug System after cataract surgery between eyes with 1-piece acrylic IOL and 3-piece acrylic IOL Methods It was a perspective study. Fifty-one patients with bilateral senile cataract had implantation of a 1-piece SA60AT IOL in one eye and a 3-piece MA60BM IOL in the contralateral eye. The amount of IOL decentration, tilt, the ACD, and the degree of PCO was measured using the Pentacam Scheimpflug System 1 day and 1,6, 12 and 24 months postoperatively. Results There were no significant changes during the 24 m follow-up period in the decentration ( 0. 37 ± 0. 16, 0. 36 ± 0. 15, 0. 36 ± 0. 16, 0. 37 ± 0. 15,0. 38 ± 0. 16), tilt (3.59±0.91,3.64 ±0.92,3.61 ±0.90,3.63 ±0.90,3.70 ±0. 89)or PCO(22. 20 ±3.99,21.96 ±4. 00,22.40 ± 4. 03,22. 53 ± 4. 00,22. 95 ± 3. 87 ) in the 1 -piece SA60AT group ( F = 1. 938,0. 785,1. 814;P ＞ 0. 05 ) or in the 3-piece MA60BM group (0. 34 ± 0. 14,0. 33 ± 0. 14,0. 34 ± 0. 14,0.35±0.14,0.36 ±0.14),(3.55 ±0.90,3.57 ±0.92,3.63 ±0.88,3.61 ±0.88,3.65 ±0.89),(21.14 ±3.88,20. 98 ±3. 87,21.23 ±3. 83,21.59 ±3. 82,21.65 ±3. 87) (F = 1. 004,0. 525,1. 963;P ＞0. 05). There was no significant difference between the two groups in IOL decentration (t = 0. 802,0. 701,0.588,0. 898,0.631), tilt (t =0. 199,0.337,0.094,0. 121,0.248) or PCO(t = 1.214,1. 119,1.334,1. 082,1. 517)at any time points (P ＞ 0. 05 ). The ACD did not change after the surgery in the 1-piece group (3.90 ±0. 99,3.88 ± 1.07,3.91 ± 1.01,3.90 ± 1.02,3.92 ± 1.02) (F= 1. 333,P ＞0. 05) but was significantly deeper in the 3-piece group ( 4. 37 ± 1.02,3.90 ± 0. 98,3.95 ± 0. 99,3.93 ± 0. 96,3.97 ± 0. 99 ) ( F = 92. 757, P ＜ 0. 05 ) one day after the operation. The ACD was more shallow in the 1-piece SA60AT group than in the 3-piece MA60BM group at all time points. However, the difference was statistically significant only at 1 day after surgery ( t = 102. 944, P ＜ 0. 05 ). Conclusions The degrees of IOL decentration, tilt, ACD and PCO in eyes with a 1-piece acrylic IOL with flexible haptics implanted in the capsular bag were similar to those in eyes with a 3-piece acrylic IOL with rigid PMMA haptics. But the 1 -piece acrylic IOL provides a better stability than the 3-piece acrylic IOL in the early stage postoperatively.