Changes In Lens Transparency Research Articles

Eph-ephrin Signaling Affects Eye Lens Fiber Cell Intracellular Voltage and Membrane Conductance.

The avascular eye lens generates its own microcirculation that is required for maintaining lifelong lens transparency. The microcirculation relies on sodium ion flux, an extensive network of gap junction (GJ) plaques between lens fiber cells and transmembrane water channels. Disruption of connexin proteins, the building blocks of GJs, or aquaporins, which make up water and adhesion channels, lead to lens opacification or cataracts. Recent studies have revealed that disruption of Eph-ephrin signaling, in particular the receptor EphA2 and the ligand ephrin-A5, in humans and mice lead to congenital and age-related cataracts. We investigated whether changes in lens transparency in EphA2 or ephrin-A5 knockout (–/–) mice is related to changes in GJ coupling and lens fluid and ion homeostasis. Immunostaining revealed changes in connexin 50 (Cx50) subcellular localization in EphA2–/– peripheral lens fibers and alteration in aquaporin 0 (Aqp0) staining patterns in ephrin-A5–/– and EphA2–/– inner mature fiber cells. Surprisingly, there was no obvious change in GJ coupling in knockout lenses. However, there were changes in fiber cell membrane conductance and intracellular voltage in knockout lenses from 3-month-old mice. These knockout lenses displayed decreased conductance of mature fiber membranes and were hyperpolarized compared to control lenses. This is the first demonstration that the membrane conductance of lens fibers can be regulated. Together these data suggest that EphA2 may be needed for normal Cx50 localization to the cell membrane and that conductance of lens fiber cells requires normal Eph-ephrin signaling and water channel localization.

Radiation effects on light scattering and cataract formation in the lenses of interventional radiologist and cardiologists

AbstractPurpose There is little information about exposure to dosages below 500 mSv. This pilot study aimed at investigating the effects of low dose radiation on lens transparency in occupationally exposed interventional cardiologists and radiologists.Methods Physicians who have performed fluoroscopically guided procedures for at least 5 years were recruited in the areas of Cologne‐Bonn and Rhine‐Main together with their non‐exposed colleagues. A questionnaire has been developed to estimate occupational exposure. Exclusion criteria comprised corticosteroid treatment, radiotherapy, chemotherapy and glaucoma. Changes in lens transparency and cataract formation were determined by slit lamp microscopy including LOCS III grading, slit lamp photography and Scheimpflug/Pentacam® imaging.Results The prevalence of lens opacification mainly found in the nuclear region was 52% (95% CI: 30‐74%) among interventional physicians and 31% (95% CI: 9‐61%) among their non‐exposed colleagues. Densitometric analysis of the cornea demonstrated a mean value 52,8% (SD: 7,4) in exposed participants compared to 45,9 % (SD: 7,2) in non‐exposed colleagues. In the lenses layers 4 (deep cortex) and 5 (supra‐nuclear layer) evidenced higher mean densities (40,5% (SD: 3,9%) vs. 31,6% (SD: 6,9%) in layer 4 and 27,5% (SD: 1,9%) vs. 23,7% (SD: 4,3%) in layer 5).Conclusion The data from the ophthalmological examinations demonstrated generally normal findings. However, classification of the mostly small cataracts and densitometric analysis of cornea and lens evidenced that low dosage exposure to ionizing radiation has an effect on corneal and lenticular transparency, albeit on a subclinical level.

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 μM) 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.

Mechanistic Analysis ofS-(1,2-Dichlorovinyl)-l-cysteine-Induced Cataractogenesisin Vitro

Chronic exposure to low concentrations of the nephrotoxic cysteine conjugateS-(1,2-dichlorovinyl)-l-cysteine (DCVC) causes cataracts in mice. This study explored mechanisms of DCVC-induced cataractogenesis using explanted lenses from male Sprague–Dawley rats. Lenses placed in organ culture were exposed to 2.5 μm–1 mmDCVC for 24 hr. DCVC caused concentration and time-dependent changes in biochemical markers of toxicity (lenticular adenosine 5′-triphosphate (ATP) content, mitochondrial reduction of the tetrazolium dye MTT, and glutathione (GSH) content) at concentrations ≥25 μm. Lens clarity was adversely affected at concentrations ≥50 μm. Within 24 hr, 1 mmDCVC altered lens ATP content (−77 ± 2%), mitochondrial MTT reduction (−40 ± 3%), and GSH content (−19 ± 4%) (percent difference from controls,p< 0.05). ATP was the most sensitive index of DCVC exposure in this model, while lens weight was not altered. The role of lenticular DCVC metabolism was investigated using the β-lyase inhibitor aminooxyacetic acid (AOA) and the flavin monooxygenase (FMO) inhibitor methimazole (MAZ). AOA (1 mm) provided nearly complete protection from changes in biochemical parameters and lens transparency caused by DCVC, while MAZ (1 mm) provided only partial protection. The mitochondrial Ca2+uniport inhibitor ruthenium red (30 μm) and the poly(ADP ribosyl)transferase inhibitor 3-aminobenzamide (3 mm) were only partially protective, whereas adverse changes in lens transparency and biochemical markers were not prevented by an antioxidant (2 mmdithiothreitol) or nontoxic transport substrates (200 μmprobenecid or 10 mmphenylalanine,S-benzyl-l-cysteine orpara-aminohippuric acid). Calpain inhibitors E64d (100 μm) and calpain inhibitor II (1 mm) were ineffective in preventing opacity formation caused by DCVC. In a small separate study, DCVC toxicity to explanted lenses from cynomologus monkeys was also ameliorated by coincubation with AOA. These results indicate that opacity formation by DCVC in rodent and primate lensesin vitrois primarily mediated via lenticular β-lyase metabolism of DCVC to a reactive metabolite. Metabolism of DCVC by FMO and perturbations in mitochondrial calcium (Ca2+) homeostasis and increased poly(ADP-ribosylation) of nuclear proteins may play a limited role in opacity formationin vitro.However, opacity formation does not appear to be the result of oxidative stress or calpain activation. DCVC toxicity to the lens was not blocked with competitive inhibitors of the amino acid and organic anion transporters of DCVC as is found in the kidney.

Free amino acids reflect impact of selenite-dependent stress on primary metabolism in rat lens

PURPOSE. A decrease in phase separation temperature, prior to nuclear cataract, has been correlated with elevated free amino acid content. Hence, we determined how selenite-induced stress alters free amino acid pools in the rat lens, following a single subcutaneous dose of sodium selenite (30 nmol g -1 body weight) in 10- to 14-day-old Sprague Dawley rats. RESULTS. Oxidative stress was evident in lenses 24 h after rats were treated with selenite. Glutathione content was decreased by 60% in the lens cortex and nucleus; the flux of glucose through the pentose phosphate pathway was increased; and glycerol-3-phosphate content was elevated. Amino acid transport, evaluated as 14 C-cycloleucine uptake, was not altered, although 14 C-glutamine was oxidized at a slower rate. Lenses from treated animals displayed, among the free amino acids, increased glutamine, proline, serine, glycine and the branched chain amino acids, while aspartate, glutamate, and taurine were less. CONCLUSIONS. A systemic delivery of sodium selenite caused oxidative stress in the rat lens. Direct effects on primary metabolism altered free amino acid pools that may contribute to transient and permanent changes in lens transparency.

Changes in light scattering intensity of the transparent lenses of subjects selected from population-based surveys depending on age: analysis through Scheimpflug images.

The physiological ageing changes of decreasing lens transparency were objectively evaluated in a total of 1,040 eyes selected from 1,685 individuals who were the subjects of population-based cataract epidemiological surveys performed in three climatically different survey fields in Japan. The lens transparency changes were evaluated from the light scattering intensity on thirteen different lens layers seen in slit images taken by the latest type of Scheimpflug camera. The mean percentage prevalence of cataracts in all the epidemiological survey subjects including grading from I to III, which was also judged objectively through documented images, was 64.6% in the Noto subjects, 46.6% in the Hokkaido subjects and 38.0% in the Okinawa subjects. The lens transparency at all of the measuring points decreased with ageing. The above changes, seen in the lenses of subjects in their 40s to 60s, were obviously more prominent compared with those seen in subjects in their 40s. Although there were some differences in transparency decrease with ageing among the subjects of the three areas, the authors tentatively propose to show the data obtained from the Noto subjects as representative of Japanese individuals. Lens transparency changes on each lens layer showed characteristic ageing changes and those of the representative four layers showed an exponential decrease in transparency. The decreasing ratio might accelerate from age as early as the mid-40s.

Evaluation of Lens Transparency Changes through Photographed Images during a 13-Month Observation Period

Since the development of the anterior eye segment analysis system, several new types of anterior eye segment biometry have been performed. The main aim of this study was to evaluate whether changes in cataractous progression or an increase in lens transparency loss are detectable during a relatively short period of 13 months by measuring the intrapupillary opaque shadow area through retroillumination images or by calculating the light scattering intensity at the deepest cortical layer of the lens through Scheimpflug slit images. Secondly, the relationship between maximally dilated pupil sizes and patients' ages and that between cases with and without diabetes were studied. Thirty-one eyes (49.2%) of sixty-three cataractous lenses showed more than 5% increase in the opaque shadow area. Forty-five eyes (60.0%) showed more than a 5% increase in light scattering intensity. 92.5% of diabetic eyes and 92.3% of nondiabetic eyes showed pupil sizes over 6.5 mm after an instillation of mydriatica. In our study the applied method guaranteed a high reproducibility; thus is might be possible to detect an increase in cataractous changes and lens transparancy in around 50% of examined subjects in a period as short a 1 year. For the evaluation of cataract progression through a retroillumination image, the recommendable pupil size is > or = 6.5 mm.

No Cataract Two Years after Pneumatic Retinopexy

This study was conducted to examine possible adverse effects on lens transparency caused by pneumatic retinopexy using sulfur hexafluoride gas. In a prospective study, both lenses of 33 patients undergoing pneumatic retinopexy in one eye were monitored up to 24 months postoperatively by slit-lamp examination and Scheimpflug photography. Pneumatic retinopexy does not cause significant lens opacifications up to 2 years after surgery. Temporary gas tamponade for pneumatic retinopexy is not associated with permanent changes in lens transparency.

Linsenveränderungen nach pneumatischer Retinopexie: Vorläufige Ergebnisse der lineardensitometrischen Bildanalyse von Scheimpflug-Photographien zwei Monate nach Operation

The small degree of morbidity and a better postoperative visual acuity are the advantages of pneumatic retinopexy in comparison to encircling procedures in the treatment of retinal detachment. The injection of air or gas into the vitreous cavity can theoretically induce a cataract postoperatively. Two months after pneumatic retinopexy (SF6-gas) Scheimpflug photography and microdensitometric evaluation of the negative were performed on 22 pairs of phacic eyes showing changes in the transparency of the lens. The deterioration of transparency in the operated eye was small but higher than that of the non-operated eye. Due to the short follow up period no prognosis is possible as to the future lens transparency changes.

Medical treatment of senile cataract: Clinical investigation of bendazac-lysine using objective and subjective methods

A modified Zeiss slit lamp coupled with a digital image-processing system was used to evaluate objectively changes in lens transparency over 1 year at 4-month intervals in 150 eyes of 92 patients affected by early senile cataract. A total of 59 patients were treated daily with 1.5 g bendazac-lysine, and 33 patients constituted the control group. At follow-up, visual acuity was also tested using Snellen letter charts at variable contrast to provide an additional parameter closer to traditional methods. Results indicate that the minimal angle of resolution at 10% contrast (MAR10) and the mean gray-level value of the lens image obtained by retroillumination (MLR) are sensitive to early changes in lens transparency. Using MAR10 as a parameter, the control group showed a significant, progressive worsening of the lens status over 12 months, whereas the treated group exhibited no significant changes. MRL indicated the same behaviour as MAR10, although lens damage was detected later in the control group. The results show that bendazac-lysine may delay the formation of lens opacities.

Influence of Certain Drugs on the Densitometry Results of Optic Lens Sections in Posterior Subcapsular Cataracts

A clinical follow-up of 157 patients with initial changes in lens transparency demonstrated that the proteolytic drug Lekosim contributes to the restoration of the optic properties, primarily in those cases where opacities are located subcapsularly and parallel to the lens fibers in the surface cortical regions. As regards the combined use of Lekosim and Sencatalin for the treatment of diabetic patients with cataracts, it was found that the former enhanced the effect of the latter. A more pronounced reduction in the optic density of the cortical regions of the lens was observed in the combination treatment with the two drugs as compared with the use of Sencatalin alone.

Reproducibility Studies with the Zeiss SLC System and Animal Cataract Models

Scheimpflug photography has become the basic method for documentation of lens transparency changes in clinical and experimental ophthalmology, due to its high reproducibility. In animal cataract studies, the reproducibility is strongly influenced by the handling characteristics of the camera used, due to limited cooperation of the animal. The reproducibility of the Zeiss SLC system, which offers a direct quality control of the image on the video screen, was tested with 2 animal cataract models, the ultraviolet B (UVB)-induced cataract and the true diabetic cataract in the Brown-Norway rat. 10 rats each of the 2 cataract models and of an untreated control group were photographed in a random order on 3 occasions on the same day by the same photographer. Quality control and densitometry were performed by the same system operator, the measurement window was positioned standardly, coincident with the optical axis of the eye. Statistical comparison was carried out in the capsular layer, that is the area of initial cataract development in both models, and in the cortical layer, into which the diabetic cataract progresses during its later stages of development. The nuclear layer was also evaluated, but has no direct relation to one of the models employed. The results clearly indicate that the reproducibility is predominantly influenced by the homogeneity or inhomogeneity of the cataract model employed. The system operator and the photographer provided that they are well trained, have minor influence on the reproducibility of the Zeiss SLC system.

Direct measurement of pH in the rat lens by ion-sensitive microelectrodes

The resting pH of the rat lens was determined using H +-sensitive liquid membrane microelectrodes and found to be 6·89 when measured in a perifusing solution of pH 7·20. The pH of the rat vitreous humour was also measured and was found to be 7·25. Attempts were made to perturb the lens pH by varying the pH of the perifusate. In the presence of alkaline solutions, the lens was able to maintain its resting pH and membrane potential but. upon perifusion with a more acidic solution, the lenticular pH equilibrated with the pH of the bathing solution and the potential depolarized. The internal pH could be manipulated independently of the external pH by perifusing the lens with Ringer solution containing 20 m m ammonium chloride. The ammonium chloride induced a rapid alkalinization and the return to control solution caused a fall in pH to below the normal resting level. The biphasic pH response to ammonium chloride was accompanied by changes in lens transparency and membrane potential.

Monitoring lens transparency during in vitro incubation by Scheimpflug photography and densitometric image analysis.

Dragomirescu et al. [1983] described a 2-chamber flow system for the incubation of lenses with an inserted photometer to measure changes in lens transparency. Mester et al. [1984] applied the method to simulate conditions occurring during vitrectomy, which occasionally leads to reversible lens opacification. Using Scheimpflug photography (a modified SL 45 Topcon camera) instead of the transmission measurements of incubated lenses has the advantage that disorders in lens transparency can be exactly localized and the sensitivity is much higher than the photometer readings. Application of Scheimpflug photography required a modification of the incubation chamber. The application of the experimental set-up was demonstrated with pig lenses under various incubation conditions. The results obtained by densitometric image analysis of Scheimpflug photos were compared with transmission measurements by photometer.