Increase in lens capsule stiffness caused by vital dyes

PURPOSE

To assess potential changes in lens capsule mechanical properties after staining with brilliant blue, indocyanine green (ICG), and trypan blue.

SETTING

Department of Ophthalmology and Applied Physics and Center for NanoScience, Ludwig-Maximilians-University, Munich, Germany.

DESIGN

Experimental study.

METHODS

Fifteen unstained lens capsules were dissected into 7 wedge-shaped parts. Three fragments were stained with brilliant blue 0.025%, ICG 0.05%, and trypan blue 0.06%, respectively, for 1 minute. Another 3 specimens were additionally illuminated using a standard light source. The seventh part served as an untreated control. All specimens were analyzed using atomic force microscopy (AFM) in contact mode with a scan rate of 0.6 Hz. Two scan regions of 10 μm × 10 μm were chosen, and stiffness was determined using AFM in a force spectroscopy mode. The force curves were performed with a data rate of 5000 Hz.

RESULTS

Staining of the samples resulted in an increase in tissue stiffness (brilliant blue: P<.001; ICG: P<.01; trypan blue: P<.05). Additional illumination after staining further increased tissue stiffness, but not significantly. Mean increase in the relative elasticity values were 1.61 ± 0.15 (SD) for brilliant blue, 2.04 ± 0.21 for brilliant blue with illumination, 1.63 ± 0.22 for ICG, 2.01 ± 0.22 for ICG with illumination, 1.23 ± 0.11 for trypan blue, and 1.39 ± 0.11 for trypan blue with illumination. In relation to unstained tissue, the relative elasticity of the stained tissue increased 1.2-fold after illumination.

CONCLUSION

Staining significantly increased the mechanical properties of the human lens capsule.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Low-intensity ultraviolet A irradiation of the lens capsule to remove lens epithelial cells during cataract surgery

PURPOSE

To assess the effectiveness and safety of low-intensity ultraviolet A (UVA) irradiation in removing lens epithelial cells (LECs) during cataract surgery and compare them with those of mechanical polishing and no treatment.

SETTING

Eyecove Ophthalmology Clinics, Pune, India.

METHODS

This prospective randomized double-masked study consisted of preoperative screening of 36 patients, of which 30 met the inclusion criteria and were recruited. The patients had routine cataract surgery. A bean-shaped capsulorhexis was performed. After the nucleus and cortex were removed, the capsular bag was irradiated from inside with low-intensity UVA in 1 group. A second group had mechanical polishing, and a third group was not treated. A small flap of the anterior capsule was removed in each patient. The flap was stained and mounted in a Fuchs-Rosenthal chamber. For estimation of effectiveness, the area of capsule covered with epithelial cells was estimated by examination under a light microscope. One day postoperatively, an examination was performed to assess the safety of each technique.

RESULTS

The area of the capsule from which the LECs were removed was significantly larger in the UVA-irradiation group than in the mechanical-polishing group (P = .001) and the no-treatment group (P = .001). There was no significant difference between the mechanical-polishing and no-treatment groups (P>.05). The area of the capsule flap that was covered with LECs was significantly less in the UVA-irradiation group than in the mechanical-polishing group (P = .017) and the no-treatment group (P = .001). The mechanical-polishing group and no-treatment group were not significantly different from each other (P>.05). Corneal edema was significantly less in the UVA-irradiation group than in the mechanical-polishing group (P<.001) and no-treatment group (P = .012). No patient in the UVA-irradiation group had postoperative lid edema; 8 patients in each of the other 2 groups had lid edema. The difference was statistically significant (P<.0001). Pupil size was significantly larger in the UVA-irradiation group than in the mechanical-polishing group and no-treatment group; the difference was significant (both P = .0001). There was no significant difference in pupil size in the mechanical-polishing group and no-treatment group. No significant difference was observed between the 3 groups in visual acuity, conjunctival edema, anterior chamber flare, and intraocular pressure.

CONCLUSION

Ultraviolet A irradiation of the capsular bag was effective and safe in removing LECs from the anterior capsule during cataract surgery.

Cataracts among Chernobyl Clean-up Workers: Implications Regarding Permissible Eye Exposures

The eyes of a prospective cohort of 8,607 Chernobyl clean-up workers (liquidators) were assessed for cataract at 12 and 14 years after exposure. The prevalence of strictly age-related cataracts was low, as expected (only 3.9% had nuclear cataracts at either examination), since 90% of the cohort was younger than 55 years of age at first examination. However, posterior subcapsular or cortical cataracts characteristic of radiation exposure were present in 25% of the subjects. The data for Stage 1 cataracts, and specifically for posterior subcapsular cataracts, revealed a significant dose response. When various cataract end points were analyzed for dose thresholds, the confidence intervals all excluded values greater than 700 mGy. Linear-quadratic dose-response models yielded mostly linear associations, with weak evidence of upward curvature. The findings do not support the ICRP 60 risk guideline assumption of a 5-Gy threshold for "detectable opacities" from protracted exposures but rather point to a dose-effect threshold of under 1 Gy. Thus, given that cataract is the dose-limiting ocular pathology in current eye risk guidelines, revision of the allowable exposure of the human visual system to ionizing radiation should be considered.

Thermal stability of UV-irradiated collagen in bovine lens capsules and in bovine cornea

The thermal stability of UVB irradiated collagen in bovine lens capsules and in bovine cornea has been investigated by differential scanning calorimetry (DSC). During UVB irradiation the lens capsules and cornea were immersed in water to keep the collagen in a fully hydrated condition at all times. UV irradiation induced changes in collagen which caused both stabilization and destabilization of the collagen structure. The helix-coil transition for non-irradiated collagen in cornea occurred near 66 degrees C, instead for the irradiated one for 3h it occurred at 69 degrees C. After irradiating for longer times (20-96h) the helix-coil transition peak occurred at much lower temperatures. The peak was very broad and suggested that collagen was reduced by UV to different polypeptides of different molecular weight and different lower thermal stabilities. The irradiation of lens capsules with UVB light in vitro resulted in changes in the thermal properties of type-IV collagen consistent with increased cross-linking. DSC of lens capsules showed two major peaks at melting temperatures at 54 degrees C Tm1 and 78 degrees C Tm2, which can be attributed to the denaturation of the triple helix and 7S domains, respectively. UVB irradiation of lens capsules in vitro for 6 h caused an increase in Tm1 from 54 to 57 degrees C. The higher temperature required to denature the type-IV collagen after irradiation in vitro suggested an increase of intermolecular cross-linking.

[The influence of ionizing radiation on the development of posterior capsule opacification in vitro]

BACKGROUND AND PURPOSE

Histologically, the posterior capsule opacification (PCO) corresponds to regenerative tissue of transformed lens epithelial cells (LECs) with extracellular matrix production. In this study, the influence of ionizing radiation on proliferating LECs and the development of PCO was investigated in vitro.

MATERIAL AND METHODS

Each four and 14 pork lenses, respectively, were irradiated with 6 MeV electrons with single doses of 8, 10, 12, and 20 Gy. 1-2 h after irradiation the lens was removed by capsulorrhexis and hydrodissection. After fixation of the capsular bag in a special device the proliferation of residual LECs was examined daily. The experiment was considered to be finished when the capsular bag was completely opacified by confluent cell proliferates.

RESULTS

Single dose irradiation with electrons in a dose range from 8 to 12 Gy significantly protracted the development of PCO with complete inhibition of PCO after application of 20 Gy.

CONCLUSION

To inhibit PCO in vitro, a single dose of 20 Gy is necessary. The actual in vitro model allows an optimal investigation of PCO formation under different external influences and is therefore very suitable for radiobiological questions.

Influence of indocyanine green staining on the biomechanical properties of porcine anterior lens capsule

PURPOSE

Indocyanine green (ICG) has recently been introduced in cataract surgery to stain the anterior lens capsule for better visualization of the capsulorhexis. The aim of the current in vitro study was to examine the effect of ICG staining on the biomechanical strength of the anterior porcine lens capsule.

METHODS

Two parallel, 8 mm anterior lens capsule strips were prepared from each of 65 porcine postmortem eyes. ICG staining combined with white light exposure of 0.5, 1, 3, and 30 min duration was conducted. Unstained, nonilluminated and 0.1% glutaraldehyde-treated specimens were used as controls. Biomechanical stress-strain measurements were performed using an automated material tester. The absorption spectrum of the 0.5% ICG solution and the emission spectrum of the light source were controlled.

RESULTS

After ICG staining combined with at least 3 min light exposure, a significant increase of stress (31%) at 25% strain and a significant decrease (7%) in ultimate strain was found. Without light exposure, there was no such effect, suggesting a light-dependent process. After 30 min of 0.1% glutaraldehyde treatment, there was a similar increase in stress (322%) at 25% strain and a decrease (47.6%) in ultimate strain.

CONCLUSIONS

ICG staining of the lens capsule causes a significant increase in elastic stiffness and a reduction in ultimate extensibility, thereby facilitating a smooth continuous capsulorhexis. The effect is due to a photosensitizing effect of ICG, leading to collagen cross-linking.

Biomechanical changes in the anterior lens capsule after trypan blue staining

PURPOSE

To examine the effect of trypan blue staining on the biomechanical behavior of the porcine anterior lens capsule.

SETTING

Department of Ophthalmology, Technical University of Dresden, Dresden, Germany.

METHODS

Fifty-five anterior lens capsules from porcine cadaver eyes were used. Two parallel 8.0 mm x 4.0 mm large capsule strips were prepared from each capsule. After trypan blue staining for various time intervals combined with exposure to white light (6000 lux) or with no light exposure, biomechanical stress-strain measurements were performed using an automated material tester. Untreated specimens and specimens treated with glutaraldehyde 0.1% were used as controls. The absorption spectrum of trypan blue 0.1% solution and the emission spectrum of the light source were measured.

RESULTS

After treatment with light and trypan blue, at 25% strain, there was a statistically significant increase in stress of up to 70.1% and in elastic stiffness of 47% and a decrease in the ultimate mechanical strain of up to 13%. There were no biomechanical changes in capsules with trypan blue staining in the absence of light or after a short illumination time of 30 seconds, indicating a light-dependent process. After 30 minutes of glutaraldehyde 0.1% treatment, there was an increase in stress of 321.6% at 25% strain and a decrease in the ultimate strain of 47.6%. The emission spectrum of the light source included the absorption peak for trypan blue at 580 nm.

CONCLUSIONS

Trypan blue staining of the lens capsule combined with light irradiation for at least 1 minute led to an increase in elastic stiffness at 25% strain and a reduction in the ultimate extensibility. This effect is probably due to the photosensitizing action of trypan blue, leading to light-induced collagen crosslinking of the capsule collagen similar to age-related crosslinking. Nucleus expression might be impeded by the increased capsule stiffness. Continuous curvilinear capsulorhexis is facilitated.

The effects of sub-solar levels of UV-A and UV-B on rabbit corneal and lens epithelial cells

The purpose of this work was to establish whether exposing cultured rabbit corneal and lens epithelial cells to ultraviolet radiation equivalent to several hours under the sun would damage the cells. Confluent rabbit corneal epithelial cells were irradiated with broadband UV-A or UV-B, and confluent lens epithelial cells were irradiated with broadband UV-A. The maximum dose of UV-A was 6.3 J cm(-2) and that of UV-B was 0.60 J cm(-2). Damage to corneal epithelial cell was studied using the terminal deoxynucleotidyl transferase mediated dUTP-X nick end labeling (TUNEL) assay and damage to lens epithelial cell was studied using the single cell gel electrophoresis (comet) assay and trypan blue exclusion assay. Lipid peroxidation was assayed using the thiobarbituric acid reaction. Both UV-B and UV-A induced cell death in corneal epithelial cells with different latent periods. UV-A damage included cell death, decreased viability and increased lipid peroxidation of lens epithelial cell. In addition, UV irradiation of the corneal and lens epithelial cells decreased the activity of catalase to thirty to fifty percent of its original value, while the activities of glutathione peroxidase and superoxide dismutase did not decrease within experimental error. Thus, even sub-solar UV radiation can cause irreversible damage to corneal and lens epithelial cells.

Measurement of oxygen production by in vitro human and animal lenses with an oxygen electrode

PURPOSE

This paper describes an advantageous method of measuring the activity of the enzyme catalase, which has an important antioxidative role in the lens. This method allows the measurement of catalase in whole lenses.

METHODS

Exposure to UVA (99% UV-A) radiation was used to stress animal and human (Eye Bank) lenses in vitro. The ability of lens catalase to convert H2O2 into O2 was measured directly, using an oxygen electrode and meter. This method is very specific, as catalase is the only enzyme that converts H2O2 to O2.

RESULTS

Catalase in the lenses of humans, rabbits, and squirrels catalyzed the production of O2 from H2O2 very efficiently. The anterior equatorial regions of these lenses were the most active O2 producing areas. More than 95% of lens catalase activity was found in the capsule-epithelium layer. Exposure to UVA radiation, up to approximately 100 J/cm2 in 18 h, strongly inhibited O2 production from 0.77 mM H2O2 by the lenses. Catalase activity decreased with increasing age. Mixed cataractous human lenses produced O2 from H2O2 at only 60% of the rate of normal lenses of similar ages. Nuclear cataracts produced O2 at only 75% of the rate of normal lenses. Alpha-tocopherol (10(-5) M) protected lens catalase activity strongly. Alpha-tocopherol is known to accumulate in and protect against cell membrane peroxidation, and against singlet oxygen formation. These oxidative mechanisms appear to contribute to catalase photoinactivation.

CONCLUSIONS

The method described indicated that catalase is a crucial antioxidative enzyme in the normal lens. Its inactivation could upset the oxidation-reduction balance in the lens and stimulate lens opacification.

Effects of UV-B radiation on a hereditary suture cataract in mice

UV-B (290-320 um, lambda max = 305 nm) radiation and the Cat2ns (suture cataract) mutation in mice affect both the anterior lens epithelium and the formation of the suture. A low dose of UV-B radiation (2.2 Jcm-2) induces similar anterior subcapsular and cortical lens opacities in wild type as in heterozygous mutant mice. The UV-B treatment of the mutant lenses, however, leads to an increase in the number of epithelial cell layers in the anterior central part as compared to the wild type indicating a more severe form of the cataract formation in mutants. In addition, mutants demonstrate a predisposition for a rupture of the posterior lens capsule, because from 2.9 Jcm-2 and higher, this phenomenon could always be observed in the UV-B treated mutants, but never in the treated wild type mice. The protein biochemical analyses were performed by gel electrophoresis and isoelectric focusing of extracts of total lenses or from defined areas of the lens (lens slice technique). These covered the patterns of those proteins already synthesized before irradiation, which in irradiated lenses in no case evidenced a difference to the untreated control, neither in the wild type nor in the mutants. In contrast, by analysing specifically those proteins, which are synthesised after irradiation, in both treated groups a protein with a molecular mass of about 31 kDa becomes discernable in both treated groups. In addition, the cataractous lenses demonstrate a significantly enhanced overall synthesis of water-soluble proteins after irradiation, which might promote the rupture of the posterior capsule at the posterior pole. The present study offers for the first time the possibility to discriminate between endogeneous (genetic) effects and exogeneous (environmental) effects in cataractogenesis and to study their interactive effects. The first set of experiments demonstrated a clear intensification of the hereditary cataract by the UV-B treatment. The study supports the hypothesis that environmental stress (like UV-B radiation) enhanced the severity of genetically triggered eye disease.

Prevalence of lens changes in Ukrainian children residing around Chernobyl

The objective of this study is to determine the prevalence and characteristics of lens changes in the eyes of a pediatric population, 5-17 y old, living in the permanent control zone around the Chernobyl nuclear reactor and to compare these findings with those from an unexposed control population. A total of 1,787 children are reported on (996 exposed and 791 unexposed). Over three-quarters of the subjects examined in this study show a form of minor change, termed focal lens defect, in the cortical and/or nuclear portions of the lens of the eye. The exposed group shows a small (3.6%), but statistically significant excess (p = 0.0005) of subclinical posterior subcapsular lens changes similar in form to changes identified in atomic bomb survivors. These posterior subcapsular changes tend to occur in boys 12-17 y old and in exposed children who report consuming locally grown mushrooms on a regular basis.

Modulating radiation cataractogenesis by hormonally manipulating lenticular growth kinetics

There is considerable evidence that the lens epithelium is the primary site of injury leading to the development of cataracts following radiation exposure. That the damaged cells of the epithelium are the progenitors of the aberrantly differentiating fibers associated with the cataract is indisputable. So too is the observation that post-radiation proliferative activity in the lens epithelium is required for cataracts to develop. The natural hormonal regulation of lens epithelial mitotic activity in the frog offers the opportunity to alter the cell cycle of the lens epithelium in vivo, thus enabling the direct examination of the role of lenticular mitosis in the cytopathomechanism of radiation-induced cataracts. The cell cycle of the lens epithelium of northern leopard frogs was manipulated by hypophysectomy (to halt mitotic activity) and pituitary hormone administration (to stimulate baseline mitosis and reverse hypophysectomy-induced mitotic suppression). Animals were hypophysectomized, irradiated and injected with pituitary hormone replacement. Irradiated animals, irradiated animals + hormone replacement and irradiated hypophysectomized animals served as controls. Cataract development was evaluated by slit-lamp biomicroscopy and correlated with histologic determinations of mitotic index and meridional row disorganization on lens epithelial whole mounts. In another study, hypophysectomized-irradiated animals received varying concentrations of replacement hormone in an attempt to quantitatively modulate lens epithelial mitotic activity and determine the effect on cataractogenesis. It was found that irradiated-hypophysectomized (mitosis halted) frogs failed to develop opacities, while those with hormonal replacement (mitosis reinstated) developed cataracts.(ABSTRACT TRUNCATED AT 250 WORDS)

Light absorption characteristics of the lens capsule

Spectrophotometric measurement of the absorption characteristics of the lens capsule was carried out on 20 cases of so-called complicated or senile cataract operated through intracapsular cataract extraction (ICCE). The lens capsule almost completely transmitted visible radiation (between 400 and 750 nm) and near-ultraviolet (UV) radiation (between 300 and 400 nm). In the UV portion below 300 nm, the lens capsule showed one absorption peak at 280 nm and rapid increase of absorbance below 240 nm. These results reveal that the capsule of the cataractous lens retains a high degree of transparency, but its function as a UV filter is negligible.

Potential acuity meter for predicting visual acuity after Nd:YAG posterior capsulotomy

We studied 30 patients with opacifications of the posterior capsule to determine if the potential acuity meter (PAM) could accurately predict final visual outcome after Nd:YAG discussion. The final visual acuity was within one line of the PAM prediction in 22 of 30 patients (73%), better by two or more lines in seven patients (23%), and worse in one patient (4%) by two lines. Although in thicker capsules the final acuity was occasionally better than the PAM prediction, the rates of false negative and false positive predictions were very low. Mild cystoid macular edema (3 patients), age-related macular degeneration (3 patients), intraocular lens status, and level of initial acuity did not diminish PAM accuracy. The PAM effectively predicts final visual acuity after YAG posterior capsulotomy, when used in a patient, unhurried manner.

Rhegmatogenous retinal detachment after neodymium-YAG laser capsulotomy in phakic and pseudophakic eyes

A retrospective study of 18 eyes in 17 patients with rhegmatogenous retinal detachments after neodymium-YAG laser posterior capsulotomy was performed to determine operative settings and to describe anatomic changes after the procedure in an effort to assess their relationship to subsequent retinal detachment. The laser energy required to create a capsulotomy did not appear to be excessive and the capsulotomy openings were not unusually large. The time between YAG capsulotomy and diagnosis of retinal detachment ranged from four to 82 weeks (mean, 28 weeks). The characteristics of the retinal detachments were similar to those after routine cataract extraction. Retinal reattachment surgery was ultimately successful in all 18 eyes. Both YAG laser and knife-needle posterior capsulotomies may increase the risk of subsequent rhegmatogenous retinal detachment as a result of opening the capsule.

Comparison of the effects of argon fluoride (ArF) and krypton fluoride (KrF) excimer lasers on ocular structures

We evaluated the effects of argon fluoride (ArF) and krypton fluoride (KrF) excimer lasers on ocular structures. We produced corneal incisions, optical iridotomy, capsulotomy, and retinotomy with these lasers. Incisions produced with ArF showed sharply defined borders with minimal coagulative effects to the adjacent structures. Cuts created with KrF showed coagulative necrosis of the wound edges ranging from two to five um in width. From our study it appears that ArF has photoablative action and KrF has a predominantly photoablative action with minimal photocoagulative effect on the tissue.

Neodymium:YAG laser capsulotomy of secondary membranes in the pediatric population

Posterior capsulotomy is occasionally performed at the conclusion of extracapsular cataract extraction because of the high incidence of secondary membrane formation. Using a Nd:YAG laser we successfully performed posterior capsulotomies on 16 children who developed secondary membranes following extracapsular cataract extraction in which the posterior capsule was left intact. Eleven patients had congenital cataracts and five had acquired cataracts. The youngest patient was four years. All had improvement in visual acuity. Preserving most of the posterior capsule provides additional support to the eye and has been associated with a decreased incidence of cystoid macular edema. It also allows secondary implantation of a posterior chamber intraocular lens in the future.

Intraocular lens design for the neodymium:YAG laser

Phacoemulsification was performed on both lenses of 24 rabbits. One eye received a lens implant with a convex-plano optic; the fellow eye received an implant with a convex-concave optic which separated the posterior surface of the implant from the posterior capsule by 0.2 mm, 0.3 mm, or 0.4 mm. A YAG laser capsulotomy was performed on all eyes immediately following surgery and an assessment of both microscopic and macroscopic YAG-induced lens damage was made. The meniscus optics with their capsule-implant separation showed significantly less YAG-induced damage than their convex-plano counterparts without this separation. Increasing the amount of capsule-implant separation beyond 0.2 mm did not enhance the degree of protection from YAG-induced damage.

Diagnosis and treatment of mysterious light streaks seen by patients following extracapsular cataract extraction

Complaints of light streaks, such as might be seen with a Maddox rod or Bagolini lens, are becoming more common with the trend toward extracapsular cataract surgery. The light streaks are usually a result of high plus cylinders somewhere in the patient's optical system. Windshields, spectacles, contact lenses, lashes, an excessive tear meniscus, intraocular lens scratches, and posterior capsular opacification are possible causes that can be easily identified and treated.

The barrier function of the posterior capsule

The permeability of the rabbit lens and human cataractous lens posterior capsule to epinephrine and trypan blue and the absorption of ultraviolet and visible light through the posterior capsule were studied in vitro. The posterior capsule served as a barrier to large nonelectrolytes or negative electrolytes other than trypan blue, but it did not impede epinephrine, ultraviolet or visible light.