Equatorial Lens Epithelial Cells Research Articles

Islands of lens epithelial cells on the posterior capsule in pseudophakic eyes

To evaluate the natural history of focal collections (islands) of lens epithelial cells (LECs) on the posterior capsule after cataract surgery. Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom. Patients in previous studies with various intraocular lenses (IOLs) and at least a 2-year follow-up were identified. Postoperative digital retroillumination images of each eye taken at 1, 3, and 6 months and 1 and 2 years were assessed for the presence of LEC islands and their incidence, etiology, time of appearance, change with time, and relationship to IOL material. Islands of LECs were identified in 39 eyes with an AcrySof SA60AT IOL, 40 eyes with a Rayner Centerflex C570H IOL, and 27 eyes with a Hoya YA60BB IOL. In all groups, the islands tended to appear within 6 months with a decreasing incidence thereafter. Floating LECs that seeded on the posterior capsule (seeded LECs) or LECs left on the posterior capsule at surgery were seen in a small number of eyes. Most islands were derived from regression of a previous LEC membrane, and a majority continued to regress. Intraocular lens material had no influence on the natural history or morphology of the islands. Islands of LECs were common postoperatively. Equatorial LECs appeared to be the major cause of clinical posterior capsule opacification (PCO). Floating LECs in the aqueous that seeded on the posterior capsule or LECs left behind after surgery did not appear to contribute to clinical PCO. No author has a financial or proprietary interest in any material or method mentioned.

Capsular bend and PCO prevention

Nishi's1 comments on the article by Nagamoto and Fujiwara2 were based on theoretical and animal studies. We would like to describe our experience based on the analysis of several thousand pseudophakic eyes obtained post-mortem. The capsular bend is based on the fusion of the peripheral posterior capsule and the peripheral aspect of the anterior capsule, thus creating a “nick” or “bend” in the capsule at the site where it contacts the posterior peripheral aspect of the square optic. It is predicated on the fact that little or no interfering material (eg, cortex or cells, specifically “E” cells, the source of posterior capsule opacification [PCO] within Soemmering's ring) rests in the space between the 2 capsules. If residual lens substance is in the space between the 2 capsules as they attempt to fuse, the process will be blocked. By this definition, the capsular bend can form completely only if there is a complete or almost complete removal of lens substance, allowing the 2 capsules to come into approximation (Figure 1). In these cases, PCO prevention is probably based on the first line of defense, namely, the complete removal of lens substance, and formation of the capsular bend is a secondary occurrence instead of the primary mechanism in retarding PCO.Figure 1: Photomicrograph of a human eye obtained post-mortem with an Alcon AcrySof IOL implanted in the capsular bag. There was complete removal of equatorial lens epithelial cells (E cells, the precursors of PCO). There is adherence of the peripheral anterior and posterior capsules around the haptic (left), extending toward the optic. A well-formed capsular bend has been created (lower left). A “cleanup” bag such as this is a prerequisite for capsular bend formation. The square-edged optic fills the bag. The biomaterial dissolves during processing, creating the large empty space (hematoxylin and eosin, original magnification ×5).In our autopsy series of several thousand eyes, we have seen numerous cases in which excellent PCO prevention was based on the barrier effect of the square-edge mechanism in the complete absence of a capsular bend (Figure 2). This seems to indicate that the capsular bend does not function as a primary mechanism in many cases.Figure 2: Photomicrographs clearly demonstrate examples of the barrier effect achieved with the square truncated edge of the 3-piece Alcon AcrySof IOL optic in the absence of a capsular bend. Retained cortex/lens epithelial cells are present in the intercapsular space in all 3 preparations (A to C), thus preventing the necessary adhesions between peripheral anterior and posterior capsules seen in these 4 preparations. The capsular bend is not necessary for effective lens epithelial cell/cortex blockage. Note the interface between the relatively exuberant Soemmering's rings (pink–red material, left) and the IOL optic (clear space, right). These are separated by the lens optic's square edge. Note also the clear posterior capsule in lower right. A: Masson's trichrome stain (original magnification ×50). B: Periodic acid-Schiff stain (original magnification ×150). C: Hematoxylin and eosin stain (original magnification ×40). D: Masson's trichrome stain (original magnification ×40).Figure 2: (continued)Figure 2: (continued)Figure 2: (continued)It is important to remember that the enhanced barrier effect provided by this optic geometry probably functions as icing on the cake by providing an additional reserve factor (in addition to the basic cortical cleanup that has proved to be of utmost importance in helping to reduce the overall incidence of visually significant PCO) in cases in which complete cortical cleanup was not achieved. As mentioned, the mechanism of action of the square edge in these cases cannot be related to the creation of a capsular bend but to a mechanical barrier effect.

Evaluation of the cataractogenic effect of viscoanesthetic solutions on the rabbit crystalline lens

To evaluate the toxicity and cataractogenic effect of solutions combining sodium (Na) hyaluronate 1.0% and 1.5% with lidocaine 1.0% on the rabbit crystalline lens. The amount of pupil dilation provided by the addition of lidocaine to the Na hyaluronate solutions was also assessed. John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA. Five solutions were injected into the anterior chamber of 18 pigmented rabbits in a randomized manner by the same surgeon, the intraocular component of VisThesia (Na hyaluronate 1.5%/lidocaine 1.0%), the intraocular component of VisThesia Light (Na hyaluronate 1.0%/lidocaine 1.0%), Ophthalin Plus (Na hyaluronate 1.5%), and a balanced salt solution; and both eyes of 2 other rabbits were injected with nonpreserved aqueous lidocaine 1.0%. The pupil diameter of each eye was measured before injection, immediately after, and 1 and 5 minutes after injection. After a follow-up of 3 months with slitlamp examinations, the rabbits were killed, and their eyes were enucleated. The crystalline lenses were evaluated from a posterior or Miyake-Apple view, and the eyes were fixated in 10% formalin for histopathologic analyses. Pupil diameter was significantly larger 1 and 5 minutes after injection in the VisThesia (P = .01 and P = .007) and VisThesia Light (P = .008 and P = .007) groups, whereas the differences were not significant in the Ophthalin Plus (P = .317 and P = .102) and balanced salt solution groups (P = .317 and P = .180). Fast and large pupillary dilation was observed in the aqueous lidocaine group, starting during the injection. No differences in the transparency of the natural lens and the red fundus reflex were noted during slitlamp examinations. Postmortem analyses from a posterior view also showed no differences in the transparency of the crystalline lens. The histopathologic appearance of the lens capsule, anterior and equatorial lens epithelial cells, and epithelial lens bow was comparable in the eyes, without signs of cell vacuolization or disruption. Intracameral injection of the solutions used in this study caused no localized opacity or overall change in the transparency of the crystalline lenses as observed during clinical and postmortem examinations as well as histopathologic analyses of the enucleated rabbit eyes. Viscoanesthesia may have application in phakic intraocular lens implantation.

Expression of c-Fos and c-Jun in Developing Mouse Lens

We carried out immunohistochemistry in embryonic eye-specific antibodies in the mouse to determine the spatial/temporal expression pattern of c-Fos and c-Jun proteins – the main components of the AP-1 transcription factor, in lens epithelial cells during mouse lens morphogenesis. c-Fos protein expression was detected in the equatorial epithelium at E14.5–P25, with a peak at P1–P8. c-Jun protein expression was detected in equatorial lens epithelial cells at E18.5–P8, with a peak at P1. During these intervals, the anterior epithelium lacked expression of c-Fos and c-Jun. They were not detected in an adult mouse lens. The expression pattern of the AP-1 transcription factor in equatorial epithelium may suggest its role in fiber differentiation.

Calcium activates SK channels in the intact human lens.

Apamin-sensitive, calcium-activated SK potassium channels have been implicated in schizophrenia and myotonic dystrophy (MD), and both conditions carry an increased risk of cataract. The presence and functional activity of SK channels were therefore investigated in the human lens. The expression of all three members of the SK channel family was quantified by PCR. Their functional activity was investigated by using electrophysiological and calcium-imaging techniques. Lens voltage was monitored by inserting a single electrode into the intact human lens, and changes in intracellular calcium were recorded simultaneously after fura-2 incorporation. Expression of all three SK family members was detected in both anterior and equatorial lens epithelial cells. Application of either G-protein (e.g., adenosine triphosphate [ATP]) or tyrosine kinase (EGF) receptor agonists induced a hyperpolarization of lens voltage that was accompanied by an increase in intracellular calcium. The calcium ionophore ionomycin also induced a rapid hyperpolarization. The hyperpolarizing responses were abolished by apamin and trifluoperazine and were accentuated by the SK channel activator 1-ethyl-2-benzimidazolinone (1-EBIO). SK channels are an integral part of the G-protein and tyrosine kinase calcium signaling mechanisms in the human lens, and their activation is inhibited by certain anti-psychotic drugs. These findings help explain why a change in channel activity, whether by abnormal gene expression or by drug intervention, can lead to cataract.

Transcription activation in lens epithelial cells after anterior capsule rubbing in rats: expression of c-Fos

Purpose To determine whether lens epithelial cells (LECs) are transcriptionally activated after a foreign body is attached to the anterior lens surface. Setting Department of Ophthalmology, Wakayama Medical University, Wakayama, Japan. Methods One eye of adult Wistar rats (N = 32) was used. After the anterior capsule of the lens was rubbed with a dull 27-gauge needle 10 times, the eye was enucleated immediately (within 1 minute) or at 30 minutes or 1, 3, or 5 hours. The 32 globes were immunohistochemically analyzed using anti-c-Fos and anti-c-Jun antibodies. Results Immunohistochemistry showed that normal LECs lacked immunoreactivity for c-Fos or c-Jun. The c-Fos protein was localized in the nuclei of LECs in the equatorial region of the injured lens 3 hours after treatment and was not detected thereafter. The c-Jun protein was not detected at any interval. Conclusion The protein c-Fos was transiently expressed in equatorial LECs after the anterior lens capsule was rubbed, indicating that equatorial LECs are transcriptionally activated by minor mechanical stimuli to the anterior lens surface.

Intracapsular ring sustained 5-fluorouracil delivery system for the prevention of posterior capsule opacification in rabbits: A histological study

Purpose: To evaluate the efficacy of an intracapsular ring releasing 5-fluorouracil (5-FU) in preventing posterior capsule opacification (PCO) in rabbit eyes. Setting: Center for Research on Ocular Therapeutics and Biodevices, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA, and Chu Morvan, Department d’Ophtalmologie, University of Brest, France. Methods: Seventeen rabbits were divided into 3 groups: Group 1, 6 rabbits (6 eyes), had phacoemulsification only (control group); Group 2, 6 rabbits (6 eyes), had phacoemulsification with implantation of an open-loop hydrogel intracapsular ring; Group 3, 5 rabbits (5 eyes), had phacoemulsification with implantation of a ring with sustained release of 0.25 μg/h of 5-FU for 9 days. All eyes were followed for 8 weeks before enucleation. Capsular bag shrinkage and the position of the intracapsular ring were assessed, and central and peripheral PCO was evaluated for intensity and area by stereomicroscopy from a posterior (Miyake-Apple) view. The residual equatorial lens epithelial cells (LECs) were counted by the same observer in histological sections. Transmission electron microscopy (TEM) of the cornea, capsular bag, and retina was done to evaluate the toxicity of 5-FU. Results: No significant difference was seen in the degree of capsular bag shrinkage in the 3 groups. The intracapsular ring was decentered in 2 eyes (1 each in Groups 2 and 3). There was a statistically significant difference ( P < .05, Student t test) between Group 1 and Groups 2 and 3 in the area and intensity of central PCO. There was no difference between Groups 2 and 3 in the intensity of central PCO. No evidence of 5-FU toxicity to intraocular structures (cornea, capsular bag, and retina) was demonstrated on TEM analysis. Conclusion: Implantation of an intracapsular ring may prevent central PCO after cataract surgery by mechanically blocking LEC migration toward the central visual axis. The potential pharmacological effect of 5-FU in PCO prevention was not demonstrated.

Immunolocalization of TGF-beta1, -beta2, and -beta3, and TGF-beta receptors in human lens capsules with lens implants.

To establish the alteration in expression pattern of transforming growth factor (TGF)-betas and their receptors during repair of lens capsules after cataract surgery, we immunohistochemically located TGF-beta isoforms and their receptors in human lens capsules before and after cataract surgery. Ten post-cataract surgery capsular specimens were obtained during vitrectomy. Three sections of the anterior capsules were obtained during cataract surgery. A whole lens capsular bag immediately after lens extraction was obtained during vitrectomy. Cryosections of these specimens were processed for immunohistochemical analysis for TGF-beta1, TGF-beta2, TGF-beta3, TGF-beta receptor type I (TbetaR-I), type II (TbetaR-II) and type III (TbetaR-III), and were observed under light micros-copy. Lens epithelial cells (LECs) lining the inner surface of the anterior capsules exhibited immunoreactivity for TGF-beta2 and TbetaR-II. Immunoreactivity for TGF-beta1, -beta3, TbetaR-I and TbetaR-III was negative. In the whole capsular bag specimen, equatorial LECs were positive for TGF-beta1 and -beta2, but not for -beta3. In post-cataract surgery specimens, antibodies for each TGF-beta isoform labelled either the LECs or ECM accumulated on the capsules. Post-surgical LECs expressed TbetaR-I and TbetaR-II, and had also TbetaR-III in seven of the nine specimens examined. Expression pattern of TGF-beta s in quiescent LECs showed regional heterogeneity. Anterior LECs exhibited TGF-beta2 immunoreactivity, while equatorial LECs were positive for TGF-beta1 and -beta2. Quiescent LECs expressed TbetaR-II. LECs proliferating around IOLs expressed proteins of each TGF-beta isoform and each TbetaR. TGF-beta s were also localized in the ECM on capsules undergoing repair. TGF-beta3, TbetaR-I and TbetaR-III are up-regulated in LECs after cataract surgery.

In-the-bag secondary intraocular lens implantation in children

Background: Surgery for congenital cataracts in early infancy usually includes a primary posterior mcapsulectomy and an anterior vitrectomy. Initially, most of these infants have aphakia after surgery. Over time, remaining equatorial lens epithelial cells produce new cortical fibers, resulting in a ring of cortex trapped between the lens equator and the fused anterior and posterior capsulectomy edges. A potential space is maintained between the anterior and posterior capsular leaflets. We describe a technique for placing a secondary intraocular lens (IOL) within the capsular bag. Patients and Methods: Eight children, ranging in age from 11 months to 14 years, who originally had aphakia after cataract extraction were operated on with the intent to reopen the capsular bag and place an IOL in the bag. Results: Secondary in-the-bag IOL implantation was successfully completed in 7 of 8 children. This was accomplished by reopening the capsular bag 360° at the edge of the fused anterior and posterior capsulectomy remnants, using the previously published vitrectorhexis technique. Residual cortical material was aspirated, and an IOL was placed within the capsular bag. In 1 child, aged 14 years, the capsular bag was reopened, but the lens was placed in the ciliary sulcus because the new anterior capsule edge could not be visualized for 360°. Conclusion: Placement of secondary IOLs within the capsular bag can be accomplished successfully for selected patients in the pediatric population. Surgeons operating on infantile cataracts without primary IOL placement can facilitate capsular IOL sequestration later by limiting the anterior and posterior capsulectomy to 4 to 5 mm and performing a generous anterior vitrectomy to help prevent secondary closure of the smaller capsulectomy. (J AAPOS 1999;3:350-5)

The eye lens cytoskeleton.

During lens cell differentiation there are a number of very characteristic morphological changes that occur. These include a 50- to 100-fold increase in cell length as the equatorial lens epithelial cells differentiate into fibre cells and the loss of the cellular organelles such as mitochondria, nuclei, Golgi apparatus and endoplasmic reticulum. Coincident with these changes are dramatic alterations in the organisation of the lens fibre cell cytoskeleton and in particular the lens-specific intermediate filament network comprising CP49 and filensin. Cell shape and cell polarisation as well as tissue integrity are all processes that depend upon the cytoskeleton and are therefore important to the lens. The unique aspects of the lenticular cytoskeleton are the subject of this review.

Postoperative complications of capsulorhexis

Capsulorhexis has become the preferred method of anterior capsulotomy, and untoward effects have not been frequently noted. Nevertheless, distinct complications of continuous tear anterior capsulotomy are now recognized. These include capsular bag hyperdistention, shrinkage of the anterior capsule opening with visual loss and/or intraocular lens decentration, and lens epithelial cell hyperproliferation on the posterior lens capsule. The latter has not been reported and may be associated with reduction or closure of laser posterior capsulotomies in the form of a “string of pearls” around the capsule opening. Current styles of capsular surgery and intraocular lens implantation in which the anterior capsule edge overlaps the lens may be responsible for these phenomena. Although altering the surgical methods may obscure these complications, eliminating the anterior subcapsular and equatorial lens epithelial cells is necessary to prevent capsule contraction and lens epithelial cell hyperproliferation.

Influence of neural retina on lens fibre differentiation in rats.

Lens epithelial explants grown in retina-conditioned medium (RCM) undergo structural and molecular changes characteristic of fibre differentiation in the intact lens. We suggest that in vivo neural retina releases a fibre differentiation factor (FDF) that interacts with equatorial lens epithelial cells and stimulates them to undergo fibre cell differentiation. According to this model, interaction with neural retina is essential for normal lens formation in embryos and for normal lens growth throughout life. Preliminary work on purification of the factor indicates that FDF activity is associated with a high molecular weight complex of 500 kd. The active component of this complex appears to be an 80 kd molecule.