The anterior lens capsule (ALC), as the thickest basement membrane in the body, is an acellular, soft, smooth, transparent membrane secreted by lens epithelial cells. The ALC has its unique biomechanical properties to serve as a barrier and separate the lens from infectious viruses and bacteria together with the posterior capsule and pericapsular membrane. However, the biomechanical and ultrastructural properties of the ALC can be changed under certain conditions. Here, we provide a brief review of the pathological changes of the ALC in several eye disorders, including cataract, aniridia, climatic droplet keratopathy, exfoliation syndrome, true exfoliation syndrome, Alport syndrome, and silicone oil tamponade.
The anterior lens capsule (ALC), as the thickest basement membrane in the body, encapsulates the crystalline lens and acts as a barrier and separates the lens from infectious viruses and bacteria together with the posterior capsule and pericapsular membrane. The ALC is an acellular, soft, smooth, transparent basement membrane secreted by lens epithelial cells (LECs). The ALC with the accompanying monolayer subcapsular epithelium represents the most important metabolic element of the crystalline lens. Recently, the biomechanical properties and biomedical engineering perspectives of the ALC were reviewed by us [
Cataract is most simply defined as opacification of the crystalline lens inside the eye, which is the commonest cause of vision loss worldwide [
In eyes with mature cataracts, poor fundus red reflex and poor visibility of the capsule makes surgery more challenging. Therefore, capsule staining is often performed to enable the round edges of the capsulorhexis visible and facilitate the continuous curvilinear capsulorhexis (CCC) procedure. Several studies have verified that biomechanical properties of the ALC would change after vital dyes staining, including trypan blue, brilliant blue, and indocyanine green [
Aniridia is characterized by underdeveloped iris and accompanied by abnormalities of the cornea, anterior chamber angle, lens, retina, and optic nerve [
Climatic droplet keratopathy (CDK) is a corneal degeneration disease and characterized by a band‐shaped pattern of subepithelial opacities and golden‐yellow spherules [
Exfoliation syndrome (XFS) or pseudoexfoliation syndrome is an age-related disease in which abnormal fibrillar extracellular material is produced and accumulates in many ocular tissues, mainly the ALC and the pupillary margin. The typical distribution of ALC deposits consists of three zones: a granular, often layered, peripheral zone; a central disc, and a clear area between them. Several studies confirmed fibrils accumulation above or in the basement membrane of the ALC in XFS eyes [
True exfoliation syndrome (TEX) is a rare disorder in which characteristic lamellar separation of the ALC occurs. The pathogenesis of TEX is not clear; although intense infrared radiation is thought to be the main causative factor, most cases are idiopathic. Histologically, a thickened delaminated structure, perpendicular fibrils and vesicular degeneration in the capsule, and degenerative lens epithelium have been documented [
Alport syndrome is a rare disorder of the basement membrane characterized clinically by progressive hereditary nephritis, sensorineural hearing loss, and ocular abnormalities. Genetically, Alport syndrome is due to mutations involving the coding for type IV collagen resulting in a defective synthesis of type IV collagen [
Silicone oil is an intraocular tamponade after vitrectomy surgery, which is used for the treatment of complicated retinal detachment [
In Citirik et al.’s study, by electron microscopy, silicone oil was detected on the posterior surface of the ALC in 50% cases and surface irregularities, pits, and depressions were present in the posterior surface of the ALC in all the ten silicone oil tamponade cases [
Clinically, rigidity of the ALC is frequently encountered during cataract surgery in silicone-oil-filled eyes [
The different pathological changes of the ALC in different diseases are summarized in Table
Pathological changes of the ALC in different diseases.
Disease | Main changes |
---|---|
Cataract | Lower surface roughness in the anterior side of the ALC and higher surface roughness in their posterior side |
Lower Young’s modulus | |
Ultrastructure morphology changes in intumescent white cataracts | |
Trypan blue staining | Decrease in elasticity and an increase in stiffness |
No difference in CCC strength | |
Aniridia | Thinner and more fragile |
Degenerative changes (degeneration, necrosis, and loss) and proliferative changes (proliferation and double layer) of the lens epithelium | |
Climatic droplet keratopathy | Plateau or “bag” or herniation-like of the lens capsule |
Exfoliation syndrome | Abnormal fibrillar extracellular material deposition |
Diffuse intracellular and extracelluar edema, transparent vacuoles, apoptotic cells, and destroyed epithelial cells | |
More affinity to trypan blue | |
True exfoliation syndrome | Thickened delaminated structure, perpendicular fibrils, and vesicular degeneration in the ALC |
Double delamination and pigment deposition on the detached membrane | |
Alport syndrome | Marked thinning and vertical dehiscence of the ALC |
Spontaneous rupture of the ALC | |
Silicone oil tamponade | Surface irregularities, pits, and depressions in the posterior surface of the ALC |
LECs with apoptotic changes and cytoplasmic vacuoles | |
Increased mechanical resistance of the ALC |
ALC: anterior lens capsule; CCC: continuous curvilinear capsulorhexis; LECs: lens epithelium cells.
The ALC, as structural support for the lens within the eye, plays an important role on normal lens growth and metabolism. However, the biomechanical properties of the ALC may change in several ocular diseases, including cataract, aniridia, climatic droplet keratopathy, exfoliation syndrome, true exfoliation syndrome, Alport syndrome, and silicone oil tamponade. These pathological changes vary from biomechanical alterations (surface roughness, Young’s modulus, elasticity, stiffness, rigidity, fragility, etc.) to ultrastructural abnormalities (increase or decrease in thickness, abnormal material accumulation, lamellar separation, vesicular degeneration, ALC dehiscence, surface irregularities, cytoplasmic vacuoles, etc.) in different ocular diseases. If cataract surgery is scheduled for these eyes, the surgery procedure, especially the capsulorhexis, would be challenging. Therefore, attention should be raised when performing cataract surgery for these patients.
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.
The authors declare to have no potential conflicts of interest.
This work was supported by a grant from the National Natural Science Foundation of China (grant no. 81800825), Tianjin Clinical Key Discipline Project (grant no. TJLCZDXKQ023), and Open Project of Tianjin Key Laboratory of Retinal Functions and Diseases (grant no. 2020tjswmq003). The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.