Capsule of lens

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Capsule of lens
Gray883.png
The upper half of a sagittal section through the front of the eyeball. (Capsule of lens labeled at center right.)
Details
Identifiers
Latin capsula lentis
MeSH D007903
TA98 A15.2.05.007
FMA 58881
Anatomical terminology
Sheep eye lens capsule with ligaments attached. The capsule is lifting off the lens showing cell fiber ends beneath. Capsule-lagaments-peel.jpg
Sheep eye lens capsule with ligaments attached. The capsule is lifting off the lens showing cell fiber ends beneath.
Microscope image of lens capsule in relation to lens cell types Lens fibre-epithelium-capsule.jpg
Microscope image of lens capsule in relation to lens cell types

The lens capsule is a component of the globe of the eye. [1] It is a clear elastic basement membrane similar in composition to other basement membranes in the body. The capsule is a very thick basement membrane [2] and the thickness varies in different areas on the lens surface and with the age of the animal. It is composed of various types of fibers such as collagen IV, [3] laminin, etc. [4] [5] [6] and these help it stay under constant tension. [7] The capsule is attached to the surrounding eye by numerous suspensory ligaments and in turn suspends the rest of the lens in an appropriate position. As the lens grows throughout life so must the capsule. Due to the shape of the capsule, the lens naturally tends towards a rounder or more globular configuration, a shape it must assume for the eye to focus at a near distance. Tension on the capsule is varied to allow the lens to subtly change shape to allow the eye to focus in a process called accommodation.

Contents

Early in embryonic development the lens capsule is highly vascularized but later during embryo development becomes avascular and transparent, serving as a diffusion barrier helping to protect the lens. It is permeable to low molecular weight compounds, [8] but restricts the movement of larger things like bacteria, viruses and large colloidal particles. [9] As the capsule contains the lens, it is clinically significant in regard to surgery of the lens. For example, it is used to contain new artificial lenses implanted after cataract surgery.

Anatomy

Micrographs and 3D drawing of a "foot" structures on eye lens capsules Figure1-micropublish4.jpg
Micrographs and 3D drawing of a "foot" structures on eye lens capsules

The lens capsule is a transparent membrane that surrounds the entire lens. The capsule is thinnest at the posterior pole with approximate thickness of 3.5μm. Average thickness at the equator is 7μm. [7] [10] Anterior pole thickness increases with age from 11-15μm.[ clarification needed ] The thickest portion is the annular region surrounding the anterior pole. This will also increase with age (from 13.5-16μm).[ clarification needed ] [11] The ligaments suspending the lens form attachments in the equatorial area and more so just to the front and back of the equator. [12] There are tens of thousands of these ligaments in a mouse lens and for the most part they appear to connect directly to the lens capsule. [13] As the lens grows throughout the life of most vertebrates the capsule is required to grow as well. [14] As shown in the accompanying micrographs and diagrams, equatorial cells can have periodic cellular processes penetrating the capsule.

A thin section showing two feet penetrating into the lens capsule. The capsule appears just under 10 microns thick in this micrograph though the apparent thickness will vary with the angle of section cut so the actual thickness may be less. Large numbers of small vesicles can also be seen Ligament club attachments.jpg
A thin section showing two feet penetrating into the lens capsule. The capsule appears just under 10 microns thick in this micrograph though the apparent thickness will vary with the angle of section cut so the actual thickness may be less. Large numbers of small vesicles can also be seen
One of the feet and higher magnification. Thin pale fibres can just be seen within the cytoplasm Ligament club end.jpg
One of the feet and higher magnification. Thin pale fibres can just be seen within the cytoplasm
Structure on the outside surface of eye lens capsule at equator showing the fused cells and vesicles associated with it Ligament anchor5.png
Structure on the outside surface of eye lens capsule at equator showing the fused cells and vesicles associated with it

The structures in the images are consistent with the laying down of new capsular material required for growth. [15] Even though the capsule is a highly elastic structure, [16] it contains no elastic fibers. Elasticity is because of the thick lamellar arrangement of the collagen fibers. [11]

Function

The capsule helps give the lens its more spherical shape in aquatic vertebrates such as fish and more ellipsoidal shape in land based vertebrates such as sheep. In humans the lens ellipsoid becomes more flattened with age. [17] The capsule is the basement membrane for the epithelial cells at the front of the lens and the rapidly growing more flexible fiber cells of the back of the lens and below the epithelium at the front. Without the capsule substrate forming a tense support these cells lose their form as in the picture of a decapsulated sheep lens.

A sheep lens with the capsule stripped off. The classic lens shape is practically lost without the support of the capsule. Decapsulated sheep lens.jpg
A sheep lens with the capsule stripped off. The classic lens shape is practically lost without the support of the capsule.

Accommodation

Normally, when ciliary muscles are in a relaxed state, the zonules will pull the capsule. Due to this zonular tension anterior lens surface is flatter resulting in more distant objects being in focus. When ciliary muscles contract, the zonular tension will reduce allowing lens to assume more spherical shape. This shape change increases the focusing power of the eye allowing closer objects to come into focus. The process of changing the lens's focusing power to see closer objects more clearly is known as accommodation.

Embryology

Lens embryogenisis Lens embryogenisis.svg
Lens embryogenisis

The lens vesicle is developed from surface ectoderm. [18] It will separate from surface ectoderm at approximately day 33 in a human and only 3 days for a chicken. Lens capsule developed from basal lamina of lens vesicle will cover early lens fibers. Capsule is evident at 5 weeks of human gestation and begins its role in protecting and supporting the lens interior. [11]

Lens protection

Early embryologic development of lens capsule give lens material an immune privilege. [19] It will also help protect the lens from virus, bacteria and parasites. [20] [11] [21]

Vascular lens capsule

During fetal development vascular lens capsule (tunica vasculosa lentis) develops from the mesenchyme that surrounds the lens. [18] It receives arterial blood supply from the hyaloid artery. [9] This blood supply slowly regresses and the vascular capsule disappears before birth. The disappearance of the anterior vascular capsule of the lens is useful in estimating the gestational age. [22] While the vascularization disappears during gestation the micrographs in this article show cells still active on the lens exterior after vascular regression. These cells may be the avascular portion of the original mesenchyme that surrounded the lens.

Clinical significance

In intra-capsular cataract extraction (ICCE), whole lens including the anterior part of the capsule is removed. During more common extra capsular cataract surgery procedures like micro incision cataract surgery, phacoemulsification etc., clouded lens is removed through opening made in anterior lens capsule. [23] The intraocular lens is then inserted into the lens capsule which is capable of rapid healing. [24] The best place for intraocular lens implantation is within the capsular bag. [25]

Posterior capsular opacification and posterior capsule rupture are common complications of cataract surgery. [26]

See also

Related Research Articles

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Glaucoma is a group of eye diseases that lead to damage of the optic nerve, which transmits visual information from the eye to the brain. Glaucoma may cause vision loss if left untreated. It has been called the "silent thief of sight" because the loss of vision usually occurs slowly over a long period of time. A major risk factor for glaucoma is increased pressure within the eye, known as intraocular pressure (IOP). It is associated with old age, a family history of glaucoma, and certain medical conditions or medications. The word glaucoma comes from the Ancient Greek word γλαυκός, meaning 'gleaming, blue-green, gray'.

<span class="mw-page-title-main">Cataract</span> Clouding of the lens inside the eye, causing poor vision

A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision of the eye. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colours, blurry or double vision, halos around light, trouble with bright lights, and difficulty seeing at night. This may result in trouble driving, reading, or recognizing faces. Poor vision caused by cataracts may also result in an increased risk of falling and depression. Cataracts cause 51% of all cases of blindness and 33% of visual impairment worldwide.

<span class="mw-page-title-main">Lens (vertebrate anatomy)</span> Eye structure

The lens, or crystalline lens, is a transparent biconvex structure in most land vertebrate eyes. Relatively long, thin fiber cells make up the majority of the lens. These cells vary in architecture and are arranged in concentric layers. New layers of cells are recruited from a thin epithelium at the front of the lens, just below the basement membrane surrounding the lens. As a result the vertebrate lens grows throughout life. The surrounding lens membrane referred to as the lens capsule also grows in a systematic way ensuring the lens maintains an optically suitable shape in concert with the underlying fiber cells. Thousands of suspensory ligaments are embedded into the capsule at its largest diameter which suspend the lens within the eye. Most of these lens structures are derived from the epithelium of the embryo before birth.

<span class="mw-page-title-main">Phacoemulsification</span> Method of cataract surgery

Phacoemulsification is a cataract surgery method in which the internal lens of the eye which has developed a cataract is emulsified with the tip of an ultrasonic handpiece and aspirated from the eye. Aspirated fluids are replaced with irrigation of balanced salt solution to maintain the volume of the anterior chamber during the procedure. This procedure minimises the incision size and reduces the recovery time and risk of surgery induced astigmatism.

<span class="mw-page-title-main">Intraocular lens</span> Lens implanted in the eye to treat cataracts or myopia

An Intraocular lens (IOL) is a lens implanted in the eye usually as part of a treatment for cataracts or for correcting other vision problems such as short sightedness and long sightedness; a form of refractive surgery. If the natural lens is left in the eye, the IOL is known as phakic, otherwise it is a pseudophakic lens. Both kinds of IOLs are designed to provide the same light-focusing function as the natural crystalline lens. This can be an alternative to LASIK, but LASIK is not an alternative to an IOL for treatment of cataracts.

<span class="mw-page-title-main">Ciliary body</span> Part of the eye

The ciliary body is a part of the eye that includes the ciliary muscle, which controls the shape of the lens, and the ciliary epithelium, which produces the aqueous humor. The aqueous humor is produced in the non-pigmented portion of the ciliary body. The ciliary body is part of the uvea, the layer of tissue that delivers oxygen and nutrients to the eye tissues. The ciliary body joins the ora serrata of the choroid to the root of the iris.

<span class="mw-page-title-main">Cataract surgery</span> Removal of opacified lens from the eye

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<span class="mw-page-title-main">Accommodation (vertebrate eye)</span> Focusing ability of eye

Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies. In this, distances vary for individuals from the far point—the maximum distance from the eye for which a clear image of an object can be seen, to the near point—the minimum distance for a clear image. Accommodation usually acts like a reflex, including part of the accommodation-convergence reflex, but it can also be consciously controlled.

<span class="mw-page-title-main">Ciliary muscle</span> Eye muscle which is used for focussing

The ciliary muscle is an intrinsic muscle of the eye formed as a ring of smooth muscle in the eye's middle layer, the uvea. It controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humor into Schlemm's canal. It also changes the shape of the lens within the eye but not the size of the pupil which is carried out by the sphincter pupillae muscle and dilator pupillae.

<span class="mw-page-title-main">Zonule of Zinn</span> Part of the eye

The zonule of Zinn is a ring of fibrous strands forming a zonule that connects the ciliary body with the crystalline lens of the eye. These fibers are sometimes collectively referred to as the suspensory ligaments of the lens, as they act like suspensory ligaments.

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Ectopia lentis is a displacement or malposition of the eye's lens from its normal location. A partial dislocation of a lens is termed lens subluxation or subluxated lens; a complete dislocation of a lens is termed lens luxation or luxated lens.

<span class="mw-page-title-main">Iridodialysis</span> Medical condition

Iridodialysis is a localized separation or tearing away of the iris from its attachment to the ciliary body.

<span class="mw-page-title-main">Glaucoma surgery</span> Type of eye surgery

Glaucoma is a group of diseases affecting the optic nerve that results in vision loss and is frequently characterized by raised intraocular pressure (IOP). There are many glaucoma surgeries, and variations or combinations of those surgeries, that facilitate the escape of excess aqueous humor from the eye to lower intraocular pressure, and a few that lower IOP by decreasing the production of aqueous humor.

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<span class="mw-page-title-main">Capsulotomy</span> Incision into the capsule of the crystalline lens of the eye

Capsulotomy is a type of eye surgery in which an incision is made into the capsule of the crystalline lens of the eye. In modern cataract operations, the lens capsule is usually not removed. The most common forms of cataract surgery remove nearly all of the crystalline lens but do not remove the crystalline lens capsule. The crystalline lens capsule is retained and used to contain and position the intraocular lens implant (IOL).

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<span class="mw-page-title-main">Secondary glaucoma</span>

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Uveitis–glaucoma–hyphaema (UGH) syndrome, also known as Ellingson syndrome, is a complication of cataract surgery, caused by intraocular lens subluxation or dislocation. The chafing of mispositioned intraocular lens over iris, ciliary body or iridocorneal angle cause elevated intraocular pressure (IOP) anterior uveitis and hyphema. It is most commonly caused by anterior chamber IOLs and sulcus IOLs but, the condition can be seen with any type of IOL, including posterior chamber lenses and cosmetic iris implants.

<span class="mw-page-title-main">Lens induced glaucomas</span> Disorder of the human eye

The crystalline lens inside the human eye has been implicated as a causative factor in many forms of glaucoma. Lens induced glaucomas or Lens related glaucomas are either open-angle or closed-angle glaucomas that can occur due to a neglected advanced cataract or a dislocated lens. It is a type of secondary glaucoma. The angle-closure glaucoma can be caused by a swollen or dislocated lens. The open-angle glaucoma can be caused by leakage of lens proteins through the capsule of a mature or hyper mature cataract or by a hypersensitivity reaction to own lens protein following surgery or penetrating trauma.

Manual small incision cataract surgery (MSICS) is an evolution of extracapsular cataract extraction (ECCE); the lens is removed from the eye through a self-sealing scleral tunnel wound. A well-constructed scleral tunnel is held closed by internal pressure, is watertight, and does not require suturing. The wound is relatively smaller than that in ECCE but is still markedly larger than a phacoemulsification wound. Comparative trials of MSICS against phaco in dense cataracts have found no statistically significant difference in outcomes but MSICS had shorter operating times and significantly lower costs. MSICS has become the method of choice in the developing world because it provides high-quality outcomes with less surgically induced astigmatism than ECCE, no suture-related problems, quick rehabilitation, and fewer post-operative visits. MSICS is easy and fast to learn for the surgeon, cost effective, simple, and applicable to almost all types of cataract.

References

  1. ↑ "Mode of Discovering the Proper Capsule of the Crystalline Lens". The London Medical and Physical Journal. 34 (202): 453–454. December 1815. PMC   5594332 . PMID   30493699.
  2. ↑ Yanoff, Myron. (2009). "Lens". Ocular pathology. Sassani, Joseph W. (6th ed.). Edinburgh: Mosby/Elsevier. ISBN   978-0-323-04232-1. OCLC   294998596.
  3. ↑ DISCHE, Z; ZELMENIS, G (April 1965). "The Content and Structural Characteristics of the Collagenous Protein of Rabbit Lens Capsules at Different Ages". Investigative Ophthalmology. 4: 174–80. PMID   14283010.
  4. ↑ Mohan, PS; Spiro, RG (25 March 1986). "Macromolecular organization of basement membranes. Characterization and comparison of glomerular basement membrane and lens capsule components by immunochemical and lectin affinity procedures". The Journal of Biological Chemistry. 261 (9): 4328–36. doi: 10.1016/S0021-9258(17)35665-X . PMID   3512568.
  5. ↑ Halfter, W; Candiello, J; Hu, H; Zhang, P; Schreiber, E; Balasubramani, M (January 2013). "Protein composition and biomechanical properties of in vivo-derived basement membranes". Cell Adhesion & Migration. 7 (1): 64–71. doi:10.4161/cam.22479. PMC   3544788 . PMID   23154404.
  6. ↑ Danysh, BP; Duncan, MK (February 2009). "The lens capsule". Experimental Eye Research. 88 (2): 151–64. doi:10.1016/j.exer.2008.08.002. PMC   2674021 . PMID   18773892.
  7. 1 2 Fisher, RF (March 1969). "Elastic constants of the human lens capsule". The Journal of Physiology. 201 (1): 1–19. doi:10.1113/jphysiol.1969.sp008739. PMC   1351628 . PMID   5773553.
  8. ↑ Kastner, Christian; Löbler, Marian; Sternberg, Katrin; Reske, Thomas; Stachs, Oliver; Guthoff, Rudolf; Schmitz, Klaus-Peter (October 2013). "Permeability of the Anterior Lens Capsule for Large Molecules and Small Drugs". Current Eye Research. 38 (10): 1057–1063. doi:10.3109/02713683.2013.803288. PMID   23885713. S2CID   21090856.
  9. 1 2 Snell, Richard S. (2012). "Development of the Eye and the Ocular Appendages". Clinical anatomy of the eye. Lemp, Michael A. (2nd ed.). Malden, MA, USA: Blackwell Science. ISBN   978-0-632-04344-6. OCLC   37580703.
  10. ↑ Salemann, M (1912). The Anatomy and Biology of the Human Eyeball in the Normal State. Chicago: University of Chicago Press. p. 165.
  11. 1 2 3 4 Clinical anatomy and physiology of the visual system (3rd ed.). Elsevier/Butterworth-Heinemann. 2012. ISBN   978-1-4377-1926-0.
  12. ↑ Shi, Yanrong; Tu, Yidong; De Maria, Alicia; Mecham, Robert P.; Bassnett, Steven (1 April 2013). "Development, Composition, and Structural Arrangements of the Ciliary Zonule of the Mouse". Investigative Ophthalmology & Visual Science. 54 (4): 2504–2515. doi:10.1167/iovs.13-11619. PMC   3621578 . PMID   23493297.
  13. ↑ Bassnett, Steven (May 2021). "Zinn's zonule". Progress in Retinal and Eye Research. 82: 100902. doi:10.1016/j.preteyeres.2020.100902. PMC   8139560 . PMID   32980533.
  14. ↑ The eye : basic sciences in practice. London: W.B. Saunders. 1996. ISBN   0-7020-1790-6.
  15. ↑ Gruijters, Wouterus TM (1 July 2024). "A new eye lens structure associated with capsule/basement membrane growth". MicroPublication Biology. doi:10.17912/micropub.biology.000828. PMC   11320119 . PMID   39139582.
  16. ↑ Bowman, W (1849). Lectures on the Parts Concerned in the Operations on the Eye and on the Structure of the Retina. Londan: Longmans.
  17. ↑ "Lens Capsule". American Academy of Ophthalmology. 1 October 2019.
  18. 1 2 Young, P (January 1858). "On the Development of the Eye in the Chick". The British and Foreign Medico-chirurgical Review. 21 (41): 187–204. PMC   5186056 . PMID   30164458.
  19. ↑ Lang, RA (January 1997). "Apoptosis in mammalian eye development: lens morphogenesis, vascular regression and immune privilege". Cell Death and Differentiation. 4 (1): 12–20. doi: 10.1038/sj.cdd.4400211 . PMID   16465205. S2CID   10466397.
  20. ↑ Karkinen-Jääskeläinen, M; Saxén, L; Vaheri, A; Leinikki, P (1 June 1975). "Rubella cataract in vitro: Sensitive period of the developing human lens". The Journal of Experimental Medicine. 141 (6): 1238–48. doi:10.1084/jem.141.6.1238. PMC   2189850 . PMID   1092795.
  21. ↑ Tham, MH; Hall, IB (July 1971). "Impacted microfilaria in the lens capsule". The British Journal of Ophthalmology. 55 (7): 484–6. doi:10.1136/bjo.55.7.484. PMC   1208424 . PMID   5557527.
  22. ↑ Hittner, H. M.; Hirsch, N. J.; Rudolph, A. J. (September 1977). "Assessment of gestational age by examination of the anterior vascular capsule of the lens". The Journal of Pediatrics. 91 (3): 455–458. doi:10.1016/s0022-3476(77)81324-3. ISSN   0022-3476. PMID   894419.
  23. ↑ Fitzgerald, CE (22 November 1879). "Peripheral Division of the Capsule of the Lens". British Medical Journal. 2 (986): 811–2. doi:10.1136/bmj.2.986.811. PMC   2240914 . PMID   20749364.
  24. ↑ McDonnell, PJ; Patel, A; Green, WR (September 1985). "Comparison of intracapsular and extracapsular cataract surgery. Histopathologic study of eyes obtained postmortem". Ophthalmology. 92 (9): 1208–25. doi:10.1016/s0161-6420(85)33875-7. PMID   4058884.
  25. ↑ Mehta, Rajvi; Aref, Ahmad A (27 November 2019). "Intraocular Lens Implantation In The Ciliary Sulcus: Challenges And Risks". Clinical Ophthalmology. 13: 2317–2323. doi: 10.2147/OPTH.S205148 . ISSN   1177-5467. PMC   6885568 . PMID   31819356.
  26. ↑ John F, Salmon (13 December 2019). Kanski's clinical ophthalmology : a systematic approach (9th ed.). Elsevier. ISBN   978-0-7020-7711-1.
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