lens capsule

File:Figure1-micropublish4.jpgThe 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.{{cite book |last1=Salemann |first1=M |title=The Anatomy and Biology of the Human Eyeball in the Normal State |date=1912 |publisher=University of Chicago Press |location=Chicago |page=165}} Anterior pole thickness increases with age from 11-15μm.{{clarify |date=August 2024 |reason=Does this mean "from 11 to 15μm"?}} The thickest portion is the annular region surrounding the anterior pole. This will also increase with age (from 13.5-16μm).{{clarify |date=August 2024 |reason=Does this mean "from 13.5 to 16μm"?}} The ligaments suspending the lens form attachments in the equatorial area and more so just to the front and back of the equator.{{cite journal |last1=Shi |first1=Yanrong |last2=Tu |first2=Yidong |last3=De Maria |first3=Alicia |last4=Mecham |first4=Robert P. |last5=Bassnett |first5=Steven |title=Development, Composition, and Structural Arrangements of the Ciliary Zonule of the Mouse |journal=Investigative Ophthalmology & Visual Science |date=1 April 2013 |volume=54 |issue=4 |pages=2504–2515 |doi=10.1167/iovs.13-11619|pmid=23493297 |pmc=3621578 }} 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.{{cite journal |last1=Bassnett |first1=Steven |title=Zinn's zonule |journal=Progress in Retinal and Eye Research |date=May 2021 |volume=82 |pages=100902 |doi=10.1016/j.preteyeres.2020.100902|pmid=32980533 |pmc=8139560 }} As the lens grows throughout the life of most vertebrates, the capsule is required to grow as well.{{cite book |title=The eye : basic sciences in practice |date=1996 |publisher=W.B. Saunders |location=London |isbn=0-7020-1790-6}} As shown in the accompanying micrographs and diagrams, equatorial cells can have periodic cellular processes penetrating the capsule.File:Ligament club attachments.jpg File:Ligament club end.jpgFile:Ligament anchor5.pngThe structures in the images are consistent with the laying down of new capsular material required for growth.{{cite journal |last1=Gruijters |first1=Wouterus TM |title=A new eye lens structure associated with capsule/basement membrane growth. |journal=MicroPublication Biology |date=1 July 2024 |doi=10.17912/micropub.biology.000828|pmid=39139582 |pmc=11320119 }} Even though the capsule is a highly elastic structure,{{cite book |last1=Bowman |first1=W |title=Lectures on the Parts Concerned in the Operations on the Eye and on the Structure of the Retina |date=1849 |publisher=Longmans |location=London}} it contains no elastic fibers. Elasticity is because of the thick lamellar arrangement of the collagen fibers.

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.{{cite web |title=Lens Capsule |url=https://www.aao.org/eye-health/anatomy/lens-capsule-definition#:~:text=The%20lens%20capsule%20is%20a,removes%20it%20with%20cataract%20surgery. |website=American Academy of Ophthalmology |language=en |date=1 October 2019}} 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.File:Decapsulated sheep lens.jpg

{{main|Accommodation (vertebrate eye)}}

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.

File:Lens embryogenisis.svg

The lens vesicle is developed from surface ectoderm.{{cite journal |last1=Young |first1=P |title=On the Development of the Eye in the Chick. |journal=The British and Foreign Medico-chirurgical Review |date=January 1858 |volume=21 |issue=41 |pages=187–204 |pmid=30164458|pmc=5186056 }} 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.{{cite book |title=Clinical anatomy and physiology of the visual system |year=2012 |publisher=Elsevier/Butterworth-Heinemann |isbn=978-1-4377-1926-0 |edition=3rd}}

Early embryologic development of the lens capsule gives the lens material an immune privilege.{{cite journal |last1=Lang |first1=RA |title=Apoptosis in mammalian eye development: lens morphogenesis, vascular regression and immune privilege. |journal=Cell Death and Differentiation |date=January 1997 |volume=4 |issue=1 |pages=12–20 |doi=10.1038/sj.cdd.4400211 |pmid=16465205|s2cid=10466397 |doi-access=free }} It will also help protect the lens from viruses, bacteria and parasites.{{cite journal |last1=Karkinen-Jääskeläinen |first1=M |last2=Saxén |first2=L |last3=Vaheri |first3=A |last4=Leinikki |first4=P |title=Rubella cataract in vitro: Sensitive period of the developing human lens. |journal=The Journal of Experimental Medicine |date=1 June 1975 |volume=141 |issue=6 |pages=1238–48 |doi=10.1084/jem.141.6.1238 |pmid=1092795|pmc=2189850 }}{{cite journal |last1=Tham |first1=MH |last2=Hall |first2=IB |title=Impacted microfilaria in the lens capsule. |journal=The British Journal of Ophthalmology |date=July 1971 |volume=55 |issue=7 |pages=484–6 |doi=10.1136/bjo.55.7.484 |pmid=5557527|pmc=1208424 }}

During fetal development vascular lens capsule (tunica vasculosa lentis) develops from the mesenchyme that surrounds the lens. It receives arterial blood supply from the hyaloid artery.{{Cite book|last=Snell, Richard S.|title=Clinical anatomy of the eye|publisher=Blackwell Science|others=Lemp, Michael A.|year=2012|isbn=978-0-632-04344-6|edition=2nd|location=Malden, MA, USA|chapter=Development of the Eye and the Ocular Appendages|oclc=37580703}} 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.{{Cite journal|last1=Hittner|first1=H. M.|last2=Hirsch|first2=N. J.|last3=Rudolph|first3=A. J.|date=September 1977|title=Assessment of gestational age by examination of the anterior vascular capsule of the lens|url=https://pubmed.ncbi.nlm.nih.gov/894419/|journal=The Journal of Pediatrics|volume=91|issue=3|pages=455–458|doi=10.1016/s0022-3476(77)81324-3|issn=0022-3476|pmid=894419}} 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.

In intra-capsular cataract extraction (ICCE), the 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., the clouded lens is removed through an opening made in the anterior lens capsule.{{cite journal |last1=Fitzgerald |first1=CE |title=Peripheral Division of the Capsule of the Lens. |journal=British Medical Journal |date=22 November 1879 |volume=2 |issue=986 |pages=811–2 |doi=10.1136/bmj.2.986.811 |pmid=20749364|pmc=2240914 }} The intraocular lens is then inserted into the lens capsule which is capable of rapid healing.{{cite journal |last1=McDonnell |first1=PJ |last2=Patel |first2=A |last3=Green |first3=WR |title=Comparison of intracapsular and extracapsular cataract surgery. Histopathologic study of eyes obtained postmortem. |journal=Ophthalmology |date=September 1985 |volume=92 |issue=9 |pages=1208–25 |doi=10.1016/s0161-6420(85)33875-7 |pmid=4058884}} The best place for intraocular lens implantation is within the capsular bag.{{cite journal |last1=Mehta |first1=Rajvi |last2=Aref |first2=Ahmad A |title=Intraocular Lens Implantation In The Ciliary Sulcus: Challenges And Risks |journal=Clinical Ophthalmology |date=27 November 2019 |volume=13 |pages=2317–2323 |doi=10.2147/OPTH.S205148 |pmid=31819356 |pmc=6885568 |issn=1177-5467|doi-access=free }}

Posterior capsular opacification and posterior capsule rupture are common complications of cataract surgery.{{cite book |last1=John F |first1=Salmon |title=Kanski's clinical ophthalmology : a systematic approach |date=13 December 2019 |isbn=978-0-7020-7711-1 |publisher=Elsevier |edition=9th}}

• Lens (vertebrate anatomy)

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Category:Human eye anatomy