biology

Lens capsule

Lens capsule is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Lens capsule rather than just read about it. In short: The lens capsule is a component of the globe of the eye. It is a clear elastic basement membrane similar in composition to other basement membranes in the body.

Key takeaways

Lens capsule belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Lens capsule to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Lens capsule from memory before moving on to harder problems.

Reference excerpt

The lens capsule is a component of the globe of the eye. 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 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, laminin, etc. and these help it stay under constant tension. 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. 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, but restricts the movement of larger things like bacteria, viruses and large colloidal particles. 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

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

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

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. 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.

Accommodation

Normally, when ciliary muscles are in a relaxed state, the zonules will pull the capsule. Due to this zonular tension, the anterior lens surface is flatter resulting in more distant objects being in focus. When ciliary muscles contract, the zonular tension will reduce allowing the lens to assume a 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

The lens vesicle is developed from the surface ectoderm. It separates from the surface ectoderm at approximately day 33 in a human and only 3 days for a chicken. The lens capsule develops from the basal lamina of the lens vesicle and will cover early lens fibers. The capsule is evident at five weeks of human gestation and begins its role in protecting and supporting the lens interior.

Lens protection Early embryologic development of the lens capsule gives the lens material an immune privilege. It will also help protect the lens from viruses, bacteria and parasites.

Vascular lens capsule During fetal development, the vascular lens capsule (tunica vasculosa lentis) develops from the mesenchyme that surrounds the lens. It receives arterial blood supply from the hyaloid artery. 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. 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), 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. The intraocular lens is then inserted into the lens capsule which is capable of rapid healing. The best place for intraocular lens implantation is within the capsular bag. Posterior capsular opacification and posterior capsule rupture are common complications of cataract surgery.

Illustrations

Worked examples

Example 1 — a first encounter with Lens capsule

Start with the simplest possible case. Write down what Lens capsule claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Lens capsule before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Lens capsule ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Lens capsule

In research: Lens capsule appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Lens capsule in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Lens capsule is common in secondary-school and first-year university syllabi. It links to neighbouring topics Human eye anatomy, so understanding it makes those chapters shorter.
In everyday life: Look for Lens capsule outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Lens capsule” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Lens capsule in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Lens capsule means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Lens capsule out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Lens capsule in simple terms?

The lens capsule is a component of the globe of the eye. It is a clear elastic basement membrane similar in composition to other basement membranes in the body.

Why does Lens capsule matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Lens capsule?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Lens capsule.