Lens I

Greek root word for lens?

Phak-

Posteriorly, the lens rests in the ________ _____

Patellar fossa

There is about a ____ mm gap between the edge of the lens and the pars plicata

0.5 mm

The lens is held in place by _______ ______

Zonular fibers

A thickening of vitreous that acts as a ligament around the space of Berger?

Hyaloid-capsular ligament (Wieger's)

Potential space in front of patellar fossa?

Space of Berger

Where zonules attach to the lens capsule?

Zonular girdle

Aqueous space around lens equator?

Circumlental space

Three parts of the lens:

Capsule

Epithelium

Lens fibers

The lens fibers are formed from the _______________ cells

Epithelial

The fibers in the center of the lens?

Nucleus

Fibers outside of the center of the lens?

Cortex

The lens is (vascular/avascular)

Avascular (after birth)

Does the lens stop growing?

No

Is the lens flexible?

Yes, until presbyopia

Lens placode forms from thickened _______ _________

Surface ectoderm

Lens pit forms as placode invaginates along with _____ ____

Optic cup

(posterior/anterior) epithelium elongate and become primary lens fibers during development.

Posterior

Do primary lens fibers have organelles?

NO

Does the lens have an anterior epithelium?

Yes

Does the lens have a posterior epithelium? (after development)

No

_____ ______ surrounds the lens vesicle during development.

Basal Lamina

After lens development, where do lens secondary fibers come from?

Anterior epithelium

Lens vascular supply during development? (2)

Anterior pupillary membrane

Posterior tunica vasculosa lentis (from hyaloid artery)

What is remanent of the anterior pupillary membrane called?

persistent pupillary membrane

What is a remanent on the hyaloid artery on the lens that looks just like a dot?

Mittendorf dot

What is a complete remanent of the hyaloid artery in the vitreal segment of the eye?

persistent hyaloid

Secondary lens fibers elongate in the ___________ region.

Equatorial

Three zones of epithelium?

Central

Intermediate

Equatorial

Central cells of lens epithelium are more (cuboidal/columnar)

Cuboidal

What do central cells of lens epithelium do?

Not much! Only undergo mitosis in disease or injury

Shape of intermediate zone lens epithelium cells?

Low columnar

Which zone of lens epithelium is home to the germinal zone?

Intermediate zone

Cells are differentiating as they approach the _______

Equator

At the equatorial zone, cells begin to produce ___________

Crystallins

What triggers lens epithelium cell differentiation?

Vitreous growth factors

As cells continue to elongate, (apical/basal) processes progress anteriorly underneath the epithelium

Apical

As cells continue to elongate, (apical/basal) processes move posterior underneath the capsule

Basal

As fibers form, they eventually lose what two things?

Nuclei

Attachment to basement membrane

What lens sutures are formed during embryogenesis? (2)

Upright Y anteriorly

Inverted Y posteriorly

Is there a suture in an embryonic nucleus?

no (only fetal)

Why do sutures form in the lens?

Lens fibers meet

Can we ever see Y sutures in the slit lamp?

Yes, although often subtle

Do lens fibers run the full circumference of the lens?

No

When is the embryonic lens nucleus formed?

During first trimester by primary fibers

When is the fetal lens nucleus formed?

Before birth, includes sutures

When is the adult nucleus formed?

Before sexual maturity

Two layers of the lens capsule?

Inner cuticular layer

External zonular layer

Is the lens capsule consistently thick?

No, varbiable

Where is the lens capsule thickest?

Ring zone 6mm from pupillary axis on anterior side

Where is the lens capsule thinnest?

Posterior pole

The inner cuticular layer is secreted by the __________ and ___________ _____ _____

Epithelium

Superficial fiber cells

The inner cuticular layer is composted of (one/multiple) lamina

Multiple

The inner cuticular layer is secreted from the (inside/outside)

Inside, pushes older capsule out

The inner cuticular layer is mostly made of type __ collagen.

IV

Does the inner cuticular layer contain elastins?

No, but arrangement of fibers makes it elastic-y

Where is the outer zonular layer found?

3-4 mm zone around equator

What is the function of the outer zonular layer of the lens capsule?

Insertion point for zonular fibers.

Cell shape in lens epithelium varies based on if cells are _______ or not.

Mitiotic

(Mitotic/non-mitotic) cells are hexagonal in shape.

Non-mitotic

(Mitotic/non-mitotic) cells have many lateral interdigitations.

Non-mitotic

Do epithelial cells have basal infoldings?

YES, numerous

What is the function of basal infoldings?

Increase surface area

Lateral features of lens epithelial cells? (3)

Gap Junctions

Zonula occludens

Desmosomes

Lens fibers are roughly __________ in shape.

Hexagonal

Lens fibers have many ________________.

Interdigitations (ball-and-socket)

What is the function of interdigitations?

Less interstitial fluid between fibers, maintaining clarity and consistent refractive index

What cytoplasmic proteins make up 35-40% of the lens weight?

Crystallins

Which region of the lens has the highest distribution of crystallins?

Nucleus

Uneven distribution of crystallins creates a _______ refractive index of the lens

Gradient (1.38-1.41)

Benefits of a gradient refractive index in the lens?

Reduce spherical aberration

Features of lens fiber cell membranes? (4)

High proportion of cholesterol

Major intrinsic polypeptide (insoluble protein)

Gap junction plaques

Actin cytoskeleton

Lens develops a ______ _____ as we age.

Yellow tinge (from pigment in ground substance)

Does the lens grow taller throughout the life?

No, stops at about 9mm at age 4

Does the lens grow wider throughout the life?

Yes, can be over 5mm in old age

Weight change in lens throughout life?

60-65 mg at birht, 200mg in old age

What happens when a lens fiber reaches the suture? (3)

Adheres to fiber from across the way

Detaches from capsule

Loses membrane bound organelles

Zonules insert into lens capsule and what else?

Basal lamina of non-pigmented ciliary epithelium

Main structural protein in zonules?

Fibrillin

How are zonules names?

By where they attach

Which condition is a mutation to fibrillin gene resulting in lens dislocation?

Marfans

4 kinds of zonules?

Ubiculo-anterocapsular

Obiculo-posterocapsular

Auxillary/secondary

Equatorial

Zonules insert more (anteriorly/posteriorly) over time

Anteriorly (this may contribute to presbyopia)

Accommodation occurs via the _______ ______.

Ciliary muscle

Three regions of ciliary muscle?

Longitudinal

Radial

Circular

If you removed your lens from your eye, it would be (accommodated/unaccommodatied) shape

Accommodated

Does the vitreous play a role in accommodation?

Some, axial length decreases when accommodating

What age does loss of accommodative amplitude begin?

about 18

Factors that likely contribute to presbyopia? (5)

Aging changes to zonules

Lens capsule becomes rigid

Lens fibers become rigid

Index of refraction of lens changes

Less elasticity at ciliary muscle insertion

A loss of accommodation can also result in a change in ________.

Vergence

Unaccommodated lens radii of curvature? (2)

Anterior 10mm

Posterior 6mm

Accommodated lens radii of curvature?

Both about 5.33 mm

What is the major refractive surface of the eye?

Cornea