LENS & CATARACT

Prof. Naimatullah Khan KundiHead, Department of Ophthalmology

Khyber Teaching Hospital Peshawar

Lens

Crystalline Lens

Position behind the iris

Refract light rays

Focuses on the retina

Lens

Functions Maintains its own clarity Provides refractive power (by contributing

to the optical system of the eye) Provides accommodation - Allows the eye

to clearly focus objects (within a 6 m range)

Absorbs UV light

Lens

Aphakia – absence of the lens Results in loss of 20 D of refractive

power A vascular – Obtains nutrition from the

surrounding fluids Glucose – provides the lens with

chemical energy required to continue growth and maintain transparency

Lens

Biconvex

Anterior Pole – The most anterior part

Posterior Pole – The most posterior part

Equator – The peripheral area

Normal Crystalline Lens Transparent , Biconvex, Avascular

Refractive Power: 15-20 of convergence

Axis: Imaginary line between Ant. & Post.

Poles of the lens

Equater: Greatest circuference

Meridians: Lines on the surface from one pole

to the other

Lens & Cataract Anatomy

Normal Crystalline Lens (Cont’d) Zonular Fibers: From CB to Lens (Ant. & Post.)

Capsule: BM that Encloses the nucleus, Cortex

and Lens epithelium

Growth: Grows Continuously through life

At birth: Wt. 90mg, AP – 3.5 mm, Equatorially –

3.5mm

Adult: Wt. 225 mg, AP – 5 mm, Equatorially – 9mm

Lens & Cataract Anatomy

Normal Crystalline Lens (Cont’d)

Older lens: More Curved – More refractive power

Refractive index decrease with age (?

Increased insoluble proteins)

Eye – Hyperopic / Myopic with age

depending upon the balance of these

opposing changes

Lens & Cataract Anatomy

Normal Crystalline Lens

Lens Capsule

Elastic, Transparent,

BM (Type IV Collagen, Laid down by epithelial cells)

Moulds the lens substance during the accommodative

changes

Outer layer (zonular lamella) serves as the point of

attachment of zonular fibers

Lens & Cataract Anatomy

Normal Crystalline Lens

Lens Capsule Thickest regions: Ant. & Post. Pre-equatorial zones

Thinnest regions: Central Post. Pole (2-4µ m)

Lens & Cataract Anatomy

Lens & Cataract Anatomy

Normal Crystalline Lens

Zonular Fibers Support the lens

Origin: Basal lamina of non-pigmented epithelium of

Pars Plana & Pars Plicata of CB

Insertion: Equatorial region

1.5 mm onto Ant. & Post. Capsule

Equatorial zonular fibers regress with age,

leaving triangular area

Lens & Cataract Anatomy

Normal Crystalline Lens

Lens Epithelium

A single layer beneath the anterior lens capsule

Active metabolically

Lens & Cataract Anatomy Normal Crystalline Lens Lens Epithelium

Newly formed lens cells migrate toward equator

Change to lens fibers

In the bow region begins the process of terminal differentiation into lens fibers

Lens & Cataract Anatomy Normal Crystalline Lens Lens Epithelium

The cells loose organells (mitochondria, nuclei,

ribosomes)

Lens fibers dependent on glycolysis for energy

production

Advantage: No light absorption/scatter

Lens & Cataract Anatomy Normal Crystalline Lens Nucleus & Cortex

New lens fibers laid down through out the life

Thus crowding and compression of older fibers

Embryonic and fetal nuclei oldest

Outer most fibers recent (cortex)

Lens & Cataract Anatomy Normal Crystalline

Lens

Nucleus & Cortex

Lens sutures (anterior

and posterior “Y”)

Formed by

interdigitations of

apical and basal cell

process

Lens & Cataract Anatomy Normal Crystalline Lens Nucleus & Cortex

SL biomicroscopy

Shows multiple optical zones, having different optical

densities

Nucleus, epinucleues, Cortex