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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