Anatomy of EYE

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Text of Anatomy of EYE


    Prof. Naimatullah Khan KundiHead, Department of OphthalmologyKhyber Teaching Hospital Peshawar

  • Lens Crystalline Lens Position behind the iris Refract light rays Focuses on the retina

  • Lens FunctionsMaintains 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

  • LensAphakia absence of the lensResults in loss of 20 D of refractive powerA vascular Obtains nutrition from the surrounding fluids Glucose provides the lens with chemical energy required to continue growth and maintain transparency

  • LensBiconvexAnterior Pole The most anterior partPosterior Pole The most posterior partEquator The peripheral area

  • Lens & Cataract AnatomyNormal Crystalline LensTransparent , Biconvex, AvascularRefractive Power: 15-20 of convergenceAxis: Imaginary line between Ant. & Post. Poles of the lensEquater: Greatest circuferenceMeridians: Lines on the surface from one pole to the other

  • Normal Crystalline Lens (Contd)Zonular Fibers: From CB to Lens (Ant. & Post.)Capsule: BM that Encloses the nucleus, Cortex and Lens epitheliumGrowth: Grows Continuously through lifeAt birth: Wt. 90mg, AP 3.5 mm, Equatorially 3.5mmAdult: Wt. 225 mg, AP 5 mm, Equatorially 9mmLens & Cataract Anatomy

  • Normal Crystalline Lens (Contd)

    Older lens: More Curved More refractive powerRefractive index decrease with age (? Increased insoluble proteins)Eye Hyperopic / Myopic with age depending upon the balance of these opposing changesLens & Cataract Anatomy

  • Lens & Cataract AnatomyNormal Crystalline LensLens CapsuleElastic, Transparent, BM (Type IV Collagen, Laid down by epithelial cells)Moulds the lens substance during the accommodative changesOuter layer (zonular lamella) serves as the point of attachment of zonular fibers

  • Normal Crystalline LensLens CapsuleThickest regions: Ant. & Post. Pre-equatorial zonesThinnest regions: Central Post. Pole (2-4 m)

    Lens & Cataract Anatomy

  • Lens & Cataract AnatomyNormal Crystalline Lens Zonular FibersSupport the lensOrigin: Basal lamina of non-pigmented epithelium of Pars Plana & Pars Plicata of CBInsertion: Equatorial region 1.5 mm onto Ant. & Post. CapsuleEquatorial zonular fibers regress with age, leaving triangular area

  • Lens & Cataract AnatomyNormal Crystalline LensLens EpitheliumA single layer beneath the anterior lens capsuleActive metabolically

  • Lens & Cataract AnatomyNormal Crystalline LensLens EpitheliumNewly 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 AnatomyNormal Crystalline LensLens EpitheliumThe cells loose organells (mitochondria, nuclei, ribosomes) Lens fibers dependent on glycolysis for energy production Advantage: No light absorption/scatter

  • Lens & Cataract AnatomyNormal Crystalline LensNucleus & CortexNew lens fibers laid down through out the lifeThus crowding and compression of older fibersEmbryonic and fetal nuclei oldestOuter most fibers recent (cortex)

  • Lens & Cataract AnatomyNormal Crystalline LensNucleus & CortexLens sutures (anterior and posterior Y)Formed by interdigitations of apical and basal cell process

  • Lens & Cataract AnatomyNormal Crystalline LensNucleus & CortexSL biomicroscopy Shows multiple optical zones, having different optical densities Nucleus, epinucleues, Cortex