Anatomi Fis Lensa
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Transcript of Anatomi Fis Lensa
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Literature review
dr. Alie Solahuddin, SpM
DEPARTMEN OF OPHTHALMOLOGY
MEDICAL FACULTY OF SRIWIJAYA UNIVERSITY/
DR. MOHD HOESIN HOSPITAL PALEMBANG
2007
Anatomy and Physiology of the Lens
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BACKGROUND
Lens is a transparent, avascular, biconvex
structure.
It lies between the aqueous humor at the
anterior of it and the vitreous humor at the
posterior of it.
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BACKGROUND
Lens has a composition of 65% water and
35% protein which consists of water
soluble and water insoluble protein.
Main function of the lens is to focus rays
toward retina.
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EMBRYOLOGY
Indentations at left and right of diencephalons (starting at22nd day of gestation)
optic vesicles
ectoderm
lens plate/ lens placode
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EMBRYOLOGY
Lens vesicle
Invagination
Lens vesicle (33rd day)
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EMBRYOLOGY
Cells of posterior wall elongates to anterior, filling the vesicles
lumen, so that the lumen is gone (40th day) primary lens fiber.
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EMBRYOLOGY
In 7th week, equatorial lens epithelial cells multiply secondary lens fiber
to the posterior and anterior of the lens sutures
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EMBRYOLOGY
Vascularization of lens in its embryonic days
Tunica vasculosa lentis grows as the lens grows
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ANATOMY
Lens is an avascular, transparant,biconvex structure with a 4 mm thicknessand a diameter of 9 mm
Lens is suspended in its position byzonula zinni (lig. suspensorium lentis)which attached to equator of the lens andconnects it to ciliary body.
It is a curved plate posterior>anterior
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ANATOMY
Differences Birth Adult
Diameter 6.4 mm 9 mm
Thickness 3.5 mm 5 mm
Weight 90 mg 255 mg
Consistency Soft and pliable Stiff
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ANATOMY
Substructures of thelens
1. Capsule is a basalmembrane formed bylens epithelial cellswhich covers the
whole lens.
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ANATOMY
Lens epithelium
isa layer of cellswhich cover theanterior part of lens.
At the equator ofthe lens, these cells
elongate into ameridian columnarcells.
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ANATOMY
3. Nucleus andcortex: Nucleus is the center of
the lens, made of theoldest lens fibers;
Cortex is formed fromthe peripheral fibersrecently formed.
The sutures formed
from the lens fibers isseen for the differingoptical densitiesbetween apical andbasal cell processes.
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ANATOMY
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HISTOLOGY
Composed of epithelial cells with several
junctions between them
Some of the important structures are:
1. Plasma membrane
2. Lens capsule
3. Epithelial cells4. Lens fibers
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HISTOLOGY
Plasma membrane
Is a selective permeable membrane which
consists of a bilayer phospholipid
Has some junctions, such desmosomes,
gap and tight junctions
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HISTOLOGY
Lens capsule
Is derived from the basal membrane of
epithelial cell. This membrane shows a
laminar structure. Each lamina consists ofseveral layer of tiny parallel collagen
filaments
Its anterior part is growing with time, unlikeits posterior part
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HISTOLOGY
Epithelial cells
Forms a single layer of cells beneath anterior
and equator capsule
These cells are cuboid at vertical cross
section and hexagonal at transversal cross
section
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HISTOLOGY
Lens fibers
Forms the nucleus and cortex of the lens
Has some unique junctions to maintain the
lens structure
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HISTOLOGY
Light micrograph of superficial human lens, close to the anterior equator showing the lenscapsule, epithelium and layers of cortical lens fibres
Zonular fibres close to
the capsule CapsuleEpithelium (transition zone)
Lens fibres
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BIOCHEMISTRY
Protein of the lens
Water soluble Water insoluble
Alpha Beta, gamma Soluble in 8molar urea
Insoluble in 8molar urea
Molecular biology of lens
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BIOCHEMISTRY
Metabolism of lens
The most important metabolism in the lens
is the metabolism of glucose
2 main pathway of glucose metabolism:
1. HMP shunt (provides 5% of ATP)
2. Glycolysis (provides the rest of ATP)
Oxidative damage and protectivemechanism (antioxidants)
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GLUCOSE METABOLISM
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PHYSIOLOGY
1. Maintenance of lens water and cation balancea. Active transport
b. Leak-pump theory
A process of maintaining the clarity of lens by the
combination of epithelial active transport andpermeability
2. AccommodationAn ability of lens to change its shape and thus itsretractile index by the help of ciliary body and
zonular fibres
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PHYSIOLOGY
Pump-leak theory
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ANOMALIES
Congenital Aphakia
Lenticonus and Lentiglobus
Lens Coloboma Mittendorf Dot
Epicapsular Star
Peters Anomaly
Microspherophakia Aniridia
Congenital and Infantile Cataract
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ANOMALIES
Acquired anomalies can be caused by UV
radiation or lens composition change
(cataract)
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LENS EXAMINATION
One of the examination of the lens byflashlight is the shadow test.
This test is used to know the opacity of the
lens Positive result shows low opacity of the
lens (immature cataract), while negative
result shows high opacity of the lens(mature cataract)
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CONCLUSION
Lens main function is to refract light and to
provide accommodation
To maintain its functions, its clarity must be
preserved The most important metabolism to maintain the
clarity of lens is the glucose metabolism
Radiation and aging can reduce the clarity oflens and promote cataract
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