dr yahya al-falki md kku-college of medicine ophthalmology-undergraduate lecture series ocular...
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DR YAHYA AL-FALKI MDKKU-COLLEGE OF MEDICINE
OPHTHALMOLOGY-UNDERGRADUATE LECTURE SERIES
Ocular Physiology
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Objectives
To be familiar with normal functions of ocular
structures.Clinical applications.
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Eye Lids
The eye lids form the anterior –most part of the visual system.
Anatomically consists of two parts.Frequent blink is essential for corneal
protection.Eye lids contribute to the tear film.They are parts of facial expressions.
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Tear Film
It is highly specialized and well-organizedMoist film.It covers the ocular surface.The rate of secretion is 1-2/minute
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The Tear Film
The Tear Film is composed of three layers:1-Superficial Lipid Layer.2-Middle Aqueous Layer.3-Posterior Mucin Layer.
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Functions
Smooth optical surface.
Cleans the ocular surface.
Lubrication
Antimicrobial activity.
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Lacrimal System
Tear secretion balanced with drainage.
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Conjunctiva
It is a mucous membrane . It comprises epithelium ,basement
membrane and stroma. It contributes to the tear film.
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Cornea
Clear refractive surface.Protective barrier .Thinnest centrally and thicker
peripherally.5 histological layers.Epithelium and endothelium are
lipophilic.
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Corneal Drug Permeability
Factors contribute to drug permeability:1-Lipid Solubility.2-Water Solubility.
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Cornea
Corneal Transparency -Partially
dehydrated. -Regular orientation
of stromal collagen. - It is avascular.Corneal shape is maintained by structural rigidity and intra ocular pressure.
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Corneal Decompensation
Endothelial cell count is lower than the threshold
number.Severe endothelial damage= irreversible
corneal oedema
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Aqueous Humour
It is clear colorless solution.It produced by ciliary body.It is different from plasma.It leaves the eye by trabecular route.
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Uveal Tract
The pupil is dynamic structure.Contraction of ciliary body permits
accommodation and trabecular outflow.Choroid has highest ocular blood flow.
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Iris&Pupil
The human pupil is circular aperture situated near the center of the iris.
Pupillary diameter regulated by:1-The sphincter.2-The dialator. contraction of the sphincter makes the pupil
smaller .Contraction of the dialator enlarges the pupil.
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Sclera
Tough Outer Coat.Comlete Sphere.It is thickest around and thinnest just
posterior toIt is avascular .It is opaque .Low metabolic demand.
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Lens
It is atransparent biconex strucure.It has low water and high protein.It is relatively hypoxic.It has the ability to change shape.It has antioxidant mechanisms.
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Accommodation Cascade
Ciliary muscle contraction
Zonules relaxe
Lens becomes more spherical
refractive power
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Presbyopia
The most common refractive disorder of older
people.It is due to stiffness of the aging
lens.
In emmetropes it is manifested at 40 what about myopes and
hypermetropes ???
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Glucose Metabolism
Lens is avascular and surrounded by aqueous and vitreous.
Glucose is metabolized through:1-Glycolytic Pathway2-Krebs Cycle3-hexose Monophosphate Shunt.4-Sorbitol Pathway.
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Diabetic Cataract
Glucose concentration in the aqueous is similar to that of plasma.
In diabetes there is increased aqueous sugar.Glucose will be converted to sorbitol.Sorbitol accumilation in the lens will lead to
diabetic cataract.
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Vitreous
80% of ocular volume.It is transparent gel.It has shock-absorbing capacity.The ageing vitreous becomes
progressively liquefied.
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Retina
Transparent light – transforming structure.It comprises photoreceptors interneurones ganglion cells retinal pigment epitheliumThe main function is phototransduction.
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Photochemistry of Vision
There are two photosensetive cells.The cones contain apigment known as
idoopsin.The rods contain apigment called rhodopsin.Light absorbed by the photoreceptor
pigments creating photochemical reactions.The photochemical product will initiate
electrical signals.
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Thank YOU