Download Ocular Physiology

Ocular Physiology
DR YAHYA AL-FALKI MD
KKU-COLLEGE OF MEDICINE
OPHTHALMOLOGY-UNDERGRADUATE
LECTURE SERIES
Objectives
 To be familiar with normal functions of ocular
structures.
 Clinical applications.
Eye Lids
 The eye lids form the anterior –most part of the
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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.
Tear Film
 It is highly specialized and well-organized
Moist film.
 It covers the ocular surface.
 The rate of secretion is 1-2/minute
The Tear Film
 The Tear Film is composed of three layers:
1-Superficial Lipid Layer.
2-Middle Aqueous Layer.
3-Posterior Mucin Layer.
Functions
 Smooth optical surface.
 Cleans the ocular surface.
 Lubrication
 Antimicrobial
activity.
Lacrimal System
 Tear secretion balanced with drainage.
Conjunctiva
 It is a mucous membrane .
 It comprises epithelium ,basement membrane and
stroma.
 It contributes to the tear film.
Cornea
 Clear refractive surface.
 Protective barrier .
 Thinnest centrally and thicker peripherally.
 5 histological layers.
 Epithelium and endothelium are lipophilic.
Corneal Drug Permeability
 Factors contribute to drug permeability:
1-Lipid Solubility.
2-Water Solubility.
Cornea
 Corneal Transparency
-Partially dehydrated.
-Regular orientation of stromal
collagen.
- It is avascular.
 Corneal shape is maintained by structural
rigidity and intra ocular pressure.
Corneal Decompensation
 Endothelial cell count is lower than the threshold
number.
 Severe endothelial damage= irreversible corneal
oedema
Aqueous Humour
 It is clear colorless solution.
 It produced by ciliary body.
 It is different from plasma.
 It leaves the eye by trabecular route.
Uveal Tract
 The pupil is dynamic structure.
 Contraction of ciliary body permits
accommodation and trabecular outflow.
 Choroid has highest ocular blood flow.
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.
Sclera
 Tough Outer Coat.
 Comlete Sphere.
 It is thickest around and thinnest just posterior to
 It is avascular .
 It is opaque .
 Low metabolic demand.
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.
Accommodation Cascade
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Ciliary muscle contraction
Zonules relaxe
Lens becomes more spherical
refractive power
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 ???
Glucose Metabolism
 Lens is avascular and surrounded by aqueous and
vitreous.
 Glucose is metabolized through:
1-Glycolytic Pathway
2-Krebs Cycle
3-hexose Monophosphate Shunt.
4-Sorbitol Pathway.
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.
Vitreous
 80% of ocular volume.
 It is transparent gel.
 It has shock-absorbing capacity.
 The ageing vitreous becomes progressively
liquefied.
Retina
 Transparent light – transforming structure.
 It comprises photoreceptors
interneurones
ganglion cells
retinal pigment epithelium
 The main function is phototransduction.
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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