ocular physiology

DR YAHYA AL-FALKI MDKKU-COLLEGE OF MEDICINE

OPHTHALMOLOGY-UNDERGRADUATE LECTURE SERIES

Ocular Physiology

Objectives

To be familiar with normal functions of ocular

structures.Clinical applications.

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.

Tear Film

It is highly specialized and well-organizedMoist 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 toIt 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

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 Pathway2-Krebs Cycle3-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 epitheliumThe 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.

Thank YOU