Download File

An introduction to the eyeball
•Anterior segment
•Posterior segment
Anterior segment consists
- Cornea
- Anterior chamber
- Iris
-Posterior chamber
-Lens
-Ciliary body
Lens is suspended from the ciliary body by
fine delicate fibrils called suspensory
ligament of the lens (Zonules)
Posterior segment consists:
-
Vitreous cavity filled by vitreous humour
Retina
Choroid
Optic nerve
Diagrammatic representation of ocular
structures
Diagram of the eye ball
Saggital section of eye
1.
2.
3.
4.
5.
6.
7.
8.
Sclera
Cornea
Iris
Pupil
Lens
Limbus
Ciliarybody
Ora serrata
Anatomy of the Anterior Chamber
• From: anterior to posterior:
-Posterior surface of cornea
-Anterior surface of iris
-Anterior surface of lens
- Peripheral recess (Angle of the anterior Chamber)
-Depth 2.5mm in the centre
-Decreases towards periphery
-Filled with aqueous humor
Angle of Anterior Chamber
Formed by:
Posteriorly
-Root of the iris
-Part of ciliary body
Anterolaterally
-Corneosclera(Trabicular tissue & Scleral spur)
(Site of drainage of aqueous)
Angles
• Canal of Schlemm
- Loose meshwork of tissue(Trabiculum)
(Between Scleral, spur and Descemet’s membrane)
- Aqueous drained by small reunite tributaries
- Small venules and aqueous vein
Formation of aqueous humor
• Filtration theory
• Ultra filtration theory
• Secretion theory
-Active ciliary secretion 75%
-Ultra filtration 25%
Walls of capillaries of epithelium of iris , Ciliarybody
&retinal constitutes a system of semi permeable
membrane separating blood from ocular cavity is
known as blood aqueous barrier
Formation of aqueous
Ultrasonographicview of angle
Formation of aqueous
• 1. Active secretion: by the non-pigmented ciliary
epithelium accounts for the vast majority.
• 2. Passive secretion: by ultra filtration and diffusion.
-Depend son:
• Capillary hydrostatic pressure,
• The oncotic pressure
• The level of IOP
Physiology of outflow
• The trabecular meshwork (trabecular) 90%
• The uveoscleral (unconventional) route 10%
• Some aqueous also drains via the iris.
-Collected in in P.C.
-Flows through pupil into A.C.
-Finally escapes through drainage channels
-At angle of anterior chamber
-Into the canal of Schlemm
- Through aqueous veins
(Approximate 2 micro Liters drains away/minute)
Aqueous humor
•
•
•
•
•
Clear fluid
Filling anterior/posterior chambers
Refractive index 1.336
Viscosity 1.025 to 1.040
Osmotic pressure slightly> plasma
Constituents
• It contains:
- Glucose
- Urea
- Proteins
- Inorganic salts
- Ascorbic acid
- Lactic acid
- Some dissolved Oxygen
Transparent media
• Cornea
• Lens
• Aqueous
• Vitreous humor
- So formation of aqueous and maintenance of
Intraocular pressure are important aspect of
physiology of the eye
- Though yet poorly understood
Intraocular pressure
•
•
•
•
•
•
•
Pressure inside the eyeball
Determined by production by ciliary epithelium
Drainage by trabecular meshwork
Normal I.O.P. ranges from 15 -20 mm of Hg
Diurnal variation: 2 mm of Hg
Variation in tow eyes of 4 or 6 mm of Hg indicates Investigation
A rise may occur some times In Morning or In evening
Factors affecting alteration of I.O.P.
• Variation in:
-Capillary hydrostatic pressure
Rise in: raise & vice versa
• Osmotic pressure of blood
•
•
•
•
Increased capillaries permeability
Change in volume of eyeball
Obstruction in circulation of aqueous
Alteration in aqueous formation