Physiology of Special Senses By Dr Abdel Aziz

Physiology of Special Senses By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology Member of American Society of Physiology of Special senses, Abdelaziz Hussein 2

Intraocular Fluids

Intraocular Fluids Aqueous humour Vitreous humour

A) Aqueous Humour

The Aqueous Humour Transparent colourless alkaline fluid that fills the anterior and posterior chambers of the eye

The Aqueous Humour Mechanism of formation • Formed continuously by the Ciliary epithelium by facilitated diffusion and active transport mechanisms • Na by active transport • Cl and HCO 3 and H 2 O follow Na passively Rate • At a rate 1 -2 µL/min

The Aqueous Humour Composition Nearly protein free (contains about 100 -200 mg/L). Na+ concentration is higher plasma Vitamin C concentration is 10 -20 times higher than plasma Bicarboante concentration is higher than plasma.

The Aqueous Humour Circulation and drainage of aqueous humour

The Aqueous Humour Functions 1. It is one of the important refractive media of the eye 2. It nourishes the avascular cornea and lens. 3. It also buffers the acid produced by the anaerobic metabolism of the cornea and lens. 4. It has a mechanical function to keep the eyes rigid and to maintain its refractory power. 5. It maintains the intraocular pressure constant by means of its steady formation and drainage

B) Vitreous Humour

Vitreous Body Hyaloid canal Retrolental space Capsule

Vitreous Body Functions It is one of the refractive media of the eye. It supports the retina It supports the crystalline lens and prevents it from falling back It maintains the spherical shape of the eye

The Middle Layer or Uveal Tract

Uveal Tract Choroid Iris Ciliary ms

The Iris

The iris Muscles of the iris Radial or Dilator Pupillae ms Circular or Constrictor Pupillae ms

Functions of the Iris 1. The pigments of iris absorb all light rays which enter into the eye except though which pass through the pupil.

Functions of the Iris 2. It prevents light from falling on the peripheral parts of the lens. Thus it prevents spherical and chromatic aberration

Spherical Aberrations

Chromatic Aberrations

Functions of the Iris 3. It regulates the amount of light which enters into the eye by regulating the size of the pupil. 4. Pupillary constriction increases the depth of focus i. e. the distance of the object can be changed but its image is still focused on the retina without change in accommodation.

Functions of the Ciliary Body 1. The ciliary muscle is essential for accommodation 2. The ciliary processes secrete the aqueous humour into the posterior chamber & give attachment to the suspensory ligament of the lens.

Functions of the Choroid 1. It is a vascular layer which provides blood supply to the eye 2. The pressure inside its vessels maintains the intraocular pressure 3. It contains melanin pigments which absorb light & prevent its reflection inside the eye which cause blurring of vision

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