Special Senses Week 12 Dr. Walid Daoud A. Professor

Physiological Anatomy of the Eye I- Layers of the eye:. Outer fibrous layer (protective):. Outer fibrous layer (protective): Cornea, sclera and conjunctiva. Cornea, sclera and conjunctiva.. Middle vascular layer (nutritive):. Middle vascular layer (nutritive): Iris, ciliary body and choroid. Iris, ciliary body and choroid.. Inner nervous layer ( light perception). Inner nervous layer ( light perception) Retina, optic disc and nerve. Retina, optic disc and nerve.

Physiological Anatomy of the Eye II- Ocular chambers: 1- Aqueous chamber: Anterior to the lens. Anterior to the lens. 2- Vitreous chamber: Behind the lens. Behind the lens.

The Cornea Transparent anterior 1/6 of outer layer of eye wall. Sensitive to pain, touch, temperature. Protection of the cornea: 1- Lids and lid reflex (blinking). 2- Corneal reflex. 3- Tears contain lysozymes (antibacterial). Nutrition and metabolism: Cornea is avascular and obtain O2 & glucose by diffusion from capillaries.

Functions of the cornea 1- Refractive power of the eye. 2- Transparency allows passage of light. 3- Regular curvature forms sharp and clear retinal image. retinal image. 4- Eye protection:. Hardness.. Hardness.. Corneal reflex.. Corneal reflex.

Causes of corneal transparency I-Anatomical: - Regular arrangement of epithelial cells. - Regular arrangement of collagen lamellae. - Absence of bl. vessels & myelinated n. fibers II-Physical: -Relative corneal dehydration: Osmotic and metabolic pumps Osmotic and metabolic pumps -Refractive index of collagen fibers is nearly the same

Factors maintaining corneal transparency 1- Vitamin A. 2- Vitamin B12 (riboflavin). 3- Moistening of corneal surface by tear flow. flow.

Intraocular fluid I- Aqueous humour: Function: Function: - Refractive medium of the eye. - Refractive medium of the eye. - Nutrition and O2 supply of avascular - Nutrition and O2 supply of avascular cornea and lens. cornea and lens. - Maintain intraocular pressure to keep - Maintain intraocular pressure to keep shape of eye ball. shape of eye ball.

Intraocular fluid II- Vitreous humour: Functions: Functions: - Refractive medium of the eye. - Refractive medium of the eye. - Supports retina and maintain globular - Supports retina and maintain globular shape of eye ball. shape of eye ball. - Prevents backward displacement of the - Prevents backward displacement of the retina. retina.

Uveal Tract 1- Functions of iris: - Regulate amount of light entering eyes. - Regulate amount of light entering eyes. - Increasing depth of focus by constriction. - Increasing depth of focus by constriction. - Limits passage of light to central parts of lens forming clear image on the retina. - Limits passage of light to central parts of lens forming clear image on the retina. - Diagnosis of disease affecting reflexes of pupil. - Diagnosis of disease affecting reflexes of pupil.

Uveal Tract 2- Functions of Ciliary body: - Ciliary muscle: - Ciliary muscle: Diopteric power of lens. Diopteric power of lens. Accomodation on near vision. Accomodation on near vision. - Ciliary processes: - Ciliary processes: Secrete aqueous humour. Secrete aqueous humour.

Uveal Tract 3- Functions of Choroid: - Gives nutrition to retina, ciliary body & iris. - Gives nutrition to retina, ciliary body & iris. - Supports the retina. - Supports the retina. - Gives attachment to ciliary muscle. - Gives attachment to ciliary muscle. - Plays role in accommodation. - Plays role in accommodation. - Choroid pigments prvent reflection of light - Choroid pigments prvent reflection of light from inside the eye. from inside the eye.

1- Coditions associated with pupillary dilatation (Mydriasis ) 2- Coditions associated with pupillary constriction (Miosis)

Crystalline lens Functions: 1- Enables eye to see near objects. 2- Refractive media of the eye. 3- Protects retina from harmful effects of UV rays which is absorbed by lens & cornea. rays which is absorbed by lens & cornea.

Errors of Refraction 1- Myopia (short-sight). 2- Hypermetropia (far-sight). 3- Presbyopia (old-sight). 4- Astigmatism.

Retina Photoreceptors: 1- Cones: for bright (day) vision. 2- Rods: for dim (night) vision. Functions: 1- Vision. 2- Light and accomodation reflexes. 3- Maintain tone, posture and equilibrium. Image formed in the retina is inverted but cerebral cortex interpret it in upright position.

Protective mechanisms of the eye 1-Lacrimal apparatus: Functions of tears: -Keep cornea & conjunctiva moist & clear. -Keep cornea & conjunctiva moist & clear. -Bacteriolytic action by lysozyme. -Bacteriolytic action by lysozyme. 2- Eye lids: Function: -Regulation of light entering the eye. -Regulation of light entering the eye. -Protection from excessive illumination or FB -Protection from excessive illumination or FB -Distribution and conduction of tears. -Distribution and conduction of tears. 3-Corneal reflex.

Hearing Physiological anatomy: 1- External ear. 2- Middle ear: bony ossicles & muscles 3- Inner ear: cochlea and vestibular appartus. appartus. Mechanism of hearing.

Taste Chemoreceptors stimulated by chemical substances: Taste buds: 3 types of cells: 1- Taste (gastratory) cell. 2- Supporting cell. 3- Transitional cell.

Types of taste sensation 1- Sweet taste. 2- Salty taste. 3- Bitter taste. 4- Sour taste.

Factors affecting taste sensation 1- Concentration of tasted substance. 2- Contrast. 3- Surface area stimulated. 4- Temperature. 5- Olfaction. 6- Adaptation. 7- Individual variation.

Smell Olfactory reception cell. Olfactory epithelium: 1- Basal cell. 2- Supporting cell. 3- Bowman,s gland. 4- Receptors. Abnormalities of olfactory sensation: 1- Anosmia. 2- Hyperosmia.