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بسم الله الرحمن الرحيم

بسم الله الرحمن الرحيم. ﴿و ما أوتيتم من العلم إلا قليلا﴾. صدق الله العظيم الاسراء اية 58. Physiology of Special Senses. By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology Member of American Society of Physiology. Refractive Media of the Eye And Image Formation. Light.

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بسم الله الرحمن الرحيم

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  1. بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58

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

  3. Refractive Media of the Eye And Image Formation

  4. Light Electromagnetic radiations

  5. Light

  6. Light • Light is a form of radiant energy, consisting of electromagnetic waves • Its velocity in air it is 300,000 km/second, but it is much slower through transparent solids & liquids e.g. in the glass it is 200.000 Km/sec • The wave-length of visible light to the human eye ranges from 400 to 750 nm

  7. Physics of Light

  8. Reflection, Absorption and Refraction

  9. Reflection, Absorption and Refraction Air Medium

  10. Reflection, Absorption and Refraction • When light rays strike a surface, they are either; • Reflected (white objects reflect all light) • Absorbed (black objects absorb all rays) • Transmitted through it, with or without refraction

  11. Refraction of Light

  12. Refraction of Light Air Incidence angle Medium Refraction angle

  13. Refractive index (RI) • It is the ratio of velocity of light in air to the velocity in the substance. • It is 1.0 for air, 1.5 for glass, and 1.33 for water

  14. Refraction of Light through Convex Lens Principal axis Nodal Point Focal Length Focus or Focal point

  15. Refraction of Light through Concave Lens Principal axis Nodal Point Virtual Focus

  16. Refractive Power of Lens • The power (or strength) of lenses is measured in diopters • e.g. the power of a lens having a focal length • 0.1 meter = 1/ 0.1 = 10 diopters.

  17. Types of Lenses • Convex and concave lenses • Spherical and cylindrical lenses

  18. Refractive Media of the Eye

  19. Refractive Media of the Eye Aqueous Humor Aqueous Humor RI= 1.34 RI= 1.33 Cornea Lens RI= 1.38 RP= +39 diopters RI= 1.40 RP= +20 diopters

  20. Outer Layer of the Eye

  21. The Cornea

  22. Histology of the Cornea • The cornea is the transparent anterior 1/6 of outer coat of the eyeball. • It is 11 mm in diameter & 1.0 mm in thickness. • 5 layers;

  23. Nutrition & Metabolism Significance • Maintains dehydration and transparency of the cornea Sources Corneo-scleral junction (O2 and glucose) Tears O2 Aqueous humour (glucose) • It contains ascorbic acid & glutathione which act as H2 acceptors in anaerobic metabolism

  24. Causes of Corneal Transparency Anatomic factors • Regular & uniform arrangement of the epithelial cells & lamellae. • Absence of blood vessels & myelinated nerve fibers Physical factors • The refractive index of various layers of cornea is the same. • Relative corneal dehydration by osmotic pump and metabolic pump

  25. Factors maintaining corneal transparency • Vitamin A • Vitamin B2 (Riboflavin) • Moistening of the corneal surface by tears • Metabolic pump of the endothelial cells

  26. Functions of the cornea 1. It is transparent structure allowing the passage of light rays into the eye. 2. The regular curvature of the corneal surface helps the formation of sharp clear images on the retina.

  27. Functions of the cornea 3. It acts as a powerful convex lens (+ 39- 43 diopters) having 70% of total diopteric power of the eye.

  28. Functions of the cornea 4. Protection of inner structures of the eyeball by • Its fibrous structure • It absorbs ultraviolet rays that fall on the eye (protect the retina) • The corneal reflex(touch of the cornea by any foreign body e.g. piece of cotton results in reflex blinking of both eyes)

  29. Corneal reflex Touch of cornea Trigeminal Nerve Pontine Center Facial Nerve Physiology of Special senses, Abdelaziz Hussein

  30. Abnormalities of the Cornea Physiology of Special senses, Abdelaziz Hussein

  31. Astigmatism • It is a condition in which the curvatures of the cornea are not the same in all directions (planes). • It is treated by cylindrical or contact lenses

  32. Keratoconus • It is a congenital condition in which there is a conical protrusion of the cornea • It is treated by contact lens or corneal grafting

  33. Corneal Opacity • It is a condition in which part of the cornea becomes nontransparent • It is treated by corneal grafting.

  34. 2) The sclera

  35. The Sclera • It constitutes the posterior opaque 5/6 of the outer coat of the eye. • It is covered anteriorly by the conjunctival membrane. • Normally, it is whitish in adults & bluish in infants & young children. • It is opaque due to marked irregularity of its fibres

  36. The Sclera • Functions of Sclera: • It protects the delicate inner eye structures • It gives attachment to the external ocular muscles.

  37. THANKS

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