Ophthalmology

1. 15 Ophthalmology

2. Ophthalmology The medical specialty that studies the anatomy and physiology of the eye and uses diagnostic tests, medical and surgical procedures, and drugs to treat eye diseases.

3. Figure 15-1 Eye

4. Anatomy and Physiology The eyes belong to a body system that consists of two identical main organs and many associated structures. Each eye or optic globe is located within the orbit, a hollowed out bony socket in the anterior cranium. The walls of the orbit are made up of several different cranial and facial bones.

5. Anatomy and Physiology (cont’d) The bony orbit surrounds all but the anterior surface of the eye. In the posterior wall of the orbit, the optic nerve, arteries, and veins come through openings in the bone to reach the eye. The bony orbit holds the eye and contains a layer of fat that cushions and protects the eye.

6. Anatomy of the Eye (cont’d) Eyelid and Lacrimal Gland Eyelids protect the delicate tissues of the eye. Eyelids continually refresh a layer of tears to keep the surface of the eye moist. Prevent foreign substances from entering the eye.

7. Figure 15-2 Lacrimal glands

8. Anatomy of the Eye (cont’d) Eyelid and Lacrimal Gland (cont’d) Sebaceous glands at the eyelids’ edges secrete oil to act as a barrier to keep tears in the eye. Eyelashes form a protective barrier to catch foreign substances before they come in contact with the eye.

9. Anatomy of the Eye (cont’d) Eyelid and Lacrimal Gland (cont’d) The lacrimal gland is located by the superior-lateral aspect of each eye. The lacrimal gland continuously produces tears that travel through the lacrimal ducts to moisten the eye.

10. Anatomy of the Eye (cont’d) • Eyelid and Lacrimal Gland (cont’d) • Tears contain an antibacterial enzyme to prevent bacterial infections. • At the medial aspects of the upper and lower eyelids, two tiny openings drain excess tears from the eye’s surface.

11. Anatomy of the Eye (cont’d) • Conjunctiva • The conjunctiva is a delicate, transparent mucous membrane that covers the insides of the eyelids and continues across the anterior surface of the eye. • The conjunctiva produces watery, clear mucus that allows the eyelids to slide easily across the surface of the eye with each blink.

12. Figure 15-3 Anterior surface of the eye

13. Figure 15-4 Internal structures at the front of the eye

14. Figure 15-5 Tissue layers at the back of the eye

15. Anatomy of the Eye (cont’d) Sclera A tough, fibrous connective tissue that forms a continuous outer layer around the eye; known as the white of the eye. Protects the internal structures of the eye and helps maintain the shape of the eye Is the site of attachment for all of the muscles that move the eye

16. Anatomy of the Eye (cont’d) • Sclera (cont’d) • Across the anterior part of the eye, the sclera changes into a transparent layer known as the cornea.

17. Anatomy of the Eye (cont’d) Cornea Allows light to enter the eye Bends (refracts) the rays of light Contains no blood vessels, not even capillaries Has nerves and is the most sensitive area on the anterior surface of the eye

18. Anatomy of the Eye (cont’d) Iris and Pupil A circular structure whose color is genetically determined. At the center of the iris is the pupil, a round opening that allows light rays to enter the eye. In bright light, muscles in the iris contract to constrict (decrease the diameter of) the pupil; this process is known as miosis.

19. Anatomy of the Eye (cont’d) • Iris and Pupil (cont’d) • In dim light, muscles in the iris relax to dilate (increase the diameter of) the pupil; this process is known as mydriasis.

20. Anatomy of the Eye (cont’d) Choroid A spongy membrane of blood vessels that is part of the internal structure of the eye. The middle layer between the sclera and the retina. Blood vessels of the choroid supply blood to the entire eye.

21. Anatomy of the Eye (cont’d) Ciliary Body An extension of the choroid that attaches to ligaments that hold the lens in place behind the iris Contains muscles that contract and relax to change the shape of the lens to focus light rays coming through the pupil Produces aqueous humor

22. Anatomy of the Eye (cont’d) Lens A clear, flexible disk located behind the pupil that is made of protein molecules arranged in a crystalline structure that is transparent Becomes thicker and more rounded for near vision or thinner and flatter for far vision Is enclosed in the lens capsule, a clear membrane

23. Figure 15-10 Light rays coming from an object to the retina

24. Figure 15-19 Hyperopia

25. Figure 15-20 Myopia

26. Anatomy of the Eye (cont’d) Anterior and Posterior Chambers The anterior chamber is a small space between the cornea and the iris. The posterior chamber is a very narrow space posterior to the iris. Aqueous humor is a clear, watery fluid that is produced continuously by the ciliary body.

27. Anatomy of the Eye (cont’d) Anterior and Posterior Chambers (cont’d) Aqueous humor carries nutrients and oxygen to the cornea and lens. The rate of production of aqueous humor normally equals the rate of drainage.

28. Figure 15-6 Aqueous humor

29. Anatomy of the Eye (cont’d) Posterior Cavity The largest space in the eye Lies between the lens and the back of the eye Is filled with vitreous humor, a clear, gel-like substance that helps maintain the shape of the eye

30. Figure 15-7 Internal structures at the back of the eye

31. Anatomy of the Eye (cont’d) Retina A thin layer of tissue that lines the walls of the posterior cavity The choroid layer lies beneath the retina and provides blood to the retina. Fundus is a general word for the retina, whose curved sides and posterior wall form part of the sphere-shaped structure of the eye.

32. Anatomy of the Eye (cont’d) • Retina (cont’d) • The optic disk is where the optic nerve enters the eye; known as the blind spot. • The macula is a dark yellow-orange area lateral to the optic disk. • The fovea, a small depression in the center of the macula, is the area of greatest visual acuity.

33. Figure 15-8 The retinae of both eyes

34. Anatomy of the Eye (cont’d) Extraocular Muscles Control the movements of the eye Attached to the sclera by tendons Under voluntary control through nerve impulses

35. Figure 15-9 Extraocular muscles

36. Physiology of Vision Light rays from an object pass through the cornea, which bends the rays to begin to focus them. The light rays then enter the pupil and pass through the lens. Muscles and ligaments in the ciliary body contract or relax to change the shape of the lens and focus the light rays.

37. Physiology of Vision (cont’d) Light rays from objects directly in the line of vision fall on the macula, and these objects produce the clearest, sharpest image. Other parts of the retina pick up light rays from objects at the edges of the visual field. The retina contains special light-sensitive cells known as rods and cones.

38. Physiology of Vision (cont’d) Rods are sensitive to all levels of light but not to color. Rods function in daytime and nighttime vision. It only takes one photon (light particle) to activate a rod, so rods can detect objects in very low light, but they only produce a somewhat grainy black-and-white image of that object.

39. Cones are only sensitive to color. There are three types of cones: those that respond to red, green, or blue light. The cones are concentrated in the macula. Physiology of Vision (cont’d)

40. It takes many photons to activate a cone, which is why it is difficult to see colors in dim light. Cones produce a sharp color image that is superimposed on the black-and-white image created by the rods. Physiology of Vision (cont’d)

41. Rods and cones everywhere in the retina respond to the light rays to create an image. The image is then converted to nerve impulses that are transmitted to the optic nerve. Physiology of Vision (cont’d)

42. The optic nerve from each eye travels to the optic chiasm, a crossing point where parts of one optic nerve cross over to join the other optic nerve. Three-dimensional, stereoscopic vision with a perception of depth and distance is created. Physiology of Vision (cont’d)

43. Physiology of Vision (cont’d) These combined nerves enter the thalamus, which interprets the sensory information and quickly sends it to the midbrain and the visual cortex in the right and left occipital lobes of the brain. The visual cortex merges the image from each eye to create a single, three-dimensional image.

44. Figure 15-11 Optic nerve, optic chiasm, thalamus, and visual cortex

45. Diseases and Conditions Eyelid Blepharitis Blepharoptosis Ectropion Hordeolum

46. Figure 15-12 An ectropion Science Photo Library / Photo Researchers, Inc.

47. Diseases and Conditions (cont’d) Lacrimal Gland Dacryocystitis Xerophthalmia

48. Diseases and Conditions (cont’d) Conjunctiva, Sclera, and Cornea Conjunctivitis Corneal abrasion

49. Figure 15-13 Conjunctivitis Barbara Galati/Phototake NYC

50. Diseases and Conditions (cont’d) Conjunctiva, Sclera, and Cornea (cont’d) Exophthalmos Scleral icterus