1. The Eye & Vision

2. The Eye and Vision  70 percent of all sensory receptors are in the eyes - only see 1/6th of eye  Each eye has over a million nerve fibers  Protection for the eye  Most of the eye is enclosed in a bony orbit  A cushion of fat surrounds most of the eye

3.  Eyelids – aka. palpebra  Meets at medial and lateral canthus  Protection and Shading  Eyelashes Figure 8.1b

4.  Meibomian glands – tarsal glands – modified sebacious glands produce an oily secretion to lubricate the eye  Chalazion (ka-lay-zee-an)- inflammation

5. Chalazion

6.  Ciliary glands – modified sweat glands between the eyelashes  Sty - inflammation

7.  Conjunctiva  Membrane that lines the eyelids  Connects to the surface of the eye  Secretes mucus to lubricate the eye  Conjunctivitis – inflammation of – sometimes known as “pink eye”

8. Conjunctivitis

9. Slide 8.4b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Lacrimal apparatus  Lacrimal gland – produces lacrimal fluid  Lacrimal canals – drains lacrimal fluid from eyes Figure 8.1a

10. Slide 8.4c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Lacrimal sac – passage of fluid towards nasal cavity  Nasolacrimal duct – empties fluid the nasal cavity

11. Slide 8.5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Properties of lacrimal fluid  Dilute salt solution (tears)  Contains antibodies and lysozyme  Protects, moistens, and lubricates the eye  Empties into the nasal cavity

12. Slide 8.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  6 eye muscles attach to the outer surface of the eye  Produce gross eye movements  Rectus muscles: lateral, medial, superior, inferior  Oblique muscles: inferior, superior  Need to be able to label on diagram & identify the motions they are responsible for

15. Slide 8.7 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  The wall is composed of three tunics  Fibrous tunic – Outer layer  Vascular tunic (uvea) – middle layer  Sensory tunic  inside layer Figure 8.3a

16. Slide 8.8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Sclera  White connective tissue layer  Seen anteriorly as the “white of the eye”  Cornea  Transparent, central anterior portion  Allows for light to pass through  Repairs itself easily  The only human tissue that can be transplanted without fear of rejection

17. Cornea transplant

19. Slide 8.9 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Choroid – posterior portion  Blood-rich nutritive tunic  Dark pigment prevents light from scattering

20. Slide 8.9 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Modified interiorly  Ciliary body – anterior  smooth muscle  Attached to lens  Iris  Pigmented layer that gives eye color  Pupil – rounded opening in the iris for light passage  Circular & radial fibers regulate opening

21. Slide 8.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Neural layer contains receptor cells (photoreceptors)  Rods & Cones  Signals pass from photoreceptors via a two-neuron chain  Photoreceptors to bipolar neurons  Bipolar neurons to ganglion cells  Signals leave the retina toward the brain through the optic nerve

23. Neurons of the Retina Slide 8.11 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.4

24. Slide 8.12a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Rods  Most are found towards the edges of the retina  Allow dim light vision and peripheral vision  Perception is all in gray tones

25. Slide 8.12b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Cones  Allow for detailed color vision  Densest in the center of the retina  Fovea centralis  area of the retina with only cones  Area of greatest visual acuity

26. Slide 8.12b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  No photoreceptor cells are at the optic disk, or blind spot  Site of optic nerve leaving eyeball

27. Slide 8.13 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  There are three types of cones  Different cones are sensitive to different wavelengths  Color blindness is the result of lack of one cone type Figure 8.6

28. Slide 8.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Biconvex crystal-like structure  Held in place by a suspensory ligament attached to the ciliary body Figure 8.3a

29. Slide 8.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Activity of ciliary muscle of ciliary body changes lens thickness to focus light onto retina  Cataracts: clouding of lens

30. Cataract Removal

31. Slide 8.15a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Aqueous humor in Anterior Segment  Watery fluid found in chamber between the lens and corne  Similar to blood plasma  Helps maintain intraocular pressure  Provides nutrients for the lens and cornea  Reabsorbed into venous blood  Blocked drainage = glaucoma

33. Slide 8.15b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Vitreous humor  Gel-like substance behind the lens  Keeps the eye from collapsing  Lasts a lifetime and is not replaced  Keeps retina firmly against wall of eyeball

35. Vision

36. Light Light must be refracted (bent) so that it focuses on the retina to form an image. Light must be refracted (bent) so that it focuses on the retina to form an image. The cornea, aqueous humor, & vitreous humor have a constant refractory power The cornea, aqueous humor, & vitreous humor have a constant refractory power The lens is the only refractory structure that can change shape in order to change refractory power. The lens is the only refractory structure that can change shape in order to change refractory power.

37. Focus Distance vision is accomplished by: Distance vision is accomplished by: Ciliary muscles relaxation Ciliary muscles relaxation Suspensory ligaments tightening Suspensory ligaments tightening Results in: Results in: Maximum flattening of lens (decreased convexity) Maximum flattening of lens (decreased convexity) Decreased refraction Decreased refraction

38. Focus Close vision is accomplished by: Close vision is accomplished by: Ciliary muscles tightening Ciliary muscles tightening Suspensory ligaments relaxing Suspensory ligaments relaxing Results in: Results in: Lens rounds up (increased convexity) Lens rounds up (increased convexity) Increased refraction Increased refraction Requires continuous muscle contractions Requires continuous muscle contractions Prolonged periods of close vision can cause eyestrain Prolonged periods of close vision can cause eyestrain

39. Lens Accommodation Slide 8.16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  The eye is set for distance vision (over 20 ft away)  The lens must change shape to focus for closer objects  This ability decreases with age Figure 8.9

40. Real Image Slide 8.17 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Real image is projected on retina:  reversed from left to right  upside down & smaller  Brain adjusts our perception Figure 8.10

41. Correcting the Eye Correct Focus = emmetropia Correct Focus = emmetropia Nearsightedness = myopia Nearsightedness = myopia Distant objects are blurry (near objects clear) Distant objects are blurry (near objects clear) Focus of light in front of retina Focus of light in front of retina Eyeball too long Eyeball too long lens too strong – too convex lens too strong – too convex Cornea is too curved – too convex Cornea is too curved – too convex Requires concave lens to correct Requires concave lens to correct

42. Emmetropia

43. Myopia

44. Correcting the Eye Farsightedness = hyperopia Near objects are blurry – distance objects are clear Near objects are blurry – distance objects are clear Focus of light beyond the retina Focus of light beyond the retina Short eyeball Short eyeball lazy lens – lens too weak – too concave lazy lens – lens too weak – too concave Cornea too flat – too concave Cornea too flat – too concave Requires convex lens to correct Requires convex lens to correct

45. Hyperopia

46. Astigmatism Unequal curvatures in cornea & lens Unequal curvatures in cornea & lens Blurred vision Blurred vision Specially ground lenses required to compensate irregularities Specially ground lenses required to compensate irregularities

47. Presbyopia Decreasing lens elasticity so lens cannot adjust for close vision Decreasing lens elasticity so lens cannot adjust for close vision Causes difficulty focusing on near objects Causes difficulty focusing on near objects Typically age related – corrected with reading glasses, etc. Typically age related – corrected with reading glasses, etc. Near point of accommodation – closest distance at which you can focus on an object Near point of accommodation – closest distance at which you can focus on an object