Eye and Vision Exercise 26 BI 232. External Features Notice the pupil which is surrounded by the...
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Transcript of Eye and Vision Exercise 26 BI 232. External Features Notice the pupil which is surrounded by the...
![Page 1: Eye and Vision Exercise 26 BI 232. External Features Notice the pupil which is surrounded by the colored iris. The sclera is the white of the eye which.](https://reader035.fdocuments.in/reader035/viewer/2022062221/56649cfe5503460f949ce23e/html5/thumbnails/1.jpg)
Eye and Vision
Exercise 26BI 232
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External Features • Notice the pupil which is
surrounded by the colored iris.
• The sclera is the white of the eye which is covered by a membrane called the conjunctiva
• Eyelids come together at lateral and medial commissures.
• The lacrimal caruncle is found in the medial commissure.
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Lacrimal Apparatus
• Consists of the lacrimal gland and its accessory structures.
• Produces water, alkaline tears.
• Contain antibacterial enzyme called lysozyme for protection from bacterial infections
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Extrinsic Eye Muscles
• Superior oblique: primarily rotates the top of the eye toward the nose and secondarily moves the eye downward
• Innervated by CNIV (trochlear)– Trochlea: Ligament sling
• Superior rectus: primarily moves the eye upward and secondarily rotates the top of the eye toward the nose
• Innervated by CNIII (oculomotor)• Lateral rectus: moves the eye away from the
nose • Innervated by CNVI (abducens)
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Extrinsic Eye Muscles
• Medial rectus: moves the eye toward the nose• Innervated by CNIII (occulomotor)• Inferior oblique: primarily rotates the top of
the eye away from the nose and secondarily moves the eye upward (also CNIII)
• Inferior rectus: primarily moves the eye downward and secondarily rotates the top of the eye away from the nose (also CNIII)
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NoseEar
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Extrinsic Eye Muscles
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Ciliary body
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1
2
A
P
1. Ciliary processes– Ciliary epithelium– Secretes aqueous humor
2. Ciliary muscle - (intrinsic eye muscle)
3. Suspensory ligament of the lensA= anterior chamberP= posterior chamber
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Intrinsic Eye Muscles of the Iris
Pupils constrict (Parasympathetic) Close vision and bright light
Pupils dilate (Sympathetic) Distant vision and dim light
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Neural pathway for vision
• After optic nerves exit the eyeballs they meet at the optic chiasm.
• Fibers from medial half of retina cross over to the opposite side.
• Optic tracts project to the lateral geniculate bodies in thalamus
• Some fibers are relayed to superior colliculi
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Histology of the Retina
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Eye Dissection
• Do eye dissection • Be able to ID structures
for quizzes and practical
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Determination of the Near Point• The minimum distance an
object can comfortably be held in focus
• Changes as we age • Hold a paper with fine print
vertically at arm’s length in front of you.
• Close one eye and slowly move the paper closer until either you see two objects or it becomes blurry.
• Have partner measure distance
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Distribution of Rods and Cones• Slowly move a small colored
object, without letting your lab partner see it, from the back of your lab partner’s head, around the side toward the front.
• With lab partner still looking straight ahead, not the angle when they are able to see the object.(rods)
• Continue to move object forward slowly until color recognition occurs
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Binocular Visual Field• Close right eye and look
straight ahead with the left• Lab partner moves an object
from behind your head from the left until you can see object.
• Measure angle with protractor from tip of nose
• Continue moving object until it disappears.
• Repeat the exercise with the other eye
• Determine the total visual field by adding the sums of above.
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Visual Acuity
• Snellen eye chart used to test visual acuity
• 20/20 normal• 20/15 you can see at 20
feet what people with normal vision see at 15 feet.
• 20/30 you see at 20 feet what people with normal vision see at 30 feet.
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Astigmatism
• The degree of curvature in the cornea or lens varies from one axis to another (is uneven or wavy)
• This causes light to focus on more than one area of the retina creating a blurry image.
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Ophthalmoscope
• Used for diagnosis of variances in the eyeball but also as a potential indicator of diseases, such as diabetes mellitus.
• Sit facing your lab partner• Have scope set at zero • Move in close to examine
the eye of your partner• Look into the pupil
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Retinal scan- Ultra-widefield
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Refraction
• Light is bent when it passes from one medium to another medium with a different density
• Light passes through these before it hits the retina:– Cornea– Aqueous humor– Lens– Vitreous humor
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Focal Point & Focal Distance
• Focal Point: The specific point of intersection on the retina.
• Focal distance: The distance between the center of the lens and its focal point. Determined by two factors:
1. Distance from the object to the lens2. Shape of the lens
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Focal Distance
• Distance from the object to the lens: the closer an object is, the greater the focal distance
• Shape of the lens: the rounder the lens, the more refraction occurs, so it has a shorter focal distance
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Accommodation
• Accommodation is an alteration in the curvature of the lens of the eye to focus an image on the retina– Near objects: Lens becomes rounder– Distance objects: Lens becomes flatter
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Accommodation
• Emmetropia is normal vision.
• The image will be focused on the retina’s surface
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Accommodation Problems
• Myopia: Nearsighted• The eyeball is too deep or
the curvature of the lens is too great
• The focal point is in front of the retina, so distance objects are blurry
• Corrected with a diverging lens
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Accommodation Problems
• Hyperopia: Farsighted• The eyeball is too shallow or
the curvature of the lens is too flat
• The focal point is behind of the retina, so near objects are blurry
• Corrected with a converging lens
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Color Blindness
• Cones are responsible for color vision.
• 3 types of cones each able to absorb light at specific wavelengths.
• Lack of one or more types of cone can cause color blindness
• Use Ishihara color plates to test
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Afterimages• Photosensitive pigment of the
rods is rhodopsin, a light-sensitive retinal and the protein opsin.
• When light strikes the retina, rhodopsin splits into its two component parts and becomes pale (bleaching)
• You can test the time for separation and reassembly of the photopigments by staring at a contrasting image on a card
• Stare about 10-20 seconds and then shuts your eyes.
Have your partner record time. You should see colored image against dark background (positive afterimage)
After a few moments you should see the reverse of the original image (negative afterimage)
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Blind Spot• The optic disc is a region
where the nerve fibers exit the back of the eye and form the optic nerve.
• This region is devoid of photoreceptors and is called the blind spot.
• Follow the instructions from your instructor or book to find your blind spot
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The End
• Spend the rest of the lab locating structures on the eye models
• Make sure that you understand the tests we did in class because you will be asked about them on quizzes and practicals