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Describe the function of "Tarsal Glands"
lubricates the eye and the eyelid
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Describe the function of the "Conjunctiva"
produces a lubricating mucous secretion that prevents the eye from drying out
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Describe the function of the "lacrimal gland"
- Secretes lacrimal fluid which contains:
- lysozyme
- Saline solution
- antibodies
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Describe the three layers of the eyeball
- fibrous layer
- vascular layer
- retinal layer
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Describe the fibrous layer of the eyeball
- dense, avascular
- two regions: sclera and the cornea
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describe the function of the "cornea"
bends light as it enters the eye
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Describe the function of the "sclera"
- protects the eye
- shapes the eye
- anchors extrinsic eye muscles
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Name the 3 regions of the vascular layer of the eye
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Describe the function of the "choroid"
- supplies blood to all layers of the eye
- it is pigmented, thus absorbs light to prevent light scattering
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Describe the function of the Ciliary Body
- a ring of muscle that surrounds the lens to manage the shape of the lens
- ciliary zonule = keeps lens in position
- ciliary process = secretes aqueous humour
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Describe the function of the "Iris"
contains the pupil which regulates the amount of light entering the eye
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parasympathetic stimulation to the iris causes _______, while sympathetic stimulation to the eye causes ___________.
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Describe the 2 layers of the retina
- Outer pigmented layer (absorbs light)
- Inner neuronal layer
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Name 3 types on neurons from the inner neuronal layer in the retina
- ganglion cells
- bipolar cells
- photoreceptor cells
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Describe what a 'cone' is
- photoreceptor
- responsible for visual acuity in bright light
- provides colour vision
- less numerous than rods
- concentrated in the central part of the retina
- exclusive to the fovea centralis
- adapt quicker to light than rods to dark
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Describe the pathway of light entering the eye
- 1)light hits the Cornea
- 2)aqeous humour
- 3)lens
- 4)vitreous humor
- 5)entire neuronal layer of retina
- 6)photoreceptors
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Describe the role of the 'ciliary body' and the 'ciliary muscle'
these structure are responsible for producing aqueous humour and managing the lens in terms of position and shape
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Describe how the eye focuses for near vision (<6m)
- 1)Accommodation of the lens (shape of lens changes to increase light refraction)
- 2) Constriction of the pupil (prevents divergent light rays from entering the eye)
- 3) Convergence of eyeballs
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Describe the cause, consequence and possible treatment for "astigmatism"
- Cause: uneven curvature of the eyeball or irregular cornea
- Consequence: refractive error
- Corrected by: eyeglasses (required additional cylinder lens), contact lens, refractive surgery
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Describe the cause, consequence and possible treatment for "hyperopia"
- Cause: short eyeball, focal point behind the retina.
- Symptoms: far-sighteness (can't read close objects)
- Corrected by: convex lens
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Describe the cause, consequence and possible treatment for "myopia"
- Cause: long eye ball, focal point is in front of the retina
- Symptoms: near-sightenness, blurred vision
- Correction: concave lenses
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Describe the sequence of "phototransduction"
- 1) Retinal absorbs light and changes shape. VISUAL PIGMENT activates.
- 2) Visual pigment activates transducin
3) transducin activates phosphodiesterase
4) Phosphodiesterase converts cGMP to GMP. cGMP levels drop. - 5) As cGMP levels, cGMP-gated cation channels close resulting in hyperpolarization.
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describe similarities between rods and cones
- absorb light
- neuron receptors
- found in inner neuronal layer
- form synapses with bipolar cells
- embedded in pigmented layer of retina
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describe differences between rods and cones
- rods more numerous than cones
- cones provide colour vision, rods shades of gray
- rods concentrated in peripheral part of the retina, cones are concentrated in the centre
- Rods provide vision in the dark, cones require light
- cones provide visual acuity
- cones are found exclusively in the fovea centralis, no rods found here
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Describe adaptation to light
- pupils constrict
- visual acuity improves 5-10 mins
- rod system turns off
- retinal sensitivity decreases
- cones and neurons adapt quickly
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Describe dark adaptation
- pupils dilate
- cones stop functioning
- rod system turned off, rhodopsin accumulates in the dark
- retinal sensitivity increases in 20-30 min
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