Week 6: The Eye Flashcards by Kati Major

Fibrous Tunic

Sclera
Outermost layer

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Vascular Tunic

Middle layer
Iris, Ciliary Body, Choroid

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Retina

Innermost layer
Pigmented layer and neural layer.

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Sclera

White of eye
Shape to eyeball
Protects inner parts
Continues as cornea anteriorly.

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Cornea

Transparent, non-vascular.
Covers Iris
Principal Refractive Medium of eye.

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Choroid

Pigmented (absorbs rays so they dont bounce)
Highly vasularised
Anterior choroid (ciliary body and iris)

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Ciliary Body

Alters shape of lens (with muscles), allows eye to focus on objects.

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Zonule

Ciliary Muscles

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Iris

Coloured part of eye
Diaphragm between lens and cornea
Alters pupil size.

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Bright Light

Circular mucles of iris contract = constriction (para)

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Dim Light

Radial muscles of iris constrict = dilate (symp)

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Retina

Nervous tissue and pigment
Photoreceptors
Role in image formation

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Ora Serrata

Junction between retina and ciliary body
Where retina transitions from non-photosensitive to multilayered photosensitive region.

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Mucla Lutea

Center of retina
Depression called fovea
Highest visual acuity
High concentration of cone receptors

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Optic Disc

Retina where ganglion neurons bend posteriorly to form optic nerve
Blind spot.

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Lens

Posterior to iris
Focuses light rays on retina
Refractory apparatus of eye
Suspensory ligaments attach lens to ciliary body

Anterior Cavity

Aqeuous humor (from blood capillaries in ciliary body)
Maintains introcular pressure
Supplies nutrients to lens and cornea

Posterior Cavity

Vitreous humor (jelly)
Intraocular pressure
Holds retina against choroid

Conjuctiva

Thin mucous membrane
Lines eyelid, covers front surface of eyeball (minus cornea)
Produces lubricant, keeps eyeball moist.

Refraction of Light Rays

Cornea - principle and fixed
Lens - varied

Lens during distant viewing

Light rays at cornea are parallel
Ciliary muscles relaxed
Suspensory ligaments tight
Lens is stretched
tall, thin shape

Lens during near viewing

Light rays divergent
Ciliary mucles contracted
Suspensory ligaments loose
Lens short, bugled, convex.

Convergence of Eyes

Six extrinsic muscles
Ensures image falls on fovea

Constriction of Pupil

During near vision
Limits amount of light through periphery of bulging lens
Light through thickest part of lens
Prevents blurred vision

Rods

20 times more numerous than cones Dim light, high sensitivity and peripheral Does not provide sharp images

Cones

Less numerous than rods Bright light, low sensitivity, central receptors High clarity and colour vision.

Fovea Centralis

Only cones # of rods increase and cones decrease with further distance from fovea.

Rhodopsin

photopigment - rods Pigment (Retinal) from Vit A Protein (Opsin) Only one pigment

What happens when light strikes Rhodopsin

Pigment breaks down, causes nerve impulse in the neuron.

Cone Photopigments

Cone Opsins (red, green, blue)

Pathway of Images (From Retina to Brain)

Photoreceptors - Bipolar Neurons - Ganglion Neurons - Optic Nerve (CN II) - Optic Tract - Thalamus - Visual Cortex

Lacrimal Apparatus Location

Gland and duct above eye, below outer eyebrow

Function of Lacrimal Apparatus

Tears

Watery solution containing: salts, mucous, Lysozyme

Functions of Tears

Clean, lubricate, moisten eyes. Protect against bacterial infections.