Visual System Anatomy Flashcards by Zohaa Qaisar

What is the Limbus?

The border between the cornea and the sclera

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What produces tears?

Lacrimal gland

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Where do the afferent nerves travel from the eye?

Cornea

Cranial Nerve V1 - ophthalmic trigeminal

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What neurotransmitter operates within the lacrimal system?

Acetylcholine * due to parasympathetic efferent nerves

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Where do the tears drain?

through two puncta - which are openings on medial lid margin

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Where do tears flow through?

Superior and inferior canalculi and gather in the tear sac

They exit the tear duct into the nasal cavity

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Where is the lacrimal gland located?

Located within the orbit - latero-superior to the globe

It is innervated by the parasympathetic nerve

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What is basal tear?

Tear even in the absence of irritation or stimulation

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What is reflex tear?

Increased tear productions in response to ocular irritation

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What is the tear film?

The healthy cornea is covered in the tear film which is a thin layer of FLUID

Made of three layers  :
- mucous area
- thick watery layer
- thin lipid layer
it allows a smooth cornea to air surface

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What are the functions of the tear film?

Oxygen supply to cornea as cornea has no blood vessels

It contains factors against harmful bacteria

both functions of the aqueous tear film layer in the middle

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What is the top lipid layer of the tear film responsible for?

Protecting tear film from rapid evaporation

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Where does the lipid layer of the tear film come from?

The lipid layer is secreted by Meibomian glands which are situated along the eyelid margins

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What is the layer adhered to the eye surface used for?

The bottom mucinous layer ensures that tear film sticks to eye surface

Mucin molecules act by binding water molecules to the hydrophobic corneal epithelial cell surface

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What is the conjuctiva?

The thin transparent tissue that covers the outer surface of the eye

begins at outer edge of cornea, covers visible part of the eye AND lines the EYELIDS

Nourished by tiny blood vessels which are more prominent when inflammed

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What is the eyeball made up of outside to inside?

Sclera : hard and opaque
Choroid : pigmented and vascular
Retina: neurosensory tissue lining inner part of the eye

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What is the function of the sclera?

Protecting and maintaining shape of the eye

has a high water content

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What is the function of the choroid?

Providing circulation * especially to the back of the eye

and shields out unwanted scattered light

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What is the function of the retina?

conversion of light to neurological impulses to be transmitted to the brain via optic nerve

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What is the cornea?

Transparent dome like window covering front of the eye

Low water content

Powerful refracting surface 2/3 of eyes focusing power

Made of 5 layers

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What 5 layers is the cornea made of?

1 – Epithelium
2 – Bowman’s membrane
3 – Stroma – its regularity contributes towards transparency
4- Descemet’s membrane
5- Endothelium – pumps fluid out of corneal and prevents corneal oedema

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What is the Uvea?

The vascular coat of the eyeball and lies between the sclera and retina

What three parts make up the uvea?

Iris
Ciliary body
Choroid

These are connected and disease to one affects the other portions

What does the Iris do?

Control light levels

Round opening in the centre of pupil

embedded with tiny muscles that dilate or contrict

Describe the structure of the lens?

Outer acellular capsule Regular inner elongated cell fibres - transparancey may loose transparency with age = cataract

What is the function of the lens?

- Transparency - Regular structure - Refractive Power - 1/3 of the eye focusing power - higher refractive index than aqueous fluid and vitreous - Accommodation - Elasticity

What is the visible portion of the optic nerve called?

Optic disk It connects to the back of the eye near the macula

What is the blind spot?

Where the optic nerve meets the retina there are no light sensitive cells = blind spot

What is the macula?

roughly located in the centre of the retina Small and highly sensitive part responsible for detailed central vision

What is the fovea?

The very centre of the macula

What is the fovea test?

Since the fovea is the most sensitive part of the retina = because it has the highest concentration of cones but low concentration of rods * hence why stars out of the corner of your eye are brighter than when you look directly as rods are on periphery of eye not fovea Only your fovea has the concentration of cones to percieve in detail

What is the corresponding anatomic landmark for the physiological blind spot?

Optic disk

What is central vision?

Detail day vision colour vision fovea with highest concentration of cone photoreceptors read and facial recognition

How to asses central vision?

visial acuity assessment Loss of foveal vision : poor visual acuity

What is peripheral vision?

Shape, movement, night vision Navigation vision

How to assess peripheral vision?

Assessed by visual field assessment Extensive loss of visual field - unable to navigate in environment, px may need white stick even with perfect visual acuity

What is retinal structure?

Made of outer layer: retinal pigment epithelium which sits infront of choroid Middle layer : made of bipolar 2nd order neuron cells Inner layer : neuroretina made of retinal ganglion 3rd order neurones

What is the function of the retinal pigment epithelium?

Made of photoreceptors = rods Used for detection of light

What is the function of the Middle layer of retina?

Local signal processing to improve contrast sensitivity, regulate sensitivity

What is the function of the inner layer of retina?

transmission of signal from eye to the brain

What two photoreceptors are there?

Rods and Cons Rods : 100X more sensitive to light and night vision Cons : colour and day vision

What are the structural differences between cones and rods?

Rods: have longer outer segment with photo sensitive pigment Have a slower response to light Cones: Shorter outer segment. 6 million cones vs 120 million rods

What happens to the outer segment distal discs in photoreceptors?

Outer segment : made of stacks of discs, distal discs which are deactivated pigments are shedded and phagocytosed by retinal epithelial cells

How are photoreceptors distrivuted in the eye?

In periphery = higher rods in central higher cones

Where can one find the highest concentration of Rod photoreceptors in the retina?

20-40 degrees away from fovea

What wavelength of lights do the following cones respond do: S cones M cones L cones?

S cones - blue M cones - green L cones - red

What is the commonest colour vision deficiency?

Dueteranomaly - shfiting of M cone sensitivity peak towards the L cone curve causing red-green confusion * check slide 34 for frequency spectrum

What is Achromatopsia?

Full colour blindness

What is anamalous trichromatism?

Colour Vision deficits can be caused by a shift in the photo-pigment peak sensitivity.

What is dichromatism?

only two cone photo-pigment sub-types are present

What is monochromatism?

there is complete absence of colour vision. This can be caused by Blue Cone Monochromatism, with the presence of only blue L-cones. Or by Rod Monochromatism, in which there is a total absence of all cone photo-receptors.

Px with blue cone monochromatism have...?

normal day light visual acuity

Px with rod Rod Monochromatism have ...?

No functional day vision

What is the colour blindness test called?

Ishihara test