Visual Systems anatomy Flashcards
What structures make up the eye?
Upper eyelid Palpebral fissure Lateral canthus Lower eyelid Pupil Iris Sclera Medial canthus Caruncle Limbus (border between cornea and sclera)
What are the main featured of the lacrimal system?
Tears produced by lacrimal gland
Drain through the two puncta, openings on medial lid margin
Flow through superior and inferior canaliculi
Gather in tear sac
Exit tear sac through tear duct into nasal cavity
What is tear film?
Maintains smooth cornea-air surface
Oxygen supply to Cornea – normal cornea has no blood vessels
Removal of debris (tear film and blinking)
Bactericide
What are the three layers of tear film?
Lipid layer
Water layer
Mucin layer
What is the function of the lipid layer?
reduce tear film evaporation - produced by a row of Meibomian Glands along the lid margins
What is the function of the mucinous layer corneal surface?
maintains surface wetting
What is the conjuctiva?
Thin, transparent tissue that covers the outer surface of the eye
What is the extent of the conjuctiva?
It begins at the outer edge of the cornea, covers the visible part of the eye, and lines the inside of the eyelids
It is nourished by tiny blood vessels that are nearly invisible to the naked eye
What are the three layers of the coat of the eye?
Sclera - hard and opaque
Choroid - pigmented and vascular
Retina - neurosensory tissue
What is the sclera?
commonly known as “the white of the eye,”
the tough, opaque tissue that serves as the eye’s protective outer coat.
High water content
What is the cornea?
The transparent, dome-shaped window covering the front of the eye.
Low water content
What is the function of the cornea?
Powerful refracting surface, providing 2/3 of the eye’s focusing power. Like the crystal on a watch, it gives us a clear window to look through
What are the 5 layers of the cornea?
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, glucose supply
What happens if you hydrate the cornea?
Becomes white
What is the Uvea?
Vascular coat of eyeball and lies between the sclera and retina.
What are the three parts of the uvea?
iris, ciliary body and choroid
Intimately connected and a disease of one part also affects the other portions though not necessarily to the same degree.
What is the choroid?
lies between the retina and sclera. It is composed of layers of blood vessels that nourish the back of the eye.
What is the iris?
Controls light levels inside the eye similar to the aperture on a camera.
Controls light levels inside the eye similar to the aperture on a camera.
What is the pupil?
Round opening in the centre is the pupil.
What is the lens structure?
Outer acellular capsule
Regular inner elongated cell fibres – transparency
May loose transparency with age – cataract
What is the function of the lens?
Refractive Power
1/3 of the eye focusing power - higher refractive index than aqueous fluid and vitreous
Accommodation
Elasticity
What is the retina?
Very thin layer of tissue that lines the inner part of the eye.
What is the function of the retina?
Responsible for capturing the light rays that enter the eye. Much like the film’s role in photography.
These light impulses are then sent to the brain for processing, via the optic nerve.
What is the optic nerve?
transmits electrical impulses from the retina to the brain
connects to the back of the eye near the macula
visible portion is called the optic disc
Where is the optic blind spot?
Where the optic nerve meets the retina there are no light sensitive cells
Where is the macula located?
Located roughly in the centre of the retina, temporal to the optic nerve
What is the macula?
A small and highly sensitive part of the retina responsible for detailed central vision
What is the fovea?
The fovea is the very centre of the macula.
What is the function of the macula?
The macula allows us to appreciate detail and perform tasks that require central vision such reading.
What is the most sensitive part of the retina?
Fovea
What is the composition of the fovea?
It has the highest concentration of cones, but a low concentration of rods
What is the anatomic landmark for the physiological blind spot?
Optic disc
What are the features of central vision?
Detail day vision, colour vision – fovea has the highest concentration of cone photoreceptors
Reading, facial recognition
Assessed by visual acuity assessment
Loss of foveal vision – Poor visual acuity
What are the features of peripheral vision?
Shape, movement, night Vision
Navigation vision
Assessed by visual field assessment
Extensive loss of visual field – unable to navigate in environment, patient may need white stick even with perfect visual acuity
What comprises the outer layer of the retina?
Photoreceptors (1st order neuron)
Detection of Light
What comprises the middle layer of the retina?
Bipolar Cells (2nd order neuron) Local signal processing to improve contrast sensitivity, regulate sensitivity
What comprises the inner layer of the retina?
Retinal ganglion cells (3rd order neuron)
Transmission of signal from the eye to the brain
What are the main features of rods?
Longer outer segment with photo-sensitive pigment
100 times more sensitive to light than cones
Slow response to light
Responsible for night vision (Scotopic Vision)
120 million rods
What are the main features of cones?
Less sensitive to light, but faster response
Responsible for day light fine vision and colour vision (Photopic Vision)
6 million cones
Describe rod (scotopic) vision?
Peripheral and night vision More photoreceptors, more pigment, higher spatial and temporal (time) summation
Recognizes motion
Describe cone (photopic) vision?
Central and day vision
Recognizes colour and detail
Describe the different cones and the colours they are responsible for?
S-Cones: Blue
M-Cones: Green
L- Cones: Red
What is deuteranomaly?
also known as Daltonism is the most frequent form of colour blindness
they don’t perceive the colour red
What is full colour blindness called?
achromatopsia
What is the colour blindness test called?
Ishihara test
