Vision Flashcards
Label the following
Where are tears produced
Lacrimal gland
What is pathway for tears
Produced by lacrimal gland
Drain through two puncta (openings on the medial lid margin
Flow through superior and inferior canaliculi
gather in tear sac
Exit tear sac through tear duct into nasal cavity
(note I think the tear duct is labelled incorrectly in the powerpoint)
What are the three ways in which tears are produced
Basal
Reflex
emotional
what are the afferent nerves in the lacrimal system
Afferrent :
cornea, crraniual nerve V1-opthalmic trigeminal
Efferent: parasympathetic
Neurotransmitter acetylcholine
what is the most superfical part of the eye
Tear film
How many layers of the tear film
3
Superficial lipid layer
Aqueous middle
Mucinous layer at the bottom
What is the most superficial layer of the tear film where is it secreted from and its function
The lipid layer on the top responsible for protecting the tear film from rapid evaporation.
The lipid layer is secreted by the Meibomian Glands,
situated along the eyelid margins.
What are the 3 layers of the tear film and their function
The lipid layer on the top responsible for protecting the tear film from rapid evaporation.
The lipid layer is secreted by the Meibomian Glands,
situated along the eyelid margins.
The Aqueous Tear Film Layer in the middle,
forms the main bulk of the tear film.
It delivers oxygen and nutrient to the surrounding tissue.
It contains factors against potentially harmful bacteria.
The bottom Mucinous Layer ensures that the tear film sticks to the eye surface.
This renders the surface of the eye “wettable”.
The mucin molecules act by binding water molecules,
to the hydrophobic corneal epithelial cell surface.
What is the middle layer of the tear film
The Aqueous Tear Film Layer in the middle,
forms the main bulk of the tear film.
It delivers oxygen and nutrient to the surrounding tissue.
It contains factors against potentially harmful bacteria.
What is the innermost layer of the tearfilm (bottom layer) and what is its function
The bottom Mucinous Layer ensures that the tear film sticks to the eye surface.
This renders the surface of the eye “wettable”.
The mucin molecules act by binding water molecules,
to the hydrophobic corneal epithelial cell surface.
What is the tear film
The healthy Cornea is constantly covered by the tear film,
a thin layer of fluid called tear film
The tear film maintains a smooth cornea-to-air surface.
Provides Oxygen supply to cornea (as normal cornea does not have blood vessels)
This is important for maintaining clear vision,
and removing surface debris during blinking. and is bactericidal
Which layer in the tear film protects the tear film from rapid evaporation?
A) Lipid Layer
B) Water Layer
C) Mucinous Layer
D) All Three Layers
What is the conjunctiva
Thin, transparent tissue that covers the outer surface of the eye
Where is the conjunctiva?
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
When are blood vessels in the conjunctive prominent
When there is inflammation or infection of the eye. This is know as conjunctivitis
What is the anteroposterior diameter of the eye
24 mm in adults
What are the 3 layers in the coat of the eye
Sclera: hard and oopaque
Choroid: pigmented and vascular
Retina: neurosensory
What is the outermost layer of the coat of the eye
The outer fibrous opaque layer called the Sclera,
responsible for protecting the eye,
and maintaining the shape of the eye.
It is tough and opaque and serves as protective outercoat
it has a high water content
What is the middle layer of the of the coat of the eye
The middle pigmented vascular layer called the Choroid,
responsible for providing circulation to the eye,
and shielding out unwanted scattered light.
What is the innermost layer of the coat of the eye
The innermost Neurosensory Layer called the Retina,
responsible for converting light into neurological impulses,
to be transmitted to the brain via the Optic Nerve
What happens if you hydrate the cornea
It becomes white
What is the cornea
The transparent, dome-shaped window covering the front of the eye
seamless
Low water content
Powerful refracting surface, providing 2/3 of the eye’s focusing power.
it gives us a clear window to look through
Made up of 5 layers
What are the 5 layers of the cornea
5 layers
1 – Epithelium
2 – Bowman’s membrane (basal membrane)
3 – Stroma – its regularity contributes towards transparency
4- Descemet’s membrane
5- Endothelium – pumps fluid out of corneal and prevents corneal oedema
There is also passage of glucose from the endothelium that nourishes the cornea
Where does cornea get oxygen from
Air
Where does the glucose in the cornea arrive from
provided by fluid between iris and cornea which is absorbed by the endothelium
What is the Uvea
Vascular coat of eyeball and lies between the sclera and retina
What is the uvea composed of
of three parts – 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
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
The foremost part of the uvea
Controls light levels inside the eye similar to the aperture on a camera.
Round opening in the centre is the pupil
Embedded with tiny muscles that dilate (widen) and constrict (narrow) the pupil size.
What is the stucture of the lens of the eye
Outer acellular capsule
Regular inner elongated cell fibres – transparency
May loose transparency with age – cataract
What is the function of the cornea
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 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 function of the optic nerve
transmits electrical impulses from the retina to the brain
where in the eye does the optic nerve cconnect
connects to the back of the eye near the macula
What is the optic disc
visible portion of the optic nerve is called optic disc
What is the blind spot
Where the optic nerve meets the retina there are no light sensitive cells. It is a blind spot
What is the macula and where is it located
A small and highly sensitive part of the retina responsible for detailed central vision
Located roughly in the centre of the retina, temporal to the optic nerve
Functions of macula:
appreciate detail and perform tasks that require central vision such reading or face recognition
Located roughly in the centre of the retina, temporal to the optic nerve
What is the fovea
The fovea is the very centre of the macula. It is the most sensitive part of the macula
Does the fovea have more rods or cones
Fovea has a HIGH concentration of cones and low concentration of rods
What are rod receptors more sensitive to
LIght
What are cones more sensitive to
detail (fine vision)
What is the fovea test
Series of letters followed by a space and then another series of letters. You stare at the star and try to read the letters on either side. Show you how small the area for central reading is
What is the corresponding anatomic landmark for the physiological blind spot?
A) Macula
B) Fovea
C) Optic Disc
D) Ora Serrata
Optic disk
What can our vision be divided into
Central
Peripheral vision
What are the characteristics of central vision
Central Vision, or Macular Vision, is responsible for detailed central fine vision and daytime and colour vision.
What happens in loss of central vision
Patients with loss of central vision will have problems with reading,
and recognizing faces.
What happens if there is loss of foveal vision
– Poor visual acuity
What are the characteristics of peripheral vision
Shape, movement, night Vision
Navigation vision
Patients with extensive loss in peripheral vision will have problems navigating the world (even if they have perfect visual acuity)
How is central vision assessed
Visual acuity assessment
How is peripheral vision assessed
Visual field assessment
Describe structure of retina
The retina forms the innermost layer of the coat of eye in the posterior segment.
- outer thin layer of Retinal Pigment Epithelium, situated right in front of the Choroid,
- Inner thicker layer called the Neuroretina.
Describe the neuroretina
Made up of phot receptors and neurons.
3 layers
Outer: consist of photreceptors
Middle: Intermediate neurons
Inner: ganglion nerve cells
Axon runs from optic nerve to brain
(NOTE: in the picture the light entering is shown at the wrong end. It should come from the outside of the eye
What is the function of the Retinal pigment epithelium
1.transports nutrients from choroid to photoreceptor cells
2. removes metabolic waste from retina
what are the two main classes of photreceptors
Rods and cones
what is the function of rods
Longer outer segment with photo-sensitive pigment
100 times more sensitive to light than cones
But slower response to light
Responsible for night vision (Scotopic vision)
How many rods in the eye
120 million
What is the function of cones
Shorter outer segment Less sensitive to light, but faster response
Responsible for day light fine vision and colour vision (Photopic Vision)
How many cones in the eye
6 million cones
Where are photopigments synthesized
Photopigments are synthesized in the inner photo-receptor segment,
and are then transported to the outer segment.
What is the structure of the photoreceptors/life cycle of photopigments
The outer segment is made up of stacks of discs.
The distal discs with deactivated photo-pigments are shedded from the tips,
and phago-cytosed by the retinal epithelial cells.
The deactivated photopigments are regenerated inside the retinal epithelial cells,
and then transported back to the photo-receptors.
What is the distribution of photrecceptors in the eye
Central part of eye which corresponds to fovea, highest concentration of cones
In the periphery higher concentration of rods
Rod photo-receptors are widely distributed all over the retina,
with the highest density just outside the macula.
The density of rod photo-ceptors gently tails off towards the periphery
Rod photo-receptors are completely absent within the macula.
What is night vision called
Scotopic vision
What is day vision called
photopic vision
Where are cone photreceptors present
Present only in the macula
Where are rod photreceptors absent
Absent in the macula
Where can one find the highest concentration of Rod photoreceptors in the retina?
A) Optic Disc
B) Fovea
C) 10-20 degrees away from fovea
D) 20-40 degrees away from fovea
20-40 degrees away from fovea
What are the different cones and what colours do they percieve
S-Cones: Blue (short wavelength)
M-Cones: Green (medium wave length)
L- Cones: Red (long wave length)
Are rods sensitive to colour
Rods are used for night vision and spatial recognition and are not really sensitive to any particular colour
What is the single peak of light sensitivity for rods
Rod vision has only one single peak light sensitivity,
at 498 nano-meters wavelength.
What forms the basis of colour vision
In humans, there are three cone photo-pigment sub-types:
the S-Cones with photo-pigment sensitive to short wavelength – colour blue,
the M-Cones with photo-pigment sensitive to medium wavelength – colour green,
and the L-Cones with photo-pigment sensitive to long wavelength – colour red.
How is yellow light perceived
Yellow light has a wavelength between the peak sensitivity wavelengths of M-Cones and L-Cones.
Yellow light stimulates both M-cones and L-cones equally.
Biologically, we experience yellow light as a combination of green and red light.
What is Deuteranomaly.
The commonest form of colour vision deficiency. also known as Daltonism
It is caused by the shifting of the M-cone sensitivity peak towards that of the L-cone curve,
causing red-green confusion
Red is not seen
What is the commonest form of colour vision deficiency
Deuteranomaly also known as Daltonism
It is caused by the shifting of the M-cone sensitivity peak towards that of the L-cone curve,
causing red-green confusion. red is not seen, other colours are
What is the percentage of colour blindness
8% among males and 0.5% among females.
92% of the population have normal colour vision
What is full colour blindness know as
achromatopsia <0.0001%
How can you get colour vision deficits
Colour Vision deficits can be caused by a shift in the photo-pigment peak sensitivity.
Anomalous Trichromatism.
or
absence of one or more of the 3 cone photo-pigments.
In Dichromatism, only two cone photo-pigment sub-types are present.
In Monochromatism, there is complete absence of colour vision.
Anomalous Trichromatism.
Colour Vision deficits caused by a shift in the photo-pigment peak sensitivity.
What is the commonest form of Anomalous Trichromatism.
Deuteranomaly
What is monochromatism
complete absence of colour vision.
How is monchromatism caused
This can be caused by Blue Cone Monochromatism,
with the presence of only blue L-cones.
or
Or by Rod Monochromatism,
in which there is a total absence of all cone photo-receptors.
Patients with Blue Cone Monochromatism have normal day light visual acuity,
what happens in Blue cone monochromatism
Patients with Blue Cone Monochromatism have normal day light visual acuity,
What happens in Rod monoichromatism
Patients with Rod Monochromatism have no functional day vision.
How is colour blindness tested
Ishihara test
The number 25 is the control number as this number can be seen by all regardless of colour blindess
