Problem 1 – a keen eye
- Vision begins when light is reflected from objects into
the eye
Light: the stimulus for vision
- Light is energy within the electromagnetic spectrum →
continuum of electromagnetic energy produced by
electric charges and is radiated as waves
- Energy in the spectrum can be described in its wavelengths → distance between the peak of the electromagnetic
waves → range from extremely short-wavelength gamma rays to long-wavelength radio waves where humans
can only see a tiny part of the spectrum
- Visible light (spectrum that humans can perceive) have wavelengths ranging from 400 to 700 nanometers
- Light can also be described as consisting of small packets of energy called photons → one photon being the
smallest possible packet of light
Eye:
- Light reflected from objects
enters the eye through the pupil
and is focused by the cornea and
lens to form sharp images of the
objects on the retina → retina
contains the photoreceptors for
vision which are necessary for transduction
- 2 kinds of visual receptors: rods (light/dark) and cones
(color/fine details) containing light sensitive chemicals called
visual pigments that react to light and trigger electrical signals
→ these signals flow through the neurons of the retina
- The signals then emerge from the back of the eye in the optic
nerve
- Cornea (transparent covering of the eye) and lens at the front
of the eye and the neurons in retina shape what we see
shape and size
- Spherical with a diameter of 24 mm
- Optic axis is an imaginary diameter line from the front to the
back of the eye, passing through the center of the lens (each
eye points in the direction defined by the optic axis)
Three membranes
- Outer layer = sclera → tough protective cover (white of the
eye and transparent cornea at the front of the eye)
- Middle membrane = choroid → lines the interior of the sclera and contains
most of the blood vessels that supply the inside of the eye with oxygen and
nutrients
- Inner membrane = retina → made out of neurons, including the receptors
that convert the light entering the eye into neural signals
Cornea
- Transparent membrane at the front of the eye
- Light enters by passing through the cornea which bends the light
,- This bending (refraction) of light is part of the process of focusing light on the retina
- Cornea performs most of the focusing process → 80% of it
- But cornea is rigid and cannot adjust how much the light passing though it is refracted → this is left to the
flexible lens which performs the fine adjustments necessary to bring light into sharp focus
Iris and pupil
- Iris is the colored part of the eye → donut shaped with an opening in the middle which is the pupil
- iris controls the size of the pupil by contracting and relaxing mainly in the response to the light intensity
- intense light makes the iris contract and the pupil smaller → reduces the amount of light that enters the eye
- in dim light the iris relaxes and the pupil gets larger and thus increases the amount of light entering the eye
- this whole process is called the pupillary reflex
- pupil can range from 2 – 8 mm
- when the pupil gets smaller → constricts; when it gets larger → dilates
- both irises work simultaneously and to the same degree (also if only light is shined into the left eye, the right eye
constricts
the three chambers
- the anterior chamber is the space between the cornea and the iris
- posterior chamber is the smaller space between the iris and the lens
o both chambers are filled with a clear fluid called aqueous humor → derived from blood, supplies oxygen
and nutrients and removes waste (constantly renewed)
- the vitreous chamber (main part of the interior eye) is filled with vitreous humor, clear more gel like fluid
- both fluids are more than 99% water
- the humors also refract light but like the cornea they cannot be adjusted
- the intraocular pressure (pressure of the fluids in the three chambers of the eye must be greater than air
pressure to prevent the eyes from collapsing like a deflated basketball but can also not be too great
lens and accommodation
- light passes through the pupil and into the lens which further refracts
the light which ensures that light focuses properly on the retina → 20%
of focusing
- focal length → the distance from a lens at which the image of an object
is in focus when the object is far away from the lens
- a weak lens doesn’t refract light much → it is thin and flat and has a
long focal length
- the power of a length is expressed in diopters
- eye adjusts the shape of the lens to change its focal length with ciliary
muscles
- the edges of the lens are stretched by zonule fibers that
connect the lens to the choroid
- when ciliary muscles are relaxed the choroid pulls on the
zonule fibres which stretches the lens and causes it to take on a
relatively thin, flat shape making it a weak lens with long focal
length appropriate for focusing distant objects → expand
- when the ciliary muscles contract, they hinder the pull of the
choroid on the zonule fibers, the lens isn’t stretching so it is
thicker, stronger with a shorter focal length appropriate for focusing light from nearer objects → contract
- this adjustment of the shape of the lens is called accommodation
- if something goes wrong with this process of accommodation the result is the focal point being in front or
behind the retina which results in blurry vision
- cornea, aqueous humor and vitreous humor have fixed level of refraction, lens can change by changing shape
,Optic nerve: transmits information
from the eye to the brain
Sclera: elastic membrane
maintaining eye shape (outer
layer)
Choroid: connects retina to sclera,
supplies nutrients to
photoreceptors
Blindspot: in the optic disc, no
photoreceptors which is why its
insensitive to light
Retina
- The goal is to form a clear picture on the retina
- Where sight begins
- The retina then transforms the image into neural
signals to be sent to the brain
- It is inverted → up becomes down, left becomes right
and vice versa
Anatomy of the retina
Main layers:
- Retina structured in three main layers (nuclear layers)
→ the outer nuclear layer, (outer synaptic layer),
inner nuclear layer, (inner synaptic layer) and
ganglion layer
- Ganglion layer:
o Consists of ganglion neurons
, o Filter info and transform raw image into new representations
o Send info through the optic nerve
o exit the eye at the optic disk (blind spot) forming the optic nerve
- Inner synaptic layer:
o Synapses between amacrine, bipolar and ganglion cells
- Inner nuclear layer:
o Bipolar, amacrine and horizontal cells
o Bipolar: making synapses with ganglion and photoreceptors
o Amacrine cells: contact with bipolar and ganglion cells
o Horizontal cells: contact with photoreceptors; lateral inhibition
- Outer synaptic layer:
o Synapses of horizontal, bipolar and photoreceptor cells
- Outer nuclear layer:
o Recodes info from light to electrical signals → transduction
o Humans have duplex retina → meaning having both cones and rods
o Cones:
▪ Daylight
▪ Faster
▪ For details (due to less convergence) and color
▪ Fewer in number
▪ Wider range
o Rods:
▪ Night vision
▪ Slower
▪ More in number
▪ Long
▪ Light sensitive
- Inner and outer segments of photoreceptors
- Vision begins when light is reflected from objects into
the eye
Light: the stimulus for vision
- Light is energy within the electromagnetic spectrum →
continuum of electromagnetic energy produced by
electric charges and is radiated as waves
- Energy in the spectrum can be described in its wavelengths → distance between the peak of the electromagnetic
waves → range from extremely short-wavelength gamma rays to long-wavelength radio waves where humans
can only see a tiny part of the spectrum
- Visible light (spectrum that humans can perceive) have wavelengths ranging from 400 to 700 nanometers
- Light can also be described as consisting of small packets of energy called photons → one photon being the
smallest possible packet of light
Eye:
- Light reflected from objects
enters the eye through the pupil
and is focused by the cornea and
lens to form sharp images of the
objects on the retina → retina
contains the photoreceptors for
vision which are necessary for transduction
- 2 kinds of visual receptors: rods (light/dark) and cones
(color/fine details) containing light sensitive chemicals called
visual pigments that react to light and trigger electrical signals
→ these signals flow through the neurons of the retina
- The signals then emerge from the back of the eye in the optic
nerve
- Cornea (transparent covering of the eye) and lens at the front
of the eye and the neurons in retina shape what we see
shape and size
- Spherical with a diameter of 24 mm
- Optic axis is an imaginary diameter line from the front to the
back of the eye, passing through the center of the lens (each
eye points in the direction defined by the optic axis)
Three membranes
- Outer layer = sclera → tough protective cover (white of the
eye and transparent cornea at the front of the eye)
- Middle membrane = choroid → lines the interior of the sclera and contains
most of the blood vessels that supply the inside of the eye with oxygen and
nutrients
- Inner membrane = retina → made out of neurons, including the receptors
that convert the light entering the eye into neural signals
Cornea
- Transparent membrane at the front of the eye
- Light enters by passing through the cornea which bends the light
,- This bending (refraction) of light is part of the process of focusing light on the retina
- Cornea performs most of the focusing process → 80% of it
- But cornea is rigid and cannot adjust how much the light passing though it is refracted → this is left to the
flexible lens which performs the fine adjustments necessary to bring light into sharp focus
Iris and pupil
- Iris is the colored part of the eye → donut shaped with an opening in the middle which is the pupil
- iris controls the size of the pupil by contracting and relaxing mainly in the response to the light intensity
- intense light makes the iris contract and the pupil smaller → reduces the amount of light that enters the eye
- in dim light the iris relaxes and the pupil gets larger and thus increases the amount of light entering the eye
- this whole process is called the pupillary reflex
- pupil can range from 2 – 8 mm
- when the pupil gets smaller → constricts; when it gets larger → dilates
- both irises work simultaneously and to the same degree (also if only light is shined into the left eye, the right eye
constricts
the three chambers
- the anterior chamber is the space between the cornea and the iris
- posterior chamber is the smaller space between the iris and the lens
o both chambers are filled with a clear fluid called aqueous humor → derived from blood, supplies oxygen
and nutrients and removes waste (constantly renewed)
- the vitreous chamber (main part of the interior eye) is filled with vitreous humor, clear more gel like fluid
- both fluids are more than 99% water
- the humors also refract light but like the cornea they cannot be adjusted
- the intraocular pressure (pressure of the fluids in the three chambers of the eye must be greater than air
pressure to prevent the eyes from collapsing like a deflated basketball but can also not be too great
lens and accommodation
- light passes through the pupil and into the lens which further refracts
the light which ensures that light focuses properly on the retina → 20%
of focusing
- focal length → the distance from a lens at which the image of an object
is in focus when the object is far away from the lens
- a weak lens doesn’t refract light much → it is thin and flat and has a
long focal length
- the power of a length is expressed in diopters
- eye adjusts the shape of the lens to change its focal length with ciliary
muscles
- the edges of the lens are stretched by zonule fibers that
connect the lens to the choroid
- when ciliary muscles are relaxed the choroid pulls on the
zonule fibres which stretches the lens and causes it to take on a
relatively thin, flat shape making it a weak lens with long focal
length appropriate for focusing distant objects → expand
- when the ciliary muscles contract, they hinder the pull of the
choroid on the zonule fibers, the lens isn’t stretching so it is
thicker, stronger with a shorter focal length appropriate for focusing light from nearer objects → contract
- this adjustment of the shape of the lens is called accommodation
- if something goes wrong with this process of accommodation the result is the focal point being in front or
behind the retina which results in blurry vision
- cornea, aqueous humor and vitreous humor have fixed level of refraction, lens can change by changing shape
,Optic nerve: transmits information
from the eye to the brain
Sclera: elastic membrane
maintaining eye shape (outer
layer)
Choroid: connects retina to sclera,
supplies nutrients to
photoreceptors
Blindspot: in the optic disc, no
photoreceptors which is why its
insensitive to light
Retina
- The goal is to form a clear picture on the retina
- Where sight begins
- The retina then transforms the image into neural
signals to be sent to the brain
- It is inverted → up becomes down, left becomes right
and vice versa
Anatomy of the retina
Main layers:
- Retina structured in three main layers (nuclear layers)
→ the outer nuclear layer, (outer synaptic layer),
inner nuclear layer, (inner synaptic layer) and
ganglion layer
- Ganglion layer:
o Consists of ganglion neurons
, o Filter info and transform raw image into new representations
o Send info through the optic nerve
o exit the eye at the optic disk (blind spot) forming the optic nerve
- Inner synaptic layer:
o Synapses between amacrine, bipolar and ganglion cells
- Inner nuclear layer:
o Bipolar, amacrine and horizontal cells
o Bipolar: making synapses with ganglion and photoreceptors
o Amacrine cells: contact with bipolar and ganglion cells
o Horizontal cells: contact with photoreceptors; lateral inhibition
- Outer synaptic layer:
o Synapses of horizontal, bipolar and photoreceptor cells
- Outer nuclear layer:
o Recodes info from light to electrical signals → transduction
o Humans have duplex retina → meaning having both cones and rods
o Cones:
▪ Daylight
▪ Faster
▪ For details (due to less convergence) and color
▪ Fewer in number
▪ Wider range
o Rods:
▪ Night vision
▪ Slower
▪ More in number
▪ Long
▪ Light sensitive
- Inner and outer segments of photoreceptors
