ocular anatomy fluid system glaucoma lens cataract phototransduction field visual acuity ocular movement errors of refraction light reflex accommodation corneal reflex visual pathway and its lesions
The visual pathway/visual system is the part of central nervous system which gives organisms the ability to process visual detail , as well as enabling the formation of several non-image photo response functions.
It detects interprets information from visible light to build a representation of the surrounding environment .
The visual system carries out a number of complex tasks , including the reception of light and the formation of monocular representations; the buildup of a nuclear binocular perception from a pair of two dimensional projections ; the identification and categorization of visual objects ; assessing distances to and between objects and guiding body movements in relation to the objects seen.
structure of eye ball,eyeball is a specialized sense organ that helps us to understand our environment. It is a sensory unit composed of three parts: receptor, sensory pathway, and a brain center
The main parts of the human eye are The Conjunctiva,
Sclera,Choroid,
Cornea, Iris, Pupil,
Anterior Chamber,
Posterior Chamber, Aqueous humor, Lens, Vitreous humor, Retina,Macula and Optic nerve.
The visual pathway/visual system is the part of central nervous system which gives organisms the ability to process visual detail , as well as enabling the formation of several non-image photo response functions.
It detects interprets information from visible light to build a representation of the surrounding environment .
The visual system carries out a number of complex tasks , including the reception of light and the formation of monocular representations; the buildup of a nuclear binocular perception from a pair of two dimensional projections ; the identification and categorization of visual objects ; assessing distances to and between objects and guiding body movements in relation to the objects seen.
structure of eye ball,eyeball is a specialized sense organ that helps us to understand our environment. It is a sensory unit composed of three parts: receptor, sensory pathway, and a brain center
The main parts of the human eye are The Conjunctiva,
Sclera,Choroid,
Cornea, Iris, Pupil,
Anterior Chamber,
Posterior Chamber, Aqueous humor, Lens, Vitreous humor, Retina,Macula and Optic nerve.
in this ppt we describe about anatomy of eyeball( cornea, sclera, choroid, iris, retina, ciliary body, vitreous etc..), dimension of the eyeball, coats of the eyeball.
This ppt file belongs to Mr. Yonas Akalu one of my best instructors ...
Vision is by far the most used of the five senses and is one of the primary means that we use to gather information from our surroundings. More than 75% of the information we receive about the world around us consists of visual information.
The eye is often compared to a camera. Each gathers light and then transforms that light into a "picture." Both also have lenses to focus the incoming light. Just as a camera focuses light onto the film to create a picture, the eye focuses light onto a specialized layer of cells, called the retina.
The human eye is an organ which reacts to light and pressure. As a sense organ, the mammalian eye allows vision. Human eyes help to provide a three dimensional, moving image, normally coloured in daylight. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can differentiate between about 10 million colors[1] and is possibly capable of detecting a single photon.
The eye is our organ of sight. The eye has a number of components which include but are not limited to the cornea, iris, pupil, lens, retina, macula, optic nerve, choroid and vitreous.
ANATOMY & PHYSIOLOGY Lecturer: Tatyana V. Ryazantseva
2. Outer eye: Eyelids The eyelids fulfill two main functions: protection of the eyeball secretion, distribution and drainage of tears
3. Lid movement The levator extends from an attachment at the orbital apex to attachments at the tarsal plate and skin. ● The lids are securely attached at either end to the bony orbital margin by the medial and lateral palpebral ligaments. Trauma to the medial ligament causes the lid to flop forward and laterally, impairing function and cosmesis.
4. Innervation - Sensory innervation is from the trigeminal (fifth) cranial nerve, via the ophthalmic division (upper lid) and maxillary division (lower lid). - The orbicularis oculi is innervated by the facial (seventh) nerve. - The levator muscle in the upper lid is supplied by the oculomotor (third) nerve.
5. Blood supply and lymphatics The eyelids are supplied by an extensive network of blood vessels which form an anastomosis between branches derived from the external carotid artery via the face and from the internal carotid artery via the orbit.
6. Blood supply and lymphatics Lymphatic fluid drains into the preauricular and submandibular nodes. Preauricular lymphadenopathy is a useful sign of infective eyelid swelling (especially viral).
The retina is the sensory membrane that lines the inner surface of the back of the eyeball. It's composed of several layers, including one that contains specialized cells called photoreceptors.
Photoreceptor cells take light focused by the cornea and lens and convert it into chemical and nervous signals which are transported to visual centers in the brain by way of the optic nerve.
In the visual cortex of the brain (which, ironically, is located in the back of the brain), these signals are converted into images and visual perceptions.
in this ppt we describe about anatomy of eyeball( cornea, sclera, choroid, iris, retina, ciliary body, vitreous etc..), dimension of the eyeball, coats of the eyeball.
This ppt file belongs to Mr. Yonas Akalu one of my best instructors ...
Vision is by far the most used of the five senses and is one of the primary means that we use to gather information from our surroundings. More than 75% of the information we receive about the world around us consists of visual information.
The eye is often compared to a camera. Each gathers light and then transforms that light into a "picture." Both also have lenses to focus the incoming light. Just as a camera focuses light onto the film to create a picture, the eye focuses light onto a specialized layer of cells, called the retina.
The human eye is an organ which reacts to light and pressure. As a sense organ, the mammalian eye allows vision. Human eyes help to provide a three dimensional, moving image, normally coloured in daylight. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can differentiate between about 10 million colors[1] and is possibly capable of detecting a single photon.
The eye is our organ of sight. The eye has a number of components which include but are not limited to the cornea, iris, pupil, lens, retina, macula, optic nerve, choroid and vitreous.
ANATOMY & PHYSIOLOGY Lecturer: Tatyana V. Ryazantseva
2. Outer eye: Eyelids The eyelids fulfill two main functions: protection of the eyeball secretion, distribution and drainage of tears
3. Lid movement The levator extends from an attachment at the orbital apex to attachments at the tarsal plate and skin. ● The lids are securely attached at either end to the bony orbital margin by the medial and lateral palpebral ligaments. Trauma to the medial ligament causes the lid to flop forward and laterally, impairing function and cosmesis.
4. Innervation - Sensory innervation is from the trigeminal (fifth) cranial nerve, via the ophthalmic division (upper lid) and maxillary division (lower lid). - The orbicularis oculi is innervated by the facial (seventh) nerve. - The levator muscle in the upper lid is supplied by the oculomotor (third) nerve.
5. Blood supply and lymphatics The eyelids are supplied by an extensive network of blood vessels which form an anastomosis between branches derived from the external carotid artery via the face and from the internal carotid artery via the orbit.
6. Blood supply and lymphatics Lymphatic fluid drains into the preauricular and submandibular nodes. Preauricular lymphadenopathy is a useful sign of infective eyelid swelling (especially viral).
The retina is the sensory membrane that lines the inner surface of the back of the eyeball. It's composed of several layers, including one that contains specialized cells called photoreceptors.
Photoreceptor cells take light focused by the cornea and lens and convert it into chemical and nervous signals which are transported to visual centers in the brain by way of the optic nerve.
In the visual cortex of the brain (which, ironically, is located in the back of the brain), these signals are converted into images and visual perceptions.
Anatomy of Eye by radhika kulvi, M.Sc nursingRadhika kulvi
The eye is a paired organ, the organ of vision. The eye is made up of various components, which enable it to receive light stimuli from the environment, and deliver this stimuli to the brain in the form of an electrical signal. Vision involves all components of the eye.
DEFINITION:The human eye is a sensory organ,that reacts to visible light and allow to use visual information for various purposes including seeing things,keeping our balance and circadian rhythm.
STRUCTURE
The eye is contained within the bony orbit of the head. The bony orbit is a cavity, comprising parts of the lacrimal bone (includes fossa for nasolacrimal duct) and the maxilla (includes caudal foramen of infraorbital canal). It is continuous with the temporal bone and the pterygopalatine fossa caudally. It is situated in the orbital cavity and is supplied by 2nd cranial nerve.
USMLE NEUROANATOMY 020 Orbit and globe anatomical structures of the eye soc...AHMED ASHOUR
he orbit and globe refer to the anatomical structures of the eye socket (orbit) and the eyeball (globe). Understanding the surgical anatomy of these structures is crucial for procedures related to ophthalmology and orbital surgery.
Understanding the surgical anatomy of the orbit and globe is vital for ophthalmic surgeons and other professionals involved in eye-related procedures. Surgical interventions aim to address various eye conditions, improve vision, and restore or enhance the aesthetic appearance of the eye and surrounding structures.
This presentation focuses in the most important tips in ocular physiology in a summarized manner .......you can watch the illustrated video in the following link
https://www.youtube.com/watch?v=eRbAOL37qus
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
7. Retina:
◦ Acts like the film in a camera to
create an image
◦ Consists of a specialized layer of
cells
◦ Converts light signals into nerve
signal then send these signals to
the optic nerve
Optic nerve carries the signals to the
brain
The brain helps process the image
◦ Rods- low light situations
◦ Cones- allows you to see color
hhttp://www1.appstate.edu/~kms/classes/psy3203/EyePhysio/human_retina.htm
http://www.answersingenesis.org/tj/v13/i1/retina.asp
8. ◦ A bundle of 1 million nerve
fibers
◦ Responsible for transmitting
nerve signals from the eye to
the brain
◦ The optic disc is the front
surface of the optic nerve
The optic disc is visible on the
retina
http://cssd.us/body.cfm?id=802
http://www.wollongong.youronlinecommunity.com.au/wollongong-online/2008/50/walkthrulife/eye-
health.html
12. ◦ Located behind the lens &
in front of the retina
◦ Filled with a gel-like fluid
called the vitreous humor
◦ The vitreous humor is
transparent,avascular&
help maintain the shape of
the eye http://www.ophthobook.com/questions/question-how-many-chambers-are-there-in-the-eye
14. Ciliary processes in posterior chamber secrete aqueous
fluid. It flows between the ligament of the lens and then
through the pupil into the anterior chamber of the eye.
Then fluid passes into the angle between the cornea and
the iris. Through the meshwork of trabeculli aqueous
humor enters the channel of Slemm, which empties into
extraoccular veins.
Functions of aqueous humor: 1) maintains intraoccular
pressure; 2) maintains shape of eyeball; 3) acts as
refractory medium; 4) supplies nutrition; 5) drains
metabolic end products.
16. Anterior Chamber Angle
◦ Located where the cornea
meets the iris
◦ Trabecular Meshwork
Site where aqueous humor
drains out of eye
If AH cannot properly drain out
Pressure build up inside eye
Causes optic nerve damage &
evetually vision loss = glaucoma http://seniorhealth.about.com/library/conditions/blglaucoma2.htm
17.
18.
19. the tissue pressure of the ocular contents
about 15 mm Hg but diurenally fluctuate (15.5 +/-
2.57)
normal range of pressures: 12 – 20
20.
21.
22. General
Diurnal variation — IOP generally higher in the morning
vs afternoon; normal fluctuation 2–5 mm Hg
Posture — higher in supine vs sitting position. Highest in
head down position
Exercise — aerobic exercise generally lowers IOP, while
isometric exercise can increase IOP
Canadian Ophthalmological Society evidence-based clinical
practice guidelines for the management of glaucoma in the adult
eye. Can J Ophthalmol 2009;44(Suppl 1):S1−S93.
23. ◦2.Sitting - going from
a sitting to a lying
position results in an
increase in IOP which
is even greater in
glaucoma patients
◦3.Total Body
Inversion - causes an
increase in IOP by as
much as 15 mm Hg
24. B. Tonometry
◦ 1. Indentation
a. the older of the 2 methods to measure IOP in humans
b. involves measuring the indentation of the cornea resulting
from a given weight
c. the Schiotz tonometer is an indentation tonometer
d. the weight of the tonometer displaces fluid in the eye and
thus affects the IOP measurement
37. Refraction of light.
- 2/3 of the of the
refractive power of
the eye
- 43 diopters
Protection:
germs, dusts and UV
light.
38. Eyelids
Precorneal film of tears
Protective
Nutritive
lubrication
Corneal reflex
Pathway
function
39. Pathway
Functions:
Protection
Testing the integrity of 5th
and 7th
nerves.
Stage of anaesthesia
40.
41.
42. Regular arrangement
The cornea does not have blood vessels.
It gets oxygen directly through the air.
It receives nutrients via :
-diffusion from the tear fluid and the aqueous humour.
Unmyelinated nerve endings.
relative dehydration: If the corneal tissue becomes
hydrated the tissue becomes opaque.
metabolic pump
Osmotic pump
43. Irregular connective tissue lamellae.
Function
Protection
Gives attachment to E.O.M
44. Accommodation is adjustment of eye lens for
various distances. Relaxation of ciliary muscle
cause decrease of refractive power of eye lens
and provides clear vision for long distance.
Decrease of parasympathetic influence to ciliary
muscle controls it. In case of parasympathetic
stimulation of ciliary muscle, it contracts, lens
ligament relax, lens get more spherical,
refractive power increases and eye can see
clear near objects.
45.
46. Fibrous tunic of eyeball is composed by avascular
connective tissue, which gives shape to eyeball and
protect structures inside eyeball.
Functional defensive mechanisms are presented by
cornea reflexes. Irritation of cornea receptors gives
impulses to parasympathetic center in medulla
oblongata (Edinger-Westfal nucleus) and than in
hypothalamus, which permits tears secretion.
Limbic system also controls tear secretion. Blinking
reflex is controlled by n. trigeminus and n. facialis, which
innervate m. orbicularis oculi.
47. When light pass into eye, pupil contracts. In darkness
pupil dilates. This is pupillary light reflex, which helps to
adaptation to light conditions. Reflex arc: light receptors -
optic nerve- optic tract - pretectal area - Edinger-Westfal
nucleus - parasympathetic fibers of n. oculomotorius
(from n. trigeminus) - n. ciliaris - m. sphincter pupillae -
decrease of pupillary diameter.
Consensual pupillary light reflex: reaction of eye pupil to
light irritation of opposite eye. It is possible due to
diverging of nerve fibers from one pretectal nucleus to
both Edinger-Westfal nuclei.
48. In old age lens of eye loose elasticity. So this
condition, when lens become non-
accommodating, called pressbiopia. It should be
corrected by bifocal glasses with upper segment
focused for far-seeing and lower segment
focusing for near-seeing.
In newborn anatomical axis of eyeball is shorter,
comparing to adults.
51. Speed of light in air 300,000 km/sec.
Light speed decreases when it passes through a
transparent substance.
The refractive index is the ratio of the speed of
light in air to the speed of light in the substance.
e.g., speed of light in substance = 200,000 km/sec,
R.I. = 300,000/200,000 = 1.5.
52. Bending of light rays by an angulated interface with
different refractive indices.
Refractive index =
velocity of light in air
velocity of light in that substance
The degree of refraction increases as
the difference in R.I. increases
the angle of incidence increases.
The features of the eye have different R.I. and cause light
rays to bend.
.
56. power of a lens α 1/f
)f(
Diopter is a measure of the
power of a lens
1 diopter is the ability to
focus parallel light rays at a
distance of 1 meter
57.
58. Cornea allows light to enter the eyeball.
Aqueous humor fills anterior and posterior
chambers in front of lens.
Crystalline lens is a transparent elastic and
biconcave lens, which refracts light and focuses
it on retina.
Vitreous body is a transparent gel enclosed by
vitreous membrane, which fills eyeball behind
lens.
60. If all refractive surfaces of the eye are added together and
considered to be one single lens and shape of eyeball is
perfectly spherical, eye may be simplified. This is model,
which shows refraction in eyeball – “reduced eye”.
Since the refractive index of air is 1,the greatest light
refraction occurs at the cornea.
61. Lens formula
1 1 1
Object distance (m)+ image distance (m)=focal distance=power of the lens
the retina is considered to be 15 mm behind the refractive center of
the eye
1 1 1
∞ + 0.015 = zero + 0.015 = 67 diopters
therefore, the eye has a total refractive power of 67 diopters
62. Size of object distance of object from lens (in meters)
=
Size of image distance of image from lens (in meters)
64. • Transparent
• Biconvex
• Lies behind iris
• Largely composed of
lens fibers
• Elastic
• Held in place by
suspensory ligaments of
ciliary body
65.
66. Loss of lens transparency
Decreased glutathione
Coagulation of lens proteins
Treatment : surgical
67. Refractive power of the lens is 20 diopters.
Refractive power can be increased to 34 diopters by
changing shape of the lens
This is called accommodation.
Accommodation is necessary to focus the image on
the retina.
70. A relaxed lens is almost spherical in shape.
Lens is held in place by suspensory ligament
which under normal resting conditions causes the
lens to be almost flat.
Contraction of an eye muscle attached to the
ligament pulls the ligament forward and causes
the lens to become fatter which increases the
refractive power of the lens.
Under control of the parasympathetic nervous
system.
71. The changes in lens curvature during
accomodation affects mainly the anterior surface
of lens:
depth of AC
Purkinjii sanson image
72. Near point
Far point
Power of accomodation
Range of accomodation
73. The Inability to Accommodate
Caused by progressive denaturation of the proteins
of the lens.
Makes the lens less elastic.
Begins about 40-50 years of age.
ttt :by bifocal lenses
79. Smaller aperture
all light rays pass through
center of lens
centralmost rays always in f
greater depth of focus
Increase depth of focus
80. spherical aberration
light rays pass through peripheral
parts of the eye lens and are not
focused sharply. This is because
of more refractive power in central part of lens. Due to this effect object loose
clear contour.
chromatic aberration:
Unequal deviation of light rays
of different wavelengths. This I
s focusing of different colors at
different distances behind lens.
Due to this object get rainbow
contour.
95. Function:
• Provide a route for blood vessels
Melanin pigment prevent reflection of light rays in the
eye.
Support retina
96. Function:
Ciliary muscle accomodation
Give attachement to suspensory ligaments.
Ciliary processes secrete aqueous humor.
97. Boundary between anterior and posterior chambers
Central hole (pupil)
98. Regulates amount of light entering the eye to
stimulate retina
Protect retina against ultraviolet rays.
Decreases chromatic &spherical aberrations.
• Smaller pupil diametergreater depth of focus.
• Pupillary reflexes are of clinical importance
99. Smaller aperture
all light rays pass through
center of lens
centralmost rays always in f
greater depth of focus
100. Controlled by two muscles of the iris
◦ Sphincter muscle (pupil constriction)
Innervated by the parasympathetic nervous system
◦ Dilator muscle (pupil dilation)
Innervated by the sympathetic nervous system
102. The pupil size is mainly determined by the
contraction or relaxation of the sphincter muscle
The sphincter muscle responds to signals coming
from the short ciliary nerve and constricts the pupil
It is innervated by parasympathetic fibers
103. Parasympathetic pathway for pupil constriction
EW nucleus (output) → Cranial nerve III↓
↓
Ciliary body Ciliary ganglion
↓ ↓ ↖
Iris sphincter muscle ← Short ciliary nerve
104. The pupil size is
secondarily determined
by the contraction or
relaxation of the dilator
muscle
The dilator muscle
responds to signals
coming from the long
ciliary nerve and dilates
the pupil
It is innervated by
sympathetic fibers
105. Sympathetic pathway for pupil
dilation
Hypothalamus → Spinal cord
↘
Superior cervical ganglion
↙
Cranial nerve V → Eyelid muscles
↓
Long ciliary nerve → Dilator pupillae
muscle
108. Parasympathetic pathway for pupil constriction
EW nucleus (output) → Cranial nerve III
Accommodation fibers ↗ ↓ ↓
Ciliary body Ciliary ganglion
↖ ↓ ↓
Iris sphincter muscle ← Short ciliary nerve
109. The signal is passed to both sides of the midbrain
so that light information given to one eye is
passed on to both pupils equally
110. Direct light reflex
◦ The constriction of the ipsilateral pupil to the light
stimulus
111. Consensual light reflex
◦ The constriction of the contralateral pupil to the light
stimulus
112. Total blindness due to bilateral cortical lesion does
not affect the light reflex
113. Total blindness in one eye due to retinal or
optic nerve problem
Shine light in normal eye – have direct and consensual
response
Shine light in blind eye – no direct or consensual
response
Loss of vision due to corneal, lenticular,
vitreous, refractive, or emotional causes will
not produce loss of pupillary light reflex.
114. In normal patients, the amplitude of the pupil response to
light is equal to the amplitude of the pupil response to
near
Light-near dissociation (i.e., near response is greater
than light response)
It may be associated with afferent defects (blind eye),
midbrain defects (Argyll Robertson pupil)
Possible causes: neurosyphilis (lesion around the
Edinger-Westphal nucleus), long-term diabetes, or
alcoholism
Presumed neurosyphilis until proven otherwise
115.
116. Both pupils are small and respond poorly or not at
all to light (no direct and consensual response)
Swift response to near (light-near dissociation)
127. Fovea is designed for
maximum resolution
◦ High spatial density of
photoreceptors (cones)
◦ Virtually no signal convergence
1 photoreceptor → ~1 ganglion cell
Outside fovea: high signal
convergence
100 photoreceptors → 1 ganglion cell
Foveal information maps to >50%
of the visual cortex
http://webvision.med.utah.edu/imag
eswv/fovmoswv.jpeg
128. Blind spot - place where optic
nerve leaves the eye
◦ We don’t see it because:
one eye covers the blind spot
of the other.
it is located at edge of the
visual field.
the brain “fills in” the spot.
129. Figure 3.18 Viewing conditions for a dark adaptation experiment. The image of the fixation point falls on the
fovea, and the image of the test light falls in the peripheral retina.
133. Rods
Named for rod-shaped outer
segments
120 million per eye
Peripheral vision
◦ Wide distribution
None in fovea
Monochromatic vision
◦ Single visual pigment
Rhodopsin
Scotopic vision (low light
conditions)
◦ “Night” vision
◦ High Sensitivity
Often respond to single photon
Slow response – stimuli added
Require 0.1% of light required by
cones to function
Low spatial acuity (resolution)
◦ High convergence of visual
information
1 rod → >100 ganglion cells
Cones
Named for conical-shaped
outer segments
6 million per eye
Abndant centrally,fovea
contains cones only
Chromatic vision
◦ 3 visual pigments
Blue cones,Green cones& Red
cones
Photopic vision (high light
conditions)
◦ Low sensitivity
1000x less than rods
Detail vision
◦ High spatial acuity (resolution)
High density in fovea
Little to no convergence of
information: 1 cone → 1 ganglion
cell in fovea
◦ Fast response to stimuli
134. Figure 3.28 Neural circuits for the rods (left) and the cones (right). The receptors are being stimulated by
two spots of light.
135. Absorption spectrum: proportion of light absorbed at a
given wavelength.
Three different types of cone pigments, each with own
receptor.
◦ Short (419 nm), medium (532 nm), and long (558 nm) wavelengths
◦ Fewer short wavelength receptors. Absorption of all cones = 560nm
in the spectral sensitivity curve
139. Rods and cones contain chemicals that decompose on
exposure to light.
This excites the nerve fibers leading from the eye.
The membranes of the outer-segment of the rods contain
rhodopsin or visual purple.
Rhodopsin is a combination of a protein called scotopsin
and a pigment, retinal.
The retinal is in the cis configuration.
Only the cis configuration can bind with scotopsin to form
rhodopsin.
140. When light is absorbed by rhodopsin it immediately
begins to decompose.
Decomposition is the result of photoactivation of electrons
in the retinal portion of rhodopsin which leads to a change
from the cis form of the retinal to the trans form of the
molecule.
◦ Trans retinal has the same chemical structure but is a
straight molecule rather than an angulated molecule.
◦ This configuration does not fit with the binding site on
the scotopsin and the retinal begins to split away.
◦ In the process of splitting away a number of
intermediary compounds are formed.
141. Vitamin A is the precursor of all-trans-retinal, the
pigment portion of rhodopsin.
Lack of vitamin A causes a decrease in retinal.
This results in a decreased production of rhodopsin
and a lower sensitivity of the retina to light or night
blindness.
142. Normally about -40 mV
Normally the outer segment of
the rod is very permeable to
Na+
ions.
In the dark an inward current
(the dark current) carried by
the Na+
ions flows into the outer
segment of the rod.
The current flows out of the
cell, through the efflux of Na+
ions out of the inner segment of
the rod.
143. When rhodopsin decomposes it causes a
hyperpolarization of the rod by decreasing Na+
permeability of the outer segment.
The Na+
pump in the inner segment keeps
pumping Na+
out of the cell causing the membrane
potential to become more negative
(hyperpolarization).
The greater the amount of light the greater the
electronegativity(Weber –Fechner law)
146. On light exposure:
cGMP is responsible for keeping Na+
channel in the outer
segment of the rods open.
Light activated rhodopsin (metarhodopsin II) activates a G-
protein, transducin.
Transducin activates cGMP phosphodiesterase which destroys
cGMP.
On dark expopsure:
Rhodopsin kinase deactivates the activated rhodopsin (which
began the cascade) and cGMP is regenerated re-opening the Na+
channels.
147. Light activates rhodopsin
activates the G-protein Transducin
activates a phosphodiesterase enzyme (PDE)
converts cGMP → GMP
↓ cGMP closes ion channel, (the dark current channel)
Hyperpolarizes the photoreceptor
148. In the Dark
Steady release of
of
neurotransmitter
Inhibitory synapse
Hyperpolarized
With Light
Neurotransmitter
release is reduced
Inhibition is relieved
Depolarizes
Bipolar cell
Ganglion cell
To Optic Nerve →
Excitatory synapse
↓ transmitter release ↑ transmitter release
Photoreceptor
↓APs ↑APs
Depolarized
Hyperpolarized
149. Spontaneously active with continuous action
potentials
Visual signals are superimposed on this
background
Many excited by changes in light intensity
Respond to contrast borders, this is the way the
pattern of the scene is transmitted to the brain
150. Transmission of signals in the retina is by
electrotonic conduction.
Allows graded response proportional to light
intensity.
The only cells that have action potentials are
ganglion cells.
◦ send signals all the way to the brain
151. In light conditions most of the rhodopsin has been
reduced to retinal so the level of photosensitive
chemicals is low.
In dark conditions retinal is converted back to
rhodopsin.
Therefore, the sensitivity of the retinal
automatically adjusts to the light level.
Opening and closing of the pupil also contributes to
adaptation because it can adjust the amount entering
the eye.
152. Dark adaptation Light adaptation
Definition
Retinal sensitivity increased decreased
Mechanism Regeneration of
photopigment
breakdownof
photopigment
duration 1:30min 1sec:5min
changes Mydriasis
Regeneration of
photopigment
Increased Retinal
sensitivity
Decreased retinal
signal discharge in
retinal nerons
Miosis
breakdownof
photopigment
decreased Retinal
sensitivity
increased retinal signal
discharge in retinal
nerons
Visual acuity poor high
Color vision absent present
153. Adaptation happens when the eye
grows more or less sensitive to light
Modeled after a PPT slide created by Dr. Kevin Richardson in 1998 and available through the American Psychological Society.
Time in Dark in Minutes
LogThresholdin
Microlamberts
8
7
6
5
4
3
5 10 15 20 25 30
154. It is the ability of the retina to discriminate different
wavelenghts.
= the cones in your eyes pick these colors
up by seeing blue, green, and red
155. Characters of colour
a. hue :– the actual ‘color’ determined by the
dominant wavelength in a mixture of light
striking the eye.
b. saturation :– purity of a color – a color is
more saturated and more pure if one
wavelength is relatively more intense than other
wavelenghts. pastel colors are ‘desaturated’ by
white
c. Brightness(lminosity) :– the overall intensity
of all the wavelengths of incoming light.
Complementary colours:-mixed together
sensation of white
156. The color Circle
- complementary colors = colors
across from each other on the color
circle
* mixing these colors results in white
* light, not pigments, makes white
157. I. Young Helmholtz theory (trichromatic theory):
Color vision is the result of activation of cones.
3 types of cones:
◦ blue cone
◦ green cone
◦ red cone
The pigment portion of the photosensitive
molecule is the same as in the rods, the protein
portion is different for the pigment molecule in
each of the cones.
Makes each cone receptive to a particular
wavelength of light
158. ◦ There are three cone pigments:
◦ Blue sensitive pigment
Short wavelength sensitive (peak wave length at 445nm)
Blue cones
◦ green sensitive pigment (peak wave length at 535nm)
medium wavelength sensitive
Green cones
◦ red sensitive pigment (peak wave length at 565nm)
Long wavelength sensitive
Red cones
159. Helmholtz 1852
Three types of coneThree types of cone
receptors are sensitive toreceptors are sensitive to
different wavelengths of lightdifferent wavelengths of light.
Short Medium Long
People see colors because theirPeople see colors because their
eyes do mixing by adjustingeyes do mixing by adjusting
the ratio of stimulus inputthe ratio of stimulus input
from these three types of conesfrom these three types of cones..
Modeled after a PPT slide created by Kevin Richardson in 1998 and made available through the American Psychological Society
160. R
G
B
Y
B
W
Eye contains 3Eye contains 3
mechanismsmechanisms
that producethat produce
antagonisticantagonistic
responses toresponses to
three pairsthree pairs
of colorsof colors..
WhyWhy??
AfterimagesAfterimages
Arranged by Dr. Gordon Vessels 2004
161.
162. Combined action of neural activity at the retina
and cerebral cortex.
163. Lack of a particular type of cone
Genetic disorder passed along on the X
chromosome
Occurs almost exclusively in males
About 8% of women are color blindness carriers
164. Colour anomaly (Colour weakness)
protanomaly: weakness of a red cone
• deuteranomaly. weakness of a green cone
• Tritanomaly: weakness of a blue cone
Colour anopia:
Dichromates:
protanopia: absence of a red cone
• deuteranopia. absence of a green cone
• Tritanopia: absence of a blue cone
Monochromates
165. Colour matching test
Ishihara chart test
Edinger green lantern test
166. Visual sensations felt after removal of the visual
stimulus.
Types :
Positive afterimage
Negative after image
178. 6/6
◦ ability to see letters of a given size at 6 meters
6/12
◦ what a normal person can see at 12 meters, this person
must be at 6 meters to see.
6/60
◦ what a normal person can see at 60 meters, this person
must be at 6 meters to see.
184. Binocular vision provides detection of distance
and three-dimensional appearance of object in
front of eyes.
This is due to central analysis of fields of vision
from both eyes.
Final visual image is formed in visual cortex.
187. Illusions of depth on a one dimensional piece of
paper or figure
Only need one eye to see the illusion
188. Cues for depth are caused by retinal disparity and
convergence
Need 2 eyes to see the illusion
Retinal Disparity = how the eye perceives an object as
it moves closer or farther away
Convergence = associated with feelings of tension in
the eye muscles
195. Tendency to perceive an object as being of one
size no matter how far away the object is, even
though the size on the retina varies w/ distance
196. Tendency to perceive objects as keeping their
color even though different light might change the
appearance
197. Horizontal cells connect laterally between the rods
and cones and the bipolar cells
Output of horizontal cells is always inhibitory
Prevents the lateral spread of light excitation on
the retina
Have an excitatory center and an inhibitory
surround
Essential for transmitting contrast borders in the
visual image
199. About 30 different types
Some involved in the direct pathway from rods to
bipolar to amacrine to ganglion cells
Some amacrine cells respond strongly to the onset
of the visual signal, some to the extinguishment of
the signal
Some respond to movement of the light signal
across the retina
Amacrine cells are a type of interneuron that
Aid in the beginning of visual signal analysis.
200. Each retina has 100 million rods and 3 million
cones and 1.6 million ganglion cells.
60 rods and 2 cones for each ganglion cell
At the central fovea there are no rods and the ratio
of cones to ganglion cells is 1:1.
May explain the high degree of visual acuity in
the central retina
201. W cells (40%) receive most of their excitation from
rod cells.
◦ sensitive to directional movement in the visual
field
X cells (55%) small receptive field, discrete retinal
locations, may be responsible for the transmission
of the visual image itself, always receives input
from at least one cone, may be responsible for color
transmission.
Y cells (5%) large receptive field respond to
instantaneous changes in the visual field.
202. Visual field of
left eye
Temporal
half
Visual field of
right eye
Temporal
half
Nasal
half
Midbrain
Left eye
Temporal
retina
Optic
radiations
Left eye and its pathways
Primary visual area of cerebral
cortex (area 17) in occipital lobe
Lateral geniculate nucleus
of the thalamus
Optic
radiations
Midbrain
Temporal
retina
Nasal
retina
Right eye
Right eye and its pathways
Nasal
half
Nasal retina
1 1
Visual field of
left eye
Temporal
half
Visual field of
right eye
Temporal
half
Nasal
half
Midbrain
Left eye
Temporal
retina
Optic
radiations
Left eye and its pathways
Primary visual area of cerebral
cortex (area 17) in occipital lobe
Lateral geniculate nucleus
of the thalamus
Optic
radiations
Midbrain
Temporal
retina
Nasal
retina
Right eye
Right eye and its pathways
Nasal
half
Nasal retina
1 1
22
Visual field of
left eye
Temporal
half
Visual field of
right eye
Temporal
half
Nasal
half
Midbrain
Left eye
Temporal
retina
Optic
radiations
Left eye and its pathways
Primary visual area of cerebral
cortex (area 17) in occipital lobe
Lateral geniculate nucleus
of the thalamus
Optic
radiations
Midbrain
Temporal
retina
Nasal
retina
Right eye
Right eye and its pathways
Nasal
half
Nasal retina
1 1
22
3
3
Visual field of
left eye
Temporal
half
Visual field of
right eye
Temporal
half
Nasal
half
Midbrain
Left eye
Temporal
retina
Optic
radiations
Left eye and its pathways
Optic
tract
Primary visual area of cerebral
cortex (area 17) in occipital lobe
Lateral geniculate nucleus
of the thalamus
Optic
radiations
Midbrain
Temporal
retina
Nasal
retina
Right eye
Right eye and its pathways
Nasal
half
Nasal retina
1 1
22
44
3
3
Visual field of
left eye
Temporal
half
Visual field of
right eye
Temporal
half
Nasal
half
Midbrain
Left eye
Temporal
retina
Optic
radiations
Left eye and its pathways
Optic
tract
Primary visual area of cerebral
cortex (area 17) in occipital lobe
Lateral geniculate nucleus
of the thalamus
Optic
radiations
Midbrain
Temporal
retina
Nasal
retina
Right eye
Right eye and its pathways
Nasal
half
Nasal retina
1 1
22
44
5 5
3
3
Visual field of
left eye
Temporal
half
Visual field of
right eye
Temporal
half
Nasal
half
Midbrain
Left eye
Temporal
retina
Optic
radiations
Left eye and its pathways
Optic
tract
Primary visual area of cerebral
cortex (area 17) in occipital lobe
Lateral geniculate nucleus
of the thalamus
Optic
radiations
Midbrain
Temporal
retina
Nasal
retina
Right eye
Right eye and its pathways
Nasal
half
Nasal retina
1 1
2
3
2
4
3
4
5 5
6
6
204. Conversion of electromagnetic radiation into
electrical signals
◦Absorption of electromagnetic radiation
◦Triggering of a signaling cascade
◦Change in electrical properties of the cell
205. Retinal
◦)aldehyde derivative of Vitamin A(
Aka retinaldehyde
◦Absorption in near ultraviolet (330-365 nm(
Induces photoisomerization
hν = energy required to promote retinal to an excited state
Rotation around the double bond more energetically favored
11-cis retinal all-trans retinal
+hν*
206. Choroid
◦ A layer of tissue that is:
Located under the retina
Separates retina & sclera
◦ Mostly made up of blood
vessels
◦ Helps nourish the retina by
carrying the blood supply to
the eye’s internal structures
http://www.cnib.ca/en/your-eyes/eye-conditions/amd/the-eye/basics/Default.aspx
212. 233
•As light enters eye, it is refracted by:
•Convex surface of cornea
•Convex surface of lens
•Image focused on retina is upside down and reversed from left to right
Light waves
Object
Cornea
Image
Retina
213. Visual image in one plane focuses at a different
distance from that of the plane at right angles
Too great curvature of cornea in one of its
planes
218. 239
•Rods
•Long, thin projections
•Contain light sensitive pigment
called rhodopsin
•Hundred times more sensitive to
light than cones
•Provide vision in dim light
•Produce colorless vision
•Produce outlines of objects
•Cones
•Short, blunt projections
•Contain light sensitive pigments
called erythrolabe, chlorolabe,
and cyanolabe
•Provide vision in bright light
•Produce sharp images
•Produce color vision
228. Absence of visual pigment components
◦Retinal → complete vision deficiency
◦Opsins → color vision deficiency
Monochromacy
Lack 2 or all 3 cone pigments
Dichromacy
Lack one cone pigment
Anomalous trichromacy
Altered spectral sensitivity of one cone pigment
Most common
229. Light → electrical signal
http://en.wikipedia.org/wiki/File:Phototransduction.png
230. Retinal undergoes a photoisomerization
◦Single photon required
◦Converts 11-cis retinal to all-trans retinal
Induces a conformational change in the opsin
molecule
Triggers an intracellular signal transduction
cascade
Closes ion channels
Changes the electrical state of the cell
233. Determination of distance of object from the
eye
By means of
◦Size of retinal images of known objects
◦Moving paralax (relative distances(
◦Stereopsis (Binocular vision(
237. Layers of retina from outside to inside:
pigmented layer;
layer of rods and cones;
outer limiting membrane;
outer nuclear layer;
outer plexiform layer;
inner nuclear layer;
inner plexiform layer;
ganglionic layer;
layer of optic nerve fibers;
inner limiting membrane.
238. Light falls on retina on inner side i.e. on inner
limiting membrane. It is a minute area of 1 mm in
center of retina. It provides acute and detail
vision.
Central portion of macula called fovea centralis.
This is composed entirely of cones.
Pigmented layer of retina contains black pigment,
i.e. melanin. It prevents light reflection through the
globe of eyeball and stores vitamin A.
239. Outer segment of photoreceptors contain
photochemicals. Inner segment contains nucleus,
synaptic body and other organelles. Photochemicals are
light-sensitive chemicals that decompose on exposure to
light and excite nerve fibers leading from eye to central
nervous system.
Rhodopsin is present in rods. Scotopsin and 11-cis-
retinal compose it. Iodopsin is photochemical pigment of
cones. Photopsin and 11-cis-retinal compose it.
Rhodopsin cycle: rhodopsin under the influence of light
converts to prelumirhodopsin – lumirhodopsin –
metaphodopsin I - metaphodopsin II – opsin – rhodopsin.
Metarhodopsin II converts also to all-transretinal (vitamin
A) – (isomerase’s action) – II cis-retinal – rhodopsin.
240. Impulses from retina pass to optic nerve – optic
chiasm (fibers from nasal halves of retina cross to
opposite side) – optic tracts – synapse in lateral
genicular body – geniculocalcarine fibers – pass
through optic radiation or geniculocalcarine tract –
primary visual cortex in calcarine fissure or medial
aspect of occipital lobe.
241. In addition to lateral genicular body, fibers from optic
tract also pass to:
-suprachiasmatic nucleus of hypothalamus for
controlling circadian rhythms;
-pretectal nuclei – for control of fixation of eyes on
objects of importance and for pupillary light reflex;
-superior colliculus – for control of bilateral simultaneous
movements of two eyes;
-pulvinar – forms secondary visual pathway.
Corpus callosum causes exchange of visual information
between right and left hemispheres.
242. .If a person remains in bright light for a long time,
photochamicals in rods and cones reduce to all-
transretinal and opsins. Most all-transretinal converts
to all-transretinol (vitamin A). So, sensitivity of eye to
light gets decreased. This is light adaptation.
If a person remains in dark for a long time, all vitamin
A convert to 11-cis retinal and than to
photochemicals. Sensitivity of eye to light gets
increased. This is dark adaptation.
243. According to Jung-Helmgolc theory there are
three types of cones for three fundamental
colors: cones for red color contain erythrolab;
cones for green color contain chlorolab; cones
for blue color contain cyanolab.
According to Gering theory there are couples of
opponent colors: green – red; yellow – blue;
white – black. Subcortical neurons percept it due
to on- and off- centers mechanism.
244. .There are three fundamental colors: red, which is
marked “protos”; green – “dateros”; blue – “tritos”. So
normal color perception is called normal trichromasia.
If a person has abnormal perception of some
fundamental color, this is prot-, daiter- or tritanomalia.
If a person percept only some two fundamental colors,
this is dichromasia.
If a person differentiates only one fundamental color
this is monochromasia. In case of black and white
vision a person has color blindness.
245. Ability of human eye to discriminate between point
sources of light is called visual acuity.
Normally a person with vision acuity 1,0 can
differentiate two point objects, which lay under the
angle 1 minute from distance 5 m.
246. Field of vision is area that is seeing by an eye at
a given instant. It has nasal and temporal
division.
Determination of extent of peripheral visual field
and thereby diagnosis of blindness in specific
portions of retina, is called perimetry.
Optic disc produces physiological scotoma in 15
degrees lateral to central point of vision in
perimetry chart.
248. Extraocular Muscles
◦ 6 extraocular muscles that
are attached to each eye
◦ Help move the eye left, right,
up, down and diagonally
◦ These 6 muscles are:
Superior rectus
Inferior rectus
Medial rectus
Lateral rectus
Inferior oblique
Superior oblique
http://media.photobucket.com/image/introduction%20to%20eye%20anatomy/trimurtulu/Eye.jpg
Describe the 7 major classes of retinal cell types (6 neurons and one glial cell type) and each of their functions.
Not all cell types are photo-sensitive (respond to light). Two types are photosensitive: a small subset of Retinal Ganglion cells (intrinsically photosensitive RGCs, ipRGCs) and all photoreceptor cells
~200-300 um
Rods and Cones differ in their structure. Named according to conical versus rod-like shapes of outer segments.
Cone structure improves visual acuity
Fovea = central region of retina, area of sharpest vision
Blind spot = location where the optic nerve (composed of ganglion cell axons/nerve fibers) leaves the eye
.
Figure 10.10 Interconnection of three cone types to provide four color responses and complementary colors
The connecting cells between the receptors and ganglion cells are not shown, to keep the illustration simple. + indicates excitation; – indicates inhibition.
Vitamin A = half a beta-carotene (get from carrots, leafy vegetables, liver, melons, pumpkins, papayas, etc)
Sufficient energy provided by the photon to promote retinal to an excited state in which rotation around the bond is more energetically favored then relaxes to stay in this conformation
Specifically electrons of conjugated pi cloud electrons excited to create an antibonding orbital near the 11-12 double bond
11-cis retinal must be replenished. This is accomplished by enzymes found in the RPE.
