5. The visual system
A coordinated pair of eyes
The appropriate protective
mechanisms
The necessary neural apparatus to
interpret visual information
6. To produce a clear
image of the external
world and transmit
this to visual cortex of
brain
8. Sclera
Collagen
Variable thickness
1mm around optic nerve
head,
0.3mm posterior to
muscle insertions
Tough, opaque, mainly
avascular
Outer wall of the eyeball
-protects intraocular
contents, preserve shape
Attachments for the
extraocular muscles
9. Cornea - anatomy
500-700 µm thick
Transparent, avascular
Forms approximately the
anterior 1/6 of the outer
coat of the eye and is
continuous posteriorly with
the sclera
5 layers:
Epithelium
Bowman’s membrane
Stroma
Descemet’s membrane
Endothelium
10. Iris and pupil (Vascular Coat)
Attached to ciliary
body
Forms pupil at center
12. Ciliary body
Connects the iris and the
choroid
Functions:
Aqueous humor
production
Suspension of lens,
accommodation
13. Aqueous Humour production
Active secretion by the
epithelium of the ciliary
processes of the ciliary
body
Function:
Carries O2, nutrients to
lens, cornea and waste
products away
Maintain shape of eye
by intraocular
pressure
Flushes away blood,
macrophages,
inflammatory cells
14. Lens
Transparent, biconvex
structure
Radially arranged zonule
fibers that insert into the
lens around its equator
connect the lens to the
ciliary body
Can change diopteric
power but amplitude of
accommodation reduces
with age
15. Choroid
Highly vascularised
structure between the
sclera and the retina
Vessel layer, capillary
layer
provides O2 + nutrition
to the outer retinal
layer,
Temperature
homeostasis
Conduct blood vessels
Absorb excess light
16. Vitreous body
Clear gel-like structure
that fills the posterior eye
98% water+ 2% collagen,
hyaluronic acid, soluble
proteins
Transmission of light onto
the retina, cushion to the
eyeball during trauma,
nutritive and supportive
role in retinal metabolism
18. 1. Retinal pigment epithelium (RPE)
Single layer
Microvilli at the apex where
the photoreceptors attach
Functions:
Melanin pigments which
absorb light (antireflection)
Participate in turnover of
photoreceptors
Recycle vitamin A to form
photosensitive pigments
19. 2. Neurosensory retina
3 main groups of neuronal cells:
photoreceptors, bipolar cells, ganglion cells
Photoreceptor cells (rods + cones)
undergo photochemical changes
(phototransduction)
Bipolar cells relay nerve impulse to
ganglion cells
Ganglion cell exit at optic disc to become
optic nerve
20. Optic disc
The location where
ganglion cell axons exit the
eye to form the optic nerve
Yellowish orange color
1.5mm diameter (may
vary), vertically oval
Central retinal vessels
enter and leave the eye
here
21. Retinal blood supply
Retinal arteries supply O2
+ nutrients to the inner
layers of the retina
Outer layers (RPE-outer
nuclear) supplied by
choroidal capillaries
SuperiorSuperior and inferior
branches, which split into
nasal, temporal
branches.
Capillaries with
nonfenestrated
endothelium, prevent large
molecules and toxins to
permeate; this forms the
inner blood retinal
barrier
22. Optic nerve
Contains over 1 million
fibres
Nerve fibres are
myelinated only after
leaving the eye
Surrounded by
cerebrospinal fluid in the
anterior extension of the
subarachnoid space
Protected by the same
meningeal layers of the
brain
23.
24. There are many diseases, disorders, and age-
related changes that may affect the eyes and
surrounding structures. The sharpness of vision is
reduced despite use of the best glasses. The
amount of light that reaches the back of the
retina is reduced, and this wear and tear results
in the development of cataract, macular
degeneration or glucoma.
25. Such conditions cause damage to the eye's optic
nerve and gets worse over time. It's often linked
to a buildup of pressure inside the eye. The
increased pressure, called intraocular pressure,
can damage the optic nerve, which transmits
images to your brain. If the damage continues, it
can lead to retinal cell degeneration and
permanent vision loss.
27. Tonometery
Tonometry measures the
pressure within your eye.
During tonometry, eye drops
are used to numb the eye.
Then a doctor or technician
uses a device called a
tonometer to measure the
inner pressure of the eye. A
small amount of pressure is
applied to the eye by a tiny
device or by a warm puff of
air.
28. The range for normal pressure is 12-22 mm
Hg. Most glaucoma cases are diagnosed
with pressure exceeding 20mm Hg.
However, some people can have glaucoma
at pressures between 12 -22mm Hg. Eye
pressure is unique to each person.
29. Opthalmoscopy
This diagnostic procedure helps the doctor
examine your optic nerve for glaucoma damage.
Eye drops are used to dilate the pupil so that the
doctor can see through your eye to examine the
shape and color of the optic nerve.
30. The doctor will then use a small device with a
light on the end to light and magnify the
optic nerve. If intraocular pressure is not
within the normal range or if the optic nerve
looks unusual, doctor may ask to have one
or two more glaucoma exams: perimetry
and gonioscopy.
31. Perimetry
Perimetry is a visual field test that
produces a map of your complete
field of vision. This test will help a
doctor determine whether your
vision has been affected by
glaucoma. During this test, you
will be asked to look straight
ahead and then indicate when a
moving light passes your
peripheral (or side) vision. This
helps draw a "map" of your
vision.
32. After glaucoma has been diagnosed, visual field
tests are usually done one to two times a year to
check for any changes in your vision.
33. Gonioscopy
This diagnostic exam helps determine whether
the angle where the iris meets the cornea is open
and wide or narrow and closed. During the exam,
eye drops are used to numb the eye. A hand-held
contact lens is gently placed on the eye.
34. This contact lens has a mirror that shows the
doctor if the angle between the iris and
cornea is closed and blocked (a possible sign
of angle-closure or acute glaucoma) or wide
and open (a possible sign of open-angle,
chronic glaucoma).
35. Pachymetry
Pachymetry is a simple, painless test to measure
the thickness of your cornea. A probe called a
pachymeter is gently placed on the front of the
eye (the cornea) to measure its thickness.
Pachymetry can help your diagnosis, because
corneal thickness has the potential to influence
eye pressure readings.
36. With this measurement,
doctor can better
understand IOP reading
and develop a treatment
plan. The procedure
takes only about a
minute to measure both
eyes.
37. Electroretinography
Electroretinography allows to examine the
function of the light-sensing cells
(photoreceptors) in the retina by measuring
the response of the retina to flashes of light.
Eye drops numb the eye and dilate the pupil. A
recording electrode in the form of a contact
lens is then placed on the cornea, and another
electrode is placed on the skin of the face
nearby.
38. The eyes are then propped open. The room
is darkened, and the person stares at a
flashing light. The electrical activity
generated by the retina in response to the
flashes of light is recorded by the
electrodes.Electroretinography is particularly
useful for evaluating diseases, such as
retinitis pigmentosa, in which the
photoreceptors are affected.
