Points covered-
Physiology of eye
Power of accommodation
Perimetry/ Visual field tests
Focusing powers of eye lenses
M.Tech Medical Device Presentation
3. Functions Of Each Part
• Cornea: Change in the medium, Causes refraction
(Change in the angle on incident light)
• Iris: Eye ring, It is responsible to control the
amount of light entering the eye. The light
incident on the iris is not absorbed, It is reflected
back
• Pupil: The black spot that we can observe in the
middle of iris, This is the part from which the light
will enter the eye.
4. Functions Of Each Part
• Lens: Focuses the incident light on the retina,
Human lens is not a rigid lens but a flexible gel
like lens.
• Fovea: In the eye, a tiny pit located in the
macula of the retina that provides the clearest
vision of all
• Aqueous humour: Present in space between
cornea and lens, Causes refraction of the
incoming light
5. Functions Of Each Part
• Ciliary Muscles: These are cilia like (fiber/
thread like muscles that control the shape of
lens. The lens shape has it’s significance in
observing the distant and close objects
6. Functions Of Each Part
• Our eyes can focus the close as well as distant
objects.
• But, For this, The power of lens must change
which is only possible when there is change in
the curvature of eye lens
• This change in curvature brought by cilliary
muscles
8. • In Case of the such distant objects, The rays
coming from the object are “Parallel”, This
means the change in angle required to focus
the light on retina is less
• This requires lower focusing power as the
focusing angle has value close to incident
angle
10. • In Case of the such close objects, The
incoming rays are widely divergent (With
different angles)
• Now, The eye needs to focus these rays on the
retina cells, As here the angle of incidence and
focusing angle has large difference, It will
require higher focusing power
11. Role of Cilliary Muscles
• Controls the focusing power of the natural
lens
• Relaxed-Lens gets elongated (Lesser
curvature) When the object is at distance, This
means lesser focusing power
• Contracted- Shorter and thicker lens (Higher
curvature), This leads higher focusing power
12. Power of Accommodation
• All these focusing is done by cilliary muscle
• This ability of cilliary muscles is called as
power of accommodation
13. Control of Accomodation
• The ciliary muscle is controlled almost entirely
by parasympathetic nerve signals transmitted
to the eye through the third cranial nerve
from the third nerve nucleus in the brain stem
• Stimulation of the parasympathetic nerves
contracts both sets of ciliary muscle fibers,
which relaxes the lens ligaments, thus
allowing the lens to become thicker and
increase its refractive power
14. Control of Accomodation
• With this increased refractive power, the eye
focuses on objects nearer than when the eye
has less refractive power. Consequently, as a
distant object moves toward the eye, the
number of parasympathetic impulses
impinging on the ciliary muscle must be
progressively increased for the eye to keep the
object constantly in focus
15. Control of Accomodation
• Sympathetic stimulation has an additional
effect in relaxing the ciliary muscle, but this
effect is so weak that it plays almost no role in
the normal accommodation mechanism;
16. Autonomic Control of Eye Movement
• Superior cervical ganglion neurons project to
the dilator pupillae muscle of the iris to
control pupil dilation. Ocular blood flow is
controlled both via direct autonomic
influences on the vasculature of the optic
nerve, choroid, ciliary body, and iris, as well as
via indirect influences on retinal blood flow.
17. Autonomic Control of Eye Movement
• The ocular projections of the autonomic nervous system influence
numerous functions of the eye.
• These include:
• 1) pupil diameter and ocular accommodation, which are controlled
by the intrinsic muscles of the eye located in the iris and ciliary
body respectively –
• 2) Ocular blood flow, which is controlled via innervation of the
vasculature within the optic nerve, the retina, choroid, ciliary body,
and iris. In mammals, these vascular beds are innervated by
postganglionic fibers from the pterygopalatine (parasympathetic)
and superior cervical (sympathetic) ganglia. In birds, the ciliary
ganglion also contributes to the parasympathetic innervation of the
choroid, and there may be a small contribution from this ganglion in
mammals;
• 3) intra-ocular pressure (IOP)
20. Action on Pupil
• Sympathetic nervous system dilates the pupil
(Contracts the cilliary muscles)
• Parasympathetic nervous system constricts
the pupil (Dilates the cilliary muscles)
21. Action on Pupil
• The iris dilator muscle is controlled by the
sympathetic nervous system, the part of the
autonomic nervous system that is involved in
arousal, wakefulness, and the fight-or-flight
response; the link between pupil dilation and the
sympathetic nervous system explains why pupils
are relatively large when someone is aroused.
• The dilation pathway is a subcortical pathway
that starts at the hypothalamus and the locus
coeruleus (LC) and connects to the iris dilator
muscle
22. Perimetry
• Perimetry is the systematic measurement of
visual field function (the total area where
objects can be seen in the peripheral vision
while the eye is focused on a central point)
• A visual field test (perimetry) will detect loss
of peripheral vision and provide a map of that
loss which will be helpful in diagnosing the
cause of the loss.
23. Simple Clinical Tests
• Hand identification:
• Physician will show his both palms from the
distance of 50 CM and will ask patient if all the
fingers of both hands are visible to the patient
• Use: One hand absent-hemianopic defect
• Both hands not visible-Altitudinal defect
24. Simple Clinical Tests
• Finger counting method:
• Physician will hold his fingers (In quadrant
pattern) at distance of 1 M with angle of 45
degree
• Use: Gross identification of defects (if any)
28. Types of Perimetry
• The two most commonly used types of
perimetry other than screen perimetry are-
• 1) Goldmann kinetic perimetry
• 2) Threshold static automated perimetry.
29.
30. Goldmann Perimeter
• The Goldmann perimeter is a hollow white spherical
bowl positioned a set distance in front of the patient.
• An examiner presents a test light of variable size and
intensity. The light may move towards the center from
the perimeter (kinetic perimetry), or it may remain in
one location (static perimetry).
• The Goldmann method is able to test the entire range
of peripheral vision, and has been used for years to
follow vision changes in glaucoma patients.However,
now automated perimetry is more commonly used
34. Automated Perimetry
• Automated perimetry uses a mobile stimulus moved by a perimetry
machine.
• The patient indicates whether he sees the light by pushing a button.
The use of a white background and lights of incremental brightness
is called "white-on-white" perimetry.
• This type of perimetry is the most commonly used in clinical
practice, and in research trials where loss of visual field must be
measured.However, the sensitivity of white-on-white perimetry is
low, and the variability is relatively high; as many as 25-50 percent
of the photoreceptor cells may be lost before changes in visual field
acuity are detected.
• This method is commonly used for early detection of blind spots.
The patient sits in front of an (artificial) small concave dome in a
small machine with a target in the center.
35.
36. Automated Perimetry
• The inputs are collected in the computer and
diagnosis is done based on the observations
