The document discusses several topics related to the eye including: 1. It describes the reduced or schematic eye model which simplifies the eye's refractive properties. 2. It defines visual acuity as the minimum angle two lines can be separated and seen individually, which is 1 minute for a normal eye. Visual acuity is measured using Snellen charts. 3. Key structures of the eye are described like the lens, changes in the lens with age like presbyopia and cataract. Cataract treatment involves surgically removing the cloudy lens and replacing it with an IOL. 4. The fundus oculi contains the optic disc and macula lutea. Various abnormalities

1. VISUAL ACUITY , LENS
AND FUNDUS OCULI

2. THE REDUCED OR SCHEMATIC EYE
• In the eye, light is actually reflected at the anterior
surface of the cornea and at the ant. and post.
surfaces of lens.
• However, in order to represent the process of
reflection in a more simplified way an imaginary
concept the reduced or schematic eye has been
evolved.
• In this concept, the lens is not considered to be
present; the ant. surface of the cornea is
assumed to possess the whole of the refractive
power of the eye with a power of +60 diopters.

3. THE REDUCED OR SCHEMATIC EYE
• The whole eye is assumed to have the refractive
index of 1.333. the total axial length of the eyeball
is about 24mm.
• The center of curvature for the imaginary corneal
surface having a power of +60 D is 5.5 mm
behind the principal plane.
• Light will therefore pass undeviated through the
center of curvature which is therefore the optical
center or the nodal point of the reduced eye.

4. THE VISUAL ACUITY
(ACUTNESS OF VISION)
• Visual acuity is defined as the shortest distance
by which two lines can be separated and still be
visualized as two lines.
• If two black objects on a white background are
separated by a space subtending an angle of less
than 1 minute then the two objects are not seen
separated but are seen fused with each other.
• When the visual angle is increased to 1 minute,
the objects are seen separately. Thus 1 minute is
the minimum angle for the normal eye.

5. THE VISUALACUITY
(ACUTNESS OF VISION)
• Clinically visual acuity for distant vision is
measured with SNELLEN’S test types. These
are a series of letters of varying sizes so
constructed that the top letter is visible to the
normal eye from 60 meters and the
subsequent lines from 36,24,18,9,6 and 5
meters respectively.
• The height of each letter, when seen from its
corresponding distance, subtends a visual angle
of 5 minutes.

6. THE VISUALACUITY
(ACUTNESS OF VISION)
• Each line in the letter subtends 1 minute of arc.
• Visual acuity for near vision is measured with the
help of words printed in small type.
• In doing the test, the subject is made to sit at
distance of 6 meters from the chart. The eyes are
tested one by one.

7. THE VISUALACUITY
(ACUTNESS OF VISION)
• If he can only see the top line, he has a VA of
6/60.This means that the subject can read that
letter from 6 meters which a normal eye should
be able to read from 60 meters.
• If he can read even the smallest line, then his VA
is 6/5; this means that the subjects VA is better
than the normal average eye which should read
the lowest line from 5 meters.

8. THE VISUALACUITY
(ACUTNESS OF VISION)
• Thus the numerator corresponds to the distance
in meters b/w the subject and the chart. This is
kept as 6 meters (20ft) as mentioned above.
• The denominator corresponds to the distance in
meters at which the smallest row of letters read
by patient should be read by normal eye.
• Thus VA decreases in the order,
6/5,6/6,6/9,6/12,6/18,6/36 and 6/60.

11. LENS
• The lens of eyeball is crystalline in nature. It is
situated behind the pupil.
• It is biconvex, transparent and possesses the elastic
property.
• The lens is an avascular structure and it receives its
nutrition from the aqueous humor.
• Lens refracts light rays and helps focus the image of
the objects on retina.
• The focal length of human lens is 44mm and its
refractory power is 23 D.
• Lens is supported by suspensory ligaments (zonular
fibers) which are attached with ciliary bodies.

12. STRUCTURE OF THE LENS
• The lens is formed of three components.
1) The capsule
It is highly elastic membrane covering the lens.
2) The anterior epithelium
• It is a single layer of cuboidal epithelial cells
situated beneath the capsule.
• At the margins, the epithelial cells are
elongated.
• The epithelial cells give rise to the lens fibers
present in the lens substance.

13. 3) The lens substance
• Lens is formed by long lens fibers derived from
the ant. epithelium.
• The lens fibers are prismatic in nature and are
arranged in concentric layers.

14. CHANGES IN THE LENS DURING OLD AGE
• After 40 t0 45 years, the lens looses its elastic
property. So, the amplitude of accommodation is
decreased.
• The person cannot see the near objects clearly.
This condition is known as presbyopia.
• In old age the lens becomes opaque and this
condition is called cataract.

15. CATARACT
• It is opacity or cloudiness in the natural lens of
the eye. It is the major cause of blindness
worldwide.
• When the lens becomes cloudy, light rays cannot
pass through it easily, and vision is blurred.
• Cataract develops in old age after 55 to 60 years.

16. CATARACT
• The lens is situated within the sealed capsule.
The old cells die and accumulate within the
capsule.
• Over the years, the accumulation of cells is
associated with accumulation of fluid and
denaturation of the proteins in the lens fibers
causing cloudiness of lens and blurred image.

17. CAUSES OF CATARACT
1. Age
2. Eye injuries
3. Previous eye surgery
4. Diseases like diabetes, Wilson's disease and
hypocalcaemia.
5. Long term use of drugs such as steroids diuretics and
tranquilizers
6. Long term unprotected exposure to sun light
7. Alcoholism
8. Family history
9. Diet containing large quantity of salt

18. SYMPTOMS
1. Painful blurred vision.
2. Poor night vision.
3. Diplopia in affected eye.
4. Need for bright light while reading.
5. Fading of colors.

19. TREATMENT
• Surgery is the only treatment for cataract.
• During surgery, the cloudy lens is removed from
eye through a surgical incision.
• The natural lens is replaced with a permanent
clear and plastic intra ocular lens (IOL) implant.
• Different procedures were followed to remove the
cloudy lens. The common methods are;

20. 1) Extra capsular extraction
• This is a rather old technique.
• A 12 mm incision is made in eye under an
operating microscope to remove the lens as a
hole.
• The post. capsule of the lens is left in place to
hold the IOL implant.
• Multiple sutures are required to seal the eye after
surgery. The sutures must be perfect otherwise
astigmatism may develop.

21. 2) Phacoemulsification
• This is current technique.
• It is the procedure in which ultrasonic vibrations
are used to break the cataract into smaller
fragments. It is done through a small (3mm)
incision.
• An u/s (or laser) probe is used to break the lens
material without damaging the capsule.
• A foldable IOL is then introduced through the
incision. Once inside the eye, the lens unfolds to
take position inside the capsule.
• No sutures are needed, as the incision is self-
sealing.

22. FUNDUS OCULI
• The post. part of interior of the eyeball is called
fundus oculi or fundus.
• Fundus is examined by ophthalmoscope.
• The fundus has two parts;
1. optic disk
2. macula lutea

23. FUNDUS OCULI

25. OPTIC DISK ( OPTIC PAPILLA)
• Situated near the center of the post. wall of
eyeball.
• It appears like pale disk.
• Formed by the convergence of axons from
ganglion cells, while forming the optic nerve.
• It contains all layers of retina except rods and
cones.
• It is insensitive to light, in other words; it is the
blind spot.
• The central blood vessels of the retina are
located right in the center of the optic disk.

26. The retinal arteries are end-arteries except at the
optic disk.
• It is important to know that ophthalmoscope
examination of the eye enables one to see into
the eye through the pupil to the retina.
• The most obvious feature of retina viewed
through ophthalmoscope is the blood vessels on
its surface.

27. • The retinal blood vessels originate from the optic
disk; where the optic nerve fibers exit the retina.
• The examination of optic disk (also called optic
nerve head) provides valuable and important
information about the state of optic nerve head,
arteries and veins of the retina, disorders of
retina, pigment epithelium and choroids.

28. Shape of optic disc
The normal disc is rounded or slightly oval.
Colour of optic disc
• Pale-pink. It is distinctly pale than the surrounding
fundus.
• Temporal side of the disc is paler than the nasal
side.
• In optic atrophy, the disc becomes more pale than
normal.
• In inflammation of the optic nerve or raised intra-
cranial pressure, the disc becomes hyperaemic
and more pink.

29. Physiological cupping
• It is the depression in the central part of optic
disc.
• The cup is paler than the surrounding disc, where
from retinal vessels enter and leave the eye.
• In glaucoma (increased IOP ) the cupping is
greatly increased and the retinal vessels get
kinked as they cross the edge of the rim.

30. Blood vessels of the optic disc
• Radiate from the disc, dividing into many
branches.
• The retinal arteries are narrower than the veins
and bright red in colour.
• It is the artery that crosses the vein.
• Spontaneous retinal artery pulsation is an
abnormal finding which may occurs if IOP is high
while venous pulsation is seen frequently in
normal eye and is absent in papilloedema.

31. MACULA LUTEA
• M. Lutea or yellow spot is small yellowish area of
retina.
• Situated a little lateral to the optic disk.
• The yellow color of macula lutea is due to the
presence of a yellow pigment.
• Fovea centralis; is a minute depression in the
center of macula lutea where all layers of retina
are very thin.

32. MACULA LUTEA
• Diameter of fovea is only about 0.5 mm.
• Fovea is the region of most acute vision because
it contains only the cones which number about
35,000.
• The part of the macula lutea surrounding the
fovea has rods also which however are much less
in number.
• Degeneration of macula lutea is common cause
for blindness.

33. CAUSES OF ABNORMAL FUNDUS
1) PAPILLOEDEMA
• This is a swelling of the optic nerve head due to
raised intracranial pressure (ICP).
• Absence of inflammatory changes.
• Little or no disturbance of visual function.
• There is an increased redness of the disc with
blurring of its margins in initial stages of
papilloedema.
• The blurring appear first at the upper and lower
margins, particularly in the upper nasal quadrant.

34. PAPILLOEDEMA
• The physiological cup becomes filled in and
disappears.
• Retinal veins are slightly distended.
• Spontaneous pulsation of the retinal veins is
usually absent.
• The disc becomes definitely swollen.
• If papilloedema develops rapidly, there will be
marked engorgement of the retinal veins with
haemorrhages and exudates on and around the
disc; but with slow onset there will be little or no
vascular change.

35. Causes of papilloedema.
1) Space-occupying lesions particularly.
liable to occur in children with tumors of
cerebellum and 4th ventricle.
2) Malignant hypertension.
• Arterial changes characteristic of this condition.
• Haemorrhages, exudates and cotton wool spots
extending far beyond the region of the disc.

36. 2) OPTIC NEURITIS
• Inflammatory or demyelinating disease may affect
any part of the optic nerve, producing an optic
neuritis.
• The characteristic symptom is loss of vision.
• There is a pain on moving the eye.
• The pupil on the affected side shows a
diminished and ill-sustained contraction to a
bright light.

37. 3) RETINAL HAEMORRHAGES.
These occur in a number of different conditions and
are due to one or more of the following factors;
a. Hypertension in which there is increased blood
pressure within the retinal vessels.
b. Decreased retinal pressure due to proximal large
vessel disease.
c. Abnormalities in the walls of the retinal vessels, as
in diabetes or occlusion of the retinal veins.
d. Abnormalities in the circulating blood, as in severe
anaemia, leukaemias, and bleeding diatheses.
e. Haemorrhages are elongated and flame shaped
when superficial, within the nerve fiber layer of the
retina, whereas when deep they are round blotches
or spots.

38. 4) RETINAL ARTERIOSCLEROSIS.
This occurs either as an exaggeration of the
general ageing process of the body or in
association with hypertension. It is characterized
by;
a. Tortuosity of the vessels.
b. Nipping, identation or deflection of the veins
where they are crossed by the arteries.
c. Copper wire or silver wire appearance of the
fundus of the eye.
d. In hypertension, flame-shaped haemorrhages
and cotton wool spots in the region of macula.