this presentation provides a quick revision on ocular anatomy & helps learning basic steps of refraction

1. ANATOMY &
REFRACTION
Presented By:
Ekta kumari
Bachelor in clinical
optometry

2. ANATOMY OF EYE

3. Eyelids :-
A mobile tissue curtains placed in front of the
eyeballs.
function: protection ,
help to spread tear
Glands of eye lids;
o Mebomian gland
oGland of zeis
oGland of moll
oAccesory lacrimal gland
Eyelash :- filter out foregin matter

4. Conjunctiva
translucent mucous membrane
which lines the posterior surface
of eye lid and anterior surface of
cornea
function - keep bacteria
and foregin material
from
geeting behind the eye

5. Sclera
functions : - surround the eye
and give shape of eye tough and
opaque tissue
Nerve supply: brances of long
ciliary nerves
it forms the posterior 5/6th portiont of
the external fibrous tunic of the eye
Blood supply: anterior ciliary artery
And long and short
Posterior ciliary
aetery

6. OPTICAL PATHWAY
Cornea
Aqueous humor
Iris
Crystalline lens
Vitreous humor
Retina

7. Cornea
Cornea is a transparent
structure which forms anterior
1/6th part of outer fibrous coat
Function - focus light as it
enters the eye
 Avascular- no blood vessels
 supplied by anterior ciliary
nerves

8.  Diameter:
Horizontal- 11.5mm
Vertical- 11mm
 Thickness:
Central- 0.52mm
Peripheral- 0.67mm
 Refractive power- +43D
 Refractive index- 1.37

9. Layers of cornea
 Epithelium
 Bowman’s
membrane
 Stroma
 Dua’s layer
 Descemet’s
membrane
 Endothelium

10. Aqueous humor
 Function :
 Maintains IOP
 Provides nutrition- by providing subtrates
and by removing metabolites from avascular
cornea and lens
 Maintains optical transparency
 Refractive index- 1.336

11. Site of production;
 capillary network of ciliary process
 composition
 water 99%
 proteins
 amino acid
 Oxygen in dissolve state

12. Pupil
 Pupil is an opening located in the center of the iris
that allows light to enter the retina
 The function: control the amount of light entering
the eye and it does this via contraction and
dialatation under the influence of autonamic
nervous system
 Size of pupil 2-4 mm in brigth
 Size of popil 4-8mm in dark

13. Iris
 Thin circular structure
 Controls the size and
diameter(3-4mm) of pupil
 It is the colour of the eye
 Diameter- 12mm
 Thickness- 0.5mm

14. Layers of Iris
 Anterior limiting layer
 Iris stroma
 Anterior epithelial layer
 Posterior pigmented
epithelial layer

15. Crystalline lens
 Transparent, biconvex
 Helps in focusing light in retina
 Helps in accommodation
 Diameter: At birth- 6.5mm
2nd decade- 9-10mm
o Thickness: At birth- 3.5mm
adult- 5mm
o Refractive index- 1.39
o Power-: 16-17D

16. 1 2

17. Vitreous humour
Largest connective tissue
Transparent, colourless,
jelly like
Gives support to eyeball
Composed of 99% water

18. choroid
 A thin soft brown coat lining the inner surface of
the sclera
 Extremly vascular
 Extend from the optic nerve posteeriorly to the
ciliary body anteriorly
 Thickest at the posterior pole and gradually thins
anteriorly

19. Retina
• Acts like the film in
camera to create an
image
 Consists of specialized
layer of cells
 Convert light signal
nerve signal
o Thickness:
at posterior pole-
0.56mm
at equator- 0.18 to 0.2mm
at ora serrata- 0.1mm

20. Layers of retina
1. Retinal pigmented epithelium
2. Layers of rods and cones
3. External limiting membrane
4. Outer nuclear layer
5. Outer plexiform layer
6. Inner nuclear layer
7. Inner plexiform layer
8. Ganglion cell layer
9. Nerve fibre layer
10. Inner limiting membrane

23. VISUAL PATHWAY

24. REFRACTION
 Objective refraction
 The optical principles of an objective refraction :
Light from a laser illuminates a very small spot P
on the surface of the retina. A portion of the light
falling on the retina is scattered and leaves the
eye again via the pupil. If the eye is relaxed and
emmetropic (normal sighted), emerging light
would be parallel after passing the dioptric
components of the eye. In a myopic (nearsighted)
eye reflected light is convergent and in a
hypermetropic (farsighted) divergent

26. AUTO REFRACTOMETER

27. scheiner’s principle

29. Non ContactTonometer
 It uses a rapid air pulse to applanate (flatten) the
cornea.
 Particularly useful for measuring IOP in children
and other non-compliant patient groups.

30.  It uses a rapid air pulse to applanate (flatten) the
cornea.
 Particularly useful for measuring IOP in children
and other non-compliant patient groups.

31. Retinoscopy
 Retinoscopy is the name given to the objective
method of determining the refractive errors by
using retinoscope.

32. Procedure
 The fundus is illuminated by means of a mirror
or by a self illuminated streak retinoscope
situated classically 1 or 1/5 meter away from
the subject.

33. Principle
 Based on Foucalt’s Principle
 Retinoscopy is based on the fact that when
light is reflected from a mirror into eye the
direction in which the light will travel across
the pupil will depends upon the refractive
state of the eye

34. Objective Method
 :-Examiner sits at 50 cms away from the patient (
Point of reversal is at 2.00D)
 :-The Patient is normally seated and looking
towards the far end of the room.
 :-Source of light is from behind the patient.
 :-The Examiner looks through a plane mirror with
central perforation, and light is reflected into the
patient’s eye.
 :-The Examiner is slowly moved from side to side
in different meridians, and movement of the
shadow is noted.

35. Speed
Brilliance
Width

36. Stages Of retinoscopy
 Illumination stage : -
Light is directed into the patient’s eye to illuminate
the retina .
 Reflex stage : -
 The image of illuminated retina is formed at the
patient’s far point.
 Projection stage :-
 The image at the far point is located by
moving the illumination across the fundus and noting the
behavior of the luminous reflex seen by the observer in the
patient’s pupil.

37. Methods
 :-In Hypermetropia, emmetropia and myopia
<1.00D = the reflex moves in the same direction.(
with movement)
 :-In Myopia of 1.00D= there is no shadow
 :-In Myopia of > 1.00D= the shadow moves in the
opposite direction. ( against movement)
 :-The procedure is done for each meridians
separately
 :-In astigmatism, they are different. If the axes are
oblique, the shadow themselves will seem to
move obliquely and the mirror is then tilted
accordingly

39. Calculation
The distance from the retinoscope to the eye is
converted into diaptoric power by formula
D= 1/F (m)
The length of a avg person arm is 50 cm.
The power of a lens that focuses parallel light
rays at 50cm is 2.00D

40. Example
• If the end point is with +4.0D lens:
• Refraction = +4.00D-2.00D = 2.00D
• Similarly with -3.50D lens:
• Refraction = -3.50D – 2.00= -1.0D
• If the end point is with +1.50D lens
Refraction = +1.50-2.00D = -1.50D
• In case of astigmatism, each meridian is to be
calculated separately

41. SUBJECTIVE
REFRACTION
 SUBJECTIVE VERIFICATION OF REFRACTION

42. S
 After objective test, it
should always be verified
subjectively by testing the visual
acuity

43. Procedures
• Each eye is to be tested separately, the
other eye being blocked, and then finally
tested together.
• Appropriate lenses, as found by objective
test, are inserted in the trial frame.
• Slight modification of the inserted lens
gives a maximum visual acuity.
• Verification may be needed with a cross
cylinder, or astigmatic fan in case of
astigmatism

44.  Pin hole occluder:
 An opaque disk with
one small holes
through it.
 Diameter 1.5mm
 It is performed in a
patients with
diminished visual
acuity to distinguish a
refractive error from
organic disease

45. Duochrome Test
 To test if the eye
has been under
corrected or over
corrected or is
properly
corrected

46. Fogging Method
 Sometimes fogging method is necessary
to induce a relaxation of accommodation
especially in hypermetropia.

47. Example
 Here, the eyes are made artificially myopic
by addition of convex lenses (Ex+4.0D).
This is then gradually lessened by a small
fraction (0.50D) until the maximum acuity
is just reached. The first lens is not
removed until the next is in position, to
prevent from accommodation becoming
active.

48. Procedure
• As a rule, the patient is given the
strongest hypermetropic, or weakest
myopic correction with normal visual
acuity.
• The addition of the correction for near
work (if necessary), and testing of the
acuity with near- types, uniocularly and
then binocularly
• Then the spectacles have been ordered
with necessary comments (Ex) Constant
wear, Near works only

49. Near Vision Assesment
• The near vision test is preferably done
at 33cm by aging method.
• It is done with distance vision correction
that is with patients emmetropic level.
• Determine the correction depend upon
the comfortness, working distance,
visual need of patients along with aging
method.

50. Indications for Cycloplegic refraction
• All hypropes having the age group of 13-26
yrs
• Eg 1%cyclopentolate for 13-14 years
• 1% tropicamide 15-26 years
• One who complains of Asthenopic symptoms.
• Who come for glass for first time
• Accommodation is abnormally active.

51. TRANSPOSITION

52. Definition
• An application of changing the lens
form one to another.
• Usually it is changed from ‘+’ form
to ‘ – ‘ form.

53. TYPES
Simple transposition.
• Applies to convert the lens into different
forms.
Toric transposition.
• Is applied only for selecting the appropriate
tools in cylindrical lens surfacing.
• Different steps followed in calculating the
surfacing tools.

54. Rule Of Simple Transposition
• Algebric sum of sphere and cylinder is a new sphere.
• Cylindrical power is a old one but
• Sign and axis of cylinder will be in opposite.
• Examples;
– +2.5 D Sph / +3.0 D cyl x 150*
– a) + 5.5 D Sph
– b) 3.0 D cyl
– c) – cyl & 60*
– Final Rx : + 5.5D Sph / - 3.0D Cyl x 60*