1. -SAHITHI GANESHULA

2. Optics of human eye
Eye as a camera
Components
Schematic eye and reduced eyes
Axes and visual angles
Optical aberrations

3. Eye as a camera
Eyelids- shutter
Cornea- focusing system
Lens- focusing system
Iris- diaphragm
Choroid- dark chamber
Retina-light sensitive
film

4. Components
The cornea
The anterior chamber
The iris and pupil
The crystalline lens
The retina

5. Cornea
 Reasons of refraction:
 Curvature.
 Significant difference in refractive indices of air
and cornea.

6.  Vertical diameter slightly less than horizontal
 Front apical radius 7.7 mm K= 48.83 D
 Back apical radius 6.8 mm K=-5.88 D
 Actual refractive index cornea= 1.376
 Power of cornea +43D (2/3 of total eye power)
 Not optically homogenous (ground
substance)=1.354, n(collagen)=1.47

7. The anterior chamber
 Cavity between cornea and iris
 Filled with aqueous humor.
 Depth of AC – about 2.5-4.0 mm
 Change in AC depth change the total power. 1mm
forward shift of lens- increase about 1.4D in power
 Refractive index of aqueous humor= 1.336

8. Iris and Pupil
• 2-4mm
Average
size:
• depth of focus increases
• Concept used as pin hole test in refractionSmall pupil
• Retinal image quality improves
• Size of blue circle increasesLarge pupil
•Regulate amount of light entering the eye
•At 2.4mm pupil size, best retinal image obtained,
as aberration and diffraction are balanced.

9. The crystalline lens
• Birth 3.5 – 4 mm
• Adult life 4.75 – 5 mm
Thickness
• Ant surface 10 mm
• Post surface 6 mm
Radius of curvature
• Nucleus 1.41
• Pole 1.385
• Equator 1.375
Refractive index of lens
• 15 -18 d.Total power
• At birth- 14-16 D
• At 25yrs- 7-8D
• At 50yrs- 1-2D
Accommodative power

10.  Lens accounts for about one third of the refraction
of the eye.
 ACCOMODATION
 Provides a mechanism of focusing at different
distances.
 OPTICAL CHANGES IN CATARACTOUS LENS
 Visual Acuity reduction.
 Myopic shift.
 Monocular diplopia.
 Glare.
 Color shift.

11. Vitreous
 Refractive index same as aqueous.

12. Retina
 Maximum resolving power at fovea.
 A concave spherical surface with r =-12 mm.
 Advantages of curvature of retina over plane image
forming surfaces of cameras and optical
instruments:
 The curved images formed by the optical system
is brought in the right order.
 A much wider field of view is covered by the
steeply curved retina

13. Schematic eye and reduced eyes
• Two principal foci
• Two principal points
• Two nodal points
Gullstrand’s
schematic
eye:
• Two principal foci
• Single principal
• Single nodal point
Listing’s
reduced
eye:

14. Schematic and reduced eyes
 It is a theoretical optical specification of an
idealized eye, retaining average dimensions but
omitting the complications.
 Useful for understanding ophthalmologic problem
and conceptualizing the optical properties of the
human eye.
 To calculate cardinal points, the radii of curvature
and distances separating the refracting surfaces
must be known.

15. Axes and visual angles

16.  OPTICAL AXIS: line passing through centre of
cornea, lens and meets retina on nasal side of
fovea
 VISUAL AXIS: line joining fixation point, nodal
point and fovea
 FIXATION AXIS: line joining fixation point and
centre of rotation

17. Visual angles
 ANGLE ALFA:angle formed between visual axis
and optical axis at the nodal point
 ANGLE GAMMA:angle between optical axis and
fixation axis at the centre of rotation
 ANGLE KAPPA:angle between visual axis and
pupillary line. Point on centre of cornea is
considered as centre of pupil.

18. Optical aberrations
 Diffraction of light
 Spherical aberrations
 Chromatic aberrations
 Decentering
 Oblique aberrations
 Coma

19. Diffraction
 Bending of light caused by edge of the aperture or
rim of the lens.

20. Spherical aberrations
A convex spherical lens refracts peripheral rays
more strongly than paraxial rays, so peripheral
rays are focused closer.

21. Why less in human eyes???
 Human cornea is periphery is flatter than centre.
 In human lens, central portions have greater
density and greater curvature.
 Iris blocks the peripheral rays, only paraxial rays
enter the system.

22. Chromatic aberrations
Different color rays have different focal length, as
refractive indices of media varies with wavelength
of incident light.

23. Why less in human eyes???
 Due to narrow spectral sensitivity bands of long
and mid wavelength cones.
 Foveal lack of blue cones.

24. Decentering
 Lens is usually slightly decentred.
 Corneal centre of curvature is situated about
0.25mm below the axis of lens.
 Clinically insignificant.

25. Oblique aberrations
 When the object is in peripheral visual field, a thin
incident narrow pencil of rays enter limited by the
pupil.
 Peripheral portion of lens forms Sturm’s conoid, so
two line foci are formed.
 Minimum in human lens due to curvature of
retina.
 Significant in biconvex/biconcave lens.

26. Oblique aberrations

27. Coma
 Different areas of lens form foci in planes other
than chief focus, producing a coma effect in image
plane, from a point source of light.

28. Emmetropia
24-25mm
43 diopters
18 diopters
Accomodation at rest

29. REFRACTIVE ERRORS
• Ametropia: a refractive error is present
• Myopia: Near sightedness
• Hyperopia(Hypermetropia): Far sightedness
• Presbyopia: Loss of accommodative ability of the lens resulting in
difficulties with near tasks
• Astigmatism: the curvature of the cornea and/or lens is not spherical and
therefore causes image blur on the retina

30. REFRACTIVE ERRORS
• Anisometropia: a refractive power difference between the 2 eyes (> 2D)
• Aniseikonia: a difference of image size between the 2 eyes as perceived
by the patient
• Aphakia: (Phakos=lens), aphakia is no lens
• Pseudophakia: artificial lens in the eye

31. Myopia
 A form of refractive error in which parallel rays of
light entering the eye are focused in front of retina
with accommodation being at rest.

33. Etiological types
 Axial(MC)-increased AP length of eyeball
 Curvatural-increased curvature of cornea, lens or
both
 Index-increased refractive index of lens with
nuclear sclerosis
 Positional-anterior placement of lens
 Myopia due to excessive accommodation

34. Clinical types of myopia
 Congenital
 Simple or developmental
 Degenerative or pathological
 Acquired

35. Congenital myopia
 Common in premature babies or with birth defects
 Stationary(8-10D)
 Associated with
 Increase in axial length
 Esotropia
 Other congenital anomalies of eye
Early and full correction under cycloplegia
Poor prognosis in unilateral cases with severe
myopia and anisometropia

36. Simple myopia
 Physiological/school myopia
 Commonest type
 Results due to normal biological variations
in development of eye
 Age of onset- 7-10yrs
 Moderate severity-<5D,never exceeds8D
 No degenerative changes

37. Degenerative myopia
 Progressive in nature
 Related to heredity, general growth process
 Heredity linked growth of retina
 Factors affecting general growth process
 Age of onset-early adult life
 Severe->6D

38. Pathophysiology
Genetic factors
More growth of
retina
Stretching of
sclera
Increased axial
length
Degeneration of
choroid
Degeneration of
retina
Degeneration of
vitreous
General growth
process
Degenerative
changes in sclera
Decrease
d vision

39. Myopic
Crescent

40. Lacquer Cracks
Breaks in Bruch’s membrane

41. Sub retinal neovascularization

42. Sub retinal hemorrhage

43. Foster – Fuchs's spots

44. Posterior staphyloma

45. Complications
 Macular hemorrhage
 Retinal tears, detachment
 Vitreous hemorrhage
 Choroidal hemorrhage
 Complicated cataract
 Nuclear sclerosis
 Primary open angle glaucoma

46. Clinical features - Symptoms
 Distant blurred vision
 Half shutting of eyes
 Asthenopic symptoms
 Muscae volitantes
 Night blindness
 Divergent squint

47. Signs
 Prominent eyeballs
 Large cornea
 Anterior chamber is deep
 Large & sluggishly reacting pupil
 Fundus examination-changes seen only in
pathological myopia

48. Optical treatment
 Concave lenses
 Children
 Adults
 Contact lenses

49. Optical treatment
 Minimum acceptance providing maximum vision
 Low myopia(<6D):
 Young children : glasses required only if
Isometropia
<2years ≥ -4.0D
2-3years ≥ -3.0D
Anisometropia:
≥ -2.5D
Give full correction under cycloplegia
Avoid overcorrection

50. Adults:
 <30years-full correction
 >30years-less than full correction with which patient is
comfortable for near vision.
HIGH MYOPIA
 under correction is done to avoid
near vision problem
minification of images
contact lenses are better(to avoid image minification)

51. Surgical treatment
 Radial keratotomy
 Lamellar corneal refractive procedures
 Laser based procedures
 PRK
 LASIK
 LASEK
 C-LASIK
 E-LASIK

52.  Miscellaneous corneal refractive procedures
 Orthokeratology
 Intracorneal contact leses
 Intra stromal corneal ring segments
 Gel injectable adjustable keratoplasty
 Intraocular refractive procedures
 Phakic refractive lenses
 Refractive lense exchange

53. Hypermetropia
 It is the refractive state of eye where in parallel rays of
light coming from infinity are focused behind the
sensitive layer of retina with accommodation being at
rest

55. Etiological types
 Axial(m.c)-decreased AP diameter of eyeball
 Curvatural-flattening of cornea, lens or both
 Index –old age, diabetics under treatment
 Positional-posteriorly placed lens
 Absence of lens-aphakia

56. CLINICAL TYPES
 SIMPLE HYPERMETROPIA
 PATHOLOGICAL
 FUNCTIONAL HYPEROPIA

57. SIMPLE HYPERMETROPIA
 Commonest form
 Results from normal biological variations in the
development of eyeball
 Include axial and curvatural HM
 May be hereditary

58. PATHOLOGICAL HYPERMETROPIA
 Anomalies lie outside the limits of biological variation
 Acquired hypermetropia
 Decrease curvature of outer lens fibers in old age
 Cortical sclerosis
 Positional hypermetropia
 Aphakia
 Consecutive hypermetropia

59. FUNCTIONAL HYPERMETROPIA
 Results from paralysis of accommodation
 Seen in patients with 3rd nerve paralysis &
internal ophthalmoplegia

60. TOTAL HYPERMETROPIA
 It is the total amount of refractive error,estimated after
complete cycloplegia with atropine
 Divided into latent & manifest

61. LATENT HYPERMETROPIA
 Corrected by inherent tone of ciliary muscle
 Usually about 1D
 High in children
 Decreases with age
 Revealed after abolishing tone of ciliary muscle with
atropine

62. MANIFEST HYPERMETROPIA
 Remaining part of total hypermetropia
 Correct by accommodation and convex
lens
 Consists of facultative & absolute
FACULTATIVE HYPERMETROPIA
 Corrected by patients accommodative
effort
ABSOLUTE HYPERMETROPIA
 Residual part not corrected by patients
accommodative effort

63. Total hyper
metropia
Manifest hyper
metropia
Facultative
hyper metropia
Absolute hyper
metropia
Latent hyper
metropia

64. NORMAL AGE VARIATION
 At birth +2+3D HM
Slightly increase in one year of life,
Gradually diminished by the age 5-10 years
 In old age after 50 year again tendency to
HM
 Tone of ciliary muscle decreases
 Accommodative power decreases
 Some amount of latent HM become
manifest
 More amount of facultative HM become
absolute

65. SYMPTOMS
 Principal symptom is blurring of vision for
close work
 Symptoms vary depending upon age of patient
& degree of refractive error
 Asymptomatic
 Asthenopic symptoms
 Defective vision with asthenopia
 Defective vision only

66. SIGNS
 VISUAL ACUITY : Defective
 EYEBALL: small or normal in size
 CORNEA : may be smaller than normal. There can be
CORNEA PLANA
 ANTERIOR CHAMBER : may be shallow
 LENS: could be dislocated backwards
 A Scan ultrasonography (biometry) reveal short axial
length

67. FUNDUS:
A) DISC: Dark reddish color, irregular
margins ,confused with Papillitis so termed
as PSEUDO-PAPILLITIS
B) MACULA: Situated further from the disc
than usual, large positive angle
alpha, apparent divergent squint
C) BLOOD VESSELS: Show undue tortuosity
& abnormal branchings
D) BACKGROUND: SHOT- SILK RETINA

68. COMPLICATIONS
 Recurrent styes,blepharitis or chalazion
 Accomidative convergent squint
 Amblyopia
 Anisometropic
 Strabismic
 Uncorrected bilateral high hypermetropia
 Predisposition to develop primary narrow angle
glaucoma
Care should be taken while instilling
mydriatics

69. TREATMENT
BASIS FOR TREATMENT
 No Treatment
Error is small
Asymptomatic
Visual acuity normal
No muscular imbalance

70. Young children(<6 or 7yrs)
Some degree of hypermetropia is physiological so no
correction
Treatment required if error is high or strabismus is
present
 working in school small error may require
correction
In children error tends normally to diminish with
growth so refraction should be carried out every six
month and if necessary the correction should be
reduced, ortherwise a lens which is overcorrecting
their error may induce an artificial myopia
No deduction of tonus allowance in strabismus

71. Adults
If symptoms of eye-strain are marked,we correct as
much of the total hypermetropia as possible,trying
as far as we can to relieve the accommodation
When there is spasm of accommodation we
correct the whole of the error
Some patients with hypermetropia do not initially
tolerate the full correction indicated by manifest
refraction so we under correct them
Exophoria hyperopia should be under correct by 1
to 2D

72. Patients with absolute hypermetropia are
more likely to accept nearly the full
correction because they typically experience
immediate improvement in visual acuity
In pathological hypermetropia the
underlying cause rather than the
hypermetropia is chief concern

73. MODE OF TREATMENT
 SPECTACLES
 CONTACT LENS
 SURGICAL
OPTICAL TREATMENT

74. SPECTACLES
Basic principle
Prescribe convex lenses (Plus lenses) so that rays
are brought to focus on the retina
Advantages
 Comfortable
 Easier method
 Less expensive
 Safe idea

76. CONTACT LENS
ADVANTAGES
Cosmetically good
Increased field of view
Less magnification
Elimination of aberrations & prismatic effect

77. REFRACTIVE SURGERY
 Refractive surgery is not as effective as in myopia
TYPES
 Hexagonal keratometry
 Laser thermal keratoplasty
 Photo refractive keratectomy
 LASIK
 Photorefrctive keratectomy
 Phakic IOL and clear lens extraction

78. PRESBYOPIA
The physiologic loss of
accommodation in the
eyes in advancing age

79.  Physiologic loss of accommodation in
advancing age
 deposit of insoluble proteins in lens in
advancing age-->elasticity of lens
progressively decrease-->decrease
accommodation
 around years of age , accommodation
become less than D-->reading is possible at
- cm-->difficultly reading fine print
, headache , visual fatigue

80. Increasing Near Point of Accommodation
with Age
Age (years) Distance (cm)
10 7
20 10
30 14
40 20
50 40

81. SYMPTOMS
 The need to hold reading material at
arm's length.
 Blurred near vision
 Headache
 Fatigue
 Symptoms worse in dim light.

82. CORRECTION

83. SPECTACLES
Plus lens
(or)
Convex lens

84. Surgery
 Monovision LASIK
 Monovision & CK
 IntraCor
 Refractive lens exchange
 Corneal Inlays & Onlays

85. ASTIGMATISM
A defect of an optical
system causing light rays
from a point source to fail
to meet in a focal point
resulting in a blurred and
imperfect image.

86.  Conus of Sturm:-
Geometric configuration of light rays emanating
from single point source & refracted by
spherocylindrical lens

87.  Focal interval of Sturm :-
Distance between 2 focal
lines
 Circle of least diffusion
At the dioptric mean of focal lines the cross section of
sturms conoid appears as circular patch of light rays –
best overall focus

88. Types
 Regular astigmatism – change in refractive
power is uniform from one meridian to
another
 With-the-rule astigmatism
 Against-the-rule astigmatism
 Oblique astigmatism
 Bi-oblique astigmatism
 Irregular astigmatism –Irregular change of
refractive power in different meredia

89.  Types of regular astigmatism
 Simple astigmatism
 Simple hyperopic astigmatism
 Simple myopic astigmatism
 Compound astigmatism
 Compound hyperopic astigmatism
 Compound myopic astigmatism
 Mixed astigmatism

91. Regular Astigmatism :
 Correctable by Spherocylindrical lenses
Etiology :
1. Corneal - abnormalities of curvature [common]
2. Lenticular is rare. It may be:
i. Curvatural - abnormalities of curvature of
lens as seen in lenticonus.
ii. Positional - tilting or oblique placement of
lens , subluxation.
3. Retinal - oblique placement of macula [rare]

92. • Symptoms :
Blurring of vision
Asthenopic symptoms
Tilting of head
Squinting [Half closure of eyelid]

93. Investigations:
 Retinoscopy
 Keratometry
 Computerized corneal Tomography
 Astigmatic fan test
 Jackson cross cylinder

94. Treatment
 Optical treatment
 Spectacles
 RGP contact lenses
 Toric contact lenses
 Surgical correction

95. Guidelines for optical treatment
 Small astigmatism- treatment is required
 In presence of asthenopic symptoms
 Decreased vision
• High astigmatism- full correction
• Better to avoid new astigmatic correction in
adults because of intolerable distraction
• Bi-oblique,mixed,high astigmatism are better
treated by contact lenses
• Correction of spherical component

96. Irregular Astigmatism
• Etiology :
Corneal -[ Scars , Keratoconus
, flap complications,
marginal degenration ]
Lenticular -[Cataract maturation]
Retinal-[scarring of
macula,tumours of retina,choroid]

97. Symptoms :
Defective vision
Distorsion of objects
Polyopia
Investigations:
- Placido's disc test reveals distorted circles
- Computerized corneal topography

99. Treatment :
 Optical treatment :
- RGP contact lenses
-Hybrid contact lenses
-Scleral lenses
- Piggyback lens
 Surgical treatment:
- penetrating keratoplasty

100.  Astigmatism correction requires prescription of
convex cylindrical lenses at 180 +/- 20 deg or
concave cylindrical lenses at 90 +/- 20 deg with the
rule and vice versa

101. Contact lenses
 Toric contact lenses
Soft lenses [SL]
Rigid gas permeable lenses
[RGP]
RGP do not conform to the asymmetry of corneal
surface but replaces it totally and also provides
clarity of vision ,more durable.
Soft lenses are more comfortable to wear ,easy to
fit, adhere more tightly to cornea .

102. Refractive surgeries
 Astigmatic Keratotomy
 Photoastigmatic refractive Keratectomy [PRK]
 Relaxing incisions with compression sutures
 LASIK surgery

103. Residual astigmatism :
 The amount of astigmatism that still
remains after correction of a refractive error.
 In the case of correction of corneal
astigmatism using rigid contact lens
,lenticular residual astigmatism is exposed.

104. Anisometropia
 Difference in refractive power between eyes
 refractive correction often leads to different
image sizes on the retinas( aniseikonia)
 aniseikonia depend on degree of refractive
anomaly and type of correction
 closer to the site of refraction deficit the
correction is made-->less retinal image
changes in size

105. Anisometropia
 Glasses : magnified or minified 2% per 1 D
 Contact lens : change less than glasses
 Tolerate aniseikonia ~ 5-8%
 Symptoms : usually congenital and often
asymptomatic
 Treatment
 anisometropia > D-->contact lens
 unilateral aphakia-->contact lens or intraocular
lens